89 928 turbo

We have a standard 7 1/2 lb spring in the waistgate, with a dial up boost controller. With the boost control off at 7lbs we made 442.9 HP and just under 500 ftlbs torqe (4200rpm) and was also at 12.25 AFR we crossed to 11.8 AFR at 4600rpm and continued rich to 10.5 AFR into 6000rpm. With future tuning, we think we should be able to pull another 20-25 hp.

89 928 turbo

7lbs - 442.9 HP/ 490 torq
10 lbs - 476 HP/ 526 torq
15 lbs - 612 HP/ 565 torq

Still lots of tuning to do with the ST both to optimize and protect....I agree with Louie on this for any forced air induction car, that ST tuning is necessary.

After the rebuild, the car (with 9:1 CR), pulled a fairly normal 270HP without the Rear Mounted Turbo

Ketchmi

Very impressive but the math is not coming out right, you are getting approx. 24.5hp per # of boost up to 7psi, then 11.3hp per # of boost up to 10psi and then 27.2hp per # of boost to 15psi? You might want to check your gauge as it may be reading high at midrange. I am usually seeing 500+ish rwhp at 10psi.

Overall you are getting approx. 22.8hp per # of boost which is what I would expect out of a well designed boost system.

Courtshark

Meant to say this earlier... what a freaking awesome showing!

So what was the A/R at 15 lbs of boost at max HP? The last 750 rpm was foregone because the A/R was leaning out, right? Also, can you measure the charge air temp? If it's super heated, water injection would be good for another 50+ hp.

The CR change makes a huge difference. Performance-wise, 7 lbs at 10:1 is about the same as 14 lbs at 9:1; at least it is in Saab-turbo-land. (I run 25 psi in my 9:1 SPG; custom turbo. My brother runs 11 psi in his 10:1 sleeper, using a stock mitsubishi TE05. The cars are nearly identically fast up to about 100 mph, and then I can pull away). Can't expect to run 15 psi on a 10:1 motor; not without water injection, the perfect turbo, and metal head gaskets anyway.

Dennis Wilson

JT,

Are you using an intercooler? With the methanol and heat loss due to rear mount it may not be required. It is confusing that at 7 and 15 lbs you have gains of 9% per pound of boost, yet the 10 lbs run had less than 8% gain. Too much methanol?

Dennis

atb

JT is running methanol injection, cometic stainless steel head gaskets (with the leak-proof option), and apparently, a perfect turbo.

Courtshark

well, 2 out of 3 ain't half bad! - Yogi Berra.

Seriously, though, what turbo is on there? No such thing as a perfect turbo... (one that generates no heat with its charge air and has no lag) but the variable vanes are purty durn close.

89 928 turbo

This is so, there is still a lot of tuning to sort out.....I think that Louie has tuned Jim's SC at 10lbs at 505hp at 6200 rpm....and so that is generally our goal at that boost level, although our HP comes on much sooner as the power curve on the turbo is much different than the straight line on the SC cars.

The_Remora

Amazing JT, congrats man!

Mongo

With that lower boost, is methanol injection still necessary to cool the charge air to avoid an overly lean state?

Dennis Wilson

Andy,

He would probably be safe without methanol at 7.5 Lbs, but since he has a 9 to 1 CR any higher would be stretching it. My 931 has an 8.5 to 1 CR with a 1 bar boost and no IC or methanol and I have to be very careful to not run too lean. This happened 2 years ago when it developed a bad connection on the DITC and it cost more than $1,500 in repairs. i.e. I would consider the methanol cheap insurance.

Dennis

Tony

FYI..ive got a snow perfromance kit just sitting on the bench here. Pump, resivour, 2 nozzles and a MAF controller. YOU would need new hose line and some of the nit picky hardware however.

$200

http://www.snowperformance.net/product.php?pk=9

AO

It's all about controlling detonation. You can run as much boost as you want as long as there is no detonation. Lower compression, higher displacement, higher AFR, intercooling, and methanol injection are all different ways to control it.

Theoretically, if you could control detonation reliably, you could run up to 30~40 psi of boost without issue. But if the motor started knocking at those pressures, something's gonna give and it won't be pretty.

Mongo

Very true. The last thing I wanna do is start cracking piston rings and burning valves in my 928.

Dennis Wilson

Andrew,

Besides detonation (fuel and ignition) running too high of boost on engines like our 928's can cause problems with head gaskets, pistons, rods and head studs. Too much boost with a standard compression ratio will cause the fuel to ignite without the ignition. i.e. you have a diesel. Even the standard 931 had beefed up components and they only ran 10 to 12 lbs of boost.

Dennis