V-Twin

The typical set-up for most FSAE cars now is either an inline-4 600cc sport bike engine or a 450cc single, but I was wondering about twins.

The main problem I see with a twin is that there aren't very many of them. There's the Aprilia, but it seems like everyone avoids that like the plague. Other than that, the only one I can think of that isn't 250cc or two stroke is a 400 made by Suzuki, but it is on a bike that is only on the Japan market.

Anyhow, the reason I was bringing twins up was that I was wondering if they are a good medium between the sporty, thirsty 4s and the frugal singles. Do they produce more competitive power and more competitive fuel economy than the other two configurations can do on their own?

The only twin I see as good though is the Aprilia because it comes as either a 450 or a 550, so it isn't too small to be underpowered or too big to offset the economy. An answer I know I'll inevitably get is that the engine is only good if the car is set up for it. As BigBird might say you wouldn't want a parfait with steak instead of strawberries, but I also think you can assess an engine beforehand to see if it is a good place to start.

Thanks for any and every reply.

There are several teams that use the Aprilia (here in Australia we at least have USyd). As far as I know, the primary issue is with starting, though I'm not sure why this is such a big hurdle for the teams that use this engine. Other options include the Suzuki SV650 engine (Tokai University from Japan used this), which cylinders de-bored. There's also the Ducati 620 (not sure of the actual capacity but they are typically over quoted). Auckland have been developing their own V-Twin + transaxle for a few years now out of 2 x YZ (WR?) 250F engines. For me, a V-Twin would be quite ideal, as they are typically more compact than a 4 whilst producing more power in a smoother manner (lower pulses for turbo, for example) than a single, and lend themselves to transaxle attachment. However, my feeling is that of the V-Twins currently on the market, the only one that seems suitable 'out of the box' is the Aprilia (which most teams struggled with at some point/are still struggling with). They are very expensive too.

Chatting with teams at Michigan, IIRC the biggest issue with the Aprilia is here in the States parts availability and tuning knowledge are lacking, making engine development a bit slower than other engine designs.

True, I'm not big on steak for dessert. And I probably would have said something like that. I'm obviously getting predictable...

Aside from availability. V-twins aren't really the ideal shape for one of our cars. V-twins are narrow across the crank (great for reducing frontal area on a motorcycle), but they tend to be longer and or taller in side view due to the splayed cylinders. And practically, intake and exhaust will tend to be more complex to design and manufacture.

I have seen one Ducati powered FSAE car, sounded lovely but the car was quite long.

Cheers,

Geoff

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Originally Posted by tromoly

Chatting with teams at Michigan, IIRC the biggest issue with the Aprilia is here in the States parts availability and tuning knowledge are lacking, making engine development a bit slower than other engine designs.

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I've never worked with the ape but I can't see it being any more of a hurdle than any other motor. Unless you're talking about little tricks internally to the motor to squeeze more out of it. Anything externally (intake, headers, fuel maping, comps etc) should be on par with any other motor. Everything that I've seen about them is that they're just a very fickle motor, sometimes they're happy, other times they're not and nobody is really sure why. Also don't they have a pretty ridiculous service schedule?

Quote:

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Originally Posted by jlangholzj

Everything that I've seen about them is that they're just a very fickle motor, sometimes they're happy, other times they're not and nobody is really sure why. Also don't they have a pretty ridiculous service schedule?

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I've probably forgotten what was exactly said, this sounds right in regard to the tuning issues people have had.

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Originally Posted by Big Bird

True, I'm not big on steak for dessert. And I probably would have said something like that. I'm obviously getting predictable...

Aside from availability. V-twins aren't really the ideal shape for one of our cars. V-twins are narrow across the crank (great for reducing frontal area on a motorcycle), but they tend to be longer and or taller in side view due to the splayed cylinders. And practically, intake and exhaust will tend to be more complex to design and manufacture.

I have seen one Ducati powered FSAE car, sounded lovely but the car was quite long.

Cheers,

Geoff

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To quote Firenze's FSUK 2010 event program entry:
"The basic idea of our cars is to
build it around two main
components: the driver and
the unavoidable Ducati twin
cylinder engine. The presence
of the Ducati engine is a pride
of ours, as we have the only
official sponsorship in F-SAE
series, and a challenge, as its
shape is not easy to position
in a race car. But what a
lovely sound when it roars!"

Sounds like steak parfait to me.

As for the Aprilia, I can think of a few examples of teams rising to new heights of success after dumping it and choosing engines that better fit the design philosophy of the car. Kansas used to run an Ape (2009 is the last one I recall), switched back to a 4 cylinder, and has scored 861 and 825 points at Lincoln the last 2 years respectively. A powerful, reliable 4-cylinder is a good fit for rocketing their car around the SCCA nationals courses. EPM (Montreal) switched from a monocoque and Ape to Rotax DS450 and spaceframe this year and placed 14th at Lincoln (their first sanctioned competition of the year) to jump 222 spots in the FS-World ranking. I can't speak for them to attribute previous performances to problems with the Ape v-twin, but I did observe lots of trouble just getting it to start at several events.

I feel like this thread is starting to become "What are the logistics like for the Aprilia V-Twin?" So let me attempt to return this back to my original intention. Do twins make a good compromise between 4cylinders and singles, balancing power and fuel economy?

http://youtu.be/_vZ6WFfiLvk

My, that Duc does sound nice. I never quite realized how tall that motor is though. I would've thought that it would be pretty easy to package due to the laid down front cylinder. Just pack it under your driver (as they appear to have done (referencing some other videos and pictures).

