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spuggy spuggy is offline
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Join Date: Jul 2003
Location: Glorious Pac NW
Posts: 2,793
Quote:
Originally Posted by billjam View Post
While I have my motor apart Iím doing lots of ďwhile Iím in thereĒ type stuff and one thing thatís high on my list of things to do is to improve power below 3,000 rpm.
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It just seems so obvious to me that the inlet manifold branches, inlet spacers and head ports should be opened up.
+1 what JFairman says...

Chap, you might need to revisit gas flow theory...

Small inlet tracts, small throttle body and small valves all make for better throttle response - and more torque & tractability - at lower RPM because the velocity of the gas at part throttle is faster than it would otherwise be. Downside is that it strangles the motor at the top end.

Big problem on an N/A motor, not so much with forced induction.

Opening up the ports and using larger valves doesn't improve low end, it improves the top-end by allowing more gas to flow at large throttle openings, but at the expense of off-boost response and tractability.

Stock 930 is pretty docile off-boost. Stick to the cams and leave the rest of the top end alone if you want a better street car, IMHO (but definately use after-market rod bolts if you're in there anyway).

SC cams are said to have better low & mid-range than 964 - which have slightly more top-end (IIRC, SC are the hottest you can use with N/A CIS because of the reversion pulses, the 964 have too much timing/overlap). SC cams are hot enough to make the idle lumpy. Tweaking the idle up to 1050 RPM makes it a lot happier...

Use good headers, intercooler and a decent modern turbo, and it gets academic quite soon anyway - my motor makes .5 bar @ 2,500 RPM under load. And with short gearing and 8:1 as well, a 930 will kick you right in the pants from idle without any boost in sight.
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'77 S with '78 930 power and a few other things.
Old 07-03-2008, 10:51 PM
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