FSAE Australian Teams: Turbo or NA?

[Engine Dude]

Hey Guys,

Just out of intrest, who is running turbo in this years Australian competition?

If so is anyone experiencing problems with the new positive seals from garrett?

Cheers

Sam

[Big Bird]

Sam,

Monash won't be running a turbo - for your info. When I was at RMIT in 2002, we ran a turbo and had all kinds of seal problems, which ate up a huge chunk of our development time. Can't tell you the solution because firstly, I wasn't involved on the engine side of things, and secondly, we never solved it anyway.

I have to ask, why are you heading down this route? I see on another thread you are from Uni of SA - so if I can offer well intentioned advice to a relatively new team, I'd advise running NA, at least until the team is more established. There are plenty of lessons to be learnt and processes to put in place just to get a simple NA car operating reliably. Go as simple as you can - when you are running consistently with the UoW's and UWA's, (which can be done NA), then that is the time to start tinkering with more elaborate designs.

Cheers Sam, good luck to you and your team.

[Eddie Martin]

I think innovation and trying new things are important in this competition but trying things like a turbo is probably best left till your team has lots of experience in fsae, or lots and lots of people. Unless you are well under 500 lbs and scoring 800 points regularly there are probably more pressing issues to address. As an example, at UoW it took 2 guys about 18 months hard work to get a turbo set up running well in the car.

[Engine Dude]

Thanks to all of you for your advice. It seems most of the people who have done sae dont recommend turbo in yound teams. I discussed this with my team at the start of the year when i read some of the 03 and 02 posts. But it seams that everyone has turbo'ed their cars and seems to think it can be done on a 20-mm resitrcted setup.

I hope our team has more people on it than this year becasue there is a lot of work to do on the engine (cooling, intake exhaust, engine management etc).

For an NA setup, when you say just do simplistic things, do you mean just design simple intake manifolds, simple cooling systems and simple exhaust systems, and then get dirveability. Like do a hell of a lot of testing.

That seems like the logical thing to do, but is there much work that you can put into a thesis if you do this??

Thanks for the advice fellas

Sam
UniSA

[Engine Dude]

RE: Geoff Pearson
RMIT FSAE 2003/4
Monash FSAE 2005

Design it. Build it. Break it.

The turbo seal problems you had, did you have the positive carbo seal from garrett in the turbo? I think all turbo's are fitted with the seal. Also, with the problem of negative pressure before the compressor, i saw a thread from a team which said they equalised the pressure by plumbing a line from the oil (crank case) to after the throttle. That way there wouldnt be a pressure difference and the compressor wouldnt suck oil from the oil throigh the seal.

Cheers

Sam.

[Denny Trimble]

Sam,
If you start out building the simplest car you can, you will learn more and put in more work than you can imagine. Just getting it all together, running, and tuning the engine and suspension, is a hell of a lot of work.

Not that I've done it four or five times... http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Colin]

Engine dude, you can look at it this way, what reason's do you have for putting the turbo on the car?. I don't want to put you off trying new things but in my opinion you don't want to explore such things as turbo's or variable inlet runner length's before you have a good NA system otherwise you don't really know what problems you are trying to overcome by using a more elaborate system. The other thing is you won't have any previous data to compare the two systems. Trust me just getting an ECU wired neatly and set up, if you haven't done one before, is a massive job in itself. As for Swinburne we looked into a turbo system this year but we will defiantly be running NA again for 2005

Good luck

[Kakarot]

man, does anyone know that a compressor side of a turbo cannot handle more that ~ -3psi. The restrictor creates close to -10psi of vacuum at 9K rpm on a 0.6L engine with like calculated 7psi of boost. The small seal never intended to be a sealant of that magnitude. It was meant to hold positive preasure and just slighly over what the impeler creates behind it.

In simple terms, Duh....
Saving people a headache.

[VFR750R]

Kararot, check previous topics on turbo and turbo issues.
i know you're trying to point out some obvious things to the rest of the forum but
A: If you are in a boost condition, the seal is seeing boost.
B: -10psi is ~20 inHg vac, which isn't at the turbo entrance nor the throat of the restrictor, check your calcs. But you will see 20 inHg once you lift off the throttle at high rpm.

You are generally correct about the seals design intent, but everybody understands that, if you have a design fix, let us know.

[Pete M]

There are two cases where the compressor inlet sees vacuum: when throttled and when the restrictor is choked. The throttle is the one that causes the big vacuum problems, as VFR has pointed out.

I don't know what restrictor you're designing but there's zero point sucking harder on the restrictor than needed to choke it. Considering that you only need approx 50 kPa absolute at the throat to choke a 20 mm restrictor, and the pressure at the end of the diffuser will be considerably higher than that, i'm not sure where the -10 psi (approx 30 kPa absolute) number you're quoting is coming from. Might want to check your compressible flow calculations.

Now, as VFR pointed out, what the inlet sees is irrelevant, the seal isn't on the inlet. The pressure the seal sees is pretty much that at the throat before the air is discharged into the scroll. I'm not actually sure what the pressure is there, it's rather hard to measure. I'm not sure if it can be assumed to be the outlet pressure, but its certainly not the inlet pressure.

Pete