In my opinion, the best way to to it would be to make a full drivetrain package, integrating 2 250cc cylinders with a transmission and diff of some sort in the back. Could create a really nice tight low CG package with it. Also, Same engine would have a near-180 degree bank angle :)

So Auckland's V-Twin minus the crank angle?

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Originally Posted by DannytheRadomski

Do twins make a good compromise between 4cylinders and singles, balancing power and fuel economy?

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On those two parameters, yes. For the power and fuel efficiency of a single but with extra weight and a CVT, you could choose the Rotax 600 ACE (no one has done it yet, but I've had a great experience with it in another SAE competition). For the power and fuel efficiency of a 4 cylinder (or worse), you could choose the Genesis 80fi. To fall somewhere in between with less weight (on par with 450-class singles) and reliability, you could choose the Aprilia 550. For compromise power and efficiency, but the weight of a 4 cylinder, you could go with a downsized SV650.

Think about this though--is more power worth more points? Check out the FSAE West 2011 results. You'll find that the same car won acceleration, endurance, and would have won fuel under the current efficiency rule.

I've always thought it would be interesting to do Ducati Supermono, but with the horizontal cylinder chopped off instead of the vertical. It would tuck nicely underneath your back and the intake and exhaust fab would be dirt simple. The engines are pretty tall and heavy, though. I haven't weighed the engines in my 620 or either superbike, but I'd guess just from picking up the 620 that they are not much, if at all lighter than the 4's.

Quote:

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Originally Posted by DannytheRadomski

Do twins make a good compromise between 4cylinders and singles, balancing power and fuel economy?

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Danny,

You seem to be suggesting that there is an "engine-spectrum" with the fours at one end making the highest power, but not very efficiently, and singles at the other end that can only make low power, but more efficiently. Not so...

POWER - As noted at length elsewhere, the maximum achievable IC engine power through the 20mm restrictor is about 120 hp. Also covered elsewhere is the historical fact that air-cooled, turboed, 450cc singles were putting out 120+hp over 40 years ago. So a "sporty four" has NO POWER ADVANTAGE over a single!

Note that I am not advising that you try to get 120 hp out of a 450cc motocross engine that was only designed for 60 hp max (the crank won't take it!). Instead, you would have to build your own, but that is not hard (ie. just copy above example), and FSAE is supposed to be an "engineering" competition. Also, the current fours are nowhere near that power yet, so no rush in developing said 120 hp single...

FUEL EFFICIENCY - This comes mostly from the overall car concept, and less so from the engine itself. This seen from many recent comp results where the fastest cars also used the least fuel. Briefly, DO NOT USE THE BRAKES, and instead GO FAST AROUND THE CORNERS.

