Turbo teams, what is your goal?

It's common sense among the FSAE community that running a turbo requires a lot of added weight and complexity with little to no performance gains. So why do some teams still use turbos?

I've been studying compressor maps of the commonly used GT12 and it looks like the 20mm restrictor will cause astronomical pressure ratios across the compressor wheel (this is likely the cause of the rampant oiling issues). It would be even worse with the E85 19mm restriction.

The obvious solution would be to switch to a larger compressor turbo that will be able to handle such pressure ratios. But then you would not be able to spool the turbo within a useable RPM range.

So my question is this: what goals are you turbo teams trying to achieve? You are sacrificing weight, fuel economy, reliability (oiling issue), cost and simplicity. What are you gaining?

you seem really negative about it, In my specific application I can have a far greater torque figure in the band where I want it. I increase torque substantially over the stock engines (non restricted) in the band where I we use it, changing the way the engine is used.
It seems to work well, we don't have any oiling issue. True enough, we do add weight but its worth it in our case.

Sorry if I'm wrong but you sound like you're trying to start something.

The idea is that the turbo smooths out intake pulses and the restrictor is at choke flow the whole time. This gives a bit more airflow, but more importantly it results in a flatter torque curve.

I've decided I don't want to run a turbo for the drawbacks you have stated. It is hard to make it come together properly. When the team tried it a few years ago they lost 3 engines in the process. That said it has worked for Cornell and other teams in the past. There are gains to be had if you do it right.

I am trying to "start something" -a thread that clears up the design goals of adding a turbo. I guess I am biased toward the negative aspects but that is all I know of FSAE turbo systems. Thats why I started this thread to learn some of the positives.

Jon, if you don't mind sharing, how much torque did you end up making? and how much of that torque is actually usable? I know a stock F4i makes around 45 lb.ft unrestricted. I cant imagine going much higher than that without spinning the tires.

Everybody who spends time working on a turbo system quickly realises that it's a lot of work, What racer-x says is absolutely correct.
quite a lot of teams out there use turbo's successfully and lots don't. It can be done and it can be very very good.
I can go into the intricacies of the maths if needs be, but I'm sure you can find it all on this forum previously if you are genuinely interested.

RaceCatt69, are you speaking from experience of turbo's failing on your FS car?

Not direct experience. But a few years ago a team tried to use a turbo and failed. I was considering redesigning their system for next years design but so far, it does not seem like a worthwhile endeavor.

RaceCatt,
Yes, I should have explained we are running a CVT so a completely different kind of engine performance is desirable..
We make around 53 lbs-ft at 8500rpm, but we also get a decently flat curve (which is also nice)
We have the redline set at 9000, we don't need to go any higher.
Our CVT will sit hapily shifting continuously at 8500 if you push hard and will keep stretching the gear ratio preventing wheel spin giving great traction and acceleration.
I should also point out that we use a Yamaha Genesis 500cc in-line twin.
I can choke the restrictor in the CVT's operating band completely where I would not be able to in a N/A system.

I should stress that the CVT doesn't only sit at high RPM, it will function throughout it's engaged rpm band i.e. 3500 - 8500 rpm and makes the car wonderfully drivable.

The CVT is a cunning way of using all the power that a Turbo application can bring to an FSAE engine

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So my question is this: what goals are you turbo teams trying to achieve? You are sacrificing weight, fuel economy, reliability (oiling issue), cost and simplicity. What are you gaining?

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Well, I stand corrected. It looks like a turbo can actually reduce weight by allowing the downsizing of the engine without sacrificing power, improve fuel economy, not cause oiling issues, and increase torque.

The only downsides being cost (although I don't have cost report data to confirm this) and complexity. I'd imagine a turbo engine is at least a 2 year design project to get it right. Seems like something only top tier teams should pursue. That being said, why aren't the majority of top tier teams going turbo?

The truth is they don't need to because they are already winning without it... If it ain't broke, don't fix it.

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Originally posted by RaceCatt69:
The truth is they don't need to because they are already winning without it... If it ain't broke, don't fix it.

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Not quite...

