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porscheboy1
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Carb & muffler combination.
Hi guys. I am restoring a 78 911SC and the 3.0 engine will be going back together with the following modifications. PMO carbs, Web Cams with solex grind # 104 / 102, J&E 9.5 to 1 pistons with dome tops with valve cut outs, re-plated nikes, Rebuilt and recurved dizzy and MSD ignition. The exhaust will be back dated but I don,t have the headers or muffler yet. I would like to use a Dansk sport muffler for the neat sound. I have been told to use a stock muffler with the carb set up because the carbs will not work without some back pressure?
Comments and recommendations please, oh knowledgeable ones. Regards, John |
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07-21-2013, 03:43 PM
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Registered
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Back pressure requirement is an old wives' tale due to mis-diagnosis of poor exhaust systems. IMHO, SSI's would be perfect for Solex cams in a 3.0 liter.
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Current: 914/6 GT Conversion, Cayman Old: Many PCars + Formula Racecars |
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07-21-2013, 04:10 PM
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Registered
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Theoretically...if you have a vacuum at the exhaust valve.. you have a sort of turbo effect.
The more you clean out the old burnt charge...the better the efficiency will be. So...for that to happen...a tuned exhaust which provides vacuum at all the cylinders would be ideal...not going to happen...physics gets in the way. But...you can get some vacuum with a tuned system in a small RPM range (coming on the pipe effect). If you use anti-reversion cones in the headers, you can spread the range somewhat. There are a number of tricks for the intake as well (tuned stacks/equal length runners/etc). Take a look at the type of things that were done to formula 1 engines in the 50's and 60's...when all they had was their brains. Bob
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Bob Hutson |
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07-21-2013, 08:19 PM
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Harley