Nevertheless, from an engine point of view, and for a given power output, a single will almost always be more fuel efficient than a four, because a single has less combustion surface area for wasteful leakage of the valuable heat energy.
~~~o0o~~~

Bottom line here is that based on Power and Efficiency it is draw-win to the single, at worst. The single also has a better chance of winning on engine-mass, but may have more vibration. Fitting primary balance shafts to the single will give it LESS vibration than conventional fours or twins, although this adds some mass, though potentially the single is still lightest. And overall shape, and transmission layout, are also big factors to consider...

Importantly, there is no need for a "compromise" by taking a position somewhere in the "middle of the crowd". All the advantages (for FSAE conditions) are at the single end of the spectrum.

Simple decision, IMO!

Z

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Originally Posted by Z

POWER - As noted at length elsewhere, the maximum achievable IC engine power through the 20mm restrictor is about 120 hp. Also covered elsewhere is the historical fact that air-cooled, turboed, 450cc singles were putting out 120+hp over 40 years ago. So a "sporty four" has NO POWER ADVANTAGE over a single!

Note that I am not advising that you try to get 120 hp out of a 450cc motocross engine that was only designed for 60 hp max (the crank won't take it!). Instead, you would have to build your own, but that is not hard (ie. just copy above example), and FSAE is supposed to be an "engineering" competition. Also, the current fours are nowhere near that power yet, so no rush in developing said 120 hp single...

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I'm not saying a car with 100 hp will earn more points than one with 60 hp, but there are some examples in the ATV drag racing community that prove the stock crankcase can hold together. This TRX450R made ~35 hp stock and now makes 128 hp with 15 psi boost and probably ~600 cc displacement: http://www.youtube.com/watch?v=yuXdmvreVgU

Damn, that was impressive!

Quote:

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Originally Posted by DannytheRadomski

I feel like this thread is starting to become "What are the logistics like for the Aprilia V-Twin?" So let me attempt to return this back to my original intention. Do twins make a good compromise between 4cylinders and singles, balancing power and fuel economy?

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I'll go ahead and basically echo what everyone else has said: In answer to your original question, I think Z summed it up best. When presented with the compromise between fuel efficiency and power, most teams will choose based on engine weight, ease of packaging in a chassis, reliability and parts availability. ;)

Twins are cool, they sound awesome, but are not particularly easy to package, and really the only one that doesn't require the FSAE equivalent of 15 years (or 5 FSAE generations) of dedicated R&D to be competitive is the Aprilia, which is expensive, has a very poor starter, intensive maintenance schedule, poor reliability, and poor parts availability in the US. Also, as I recall the SV 650 engine weighs the same as most 4s, so that more or less kills it.

Quote:

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Originally Posted by Z

Danny,
POWER - As noted at length elsewhere, the maximum achievable IC engine power through the 20mm restrictor is about 120 hp. Also covered elsewhere is the historical fact that air-cooled, turboed, 450cc singles were putting out 120+hp over 40 years ago. So a "sporty four" has NO POWER ADVANTAGE over a single!

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Wrong. With the air restrictor a single cylinder na engine will never produce as much power as a 4 cylinder, due to the fact that you can not keep a constant pressure difference over the restrictor. And please dont start with turbocharging a single cylinder for fsae. It just doesnt make any sense at all.

Quote:

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Nevertheless, from an engine point of view, and for a given power output, a single will almost always be more fuel efficient than a four, because a single has less combustion surface area for wasteful leakage of the valuable heat energy.

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almost. In this case: not. Your heat transfer losses are a little lower with a 1 cylinder engine, but due to the fact stated above your pumping losses will be higher. Friction will be lower, but the burn rate will be slower and so on. Making such general assumptions is very difficult for a complex system like an engine.

Quote:

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Importantly, there is no need for a "compromise" by taking a position somewhere in the "middle of the crowd". All the advantages (for FSAE conditions) are at the single end of the spectrum.

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Perhaps in your ideal world in your mind. In reality there always is. And please dont start a rant about the philosophical nature off this topic.

RenM,

So your turboed-four will beat my N/A single, eh? Yes, of course!

But my turboed-single will thrash your turboed-four, after I remove your crankshaft! Or, putting it another way, why do you put the artificial constraint of "na" on the single design?

[Mini-Rant] (Not for RenM's eyes, but for the rest of you. :))
Despite what you may think, Engineering is primarily a fashion industry.

Not so long ago everybody knew that a single-cylinder car had a snowflake's chance in hell of doing well in FSAE. That is assuming anyone was mad enough to try! Yep, you definitely needed a four, preferably turboed, to have any chance at all. And "the future" was most certainly something like the WWU V-8.

Like everything in life, more is always better.

But then a quietly-spoken team from Japan (= "TD") came to the Oz-2002 comp, and, although banned (!), showed that their 450cc single car was quite fast. Some RMIT students (= "BB") saw this, and a few years later they conquered the world. Slowly, slowly ... other raving-lunatics/rational-thinkers (take your pick) made the move. Now in 2013 the singles are regularly on the podium, sometimes without a four in sight.

But good fashion works better with a lot of complexity. Things like "engineering reasons" can go take a flying jump! So fashionable young people (like RenM?) dream up excuses for why simplicity CANNOT work, and things MUST be complicated.

For example, "burn rate will be slower" in singles, because the flame thinks "Hmmm, I can't sense any other cylinders attached to this crank, so I better slow down!". Or maybe the bigger bore (err, like the 96 mm bore of F1 engines) and slow burn-rate make the single rev slower than your ride-on lawn mower. And "pumping losses will be higher", because, err..., you can't S/C or T/C singles. Well..., unless you are an ATV-drag-racing nut, and that "just doesn't make any sense at all"! Or something else that sounds really technical...

And if you just want to be "reasonably" fashionable (ie. not at the outrageously fashionable end), then you should stay somewhere in the middle of the crowd. That "middle" used to be fours, because the spectrum extended from (ughh) singles at one end, all the way to V-8s and more (ahhh, Veyron W-16, sighhh...) at the other end. Nowadays the "middle" is probably twins, hence this thread.

But ... what engine does that GFR-2013 car run again??? [End Mini-Rant :)]
~~~o0o~~~

Mbirt,

Nice engine, and I believe those power figures. With the extra bore-n-stroking I guess it also has a stronger piston and rod. My main concern would be the fatigue life of any crank with a big-end much less than about 40mm, with crank life maybe measured in minutes at 120+ hp. I reckon the simple fix is to beef the BE up to ~50 mm, and maybe also thicken the crank-webs, bigger crankcase bolts++. For the cost of a few extra kilos it should be possible to get fatigue life up to thousands of hours.

But that's just my reckoning, and I have NO PRACTICAL EXPERIENCE AT ALL (or so some say)! :)

Z

(PS. BTW, the generally better thermal and mechanical efficiency of a single over a four means that it should be able to extract MORE power from the air that can be sucked through the restictor. So win-win-win++...)

i am of course comparing a single na to a 4 cylinder na.

Thx for noting when the rant starts.

I have no where argued that a car with a 1 cylinder engine is not competitive. Dont read anything into my words, that i didnt write.
However i do argue against your 1 cylinder is better in any way. Now in 2013 singles are winning, as are cars with fours. This only shows thats there are always compromises to be made and that there is not a single best concept for fsae.

To the technical side of things: slower burn rate is a geometrical thing. Simplified the burn speed remains constant. With a larger bore the flames travel longer.
Sure you can turbocharge a single, but it wont work very well especially in fsae configuration. If you had taken your time and dig a little deeper than just the surface of this topic you´d know that in fsae conditions a turbocharger has to deal with hugely unfavourable circumstances.
The overall massflow is very low, leading to small turbochargers. Small turbochargers do however always have a bad overall efficiency.
Your exhaust gas flow is hugely pulsed as is your intake, requiring a large charge pressure.
The dynamics in an fsae car are enormous. The turbo has to be accelerated in a very short period of time. For acceleration you need power, so you close your wastegate and your exhaust backpressure rises.
Because of these points you will not be able to reach a positive pumping loop in an turbocharged fsae single, even though it is possible under different circumstances.

GFR 2013 is massively fast, because the whole package works very good together. But it does not show that a single is the only concept to go. It rather shows that there are always downsides like reliability issues.

