AFR
11-26-2014, 10:09 AM
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AFR
Hi,
I need some advice regarding appropriate AFR for a 964 3.3T with stock CIS/WUR.
I recently installed EBC and had my workshop measure AFR for different boost levels. Results were max AFR of 12 at 0.8 bar and 12.5 at 0.9 bar, where max values were reached in the upper rpm range (I think), ie above 6k rpm. Engine/fueling/turbo is stock, but exhaust has been upgraded with headers (rarlyl8), Tial WG, cat-bypass and free-flow muffler.
Do these AFR results sound normal/expected to you, given the setup of my car? Should it be safe to run 0.9 bar with an AFR of 12.5, even on the track? I've read some previous threads regarding AFR and there does not seem to be consensus on what level of AFR is safe/appropriate? It would be interesting to know if anyone is actually running AFR close to 12.5 on the track and how it is working out? Thanks.
I need some advice regarding appropriate AFR for a 964 3.3T with stock CIS/WUR.
I recently installed EBC and had my workshop measure AFR for different boost levels. Results were max AFR of 12 at 0.8 bar and 12.5 at 0.9 bar, where max values were reached in the upper rpm range (I think), ie above 6k rpm. Engine/fueling/turbo is stock, but exhaust has been upgraded with headers (rarlyl8), Tial WG, cat-bypass and free-flow muffler.
Do these AFR results sound normal/expected to you, given the setup of my car? Should it be safe to run 0.9 bar with an AFR of 12.5, even on the track? I've read some previous threads regarding AFR and there does not seem to be consensus on what level of AFR is safe/appropriate? It would be interesting to know if anyone is actually running AFR close to 12.5 on the track and how it is working out? Thanks.
11-26-2014, 12:29 PM
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With values of 3.6's being what they are, why risk one at the track unless you are a hedge fund billionaire?
Beyond that issue, a stock 3.6 making 12.5/1 afr over 6000 rpm is within spec. I would expect to see that if a wur is set to factory specs. That's what the calibrators at Porsche found to be a safe value. This was established through extensive testing, so I would trust it.
When my engine was stock with headers and sport muffler, factory settings yielded similar results. Low speed afr was 11.5/1 and topped out at 12.6/1 at 6200 rpm. I didn't ever rev beyond 6000 in normal spirited driving because the stock K27-7200 turbo and cams ran out of flow beyond that engine speed.
CIS cannot deliver fuel under boost in a linear fashion. Some run an boost signal interrupt on stock engines but I don't agree with having 13.5/1 afr at boost onset, when engine load is at it's greatest.
If you are concerned about extended time at boost on the track (I certainly would be) you should get an Andial intercooler like the one used on the IMSA 964 Turbos in 1991-1992. They can be hard to find but would be good insurance. Another alternative would be a good aftermarket, full bay intercooler. Talk to Chris at Turbokraft. He's a good source of info as well as parts.
Beyond that issue, a stock 3.6 making 12.5/1 afr over 6000 rpm is within spec. I would expect to see that if a wur is set to factory specs. That's what the calibrators at Porsche found to be a safe value. This was established through extensive testing, so I would trust it.
When my engine was stock with headers and sport muffler, factory settings yielded similar results. Low speed afr was 11.5/1 and topped out at 12.6/1 at 6200 rpm. I didn't ever rev beyond 6000 in normal spirited driving because the stock K27-7200 turbo and cams ran out of flow beyond that engine speed.
CIS cannot deliver fuel under boost in a linear fashion. Some run an boost signal interrupt on stock engines but I don't agree with having 13.5/1 afr at boost onset, when engine load is at it's greatest.
If you are concerned about extended time at boost on the track (I certainly would be) you should get an Andial intercooler like the one used on the IMSA 964 Turbos in 1991-1992. They can be hard to find but would be good insurance. Another alternative would be a good aftermarket, full bay intercooler. Talk to Chris at Turbokraft. He's a good source of info as well as parts.
11-26-2014, 01:30 PM
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Thanks alot for your reply Metal Guru! I have '91 3.3 turbo but I guess your points are still valid?
So the IMSA 3.3 turbos had andial intercooler which is more efficient/reliable when driving on full boost for extended periods, such as on the track? What about the turbo S leichtbau '92? Did the factory do anything do make the engine more reliable during track use? Did it run close to 12.5:1?
So the IMSA 3.3 turbos had andial intercooler which is more efficient/reliable when driving on full boost for extended periods, such as on the track? What about the turbo S leichtbau '92? Did the factory do anything do make the engine more reliable during track use? Did it run close to 12.5:1?
11-26-2014, 02:26 PM
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Thanks alot for your reply Metal Guru! I have '91 3.3 turbo but I guess your points are still valid?
So the IMSA 3.3 turbos had andial intercooler which is more efficient/reliable when driving on full boost for extended periods, such as on the track? What about the turbo S leichtbau '92? Did the factory do anything do make the engine more reliable during track use? Did it run close to 12.5:1?
So the IMSA 3.3 turbos had andial intercooler which is more efficient/reliable when driving on full boost for extended periods, such as on the track? What about the turbo S leichtbau '92? Did the factory do anything do make the engine more reliable during track use? Did it run close to 12.5:1?
Everything I stated is valid for your 3.3.
The key to track use is to have an intercooler that won't get heat soaked due to high duty cycle use. It has to keep cooling the charge air effectively or hp drops (thermodynamic efficiency) and thermal load on the engine increases. Bigger is better in all dimensions.
The "S" had a stock intercooler as far as I can determine. I don't think anyone knows much more than that about that engine regarding fueling strategies but I can virtually guarantee it topped out at 12.5/1. We would have to see if the part number for the wur differed from a stock car.
Now if you were to score a Secan intercooler you'd have no worries at all but the are as rare as unicorns and twice as expensive.
