High Performance 3.0 SC
 

Wayne,

Your book lists a 3.0 SC HP motor as one of your top choices for rebuild combinations. Can you elaborate a little on the requirements of this set-up?
I notice that you use 10.0 : 1 pistons. Are twin plugs required here? What size carbs? Will Weber 40s work? Is there a resource that I can go to that gets more specific about this motor? What are the expected HP and TQ numbers?

Thanks!

Lindy
78 911 SC

Where is Wayne?

He's a busy boy, these days. The forum members are as good and often better respondents to these kinds of questions. There is a lot of expertise here, including many of the best engine builders out there.

Regarding your question, while I am not a professional engine builder (I do consider myself an encyclopedia of 911 engine knowledge :)), here are the basics:

First, I agree with Wayne - a modded 3 liter is one of the best bang for the buck, most relaible options you can build. The aluminum case, relatively short stroke crank and availability of parts make it an ideal platform for a hot rod motor.

10:1 CR is typically a bit high for single plugs; while you could get away with it with 92 octane gas and by altering timing, this is robbing Peter to pay Paul. Compromising on timing to accomodate higher CR is counterproductive, as you want good timing so your motor responds crisply. This is of course cam and intake dependent, since dynamic compression is affected by both cam overlap and the volumetric efficency of a motor at a given RPM. A 10:1 static CR on SC cams would be a no-no IMHO, while 10:1 on single plugs using GE60s would be just fine.

Regarding induction (carbs), again this is dependent on how you high want to rev the car, which again goes back to intake dimensions and cam choice. A GE60 is designed to rev over 7500RPM and 40mm carbs would run out of breath at those revs; you'd want 46mm PMOs (46mm Webers are crap). For a lower peak RPM cam(like an SC or 964 cam), 40mm Webers would a great choice.

As far as torque and HP, I would recommend searching the forum for other people's 3 liter builds. The specifications are highly varied, as are the performance numbers. You can get anywhere from the stock 180HP with a nice flat torque curve, to 300HP and very top heavy powerband, depending on the choices you make.

Don't forget, as power goes up from stock, the costs associated with making that power goes up in a 'J' curve in terms of dollars. your best bet is to first set a budget for your project, then work back from there.

I hope this helps.

Here's a good example. Not inexpensive though.

PM me for more details

http://forums.pelicanparts.com/porsche-911-technical-forum/246563-another-rsr-clone-project-dyno-day.html