V-twin?

How much power do you really need to win this competition?

There are other 2 cylinder options.

Honda makes a 470cc parallel twin
Kawasaki makes 300cc and 650cc parallel twins
Yamaha makes a 500cc parallel twin

Quote:

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Originally Posted by Mbirt

EPM (Montreal) switched from a monocoque and Ape to Rotax DS450 and spaceframe this year and placed 14th at Lincoln (their first sanctioned competition of the year) to jump 222 spots in the FS-World ranking. I can't speak for them to attribute previous performances to problems with the Ape v-twin, but I did observe lots of trouble just getting it to start at several events.

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Yeah I was team lead at EPM last year and basically came to the point where the team was trying to make a cool car instead of scoring points. Me and my co captain decided to change that. Looked at what was available to us (BRP's racing department is two hours away from our school and I'd worked at BRP in the powertrain department for 8 months so sort of had a lay of the land as to the reliability of those engines), so that was a no brainer. As for the spaceframe, again mainly a question of available resources and team size(carbon is labor intensive, think sanding molds)

Can't really say the Ape was the reason for our recent sucky years. More a question of team organization and management. However, I will say that we blew one engine on the dyno (overcooled water system and uncooled oil system meant we pushed the engine too hard because we didn't have an oil temp sensor at first). If we,d done that on the Ape, would have cost us an arm and a leg (that's 6000$ for you people who don't know Limb Currency).

But I'm pretty sure with the guy that took care of the engine last year that it would have run anyway, just more expensive and more time consuming(the Aprilia needs a custom trigger wheel coz the stock one isn't great from what I understand). On top of that the Aprilia shop manual isn't great (read utter crap) and the alternator seal can really wreak havoc if you're not careful (all the oil that lubricates the piston and crankshaft goes through the alternator casing through a seal to the crank shaft, if you nick the seal while installing the alternator cover, you just blew an engine). On top of that, the starter motor is undersized so if your calibration is off and you,re not starting, you need at least 4-5 starters around the shop at all times. Overall the Aprilia is sweet on paper, just extremely expensive to run and very finecky. Just have to treat the aprilia like a race engine(ie change a shit ton of expensive parts ever so often). If you want to run it,, you need a solid team of guys to get the thing down to a Tee.

As to starting the Aprilia starting issues, in our case, it was mainly a question of extremely crappy(read inexistant) engine calibration before 2013. Team was too focused on fabricating the damn tub and not worried enough about having a functioning car(back to those pesky management issues). That coupled with retarded fuel injector placement(wet the wall more than sprayed on the valvetrain)and a fuel pressure regulator that wasn't hooked to the plenum meant that it was a recipe for disaster(Again, keep in mind we were retards for a while).

That pretty much sums up the question of the Aprilia.

As an aside, one engine configuration that hasn't been discussed is a snowmobile inline twin. If you want a decent compromise, I think that,s what I'd do if i wanted something in the middle without engineering a crankcase. A Skidoo inline twin http://www.ski-doo.com/technologies/...gies/4-strokes 600 is around 40kg for 60 HP(1.333HP/kg). (that's only 6 kg more than their 450 btw). Say you make a transaxle for it that ways say 5-6 kg and you've got a pretty neat package. I know for a fact that RMIT ran the Phazer 500 inline twin for a while as well as sherbrooke. They're nice little engines. If you engineer your own gearbox, you can basically run it so the crankshaft is longitudinal which means your headers come straight out the side, avoiding the heat management around the gaz tank and other stuff that gets crammed under the driver seat that inevitably comes from a laterally oriented crank. The engineering workload og engineering a gearbox is probably less of a hassle than engineering a crankcase.(just reuse a gearbox from another engine. and make a case around it)

Finally, as an answer to your original question(I know long way to get to the point). Yes they're a good compromise. As i recall, calibrating like retards we got something like 55Hp(or as I like to call it , the point of diminishing returns from a power point of view in FSAE(considering no aero)) out of the APE for 35kg(weight of a single). So they're awesome. They're as much of a pain to package as any other engine seeing as things tend to get tight no matter what. If that engine were easier to work with, it would be perfect. Low effort to get a decent amount of power, you can concentrate on other things while having a nice light package. Or go balls to the wall and put a turbo in to get a nice light package with as much power as a NA inline 4.

PS: power to weight summary

Single BRP = 1.22 hp/kg. (43HP - 35 kg)
Inline twin = 1.33 hp/kg (60HP - 45kg with gearbox)
Aprilia 550 = 1.5 hp/kg (53 Hp - 35kg)
Inline 4 = 1.44hp/kg (80 HP - 55kg)

We tossed around the idea of the Ski-doo/ROTAX 600ACE for a while since we had a few of them and experience on the snowmobile side. Its not a svelte engine by any means. 4 stroke snowmobiles are expected to be more reliable and fuel efficient than their 2 stroke brethren at the cost of some weight and power. From a fuel economy standpoint the 600 is hands down the best engine in the industry. However, like you mentioned it is like 90-100 lbs and doesn't have a gearbox. It is also incredibly tall (one of the other Kettering guys might have a reference pic next to a WR450). On the plus side, it is amazingly knock resistant when combined with boost and high ethanol fuels. If you did it right and relocated the dry sump tank (which is the backside of the motor stock) so you could lay it down a little bit, even if you coupled it with a CVT it would probably make a nice package for sure.

For peak power out of it, FWIW, we were making about 85-90 hp at the crank, which seemed to be about peak for all the other teams running the same engine.

