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Lukesportsman Lukesportsman is offline
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Join Date: Apr 2003
Location: Terre Haute, IN
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I know that in many engine families we go short stroke for more rpm. BUT there aren't too many Porsche engines made from the factory that spin any higher than a 3.6 GT3RS engine. With regard for the Porsche engines, its seems quality rods and valve train determine rpm more so than stroke/crank or engine size.

I'm pretty certain that you can install newer heads on a smaller bore space block, BUT it will require a lot of work ie welding and drilling if I'm correct. I'd think some ported E heads or S heads would easily flow more than enough under boost. S/ RSR spec heads aren't short on flow and would outflow some CIS heads anyway. Off boost port flow could be miserably slow without compression or camshaft. I'm sure CMW could make you some killer heads to your spec's....but you might have a power curve like french curve towards redline with nothing below 4000rpm.

Larger bores are of course going to help unshroud valves, but yet cause more flame front issues. I'd think Nickies would be able to maximize bore and maintain strength. At this point, you'll probably want to entertain the dual plug thing for a big bore high rpm engine under boost. If you go down to a 2.4-2.8 engine and then drop compression to 7-7.5:1 you've better get the gear ratio down for off boost torque deficit. I'd think you'd break a 7:31 so maybe a 8:31 with short stack gears.

Jmho...great project for track. Street, by the time you get compression down and rpm up your going to have a pig off boost. Your going to need to look for a nice little GT turbo for spool and I'd seriously consider the SSI route the Brian and Ben have put together for a torque throttle repsonsive turbo. Most aftermarket turbo headers will be BIG. Most KKK options that are improved will be BIG. Custom cam is probably easily doable. There has been many 2.x turbos ran on the track, just not sure of "streetability". I don't know your experience so nothing personal. These two valve hemi air cooled dinosaurs don't do well with high boost levels and therefore you can't make up displacement with psi like many 4 valve water pumpers. As you surely know a low boost 3.6 will walk all over this on the street. Not only due to engine/torque curve, but tranny options and little to NO weight benefit with a boxster of a 2.0 to a 4.2 liter. Small block ford weighs about 450lbs and a big block weighs like 720lbs. There might be a 40lb difference between a big and small block Al boxster engine.

I just feel your maximizing the short comings of Porsches own 3.0. Unlike so many engines, head temp is your limiting factor and you just can't cheat that. Interesting project and I wish all the best. I'm sure I sound like a dark cloud...just devil's advocate. In the right chassis and properly geared this could be a real screamer. Cheers
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Luke S.
72 RS spirit 2.7mfi, 73 3.2 Hotrod on steelies, 76 993 3.3efi TT, 86 trackrat, 91 C4s widebody,02 OLA winning 6GT2, 07 997TT, 72 914 v803996TT
Old 12-13-2007, 04:28 PM
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