Quote:
Originally Posted by Myazel
My 40 series Zeniths have 32mm venturis in them which look easy enough to open up to 35 or 36mm as I have a rather complete machine shop here at the house and a background in such work.
Knowing that the 2.7 RSR engine ran 8.5 to 1 pistons back in the day with similar intake and exhaust geometry (although more cam) I felt the combination I had in mind should get me somewhere north of the factory horsepower rating of between 165 and 175 depending on what you are reading.
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You don't want to open the venturi up much past 34mm, or you will kill the venturi effect. Opening up the vents on a stock-ish engine won't do anything but make a poor running engine. With your engine I wouldn't go bigger than 32mm, in fact as is I'd likely keep the 30mm vents.
I have 34mm vents in 40mm webers on my big port 3.0SC with big cams and twinplug. IMHO if I wanted bigger vents I need to step up to the 46mm carb.
Modern cam grinds with proper carb pistons you can easily bump the CR close to 9.5 on single plug. It's the only way (plus head work, etc.) to get close to the performance numbers you want.
Once you start down the performance slippery slope the gain increments are
very small, it's the sum of all the mods and parts that shows the larger gains in HP.
Porsche prices... bring money.