Quote:

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Originally Posted by RenM

To the technical side of things: slower burn rate is a geometrical thing. Simplified the burn speed remains constant. With a larger bore the flames travel longer.
Sure you can turbocharge a single, but it wont work very well especially in fsae configuration. If you had taken your time and dig a little deeper than just the surface of this topic you´d know that in fsae conditions a turbocharger has to deal with hugely unfavourable circumstances.
The overall massflow is very low, leading to small turbochargers. Small turbochargers do however always have a bad overall efficiency.
Your exhaust gas flow is hugely pulsed as is your intake, requiring a large charge pressure.
The dynamics in an fsae car are enormous. The turbo has to be accelerated in a very short period of time. For acceleration you need power, so you close your wastegate and your exhaust backpressure rises.
Because of these points you will not be able to reach a positive pumping loop in an turbocharged fsae single, even though it is possible under different circumstances.

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I also wanted to show how unsubstantiated several of these points are, but I was getting way too into it and wasting too much time. So I'll keep it simple.

1. Burn speed remains constant eh? The single-cylinder engine has a greater quench percentage of bore area area than a 600/4, so that helps with turbulence. High charge density is also possible with good intake designs that negate the effect of the restrictor on a pulse-by-pulse basis. We're not the only single-cylinder team running only 30 degrees max ignition advance at WOT.

2. With an 85+ hp KTM and several fuel economy wins, tell Wisconsin that turbocharging a single doesn't work well in FSAE. I don't consider 65-72% compressor efficiency to be bad at all. And large exhaust pulses work great for quick spool, it's the boost creep due to insufficient wastegate flow that gets you.

3. The "pea shooter" exhaust tips dirtbikes and ATV's come with stock are smaller than the turbine housing restriction--it's no big deal.

Quote:

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Originally Posted by Mbirt

I also wanted to show how unsubstantiated several of these points are, but I was getting way too into it and wasting too much time. So I'll keep it simple.

1. Burn speed remains constant eh? The single-cylinder engine has a greater quench percentage of bore area area than a 600/4, so that helps with turbulence. High charge density is also possible with good intake designs that negate the effect of the restrictor on a pulse-by-pulse basis. We're not the only single-cylinder team running only 30 degrees max ignition advance at WOT.

2. With an 85+ hp KTM and several fuel economy wins, tell Wisconsin that turbocharging a single doesn't work well in FSAE. I don't consider 65-72% compressor efficiency to be bad at all. And large exhaust pulses work great for quick spool, it's the boost creep due to insufficient wastegate flow that gets you.

3. The "pea shooter" exhaust tips dirtbikes and ATV's come with stock are smaller than the turbine housing restriction--it's no big deal.

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Many things work if you try hard enough, strive to collect data, and test to optimize.

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Originally Posted by EPMPaul

As an aside, one engine configuration that hasn't been discussed is a snowmobile inline twin. If you want a decent compromise, I think that,s what I'd do if i wanted something in the middle without engineering a crankcase. A Skidoo inline twin http://www.ski-doo.com/technologies/...gies/4-strokes 600 is around 40kg for 60 HP(1.333HP/kg). (that's only 6 kg more than their 450 btw). Say you make a transaxle for it that ways say 5-6 kg and you've got a pretty neat package. I know for a fact that RMIT ran the Phazer 500 inline twin for a while as well as sherbrooke. They're nice little engines. If you engineer your own gearbox, you can basically run it so the crankshaft is longitudinal which means your headers come straight out the side, avoiding the heat management around the gaz tank and other stuff that gets crammed under the driver seat that inevitably comes from a laterally oriented crank. The engineering workload og engineering a gearbox is probably less of a hassle than engineering a crankcase.(just reuse a gearbox from another engine. and make a case around it)

Finally, as an answer to your original question(I know long way to get to the point). Yes they're a good compromise. As i recall, calibrating like retards we got something like 55Hp(or as I like to call it , the point of diminishing returns from a power point of view in FSAE(considering no aero)) out of the APE for 35kg(weight of a single). So they're awesome. They're as much of a pain to package as any other engine seeing as things tend to get tight no matter what. If that engine were easier to work with, it would be perfect. Low effort to get a decent amount of power, you can concentrate on other things while having a nice light package. Or go balls to the wall and put a turbo in to get a nice light package with as much power as a NA inline 4.

PS: power to weight summary

Single BRP = 1.22 hp/kg. (43HP - 35 kg)
Inline twin = 1.33 hp/kg (60HP - 45kg with gearbox)
Aprilia 550 = 1.5 hp/kg (53 Hp - 35kg)
Inline 4 = 1.44hp/kg (80 HP - 55kg)

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Thanks for the input, Paul. I was hoping you would drop in and tell us about the engine change.

I've updated your hp/kg list with some real numbers achieved by teams. I've squeezed 90 hp out of a 600 ACE with turbocharging and E85 for another competition, so I've included that figure. It doesn't look very impressive stock at 60 hp and 40 kg. 35 kg is heavy for a single cylinder, Hondas and Yamahas are closer to 31-32 kg. 43 hp is also low, 50 is easily achievable, 60 can be had from 450 cc with some effort. Same goes for the Ape, one team has hit 78 hp.

Single = 1.88 hp/kg. (60HP - 32 kg)
Turbo single = 2.30 hp/kg (85HP - 37 kg)
Turbo 600 ACE = 1.8 hp/kg (90HP - 50kg with turbo and gearbox)
Aprilia 550 = 2.23 hp/kg (78 Hp - 35kg)
Inline 4 = 1.64hp/kg (90 HP - 55kg)

How much power do you need?

