V-Twin

[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.

[Mbirt]

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.

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

[MCoach]

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.

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.

[EPMPaul]

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...

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

[Z]

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

[mech5496]

@HenningO

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

[rjwoods77]

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.

[RenM]

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

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.

[Leibi]

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

[jordan.k]

@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

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.