Metal Guru

If you are running CIS, you don't have much choice. I've seen dyno results from others where their afr with CIS is 13.5/1 at max rpm, so I don't feel bad at all about being at 12.3/1. I've confirmed that I have equal fuel to all cylinders and I'm not running crazy boost and I've had no issues whatsoever.
All engines, either supercharged of normally aspirated, make maximum torque at 12.5/1 afr. Running 11.5/1 is far from optimal but to avoid being at 13/1 up top 11.5/1 in the mid range can't be avoided. Running too rich will destroy your engine too.

bogey1

I think the A/F ratio's that are safe depends on how you drive the car frankly. Running 12.3/1+ on the track or high speed long pulls can bring thermal expansion into play. Probably fine for spirited street use. I understand being too rich has its issues but I personally agree that 11.5/1 is a nice balance between safety and performance. The price tag from being too lean is significantly more than having it a tad bit rich. Way too rich and you have big problem though....

rodolf

Wowww... Your translation hurts my eyes Maybe my english is as poor as your french

For torque conversion : 1 FT/LBS = 1.356Nm (at 425HP : 550Nm, with EFI at 500HP : 670Nm)

STOCK intercooler is better than my blownsix intercooler for power less than 500HP, with my Blownsix IC, at 425HP, i've got more turbo lag !! And no more power than stock IC.

JBurer

Yeah yeah, ok - it's been a decade since I've spoken French regularly!

Regarding the results:
The big limitations of my system are the OEM heads and intercooler - I don't know all the details of your build, but I believe you addressed both of these items while you were CIS. Those modifications are likely the reason you had similar power with CIS that I have with EFI.

I also believe you had a non-catalytic converter exhaust. A non-cat exhaust translated into a documented 15rwhp increase in my car.

Post your full engine modification specs and we'll see if any other's who have performed staged modifications can chime in on rough horsepower increases they've seen. With some intake modifications, headwork, a more efficient intercooler and a non-cat exhaust, I'd be surprised if I weren't in the 500rwhp ballpark.
Best,
John

JBurer

PS About 80-85 degrees F ambient when I did my runs. What was the ambient air temp when you did yours?

rodolf

Same as you, 25/30°c

rodolf

John,

at 425HP with CIS, my heads were STOCK !

Only WITH EFI conversion, i've opened my heads to 38mm as my manifold ported to 38 by Turbokraft, result in 500HP.

+15rwhp with non-cat exhaust are in yours dreams Between +5 and +10HP with bypass cata..

What is your boost pressure ??

At 425HP/CIS : 1.0bar (1.1 peek). At 500HP/EFI : 0.9bar (1bar peek).

What is your A/R for your turbo GT3582 ? Mine is A/R 0.82 (TK offer GT35 with A/R 0.60 !...).

JBurer

Rodolf,
Do you recognize this car? http://www.turbokraft.com/gallery/v/Bruce/
It's the Turbo I own and it appears you used it as a baseline for building your car per conversations with Chris back in 2008 -
http://www.club911.net/viewthread.php?tid=72763

Straightpipe netted 15rwhp at 1 bar of boost. Dynoed at TurboKraft's facility when the car was built.

Makes the same power now as it did October 2005 with the cat exhaust.

Apples to apples, I'm at 440 with EFI, no cat and 1 bar. Another 1psi of boost to equalize... 10 or so wheel horsepower? 425 CIS versus 450 EFI.

Something I read in one of your posts indicated your timing is advanced 5 degrees more than mine at 1 bar. That can make a difference - both in ultimate power and in longevity.

My system and tune has almost 20,000 miles on it and runs great.
How many have you put on yours?

bogey1

all of this would be interesting if done on the same dyno. there is so much variation with each dyno, this comparison is not an apple to an apple. 425 to the wheels is the highest I have ever seen on a CIS car and frankly suspect on stock heads. If your timing is >19, your asking for trouble in the long run.

rodolf

Yes Bruce's car was my goal for my EFI conversion, but with 425hp with CIS i went more power with EFI. Today i've get 500, not enough for the hard work, so i would prefer stop running and change my camshafts to be sure to get 530hp with only 1bar boost.

The values of timing are not very important, most important is the tunning on the dyno with all sensors, if no knockout, good degree, no problem, each engine is different.

Quadcammer

Its simply a matter of heat. Running the engine richer allows the extra fuel to cool the combustion chamber. Its sacrificial if you will.

You would need to get well into the low 10s or even fatter before you need to worry about getting enough fuel into the ringlands to balloon a piston crown.

I ran my 20psi DOHC V8 (on 93 octane) at 11.8:1 at the top end to keep the EGTs in check. Made 700rwhp with 283 cubes, so it was a pretty solid combo.

Metal Guru

Dilution of the oil with fuel is the greatest risk of running overly rich.
I'm certain the factory didn't intend for everyone's Turbo to run at 11.5/1 to improve longevity under boost. Running that fat has negligible effect on combustion temperatures anyway.

Quadcammer

If you have reasonable ring gaps and rings that aren't worn excessively, its gonna take a really REALLY fat mixture to significantly dilute 12 quarts of oil. Furthermore, given that this rich mixture only happens at WOT, this is really only a concern if you do a lot of track work (when you would be changing the oil more often anyways).

I've seen what detonation does to even 2618 alloy pistons. I'll leave a few hp on the table for that negligible difference in EGTs, especially given that we are dealing with aircooled $30,000 engines.

You tune your FI 911 however you want, and I'll do the same, but recommending a 12.xx:1 a/f to others is playing with fire.

Metal Guru

With fuel dilution, the damage starts at the rings. The oil is washed away from the cylinder walls.
CIS cars get rich at mid range; they get lean at the higher engine speeds.
I've never seen a Turbo with stock wur and stock fuel head running at 11.5/1 above 5500 rpm so I'm not advocating that anyone run lean; it's just the cards that the factory dealt us. As bogey1 pointed out, it's probably no big deal on the street (if it were we'd hear about a lot more blown engines).
So Quadcammer, how is it that you are able to have 11.5/1 across all engine speeds (assuming you are running stock CIS). Details, please.

JBurer

Great contributions and appreciate the opinions. I agree and disagree with both Quad and Metal on different aspects. My personal opinion falls into the conservative is better crowd. I'd rather have slightly worse gas mileage and risk oil dilution (which I don't think is an issue) than have a car tuned spot on for premium fuel and get a bad tank of gas. High 10's at torque peak and mid 11's past it are where I'm comfortable.

That said, there really are too many factors at play to make a blanket statement on what's safe for an aircooled motor.

If you:
- know air temp won't exceed X degrees (140 F?)
- know all cylinders are getting equal air flow
- know the octane rating is sufficient
- know injectors are flowing at the same rate
- know that timing values are appropriate (and consistent)

12:1 afr (and, I understand as lean as 12.5:1) is 100% OK for an aircooled turbo motor. Tuner who built my car indicated 12 flat was appropriate past torque peak for my build, and I recently saw some documentation on a 740hp 3.8 aircooled turbo MODE build that was tuned for 12.1 near torque peak and leaner to redline. Car that saw track time.

I don't know that all of those items are always as I'd want them to be with any of my cars, so I've always erred on the side of conservatism!