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Registered
Join Date: Oct 2006
Location: MYR S.C.
Posts: 17,321
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valve adjustment and power
i saw a post somewhere else where someone suggested to adjust the valves (non-porsche) to .006 instead of .010, that it would help if they wanted more power in the upper RPM's.
jsut a quick estimate, but i think on a porsche .004" lift is equal to about 1 degree of crank rotation....no? so if you adjusted the valves to .008, the cam timing would retard 1 degree? i will have to research more until someone chimes in.
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86 930 94kmiles [_  _] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD88 BMW 325is 200K+ SOLD 03 BMW 330CI 220K:: [_ _] RUNNING: [__] NOT RUNNING:01 suburban 330K:: [_ _] RUNNING: [__] NOT RUNNING:RACE CAR:: sold |
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10-27-2011, 11:39 AM
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Chain fence eating turbo
Join Date: Dec 2008
Location: Austin, TX
Posts: 9,173
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Risk vs reward issue to me.
Risk banging a piston for like 2-5hp (just throwing out for reference)...... 
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Cory - turbo'd '87 C3.2 Guards/Blk, 3.4, 7.5:1 CR, 993SS cams, Borg-Warner S366 turbo @ 1.2-1.5 bar, Treadstone full bay IC, 70mm TB, TiAL F46 WG, HKS 1 1/2" BOV, twin 044 pumps, MicroSquirt AMP'd w/GM smart coilpack, Bilstein coilovers, Tramont replica Speedlines (285's rr, 225's frt), Big Reds frt, 993 rr., tower brace, MOMO wheel |
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10-27-2011, 11:57 AM
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Flat Six
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Quote:
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Dale 1985 Carrera 3.2 -- SOLD 2026 Jaguar F-Pace / 2025 Ford Bronco Sport |
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10-27-2011, 01:03 PM
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Registered
Join Date: Mar 2007
Location: Rockville, MD
Posts: 794
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Theory is that if the valve closes slightly sooner, it increases dynamic compression. I tried it and couldn't tell any difference with seat dyno or lap times.
Chuck |
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10-27-2011, 01:25 PM
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Registered
Join Date: May 2003
Location: Columbus, Ohio
Posts: 1,108
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I think that thighter valve clearance would increase valve lift but I was told that tighter vales hurt acceleration and can burn valves. Hard to justify .001 or .0015 decrease or increase since it is so small it would hardly do anything for power.
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10-27-2011, 01:59 PM
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Flat Six
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As a point of reference Web Cam (Web Cam Inc. - Performance and Racing Camshafts) lists a number of factory and custom grinds for 911s, including these two for carbureted engines:
Lift (I/E) ----------- Duration @ .050 lift (I/E) .450 / .400 --------- 232* / 222* .475 / .440 --------- 256* / 238* First cam described as "Good overall performance for carbureted engines. Very borad power range in off-road racing engines." Second cam described as "Excellent profile for the 2.7 liter engines. Good torque and better acceleration. Designed for hot street and club racing. Carburetors or mechanical injection." Assuming your rough estimate of 1* difference in duration is accurate, seems hard to believe it'd make any noticable performance difference compared to the 24* / 16* differences in the cam durations above.
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Dale 1985 Carrera 3.2 -- SOLD 2026 Jaguar F-Pace / 2025 Ford Bronco Sport |
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10-27-2011, 02:45 PM
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1985 Porsche Carrera