I agree that forced induction should improve the performance (power/weight, efficiency) of the car and overall competition points, but at a large cost in resources (people, time, money). There are other areas where larger or similar performance gains can be made for equal or less cost, so resources tend to be invested in these cheaper gains. I don't think top teams are leaving easily achievable performance sitting on the table just because they are "already winning without it". I suspect that every team, regardless of where they finish, looks at their available resources and spends them in the areas that they believe will provide the most value to their team.

I'm with Chris here. But you should mention that you can gain much more if you put a turbo on a single as intake pulses cost you much more as for example with a 4-cyl (in a 4-cyl there is always one cylinder sucking air through the restrictor in the single there is only one which is sucking for 25% of the time, simply spoken).

Our 08 car had 80% of its maximum torque at something around 4,500 rpm and overall a really flat torque curve. Looking at that we are sure, that with a 4-cyl there is VERY little you can possibly gain by adding a turbo, so it's definitely not worth it. I think a lot of teams underestimate how much you can gain by proper engine tuning in combination with good intake and exhaust design.

The interesting thing about this topic in my opinion is that in the 90's turbo teams like Cornell were very succesful. Since then the rules haven't changed in a way that should change anything of the potential you can gain by adding a turbo but I think it's quite some time ago that one of the major events was one by a turbo car.

@RaceCatt: You can be sure the reason why top teams aren't using a turbo surely isn't because they can win without it. If they were convinced they would improve their overall performance by using a turbo you can be sure they would do that http://fsae.com/groupee_common/emoticons/icon_wink.gif

I have shared this pearl (?) of wisdom on here before, but it will be well buried now. It seems to be the right time to share it once more.

After much experience with turbos in 2002, and with the implementation of the 450 single in 2003, we considered using a turbo to compensate for the power deficit of the 450. We undertook a simple experiment to determine how turbo location affected overall engine performance. Basically, we found that the critical dimension was the distance between the turbo body and the exhaust port - the further the better. For example, the car performed at its best when we were competing in Bruntingthorpe in the UK, while the turbo was located in a bin in Melbourne, Australia.

http://fsae.com/groupee_common/emoticons/icon_smile.gif

^ We have that quote hung up in our design office http://fsae.com/groupee_common/emoti...on_biggrin.gif

Nice one! http://fsae.com/groupee_common/emoti...on_biggrin.gif

As alluded to by Jon, one of the benefits is being able to gear the car a lot taller and get the same tractive force as an N/A car. This allows you to do crazy things like run accel in one gear, even without a CVT.

Also, if you want it, a turbo allows you to have a flat power curve for most of the rpm range as opposed to a flat torque curve, since you can choke the restrictor at a much lower RPM.

Mr. Catt, how did you decide on the boost pressure you want to run? I can believe 18 psi will give you extreme PR's, but that's also an easy way to melt a piston. There are other turbos besides GT12's that match well to an fsae engine too. Many people ignore the turbine match but I'd say that's more important for our case.

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Originally posted by Big Bird:
the car performed at its best when we were competing in Bruntingthorpe in the UK, while the turbo was located in a bin in Melbourne, Australia.

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It seems like that would cause a lot of lag... http://fsae.com/groupee_common/emoticons/icon_smile.gif

One positive about a turbo that nobody has mentioned is that it can take a lot of noise out of the exhaust. Your muffler can be made considerably smaller, which offsets some of the weight gain of the turbo itself.

For me a turbo has been on that list of things I would love to try out on a FSAE car, but never thought it was worth the resources. If I remember correctly UTA used to do a 250cc four with a turbo. That is the sort of concept I could get behind.

Run the 250cc up to its proper redline with a turbo. Design it such that you need either a very small muffler or none at all. Couple it with either a one or two gears (removing others from the case) or a CVT (different tuning strategies). You now have a powertrain that could outpower a single, but still with a low weight. Keep the rest of the car super simple with a spool, no fancy shifters, direct acting shocks, no electronic displays (including no tacho). You have more complexity in the powertrain, but you have taken it out of everywhere else, this keeps it more achievable. Lets call it the turbo go-kart. The added bonus is that the 250 fours and turbos can be found for very low cost.

