Yes, we have octane ratings of 87 / 91 / 93 at every gas station here.
PROJECT " LAID BACK 2 " - 1978 SALON 2 DOOR AEROBACK
- Thread starter JAMCAR223
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Thanks for the info as it explains plenty. The hydraulic intensity of this is big, which implies this cam is much bigger than the 204/214 numbers give it credit for. And that explains why many would recommend it. Usually (in the SBC world) cam duration specs at .050 lift assumes a modern hydraulic intensity of 42-48 degrees. But this cam has 76 degrees of hydraulic intensity. As compared to modern grind of an equivalent Comp XE grind, your cam is more like a 214-217/224-227.
Cam's with large hydraulic intensity are 2-3 times easier on the valve train and cam than the aggressive, modern grinds. Especially in moderate lifts. Not knowing Jim Lapikas, I give him kudos for recommending this.
It is a reliable cam, ran a couple for years. It is known to bleed off compression but a 8.5 to 1 Olds 350 is different than a 400+ ci 9.8 to 1 motor, if he 0 decks the motor. I also didn't degree my cam, so it could have been off. My timing set was accurate, I advanced it two degrees but the cam could have been off even if the timing set was accurate. I had 135 to 155 psi with this 204/214 cam in a 8 to 1 403 installed straight up, again not degreed but the timing set was checked with a degree wheel in a later build. He will be at 9.25 to 1, maybe slightly higher with just a clean up on the deck, so he may be fine. Those Speedpro pistons usually sit .025" in the hole like factory pistons, so he can adjust quench with decking or head gasket thickness. Olds like a lot of timing part throttle compared to other makes.
1967 60cc #4 castings - cleaned, pressure checked, hardened valve seats, filled exhaust crossovers, new bronze guides, Edelbrock 2.07 & 1.68 BBO valves, .500 lift springs, stage 1 porting. Possibly the last set of cast iron heads he ever does.
I calculate 9.6 to 1, maybe slightly more depending on the clean up on the block. I still say you are flirting with disaster. My 350 pinged with 9.6 to 1 with similar quench and that cam advanced two degrees on the timing set. I didn't degree it but will this time, maybe my cam is out of spec. My heads have filled crossover's, not sure if that effects anything, would probably help if anything. If I can find a single piston and rod, I plan on polishing the chambers from 55 to 60CC to get under 9.5 to 1 with better quench, reuse my .028 head gaskets, since only 91 is available here. Let us know what timing you can run on your 408 with 93. I plan on just under 50 total, 20 base, 18 mechanical and 10 vacuum with a 6AL box.
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