Gear-Heads! Altering Compression Ratio Another Way...
04-27-2004, 09:08 AM
#31
Three Wheelin'
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Originally posted by Dan Perez in this thread: https://rennlist.com/forums/showthre...10#post1241710
whether right or wrong, always good to consider alternative views
http://theoldone.com/articles/itisd...ehardheads.html
whether right or wrong, always good to consider alternative views
http://theoldone.com/articles/itisd...ehardheads.html
10-26-2005, 05:51 PM
#33
I wish lag was here to tell us how this went if he did it. I was disappointed in not seieng you when I visited Tim Murphy in September Lag.
10-26-2005, 08:40 PM
#35
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That's basically what we've done with our 3000GT....we run long duration (300 degrees intake) camshafts to lower the CR,and with a proper backpressure from the turbo (less backpressure than boost pressure) we ran 30 psi on 98RON (that's 92.5 US rating) without any problems. Backpressure is CRITICAL...get it lower than the boost,then you can think of going over 22 with a reasonable amount of safety. Long camshafts induce bad low-rpm power,you say? Nope. With a well-matched DBB turbo you see a few psi of boost even at very low rpm,and this more than makes up for your lost "camshaft induced torque"... don't mention emissions though,as soon as you're off idle it needs to run rich to run smoothly. 601.4ft/lbs at the wheels ( 4WD) on pump from a 3-litre,anyone...?
12-06-2007, 06:45 PM
#37
Guys, when I built my supercharger engine (5 litre 32 valve) for a road car, I fitted GTS cams as i thought they would be better for a sc car. I found that when I was running the engine in, the car (without sc) it had better torque than a standard S4 and similar top end. Stage 1 SC worked well (about 7psi), and also at Stage 2 (nearly10psi), although I found with the higher boost, the blow off valve seems to open more than I would expect - I assumed this was because I hadn't adjusted it correctly, but now I wonder if it is a symptom of the set up I chose.
Regarding compression, I expected no or little change due to the cams (engine/pistons built to c 9.7:1), however I recall when I did the initial compression tests the readings were higher than I expected, but maybe that was simply because the engine was a close to a brand new 928 engine as you can get (re-honed, new pistons etc)
Adrian
Regarding compression, I expected no or little change due to the cams (engine/pistons built to c 9.7:1), however I recall when I did the initial compression tests the readings were higher than I expected, but maybe that was simply because the engine was a close to a brand new 928 engine as you can get (re-honed, new pistons etc)
Adrian