If someone could make a graph of engine power on the x-axis and time/effort/resources on the y-axis and the compared it to the attached graph, engine selection would be pretty easy I would imagine!

Attached graph is done in OptimumLap using the "default FSAE Aero car", which weighs 230 kg, has average FSAE aero and is using a CVT (to make comparison between different power levels more relevant), the car was run around the 2012 FSG endurance track.

Hi,

@EPMPaul: why is the stock Aprilia trigger wheel bad? We had no issues with the cam signal in the years we used/use the Aprilia (2009 until now)? The manual is not the best, but all torque values are given and with reading the Ape forum and especially Allen Noland's facebook page the engine can be assembled right and ways better than it comes from the Aprilia plant. The oil seal in the alternator cover is one thing often made wrong by Aprilia but the problem of shearing the o-rings on the hollow pin between left crankcase and the alternator cover during assembly can simply be solved with two chamfers and a bit of sand paper to round the edges. The starter motor is a well known problem but the forum knows help. In this and other forums there are endless threads discussing the Ape. Aprilia put a lot of hope in the SXV/RXV but the bike was no success (most reasons were self-made problems from Aprilia). Now the production seems to be stopped, a new model can not be seen on the horizon, bikes and engines are getting fewer with the typical effect on prices and numbers of new/used engines...

35 kg is the weight for the standard Ape with oil and water. Our's is dry at about 31 kg.

IMO a low-weight V-twin is the best solution for FSAE. It weights almost the same like a single, has a wider usable speed range, more power (the Ape is closer to an inline-4 than a single), runs smoother and has less vibration. Packaging is more complex (two heads --> two exhaust header, two airbox runners, two coolant hoses), but it's worth the effort.

Regards,
Leibi

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Originally Posted by Mbirt

I also wanted to show how unsubstantiated several of these points are, but I was getting way too into it and wasting too much time. So I'll keep it simple.

1. Burn speed remains constant eh? The single-cylinder engine has a greater quench percentage of bore area area than a 600/4, so that helps with turbulence. High charge density is also possible with good intake designs that negate the effect of the restrictor on a pulse-by-pulse basis. We're not the only single-cylinder team running only 30 degrees max ignition advance at WOT.

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You will get higher turbulence and thus a higher flame speed with a single compared to a four, especially as most 4 cylinder engines cylinder heads are optimised for a large filling rather then for turbulence and the low average piston speed resulting from the decreased rpm due to the restrictor. However this was an argument against Zs "everything gets better with a one cylinder engine". And i have not writen anything about a 4 cylinder engine. I meant in comparison to a two cylinder engine and my arguments stands.

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2. With an 85+ hp KTM and several fuel economy wins, tell Wisconsin that turbocharging a single doesn't work well in FSAE. I don't consider 65-72% compressor efficiency to be bad at all. And large exhaust pulses work great for quick spool, it's the boost creep due to insufficient wastegate flow that gets you.

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in 2012 Wisconsin won fuel economy at FSAE, however they were almost 20% slower then the team that won endurance. Its easy to save fuel when you are going slower.
in 2011 Wisconsin had the same fuel consumption as Tu Munich with a 4 cylinder engine.
I dont see how this is an argument that a turbocharged single can work excellent. And you don't take into account that a turbocharged single will be much harder to drive then a naturally aspirated car.
The problem is that FSAE straights are extremely short. When the longest straight only lasts for 3 seconds you can not afford to have your boost pressure build up for over a second, especially if you consider that the distance traveled is the acceleration integrated twice over time.

65% compressor efficiency isn't that bad, however its in an area of the compressor map that wont be used too often and 60% turbine efficiency is bad. Plus you get a really bad overall turbine efficiency due to your wastegate. Turbines work way better with a more constant gas flow as their efficiency drops in the slopes of the massflow. What is the point in having one large pulse, that you can not fully use and for the rest of the cylce you are left with no power at all, slowing the turbo down. Believe it or not on a 2 cylinder engine, you will get the same overall engine efficiency with a modern mechanical supercharger as with a gt12 as turbocharger, and i bet its not getting any better with a single.

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Originally Posted by EPMPaul

Single BRP = 1.22 hp/kg. (43HP - 35 kg)
Inline twin = 1.33 hp/kg (60HP - 45kg with gearbox)
Aprilia 550 = 1.5 hp/kg (53 Hp - 35kg)
Inline 4 = 1.44hp/kg (80 HP - 55kg)

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I dont think that the power to weight ratio of the engine is very meaningful. Youd have to compare the power to overall weight (including driver) to get a real comparison:

Driver weight: 70 kg, Car weight taken from Homepage

Gfr 450 single: 158 kg 55 Hp -> 228 kg -> 0.24 hp/kg
Erlangen 550 V2: 165 kg 76 Hp -> 235 kg -> 0,323 hp/kg
Stuttgart 600/4: 167 kg 90 hp -> 237 -> 0.38 hp/kg

On the subject of exhaust pulses, would a crossplane inline four be best for this? I know there are a few of those, but I think they are all literbike engines.

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Originally Posted by DannytheRadomski

On the subject of exhaust pulses, would a crossplane inline four be best for this? I know there are a few of those, but I think they are all literbike engines.

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No, check out exhaust design for flat-plane vs. cross-plane v8 engines to discover why.

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Originally Posted by HenningO

How much power do you need?