Conceptually I don't see how a turbo works well with a 600 these days. Increasingly 600s have a significant power advantage due to more teams adopting singles. Where they lose out is weight. Maybe tuning the turbo to try and improve fuel economy, but the inroads you would make on the singles fuel consumption would be pretty minimal.

I don't see the point of a turbo on a single. The biggest attraction of the single to my mind is the simplicity. You know about the intake pulses and that you are trading off power. However you get a big gain in weight, easy intake and exhaust design, tuning, cost, and packaging. A turbo is a bandaid solution for those that just wanted more power in the first place. You might as well be better off trying to get one of the twins working properly.

Where I think turbos may be appealing is if you are running a smaller engine where 20mm is less of a restriction, or you couple it with a CVT and tune heavily at a small rpm range. But you would carefully need to reallocate team resources to account for the initial powertrain development time.

Kev

How does the turbo smooth intake pulses when it is powered by corresponding exhaust pulses? Does a turbine wheel really have that much inertia? Seems like intake geometry would have more control over pulse smoothing than a turbo. Unless you were to build a lot of extra pressure in the exhaust manifold, but then you would have parasitic loss due to the engine having to compress the exhaust gasses.

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Originally posted by GXP_Matt:
As alluded to by Jon, one of the benefits is being able to gear the car a lot taller and get the same tractive force as an N/A car. This allows you to do crazy things like run accel in one gear, even without a CVT.

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That would be true while the turbo is making boost, but what RPM are you spooling at? Unless your spool time is very close to zero, it doesn't make sense to use a taller gear for the 400 milliseconds gained from not shifting.

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Originally posted by RaceCatt69:
How does the turbo smooth intake pulses when it is powered by corresponding exhaust pulses? Does a turbine wheel really have that much inertia? Seems like intake geometry would have more control over pulse smoothing than a turbo. Unless you were to build a lot of extra pressure in the exhaust manifold, but then you would have parasitic loss due to the engine having to compress the exhaust gasses.

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The turbine does have inertia, you have a light mass but it is spinning at tens of thousands of revolutions per minute. That is why you have turbo lag and have some residual "boost" even after you let off the throttle. On top of that you can tune where the exhaust pulses reach the turbo. You will never get a perfectly smooth flow but you can make it better.

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Originally posted by Kevin Hayward:
The added bonus is that the 250 fours and turbos can be found for very low cost.

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I think four cylinder 250cc motorcycles are only really common, and therefore low cost, in Australia and Japan due to the unique motorcycle learner restrictions here.

Turbocharging one of these engines might be one of the few cases in FSAE where the engine is producing greater power and torque than the standard bike. I wonder how well they would hold up to the higher cylinder pressures.

I am a little surprised that a four cylinder 250cc car hasn’t been tried in Australia before, since the sound of 20,000 RPM must appeal to those that want a mini F1 car.

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Originally posted by nowhere fast:

Turbocharging one of these engines might be one of the few cases in FSAE where the engine is producing greater power and torque than the standard bike. I wonder how well they would hold up to the higher cylinder pressures.

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Actually a seemingly large number of single cylinder teams make more power on their engine than it was stock. Pretty sure UAS Graz was at 90 hp, I think Wisconsin was close to that last year both with turbos, and we're near 60 hp N/A, and Ive heard that number from a few other teams.

Our engine is 35hp stock.

Most of the electric-start 450's come in a relatively conservative state of tune for the purpose of either meeting emissions or to better suit the matching vehicle despite the engine's shared architecture with a motocross bike. Yamaha used to advance the YFZ450 quad's exhaust cam an entire tooth from the YZ450f motocross bike's timing to help in derating in combination with a choked "pea-shooter" exhaust tip.

Many teams not running 600/4 sport bike engines exceed stock power naturally aspirated. On the high end, I've heard 78 hp from Erlangen's Aprilia and 82 hp from UM-Dearborn's Genesis 80fi (not a huge increase, but impressive nevertheless for a restricted 180 deg parallel twin).

Nathan,

You make a good point about availability likely being better in Australia. I had assumed that due to UTA's early 250 car and the heads on the Western Washington v8 that they were fairly common in the US as well.

There are a lot of them around south east asia. So it might suit some of the teams in that area.

