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Old 09-13-2002, 11:03 PM
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Post gas for high compression

I have a 1968 big block camaro that has been hibernating for 20 years. It's a 427 with closed chamber rectangular port heads and 12.5 to 1 pistons with steel crank. The mechanic who's getting it running again thinks the compression is too high, even with octane booster, to try to drive on the street now. I really don't won't to be taking the engine apart now, as it was running fine when I parked it. Any ideas?

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Old 09-13-2002, 11:25 PM
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Av fuel (if you can get it) is the cheapest but race fuel is the best. Mix 50/50 tanks of regular and Av fuel and see if it detonates, hope you aren't going to drive it much. It will cost you a fortune.

You would be better off dropping to even 8.5 to 1 so you can run regular fuel or 9.5 to 1 if you run premium, but that will cost you a set of pistons and a rebuild kit at the least.
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Old 09-14-2002, 06:30 AM
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Ahh, the hell with gas prices, at $5.00 a gallon at least you know your gettin the good stuff.
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Old 09-14-2002, 10:02 AM
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If the engine has a true compression of 12.5:1, then you are almost forced to use a good grade racing fuel only. I had a small block with this much compression on the street, and even with blended fuels and octane boost, I had to turn the timing back to avoid detonation. The thing is, you'll make more power with 10.0:1 with the timing optimized, as opposed to backing the timing down with 12.5:1. compression ratios of 12.0:1 and higher need 105 octane to be safe, and if you plan to drive it very much, it's a pain in the #@*&$$#% to find racing fuel when you're on empty, and that probably doesn't take long with that big rat.
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Old 09-14-2002, 11:52 AM
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If you don't want to tear it down at this time your going to need 100+ octane. Like 4Jaw said you will need racing fuel @ 4.90 a gallon and 92 octane @ 1.90 a gallon mixed at about 50%.= 3.40 a gallon = about 34 cents a mile. A 100 mile trip will cost you $34.00.Back in 68 I put a 427 L88 in my 67 Camaro. 100 octane gas was about 50 cents a gallon. A 100 mile trip cost me about $5.00 and if I remember right that was a drain on my funds. Needless to say it did'nt get driven much on the street. I used to run 3.55 gears on the street and it was a dog,to get that 427 with 12.5 CR to shine on the street you'll need some 4.56s ( 8 miles a gallon)But if you want to have fun with it and drive it you will need to do something with the CR. I have a LS7 in my boat that was built strickly for drags. The engine builder that help me set up the motor suggested that I mill the piston domes down to 10.5:1 and that I wounld'nt notice the differance. He was right. The only differance I found was that it quit burning the electrodes off the plugs. The LS7 is an open chamber head and you have a closed chamber. In an open chamber you have more of a dome to work with. Any how you need to see if you can cut the domes on your stock forged TRW pistons down to where you have about 10:1 CR you will need about .200 dome thickness after they are cut. You can get a couple of CCs by using a .051 compressed thickness head gasket instead of the stock .039.I don't know if they still have "E Econorail" dragters at the drags ( that used to be a BBC 4 barrel carb dragster class)But if you can find one of those guys they know all you ever need to know about a BBC. So anyhow if you have your pistons cut,have the cylinders honed with a toruqe plate,new rings,rebalance the engine,new rod and crank bearings and a gasket set you will have about $700.00 in it if you do the work yourself. Add about $165.00 for a good valve job. With the stock chevy hi rise and 750 to 800 cfm holley you should have close to 500/550 HP. You may still need a little octane booster with this combo but I think you could live with it as a daily driver. Your looking at about 10 to 12 miles a gallon. Try some 4.11 gears it should work OK with this set up.
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Old 09-14-2002, 12:35 PM
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Convert to propane, then you could run even 14 to 1, no pollution so the tree huggers couldn't hassle you either. Overall the conversion to propane would probaly cost equivalent and keep the internals of your engine spotless.
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