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#21
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Whether the cam is advanced on point or retarded. The intake valve is open before TDC. Check out a Comp Cams Master Lobe Catalog and it will tell you what the lifter raise is at TDC for a couple of different ICL for any give lobe.
Stan
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Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
#22
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Yes, but is it open more than the exhaust valve at TDC overlap? That's what we are trying to accomplish.
I'm not pushing the idea, just trying to explain it, but I do know I've tried it on several engines and have had excellent results. Paul and Jeff are a lot smarter than me so not only am I flattered when they share a tip or trick, I'm more than willing to try it. Since Paul has shared this with others on the forum in the past I don't think it's a secret anymore. It's worked on my 11:1 302 Chevy with iron heads that has logged 50k miles over the last 5 years, my 10.13:1 Pontiac with Iron heads that has logged nearly 25k miles now, my fathers 10.84:1 571 Pontiac with aluminum heads, and a couple other engines I've built including another Pontiac with 9.98:1 and iron heads. All of them are running the same crappy California 91 octane pump gas they sell here in Arizona, and doing it in the desert heat. I really like the results I've obtained and will continue to play with this more in the future. |
#23
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Engine is a 462 with iron 1972 7F6 iron roundports, milled to somewhere around 100 ccs. (can't find my notes). Cam is just a RAIV with Rhoads lifters. Distributor (second one installed chasing this problem) is a Davis Unified HEI. Roundport HO manifolds. Pings like crazy under load. In a 72 GTO.
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#24
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Engine is a 462 with iron 1972 7F6 iron roundports, milled to somewhere around 95-100 ccs. (can't find my notes). Cam is just a Crane RAIV with Rhoads lifters. Distributor (second one installed chasing this problem) is a Davis Unified HEI. Roundport HO manifolds. Pings like crazy under load. In a 72 GTO.
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#25
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Just a rough guess but a 455, with a flattop piston and 95-ish cc head is probably going to be around 9.5:1 compression at best. Even lower if your CC is more than 95.
That honestly shouldn't have a detonation issue with the RAIV camshaft. That cam, being what I'd consider the smallest choice I'd make in a 455, should still do a pretty good job at controlling cylinder pressure at that compression ratio. Even if other things at play aren't optimized like pistons at zero deck and where the cam is installed. |
#26
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@FormulaJones, that's what I was expecting too. So it's been a puzzle why it has such problems. The advanced cam timing is the what I'm left with at this point.
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#27
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my understanding is RAIV likes to be at 110 ICL in a 455. do you know where it is currently?
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1979 Firebird Trans Am 301/4spd (Now 428) 1977 Firebird Formula 400/Auto 2007 Grand Prix GXP 5.3L |
#28
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Like Grandville mentioned, the RAIV camshaft tends to run best around 109-110 ICL from the many who have tried them in 455's.
Personally I don't know where that puts the intake/exhaust relationship at TDC overlap because I haven't messed with a RAIV grind since I learned that trick from Paul C. But I bet someone like Stan could probably run his numbers and give us a pretty good idea where that might be. My guess, being that this cam is generally on a 113 LSA, you would have to go more than 109-110 ICL to get the intake valve open to at least .030" more than the exhaust valve at TDC overlap. The last wide LSA cam I played with on this scenario was an 068 on a 114 LSA and I moved it forward quite a bit and still only got the intake about .025" open further than the exhaust at TDC overlap, and I stopped there. The wider LSA cams are harder to accomplish this with. |
#29
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I don't remember and don't have any notes anymore on this. Maybe before I take the timing cover off I should do a compression check with all the plugs out....
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#30
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Quote:
If it's around 170-180 psi it should run on 91 octane just fine. I find that when they start getting up around 200-210 they get really finicky on pump gas. |
#31
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What does this mean in English?
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Jeff |
#32
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RETARDED!Sorry,Tom
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