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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
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Quote:
Originally Posted by Cobalt View Post
Normally and theoretically I would agree with you but more often than not the hp gain is not as much as you are calculation states for the 964 3.3 liter motor. At least from the cars I have seen this done to as a lone modification. Not sure why that is. The engines were known to be strong to begin with had no known vacuum leaks and should produce more but they did not. Basing it on the US spec which started at 315 hp the most power the charts showed for these cars was 335 & 340bhp give or take. However, using your calculation my turbo which started at 355bhp did come in at 333.6 rwhp or roughly 390bhp by just adding a 1 bar spring. So the calculation appears to work for my motor albeit a small % low. What is even more confusing is the 3.6 came with slightly more boost stock so the increase in boost is less than on the 3.3l.

On second thought I don't know who did the tuning on these other cars just what the results showed and that might have an impact if the car was not properly tuned.

Why do you feel a 1 bar spring will trigger the fuel pumps to cut out? This is normally set at 1.1 to 1.2 bar. If everything is working you should not have that much creep
Sorry but my spell check did not work.

Porsche sized the K27-7200 almost perfictly to match the fueling of 930 CIS fuel head. What is happening with the C2T 3.3 is it dose start to run up against the limits of the turbo. Thus, it can not maintain full boost to red line.

The C2T 3.6 is alread at the limit for the 7200. Adding boost will mostly help in the mid range but there will be little gain up top.

The limit of the K27-7200 is in the 370-380hp range. Again this is about the limit of the fuel head. To deal with this Porsche changed the on boost control pressure that gets a little more fuel for the 3.6.

I would use that simple caluclation as the most just changing boost would get. In most cases losses in effecency will make the gain a percentage of this.

Changing the exaust increasses effecency with not change in boost. This can add HP. Changing the turbo to one with a larger more effecent compressor wheel will see increasses in effecency from not heating the air as much and allow the car to maintain boost higher into the upper RPM range.

The 3.6 if taken to 1 bar is potentally a 400hp motor. However severl things have to be addressed to do this. It needs a turbo cappable of supporting it, it needs a fueling strategy, it needs the restrictive cat to be removed, it may need the intake ports to be opened up a bit.

As to triggering the overboost switch. All WG's tend to overshoot there target at first and then stabilize at there target pressure. They also start to leak boost some before they hit there target level. Some of the electroic boost controlers go through a set up and learn how the WG responds. With this the can keep the WG clamped untill the desired boost level is reached. They also work on the other end to keep it from over shooting.

Not an expert, just my thoughts.
Old 02-27-2009, 06:15 AM
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