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Cobalt Cobalt is offline
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Join Date: May 2004
Location: New Jersey
Posts: 1,592
Originally Posted by 911st View Post
Typical boosted CIS fuel curve. With the triggering of boost enrichment it first goes to rich untill the metering plate stalls out. Then the motor has to increass rpm enough to use up the to much fuel to get the AFR's back to something that makes sense. Would be more fun to run a boost controller that would boost higher at low rpms and pull back as the fuel runs out.

A factory stock C2 Turbo's AFR curve is a beautfull thing and near perfict bot pre- and post-boost to red line. Once we turn up the boost the metering plate gets out of the area where the cone around it is calibrated to air flow expectation. It dose not travel very far before it starts to stall. I wonder if the 3.6 made some changes in the cone area.

That cone around the metering plate is like the rpm by air flow map on EFI, or a space cam on MFI. Change the air flow expectations and ya get our of wack.

If I was running a CIS turbo on the track, I would want AFR and EGT readings. Running some race fuel is also a must on a track turbo from what I hear. Again, anyone that runs a CIS turbo on the track without a EGT is playing about $10k or more worth of chicken.

If you have tested your AFR's with a wide band and are and they are good, that is great. I am supprized if it can support 450fwhp with out some fueling help above 5k.

Stephen was a help in my being able to learn about CIS. I used to frequent a Turbo board where we used to hang out and play what if. I am thinking your may have been there to. Back then he and others thought the USA head, lines, and injectors were a limitation and the euro head was the thing. I did not belive this as the cross section of the USA lines though smaller than the euro, still where plenty large for to deliver more than enough fuel with fuel pressure delivery an the spraying full time like CIS dose.

With the IA head came disabling the Lambda function by closing the internal passage and in effect making the USA heads euro heads. I am not a big fan of this as it kills the Lamda function and cold start function on a C2T.

Most do not know this but there even more fuel flow is available from a stock USA head than the IA head by ensuring full travel of the metering plate at upper air flows and playing with the lambda frequency valve which can do the same thing as recalabrating the the euro head dose.

Thinking back to somthing you said earlyer. It sounds like you might be getting a little boost creep with your HF. Though it seems a very acceptable level. This is best watched under full throtle in a higher gear.

For the record I also monitor my EGT and my I/C temps output side on the street. I enjoy this car too much to take unnecessary risks. I was at the shop I use last night and he said my car will have no problem flowing the fuel I need and the charts and in his case meters don't lie. He never trusts a static dyno test and always straps gauges onto the car to monitor all required parameters under actual real time conditions before he releases if for use. His opinion was if the numbers are good under all load conditions he feels confident that the car is running fine and will stand behind it if something proves otherwise down the line.

I agree messing with CIS is tricky and after several SC's and CIS injected cars I know what can go wrong and have no desire to go there. What I don't understand is why was Porsche so cheap with the CIS system used? My father has a 75 450SL since new using CIS and his fuel head will allow you to adjust each cylinders fuel flow individually. One chance we all take by running higher boost and monitoring parameters at one point is you can have an imbalance in the cylinders and not be aware of it and still show acceptable numbers. Of course many factors come into play. Although it would be nice to be able to test each cylinder or bank of cylinders and make fine adjustments so that no one cylinder is an issue. I figure for the amount I drive this car and that it is not tracked I should be OK, As far as tracking a turbo it is a crap shoot and so much can go wrong if not monitored properly. That is why I am happy beating up on my C2. It is a tough car handles well and is fast enough to have fun and cheap enough not to cry over if something goes wrong.

As far as boost creep the charts I have were done in both 4th and 5th gear and show similar readings. So long as i don't exceed 14.8PSI I think I am OK. Using David's gauges I find that after viewing most spirited drives I am seeing peak boost readings of no more than 14.6 so even less than what i see on the charts although i have seen numbers as high as 14.9 PSI but not very often.
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
Old 02-28-2009, 05:51 AM
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