If someone could make a graph of engine power on the x-axis and time/effort/resources on the y-axis and the compared it to the attached graph, engine selection would be pretty easy I would imagine!

Attached graph is done in OptimumLap using the "default FSAE Aero car", which weighs 230 kg, has average FSAE aero and is using a CVT (to make comparison between different power levels more relevant), the car was run around the 2012 FSG endurance track.

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I have a graph that looks just like that except based on our car. After 60hp, you reach a very diminishing returns area. Go check out the velocity overlay of the track map and you'll notice how many sections that you're spending in a low gear and low speed. Power's effectiveness drops off a lot because you spend lots of time in the "traction limited" zone. You hit a wall where you just run out of grip.


Gotta get that grip to put down that power.

Then again, grip is just a four letter word.

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Originally Posted by Leibi

Hi,

@EPMPaul: why is the stock Aprilia trigger wheel bad? We had no issues with the cam signal in the years we used/use the Aprilia (2009 until now)? The manual is not the best, but all torque values are given and with reading the Ape forum and especially Allen Noland's facebook page the engine can be assembled right and ways better than it comes from the Aprilia plant. The oil seal in the alternator cover is one thing often made wrong by Aprilia but the problem of shearing the o-rings on the hollow pin between left crankcase and the alternator cover during assembly can simply be solved with two chamfers and a bit of sand paper to round the edges. The starter motor is a well known problem but the forum knows help. In this and other forums there are endless threads discussing the Ape. Aprilia put a lot of hope in the SXV/RXV but the bike was no success (most reasons were self-made problems from Aprilia). Now the production seems to be stopped, a new model can not be seen on the horizon, bikes and engines are getting fewer with the typical effect on prices and numbers of new/used engines...

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For the trigger wheel issue, we never got to the point of solving it but from what I understand(spoke to a couple teams (Auburn in the case of this piece of information) that ran it in the past) it gave a fairly weak pulse, this is heresay so I can't testify to this absolute truth but that,s my understanding of some of the issues with the Aprilia. I'm not an engine guy to start off with( I only worked on the engine last year because of lack of personnel in the area). I have an okay understanding of our current engine but concerning the Aprilia, it's mostly stuff I've heard of over time.

Again, I agree, if you,re a well organized team and have ressources, they're fairly easy to work around. The question is always a question of how much expertise and knowledge and research you need to gather to get the thing to run decently. Overall, if our team could run it I,d love to try it but we don,t have the personnel and cash and knowledge transfer in place right now to insure that it runs well day in day out. If the information is all in the shop manual it's easier to work with and can avoid costly mistakes.

@HenningO: Funny you should post that, that's one thing that's always made me curious about the hunt for huge amounts of power. Every time I've tried to validate it or researched it, it always seems like a losing proposition to pack on the pounds and spend large amounts of time/money in order to have more than 60 horsepower. Worst thing is, this isn,t news. I've seen charts like that on a paper by the UoT http://www.mie.utoronto.ca/undergrad.../files/201.pdf that dates back to 2008(great paper BTW, cool introduction for anyone looking for an introduction to lapsim). And the trend is the same at Lincoln and Michigan(I played around with it the other day wondering just how much power really made a difference for the added invesment).

@RenM: agreed, from a point of view of on track performance, comparing engine weight is moot. On non aero cars however, the weight of the car is usually pretty much determined by the size of the engine (good 4 cyl is 400lbs(200kg), good single is 330lbs(150kg)) Ancillaries also usually grow with the increasing horsepower so while it's not relevant to car performance, there is some correlation to overall weight. When you start playing with aero, then other considerations like managing the interaction between the amount of power and drag means you need to scratch your head a little more. Finally seeing as some of the configurations we,re talking about haven't managed to get to a formula SAE, I find the hp/kg(engine) is an okay metric for the purposes of this thread

Q1. When is a problem REALLY a problem?
A1. When it INEVITABLY leads to bad things happening.

Q2. When is a problem NOT REALLY a problem?
A2. When the bad things that people tell you will happen, NEVER happen!

The "burn rate" issue for FSAE singles is in that second category. I hinted at that (spelt it out?) when mentioning that F1 engines have a bore of ~96 mm (ie. like a typical FSAE single), yet rev to 20,000 rpm. "Burn rate" might become "a problem" when you try to rev your FSAE single to 30,000 rpm, but until then, NO PROBLEM!

Likewise with turbo-charging. As noted by others above, much of FSAE racing is traction-limited. Use more than ~60 hp (= half of what is possible) on most parts of the track and you just turn good tyres into blue smoke, but don't go any faster. The few places that you might be able to beneficially use 120 hp is at the ends of the longer straights (which includes the Accel. event).

Bottom line here is that a turbo can give you the extra power at the ends of the straights (if you really want it), but "turbo-lag" is NOT A PROBLEM. Oh, and plenums can smooth out big pulses, but "plenum lag" is ... (again, see A2^). And many other FSAE "problems" have A2 as the answer...

Honestly, the only reason I can think of for using more than one cylinder in FSAE, is "Well, we've got this multi-[insert 2/3/4...]-cylinder engine sitting right here on the bench, it's free, we've got lots of spare parts, and it works ok, sort-of...". Even then, you might be tying an anchor around your neck...

Z

@HenningO

Same here...you might want slightly more with a heavy aero car, or slightly less in a lightweight non-aero.