Kev

Kev, the 250 4 cylinders aren't unheard of around here but the market is "flooded" with 600 four cylinders and dual sport 450 singles.

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Originally posted by Kevin Hayward:
Nathan,

You make a good point about availability likely being better in Australia. I had assumed that due to UTA's early 250 car and the heads on the Western Washington v8 that they were fairly common in the US as well.

There are a lot of them around south east asia. So it might suit some of the teams in that area.

Kev

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Not exactly. Dr. Woods told me he used to fly over to Japan and fill his suitcases with CBR250 parts, then fly back. I could have sworn that WWU's heads were off of something else, but you're probably right. The 4-cylinder CBR250 bikes and engines have always been grey market in the US, as they've never actually been sold over here. They're definitely an Asian and Australian oddity.

The WWU heads were indeed from a Kawasaki 250/4, but I'm not sure if source bike was any more popular in the US than the CBR250RR. I've heard that UTA was not at all pleased with the CBR250RR's reliability--a big issue when your parts supply is only as big as your professor's suitcase.

The easiest way to get the best engine is to make one. It's so easy I don't know why anyone doesn't do it... Just save all of your teams red bull cans and when you have 100lbs. or so (depends on how big it is) melt them down and pour into sand molds to make cylinders, head, and other etc. When the mold is done touch it up with some machining. If you have spare pistons, rods, valves, or etc. just design the engine so that they can be utilized. You'll invest in some custom ground camshafts if you have half a brain. Assemble everything and voila! You have a Super Optimized for Displacement and Oxygen Maximizing "Eco-recycled" Engine. or S.O.D.O.M.E.E. for short.

I've given away too much secrets already so you're on your own trying to figure out the transmission and crankshaft.

Turbo's are indeed not easy to justify.

I do believe though, that it might be easier to run a turbo, than design an intake (and exhaust) manifold correctly. As people said, it evens out pulses and it pretty much pushes air in the engine. It is more dangerous, as one can blow up an engine easier though. (I agree with almost everything else said)

There are not a lot, but a few options on turbo's, and i have seen one spool to 22-24psi MAP between 3500-4000RPMs.

You can run accel in one gear. you can also probably run endurance/autocross, with three. Removing the 3 gears from a gearbox, does save some weight.

You add weight, and packaging complexity. Some design aspects are easier. Low and mid range power can be much higher. But, one thing that is hard to do on turbo's is drivability. It does need tuning.

Running a turbo usually means also running lower lamda values at WOT, so worse fuel consumption. However a low boost, lean burn turbo, can be tuned for efficiency as well. Most importantly, a turbo can be efficient at low throttle position, and powerful at high. Gives the driver best out of both worlds.

To sum up:
Turbo +'s:
-More power before choke
-Less design effort in intake/exhaust tuning
-More options on engine tuning (power, fuel economy, drivability)
-More options on gearing

Turbo -'s:
-Packaging complexity
-Mistakes can easily kill an engine
-Tuning complexity - adds another thing to control - boost map
-Weight (Even though one can eliminate/undersize other components)
-Current rules with throttle body before the turbo.

So if i was to design a turbo engine for FSAE, my main goal would be to get the most out of the engine. Try to use fuel and air efficiently and at a rate that the DRIVER needs. (If my team's drivers cannot handle the power, it might as well not be on the car) However, for marketing it is a somewhat different story, as your target group is not your 4-5 drivers.

Excellent first post, Tinomik. Glad to have you around here.

Seems like lots of good posts here, so I'll keep mine short: with most comps still having a ~30% enduro finishing rate (of all teams entered), I would say reliability is pretty important. And I noticed a lot of cars failing to restart after the drive change (I'm going to assume engine could not restart, or dripping fluids are the main causes).

To me, the engine causes a lot of reliability issues, so by keeping it as simple as possible, you have more time to work on the other parts of the engine, that might otherwise cause you to DNF. Lots of teams talk reliability, but it appears that very few do. ACtually, this just reminded me of the number of times GFR (a winning team) has DNFed at comps...

For me: drivers and tyres/suspension make your car go fast; engines make your car unreliable.

