Turbo teams, what is your goal?

[Big Bird]

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.

[acedeuce802]

^ We have that quote hung up in our design office

[Bemo]

Nice one!

[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.

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.

[Crispy]

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.

It seems like that would cause a lot of lag...

[Kevin Hayward]

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

[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.

[RaceCatt69]

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.

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.

[Racer-X]

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.

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.

[nowhere fast]

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

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.