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Join Date: Jul 2005
Location: Las Vegas, NV
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Porsche cam questions

Hey all,

The past few years I have been up to my neck in Ferrari stuff and their various cam options and streetable capabilities. I am wondering what a good early 911 with carbs or mechanical injection can handle in terms of cam lift/duration on the street without being unweildy.

For instance, a Ferrari 308 engine with webers can handle about 303ish degrees seat to seat duration or 253 @ .050 .370 lift. Lift with stock springs is limited to .380, and these engines run best with tight lobe angles. 10:1- 10:5.1 compression. Say 104 intake and 104ish exhaust lobe centers. The thing is, in stock form, a 308 head intake and exhaust ports flow nearly the same. Intake ports require a bit of porting to make things flow the way we want them to, but getting 120cfm average @ 28" is pretty easily done with just a good quality valve job, so for these purposes that's what I will say the norm is. With the above cams and heads set up correctly, 275bhp @ 7700rpm is the norm and makes for a very drivable car. Shift point about 8.2k. Ferrari's period racing cams, 'P6' cams are a bit hotter at 266 dur @ .050 and .376 and the car is just not friendly on the street. I would think with a good injection system this could be tamed quite a bit, but that's a whole different thread.

What is the 'norm' cam for hot street setup for 911s? I do not want an unweildy engine on the street. About what is the average head flow with these things?

Thanks much all.
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Old 12-28-2009, 08:09 AM
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Porsche 911 engines come in sizes between 2.0 and 3.8 liters. They have many different intake and exhaust options as well as twin plug or single plug. We might need a little more info to answer your questions.

-Andy
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Old 12-28-2009, 08:32 PM
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I am looking at the RS or S clone variety engines with mechanical injection. 2.7-2.8 liter-ish.
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Old 12-29-2009, 07:47 AM
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I have owned a 2.4 S, a 2.7 RS replica and now have a 3.0 SC engine. The RS spec engine started with Solex cams (similar to "E" cams). I changed to "S" cams in hopes of more power (it is a race car). I found the Solex cams to be better than the "S" cams overall and even on the track. The "S" cams only seemed to have slightly more power at 7000 plus RPM and less torque below that. The engine had 36mm ports (same as the 2.4S engine). Both of these cams are "old" technology. A more modern choice would be the GE 40, or GE 60. The GE 40 is also known as the "mod S". I don't have the duration numbers in front of me. Much of the character of these cams has as much to do with the large overlap at intake TDC as the duration. Power for these cams peak around 6800 to 7200 RPM.

You will find that in building a 2.7/2.8 engine with a Mag case the practical RPM limit is 7500 based on longivity. Above this the flywheel likes to come off and the case likes to crack. You can get about 240 HP out of these engines and have a long life, reliable engine.

-Andy
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Old 12-29-2009, 07:32 PM
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Old 12-29-2009, 07:32 PM
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