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Cobalt Cobalt is offline
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Join Date: May 2004
Location: New Jersey
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Originally Posted by 911st View Post

I love dyno charts.

I hope you are right about the 3.6 fuel head. The only difference I could detect was at the WUR that has a lower control pressure on boost than the 3.3.

It is interesting but the factory limminted boost to .9 bar with its special C2T's because of the fuel heads limitations. The limit is not really the head, it is more with the cone profile that the metering plate rides in.

There is a lot more fuel hiding in the stock head. Using an Andial of similar approach to lower control pressure, a reprofiled metering plate to move farther with the higher air flows levels, or triggering the cold running function on the 91-94 turbos that changes the duty cycle on the factory lambda frequency valve at the fuel head are all ways to do so.

On the dyno chart for the 3.3, the AFMs are to lean after 5500rpm. It might be ok on the street. However, not for a track car. If he is short shifting he might get away with if for a while. If he spends much time above 5500, his time will come.

My thoughts and work with a guy back in Colorado (Brent) about five years ago resulted in what is basically the IA head. Mostly it is a head that has been adjusted to be out of adjustment. This can be good for about 10-20% more fuel but it comes at all air flow points. When we first started playing with this we found it made for way to much fuel on first boost. I then proposed using an RPM switch to delay triggering of the WUR enrichment until the point where we needed it. This hurts throttle response by keeping the CP high for longer and slowing down the metering plate but it dose help the fuel curve on first boost.

I ended up taking a different approach with my C2T 3.3. I stepped back to a K27-7200. This limited my top end some but it came in a lot harder and faster. To this I changed how the compressor bypass valve worked to a unit that flowed more an stayed open at steady state rpm and opened immediately with throttle. Lastly I plumped a frequency valve around the WUR and used it to dial in my AFM's at all points and to quickly open the metering plate with acceleration. I may not have had the HP of some but my power under the curve was solid and my throttle response was only matched by an EFI conversion.

Not an expert, must my thoughts.
As others said for not being an expert you have sure done a ton of research. There is always so much more to learn.

I have gone over this multiple times with some local shops I have complete faith in and they don't seem to have the concerns that you do about the 964 but totally agree about the 930's. One shop in particular does primarily turbos and have built some serious cars.

I totally agree with the AFR's on the 3.3 and how he survived a season let alone a week with those numbers I have no idea. I would have expected the car to have detonated long ago. Although he might have made adjustments later he never noted them to me. I only posted that chart to show that higher numbers can be achieved although I agree it is way to lean for my comfort zone. But when you think he is getting nearly 535BHP out of a 3.3 on CIS is just crazy but apparently doable although highly risky if not bordering on stupidity.

IIRC after speaking to Stephen at IA some 4-5 years ago, he also felt that the 964 could flow more fuel than the 930 although recommends the fuel head mod. He supplied me with the spring when I purchased the HF K27. All I can go by are the readings I get from my gauges and dyno charts. David's (C2turbo) Inyourfacegauges are very accurate and my AFR's look much different than the 3.3l I posted. .

I don't have the charts on this PC to post otherwise I would, but the readings are similar to the ones for the other 3.6T I posted. Here is the chart of the AFR's and torque. I would be curious to your opinion of these numbers but I think they are relatively consistent with what I want to see to be safe. The problem with the CIS is there is no way to flatten the curve and are limited by how the system is functioning and must make compromises. Although as you can see this particular 3.6 T is making just over 445bhp. I do know this motor did die eventually after many track hours although from what I was told it was a mechanical failure and had nothing to do with fueling issues.

Anthony PCA affiliate '77 member '83 '90 3.8 RS tribute, '93 964 C2, '93 928 GTS 5 speed, '94 Turbo 3.6, M '15 Boxster GTS18 Macan GTS
Gone worth mentioning '71 E '79 SC, '79 built to '74 3.0 RS tribute (2390 # 270 hp), '80 928 euro 5 speed, '74 2.0l 914, '89 944 S2,'04 Cayenne TT '14 boxster, '14 Cayenne GTS many others

Last edited by Cobalt; 02-27-2009 at 11:20 AM..
Old 02-27-2009, 11:16 AM
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