FSAEracer03

Well... I agree the number seems like a serious low ball, but that equation is a little wrong. Thermodynamics isn't as simple as a single equation. Efficiency and size are inversly proportional, and a lot of that depends on head flow.

But yeah... I wouldn't be surprised if that figure was far on the low side

wjk_glynn

The 968 Turbo S was built as a homologation special for the 968 Turbo RS. This was necessary because Porsche wanted to compete in the German ADAC series. That series put limits on the power-to-weight-ratio (which was 337-bhp in the case of the 968 TRS). This meant that the engineers weren't going after ultimate power. But they did shoot for torque. The 968 TS delivered a peak torque of 369 ft-lbs.

So while the engine is capabable of more than 305-bhp, that wasn't their goal. In addition, the top speed of 174-mph is roughly in the ball park of 300-bhp, so the official number is probably fairly accurate.

Karl.

Oddjob

The other thing to remember about the output of the street 968 Turbo S, is the comparison/competition with the 911 Turbo 3.6. I don’t remember the sale price of the 968 Turbo S, but I recall it was less than the 911 Turbo 3.6. From a marketing standpoint, Im guessing that Porsche did not want an upgrade of the entry level 968 to outperform the flagship 911 Turbo, so they may have intentionally kept the power low. But even with 305 bhp, the performance of the 968 Turbo S was very close to matching/exceeding the 355 bhp 911 Turbo 3.6. And 10 years ago, that was a lot of power and performance. I remember car magazine comparisons where the 911 Turbo 3.6 would out accelerate the Dodge Viper RT10 and Corvette ZR1, so even with only 305 bhp, the 968 Turbo S would definitely perform with the supercars of the time.

There is an old Excellence article on the 968 Turbo that was probably out in a 93-94 issue. The car in the article was yellow and it gave some stats but I don’t recall that it was very technical. Unless Karl Glynn has some quick access to the Excellence Archives (?), I will dig it out tonight and post anything of interest.

Jason @ Paragon Products

It's a track car as it's in the U.S. as a race car only. It does have functional wipers, lights, turn signals etc., but the Mobil 1 graphics kind of make it stand out in the crowd if you tried to take it to the grocery store ;-)

Matt H

Jason, you need to spend more time in college station. I cant count the numbers of times I have driven from the track into town in full on race cars! They dont even care there, somehow, they sort of expect it
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Jason @ Paragon Products

Yeah Matt, problem is, technically the car could be seized and subject to export...probably not worth risking it.

Matt H

hahaha, in College Station? You kidding me? If they took every illegal car off the road everyone would be walking! I would be more concerned about the fact that traffic laws have apparently never been enacted there. It may be the worst city in the US to drive in! Man, I miss going down there.
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Jason @ Paragon Products

No, I understand, but in the back of your mind you always think about the possibilites. Just not worth it...not to mention that 2000# springs produce a pretty stiff ride ;-)

Matt H

Yeah, you're right about the springs...who needs fillings anyhow?
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Oddjob

Some Specs from the June '93 Excellence:

Cost DM175000 for the street Turbo S
Under DM250000 for the race Turbo RS

Factory Performance:
0-60mph: under 5 seconds
174 mph top speed

single cam, 3.0 ltr
305bhp at 5600 rpm
369ft-lbs at 3000 rpm
7.5:1 compression
1.0 bar max boost
kkk turbo

6 spd trans with 75% locking LSD
Longer 5th and 6th gears and final drive
stronger clutch

Brakes:
ABS
Same as 911 Turbo S calipers and rotors

Stiffer springs and shocks.

Delete: PVC undercoating, power windows, power seats, central locking, rear seats, sunroof.
Weight 2867 lbs

*****
Thats about the meat of it. Doesnt get any more technical than that. I cant vouch for the accuracy either.

Pic of the engine bay looks just like a 944T. Intercooler, pipes, airbox, head, intake, cam tower, distributer, ign wires, fuel rail, etc are straight from the 944 Turbo parts bin.

Danno

"Well... I agree the number seems like a serious low ball, but that equation is a little wrong. Thermodynamics isn't as simple as a single equation. Efficiency and size are inversly proportional, and a lot of that depends on head flow."

yeah, that's true. Trying to suck in 20% more air through the same-size valves wouldn't yield an automatic 20% increase in flow...

"The 968 Turbo S was built as a homologation special for the 968 Turbo RS. This was necessary because Porsche wanted to compete in the German ADAC series. That series put limits on the power-to-weight-ratio (which was 337-bhp in the case of the 968 TRS). This meant that the engineers weren't going after ultimate power. But they did shoot for torque. The 968 TS delivered a peak torque of 369 ft-lbs."

Karl's got the inside scoop! They actually had to de-tune the car to meet the homologation requirements. They did that by reducing the size of the exhaust-ports on the 968 TurboRS's heads compared to the 951. I assume this was just through a thicker ceramic insert. This does have the effect of increasing low-end torque. Does anyone have a dyno-chart of a 968 TurboS or RS?

"single cam, 3.0 ltr
305bhp at 5600 rpm
369ft-lbs at 3000 rpm
7.5:1 compression
1.0 bar max boost
kkk turbo

Ok, the lower 7.5:1 compression makes sense now. That's why you couldn't scale up an 8.0:1 compression 951 TurboS into a 3.0L and have the numbers match. One the other hand, you could go the other way and increase compression. One of my customers just did a dyno-run with a 9.6:1 951 and he got 351 rwhp & 362 lb*ft @ 1.17bar (413 bhp & 426 lb*ft crank). Amazing what you can do without being limited by a rulebook along with the advancement in 15 years of technology

wjk_glynn

Unfortunately, there were a few mistake in that article.

Here are some corrected specifications:

Compression ratio was 8.0:1
Maximum boost was 1.05 bar between 3,000-rpm and 4,500-rpm
Max torque was 369 ft-lbs @ 3,000-rpm
Max HP (PS) was 305 @ 5,400-rpm (where boost was 0.85 bar)
Gear ratios:
- 1st is 3.182
- 2nd is 2.000
- 3rd is 1.435
- 4th is 1.111
- 5th is 0.882
- 6th is 0.711
- Reverse is 3.455
- Axle Ratio is 3.400

The TS used a modified K26 (K26-2970-MXB8.11). This K26 has a bigger air intake like the K27 and the compressor is not the usual 5726, but a 5728.

The TRS used a K27.2-3072-GD11.11. It appears to be a modified version because it has a 11.11 stamp on it.

Porsche published quite a bit of technical information about the 968 Turbo S in the 3/93 issue of Christophorus. This included dyno charts...

Karl.