Rex,

I'm not sure that a lot of teams truly consider how great a cost it is not to finish endurance (especially for teams only competing once a year). Have a look at any comp and try and find the teams that have finished the endurance for at least 3 years running (same length of time world rankings are based on). The list is very small.

A bad finish means that your drivers didn't get proper comp experience. If they are back next year they will be further behind those that did.

The supporters of the team lose some confidence in the team. This could mean sponsors leaving or reducing involvement. This may mean the school putting more pressure to change designs, a reduction in resources, or even adding reasons to those in the schools that don't want these sorts of programs. Basically the team hasn't delivered on its primary goal.

This adds to more pressure being on the team at the next event. Now imagine this over three years where there are continuous non-finishes. Resources will be reduced, expectations lower, drivers and team less trained, and the team will be near the point of collapsing.

Contrast this to a more reliable approach with three years of continuous finishes. Chances are each year will be a little better than the last. Drivers are better trained, sponsors have stayed with the team with maybe a few extras, the school is right behind the team, and each year the team is more confident and the designs continuously improve. This is a team that can begin to think of winning comps.

Where does a turbo fit into this? I would say it is one of those systems that should only be looked at once a team has a track record of building cars that finish events. A team in that position will have learned to approach new designs conservatively and with a lot of testing. It will be team that will gain a performance advantage from the turbo rather than a reliability concern.

Kev

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Originally posted by Rex Chan:
For me: drivers and tyres/suspension make your car go fast; engines make your car unreliable.

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That might as well get printed and up on a workshop wall... http://fsae.com/groupee_common/emoti...on_biggrin.gif

Actually, drivers make your car go fast.

"Engines make your car unreliable", i am not so sure about that.

A good part of chassis/suspension "unreliability" gets filtered out in brake test and other events early on.

Also engines do require more money for testing and such. If one looks at like formula one teams and what not, a big big portion of the budget goes to the engine.

Lastly, all teams use commercially available engines. These guys work for years in their normal applications, in bikes and what not. Reliability in an FSAE setting means knowing your engine, which means breaking your engine at some point. That costs money and time to repair. Engines fail because people do something wrong. And engines are complex to start with.

However, drivers are by far the most important aspect. A pro driver will be able to use more power. They are able to use any engine better, by just braking at the right spot. With that said, brakes help a lot in getting more out of an engine.

So:

Driver>Tyres>Brakes>>everything else

in my opinion. Susp/chassis vs engines seems preety equal compared to the rest.

Has anyone ever tried a supercharger? That makes more sense to me, be cause you don't have to balance the low power gains vs. turbo lag. Supercharging has fallen out of favor with most small engines in general. This was an idea I've had for a while.

Also, I like what Tinomik said about drivers being the most important. But I disagree I think suspension and brakes should be most important if you aren't developing your own engine.

Danny,

Yes, teams have tried superchargers before.

Kev

Superchargers sound very heavy. Also, one would have to get a belt to them from somewhere. With integrated gearbox, that sounds a little bit problematic. Lastly, as superchargers use engine power directly, you will end up with less power at choke.

Tinomik,

For the CBR600RR you could take a belt drive off the mechanical water pump drive. There are pretty good reasons to run an electric water pump as it is, so any engine that comes with a mechanically driven water pump can potentially drive a small supercharger.

Kev

And where do we mount our dry sump scavenge pumps, then? http://fsae.com/groupee_common/emoti...on_biggrin.gif

Just joking, it could obviously be done (if the oil pressure pump / water pump drive chain manages the power needs of the supercharger). You could also use the timing hole cover, etc. etc....

Sophia (Japan) has been using them for a few years at FSAE-A.

I do agree that *we* make these motorbike engines unreliable. However, I disagree with Tinomik about breaking engines at some point - talk to current FSAE teams, and keep a close eye on a few main things (water/oil temps, and oil pressure).

ALso, brake test/accel/skidpad do not really "filter" out anything. Lots of testing (and lots of problem free track days leading up to comp) gives you that confidence.

Superchargers aren't any heavier than turbos are. A centrifugal supercharger is basically a turbo hooked up to a belt. Finding mounting points might be hard, but I think it would make more sense than a turbo.