Waynes Top Engine Picks - Questions for JW or Wayne
 

I'm currently building a 3.0 USA SC with Waynes hot pick suggestions:

Keeping CIS
9.8:1 JE's
Elgin SC330 Cams (Step below 964's)
SSI's 2/1 sport muffler
Bore/Blended intake/runners ~37mm.

I was told this combination would cause lean running and possible detonation with leaving the CIS stock. Would replacing the fuel distrib. and WUR with the 81-83 Euro units help (as the Euro's also had 9.8:1)?

See thread for more detail:

http://forums.pelicanparts.com/porsche-911-technical-forum/113153-cis-gurus-help-me-safely-inject-my-hot-rod-3-0-a.html

Bump....

Obviously I will need to increase the fuel flow to keep up with these mods. Are there other ways to mod. k-lambda CIS other than decreasing the control pressure via the shims and increasing the idle CO? Any thoughts as to how will this affect the A/F throughout the RPM range and WOT? I have a feeling it will start rich and continue to lean out as RPM's increase, possibly a function of the fuel distrib flow curve. Just looking for some verification.

You shouldn't have a problem, this motor has been built many times before with good success (that's why it ended up in my Pick's section). I'm missing your argument as to why you need to increase fuel flow? The air pumped in and out of this engine would be exactly the same with your new setup as the old setup. Therefore, the air fuel mixture will be the same as well (theoretically). Steve's comments on Rennlist were directed at someone who was doing all these mods, *and* increasing displacement. I have indeed heard of problems running the 2.7 CIS on 3.0L motors - the one I know of never ran correctly.

My advice is to build the engine, and spec it on a CO meter when it's done. At that point, if you have problems, you can address them then...

-Wayne

The concern came after reading some of Steve's replys on similar mods and talking to him presonally about my specific setup. His personal opinion was CIS in stock form does tend to run on the lean side (not helpful for higher CR) and richening (increase fuel flow) will be needed to keep CHT down, prevent detonation, etc, etc....

Wayne, I'm going to do just that....build, break in, and dyno to get true results. Currently building a little cabin A/F meter to give me a general idea of whats goin on.

Thanks for the advice.

Steve is probably right, but you have the right idea. Build the engine, and see how it runs. The fuel system is one thing that you can always alter and change. Particularly with CIS, it's very easy to swap components or even modify the WUR to give slightly more fuel flow.

The *only* concern with this strategy (and it doesn't really apply to your car) would be for modifying the 3.2 engines with Motronic. There's a very small paragraph in the engine book (almost too small, as I had to stuff it in at the last minute) that mentions you should be careful about boosting the CR on a Motronic car without a knock sensor (which the Carreras don't have in their particular version of Motronic). This is because you cannot retard the timing if you start to get detonation. The timing is controlled by the pre-programmed computer from the factory. The only solution would be to rechip the computer, or remove and replace the Motronic with an Engine Management System (big $$$). If you don't, and your engine continuously detonates due to too high compresson, it will slowly blow itself apart. The 3.6 cars don't have this problem (in general) because they have knock sensors that can sense the detonation and back the timing off (they also run at 11:1 or so compression).

-Wayne