Lizard928

12.2:1 AFR is common for alot of the "tuner" cars to run with high boost.

Fabio421

At 10psi of boost pressure I would think you would be seeing about 454 hp at the wheels. And you should have gained way more than 7 HP by bumping the boost up 2 psi from 8 to 10. I think the turbo may be too small for your application. It seems that it can't flow enough at high RPM and is becoming a restriction. Then again, what do I know

As for the intercooler, with the turbo mounted that far back, I would bet you are shedding quite a bit of heat through the compressor outlet tube on its way to the engine. Are you using aluminum or steel for this piping? Adding an intercooler to this setup will add a heck of alot of volume to fill. Normaly an intercooler is a no brainer, but with this much charge piping to fill it may be better to leave it off for now.

Do you have the exhaust piping to the turbo ceramic coated or wrapped to retain heat?

In closing I say good job. I saw pictures of this install a long time ago and wondered what happened to it. Keep it up and you will work out all the details. Another interesting boost option for 928's. Keep us posted as to your progress.

Z

Some brand new turbo cars are run at 14.7: AFR, from the factory, with more boost than this, and with a warranty.

heinrich

Exactly. The little 944 turbo runs 2 bar right from the factory, with 65lb injectors ... and that's with a 1977 VW Bus engine basically.

heinrich

CF and steel

Courtshark

Forget intercooling... go with water injection to cool the charge air. It will flatten out those HP waves in the upper RMPs fo sho.

89 928 turbo

Good comments Fabio....

"At 10psi of boost pressure I would think you would be seeing about 454 hp at the wheels. And you should have gained way more than 7 HP by bumping the boost up 2 psi from 8 to 10. I think the turbo may be too small for your application. It seems that it can't flow enough at high RPM and is becoming a restriction. Then again, what do I know

As for the intercooler, with the turbo mounted that far back, I would bet you are shedding quite a bit of heat as through the compressor outlet tube on its way to the engine. Are you using aluminum or steel for this piping? Adding an intercooler to this setup will add a heck of alot of volume to fill. Normaly an intercooler is a no brainer, but with this much charge piping to fill it may be better to leave it off for now.

Do you have the exhaust piping to the turbo ceramic coated or wrapped to retain heat?"

..........You have our final punch list down pretty well....We have the exhaust presently wrapped with manifold tape to the Turbo in the rear to maintain heat......454hp at that level boost is about right, so we are only 50 or so out....your right about the RMT shedding heat on the way up to the front of the car. What we have measured is at 5-6 lbs, the air at the turn of the carbon fibre elbow is 20-30 degrees over ambient...that likely changes significantly at 10.6 and higher. Air in = Air out.........we are working on a more efficient crank ventilation system with Louie's advice. The bump from 8-10 lbs should have yielded more...we anticipated it would push us over 400. AFR is a little conservative at 11.5 to 12ish on the recommendation of several of our friends who build turbo cars for a living ........ http://horsepowerconnection.com/.

We think there is some help in some final timing adjustments, but finding the turbo's work a little different than the SC cars.....we tune for "high boost" 12lbs of boost at WOT and have a "low" boost setting at some lower number and WOT, and end up going a little rich....with open loop.

STS is going to go over our numbers a bit too.....just to backcheck. The wheel is rated to 600 hp so we are pretty confident with that, but depending on sizing for the exhaust side, is the shift in the power curve. We have worked with three different sizing....S-Med-L...the smallest reduced the lag time but ran out on the high end, the largest did just the opposite and it was sluggish for street driving. The middle of the road is where we are targeting, but it will be an choice for anyone to make. The two pound fade needs to be located......boost controller QC, unknown leak, wastegate seating....?

we'll get there.......

89 928 turbo

Intercooling..........

Less of an issue at lower boost levels, don't like putting things in front of the radiators....we are working with Snowperformance... http://www.snowperformance.net/ on a methanol solution.

they seem to be one of the best around and we have that enormous windshield washer reseviour just wasting away........I just hate drilling holes in the throttle body....but it will help solve a lot of the higher boost issues, protect the engine a lot more.

We are going to sort out the other issues first though, because I don't want to mask a problem with chemicals unless it solves them.

SwayBar

Is that at WOT?

If so, then surely the factory compensated with a lower compression ratio, cam-timing specific for a turbo, etc, etc. Also, they were not going for max hp either since running stoich at WOT will not produce as much power as 12.5:1.

Hmmm, on the other hand though, if this is a direct injection engine, then that's a whole other world I know nothing about, as well as it's implications with respect to forced induction tuning.

Let's have some link-age, man!

Back at the ranch though, our 928's have none of the above.

Tom. M

Actually..JT's motor was built with boost in mind...the CR is 9:1..and ring tolerances were adjusted to compensate for boost.....

he should be able to boost 10psi without too much of an issue..

I think the stock 951 is 8:1 ?....

Later,
Tom
89Gt(former rear turbo GT )

Jim R.

Nice work guys, I was wondering what happened to this project.

Jim

NickT

Are there any pictures of this setup? Sounds very interesting.

Fabio421

Click the link that was posted at the begining of the thread. There are pics there.

atb

Dude, warranty is voided at anything above 7.5 psi.

Fabio421

You should see a reduction in inlet temps if you change to aluminum piping on the compressor outlet side.

BTW, your website doesn't seem to be working fully. Maybe its just not ready yet.

Thanks for sharing guys.