CIS performance?

Everything I have reads says that you cannot get much additional hp out of a CIS engine. Why is this? I would think that someone would build larger throttle bodies and injectors. I have a 79 SC and would like to improve the power but don't want to invest in a bunch of other parts if the CIS is going to limit their effectiveness.

Thanks

The throttle body on the carburators for the CSI fuel injection is sized for a certain amount of cfm. Your engine requires a certain amount of cfm along with the correct gas mixture. You can only cram in so much air and fuel into a cylinder during the intake and compression storke. To increase performance, you need to ram more air and gas into the cylinder. You can do this with a ram charger, or a turbo. Otherwise, you need to increase cylinder size to increase hp.

Steve.

I just did a top end rebuild and was very successful in the addition of the newer 964 cams on my 79, 3.0... got them from Pelican...I have not dyno'd the motor, but have had a number of profesional mechanics drive the car... they said that there was a vast improvement... and just had my first "top time of the day" at an autocross, result after the rebuild...AND, I drive the car every day to work.

Just my $.02.

Mikez:
I thought 914's always got TTOD's. (heh, heh)
JPIII

They usually are..just the first time with my fat butt in the driver seat...

Bruce Anderson's book has a pretty decent section on boosting power on a 3.0 CIS.

As he points out, the biggest boost can be had by backdating to the pre-75 3 into 1 type exhaust. This is good for between 17 and 22 hp at the rear wheels. It is the exhaust, not really the intake (throttle body, etc.) that is the limiting factor on the SC.

I think that's about the only mod I would do as far as things external on the engine. I never really believed in things like bored out throttle bodies, etc. To me, 99% of things like that are gimmicks and a waste of money. For example, making the bore of the throttle body a little bigger would not have cost Porsche anything more, and I doubt that they left hp on the table by neglecting such a simple thing. Same with bigger fuel injectors, more fuel pressure, etc. I remember people tinkering with Euro CIS units, bigger injectors, more fuel pressure, etc. when these cars were new. It was a waste of time then, as it is now. The CIS system, which I think is great, is not really a performance oriented system, its more about emissions and economy.

If you want to crack the engine open, the sky becomes the limit, with things like cams, headwork, displacement, possible carbs, etc.

Brian

RK:

Brian is right. I also have a 1983 SC which I use primarily at the track, and I always have the fastest (almost always?) SC.

The only thing I have done is to put on the 1974 SSI exhausts (not cheap, but they can be had at swap meets), and have boosted the fuel pressure. No cams, no Euro fuel distributor, but lots of simple suspension mods to make it go faster.

But you failed to specify what kind of power you wanted; i.e., track type which is really not horsepower but torque related; or stop light power drag racing, which is also torque, etc. But drag racing is also a question of the driver's reaction timing, and track events is really about driver's skill. Our experience at PCA is that a good set of new tires and some driving lessons at the track are worth any amount of extra dollars spent on the hardware. The software between the ears and the contact points on the seat are worth at least 50 HP........Andras

I have a 78SC and have done heavy research on mods. The best bang for the buck is SSI / big muffler combo. I puchased used SSIs and made a dual outlet muffler from stock. Ram air and weight loss are free - find a way to get it. Everything else is expensive and shows diminishing returns. I am very happy with the street performance and drivability of this setup.

How much louder would you guys say the SSI set up is over stock?

Depends entirely on the muffler. I used a stock '73(hotdog) muffler first with the SSIs, it was stock quiet with noticable power gain. I then modified the same muffler to dual outlet. The noise level can be muffled as much as you like by the internal muffler mods and exhaust tips. I am very pleased with the sound (and so is my wife). A few more horses were found as well. After 30mph you can no longer hear the muffler, at idle it sounds very good.

Has anyone done a dual exhaust with two seperate mufflers and without a cross over and THEN did a cross over?

I have done the first and I am wondering if the latter would be advantageous...

[This message has been edited by mikez (edited 12-09-1999).]

What about B&B headers? Do they perform any better than SSI systems and is there a drop in heater performance?

Also, someone talked about Euro fuel distributers for the CIS system. My car is a Euro SC so how would I know if I have one and what are its supposed advantages?

Thanks