With a good team to properly develop this engine that 50-60hp number being thrown isn't hard to get with this.

http://www.youtube.com/watch?v=sqztOLYcwek

Briggs and Stratton racing was getting 75hp out of a nearly identical setup without a restrictor.

http://eknclassic.com/viewtopic.php?...7c103d878c9080

UB was getting an about 40hp out of it with much room for growth. It is air cooled/oil cooled by forced air via squirrel cage blower so no water cooling ancillaries are necessary. Pushrods made the size of the engine very small in comparison to anything else I have seen in a FSAE car. The rear axle centerline from the main roll hoop centerline was 19" on this car. If you relocated the oil filter housing you can tuck a 4" OD differential under the rearward cylinder and get a 17.5 to 18" dimension. You can get that down to close to 16.5 depending on chassis/seat/firewall design and mounting the diff directly to the engine block. The cam sensor is 13" off ground to give you a side view height reference and most of the engine is below that. I often hear how packaging was is an issue for a v twin but it is absolutely not the case with this one as the side ports free up most of those space issues. Weight is on par with a 450 single once you ditch the 20lbs flywheel and go with an aluminum one. I often thought in the years after FSAE that I would/could have gone with something different but rehashing it again I think there was/is tremendous possibilities with it even with it's restrictive industrial architecture seeing as how downsized the vehicles have gotten as of late.

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Originally Posted by Z

The "burn rate" issue for FSAE singles is in that second category. I hinted at that (spelt it out?) when mentioning that F1 engines have a bore of ~96 mm (ie. like a typical FSAE single), yet rev to 20,000 rpm. "Burn rate" might become "a problem" when you try to rev your FSAE single to 30,000 rpm, but until then, NO PROBLEM!

Likewise with turbo-charging. As noted by others above, much of FSAE racing is traction-limited. Use more than ~60 hp (= half of what is possible) on most parts of the track and you just turn good tyres into blue smoke, but don't go any faster. The few places that you might be able to beneficially use 120 hp is at the ends of the longer straights (which includes the Accel. event).

Bottom line here is that a turbo can give you the extra power at the ends of the straights (if you really want it), but "turbo-lag" is NOT A PROBLEM. Oh, and plenums can smooth out big pulses, but "plenum lag" is ... (again, see A2^). And many other FSAE "problems" have A2 as the answer...

Honestly, the only reason I can think of for using more than one cylinder in FSAE, is "Well, we've got this multi-[insert 2/3/4...]-cylinder engine sitting right here on the bench, it's free, we've got lots of spare parts, and it works ok, sort-of...". Even then, you might be tying an anchor around your neck...

Z

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the burn rate is not an issue just as the heat transfer losses are no issue for a multi cylinder engine. Its just something that decreases your efficiency.

With our 4 cylinder car, we can quickly use our power when accelerating out of corners without being too limited by traction problems.
Gaining speed at the end of a straight is not useful. It will not make you any quicker and just increases your fuel consumption. Turbo lag IS a problem. I have yet to see a single or twin cylinder engine which looks very drivable. KIT and Wisconsin certainly font. Big pulses can only be dampened to a certain amount and you don't want to do this on the exhaust side, because it increases your diffusion losses resulting in a lower turbine efficiency (thats why you do pulse turbocharging).

There are a lot of good reasons for teams to go for a multi cylinder engine just as there is to go for a single. Its a question of concept and balancing compromises. But as you have never done this in practice, we of course cant expect you to understand this aspect.

Hi,

@RenM: we did this chart comparing the overall power-to-weight ratio of cars with a n/a single, a v-twin and a four. We took a standard car weight and added the engine weight plus a factor multiplied with the cylinder number to take the increasing influence of periphals like exhaust headers or intake runners into account. We have less power than you and our car weights more than the singles, but our overall power-to-weight ratio is almost the same as yours by our overall weight being close to the singles. We win none of the disciplines like overall weight, maximum power, maximum torque, overall power-to-weight ratio but IMO the Aprilia is the best compromise. Everyone has to do his own decision and there is no ultimate FSAE engine or ultimate FSAE car.

Some people here seem to have problems with other peoples decisions ;-)

Every concept has its advantages and is a compromise. How many cylinders you choose is determined by how important you weighten each factor. This is beneath all the science and lap simulation etc. a subjective decision done by the responsible people with everyone having his own opinion. I'd not underestimate factors like i.e. an engine teamlead having been grown a up in a motocross family which drives KTM singles since 10 years with success.

@Paul: I don't understand why the crank signal is an issue. The Aprilia has a 30-2 flywheel which is used pretty often in the automotive industry. I was last year in Rapid City, SD, with Formula Hardrocker Racing. Those guys bought the Auburn Aprilias and I saw some quite interesting things. There were flywheels with tooth cut off and on one flywheel the two missing teeth were welded in with some of the teeth cut off from the others. But how will you determine TDC with a 30-0 flywheel ? ;-)

Regards,
Leibi

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Originally Posted by Leibi

@Paul: I don't understand why the crank signal is an issue. The Aprilia has a 30-2 flywheel which is used pretty often in the automotive industry. I was last year in Rapid City, SD, with Formula Hardrocker Racing. Those guys bought the Auburn Aprilias and I saw some quite interesting things. There were flywheels with tooth cut off and on one flywheel the two missing teeth were welded in with some of the teeth cut off from the others. But how will you determine TDC with a 30-0 flywheel ? ;-)

Regards,
Leibi

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We were very confused by this but luckily we had enough spares to run stock flywheels! I was wondering if you'd remember seeing those flywheels.

The Ape can be temperamental and we definitely had our share of issues with it at SDSMT. With that being said, I attribute those to team and management issues.