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#21
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Too many things can effect the driving.Quality of fuel where you live,if you drive in a lot of stop and go traffic where your engine temps get high.There is no hard firm number IMO.Tom
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#22
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91 octane pump fuel for the last 20 years here in Arizona. It's all 10% plus ethanol here.
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#23
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Quote:
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 |
#24
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Run the 6X-4 heads. Just get the CR to 9.25 and you will be fine. A little insurance does not hurt. And the difference in power in 9.75 is not worth it IMO. Long time iron head pump gas guy here.
The 6x-4 is the best D port Pontiac head they ever made. So run it. The Super Stock guys love that head. Run a little more cam than you would like with Rhodes lifters. Make some power with this thing and have some fun. Do a Jim Hand port job on those things ! 670 heads are the worst 400 head. Very old school, closed chamber. All those little cuts in the later heads were 10 years ahead of their time. Swirl is good, use them. If it were me, there would be no question on which head to run. 670s vs 6X-4 ? Just about all the other big valve, screw in stud D ports are better than a 670. Get your power with air flow and a little less CR. Mild port job on the X heads, put a cam in it. Rhodes will tame it down and you will still have the top end. Last edited by Dragncar; 05-26-2024 at 12:18 PM. |
#25
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Quote:
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72 lemans,455 e-head, UD 255/263 solid flat,3.73 gears,,,10" 4400 converter,, 6.68 at 101.8 mph,,1.44 60 ft.2007 (cam 271/278 roller)9"CC.4.11gear 6.41 at 106.32 mph 1.42 60 ft.(2009) SOLD,SOLD 1970 GTO 455 4 speed #matching,, 3.31 posi.Stock manifolds. # 64 heads.A factory mint tuquoise ,69' judge stripe car. 8.64 @ 87.3 mph on slippery street tires.Bad 2.25 60ft.Owned since 86' |
#26
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I am sure you can run 9.75 CR on a 455 with iron heads and get away with it. Its just the OP sounds like a bit of a newbie and a little insurance is a good thing. No one wants a blown head gasket from a bad batch of gas on a hot day. Make the heads flow and having just over 9-1 is a good street pump gas recipe for a Pontiac. |
#27
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My vote with the 068 cam is for 9.1 compression for 91 octane or 9.3 for 93 octane (Funny how it works out). Larger cam, lower gears, cooler climate, or cutting a deal with the devil can allow higher compression ratios. Just not worth it to chance hammering out the rod bearings with a marginal tank of gas on a nice warm summer day.
Half a point drop in compression is a 2% reduction off maximum power, but having to cut back timing to avoid detonation might cost 10%.
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Mick Batson 1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon. |
#28
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Also note that not everybody’s fuel of a given octane level provides the same knock protection.
The blend of a fuel may work better at a lower or higher engine temp then another brand pump fuel of the same octane.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#29
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Mine likes 34 degrees total timing, that's where it dynod best and runs at the track the best.
Just 91 pump fuel with 10.13:1 and that little 068. Tight quench and making sure the icl is where it needs to be is your friend. If it were going to pound out rod bearings it would have done that 25 years ago. Ive put about 60,000 miles on it in just the last few years. Things just have to be right. I do agree if someone isn't that tune savvy and/or don't pay attention to build details then by all means take some compression out of it |
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