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Old 02-19-2003, 09:43 AM
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Post compression on my 383

i have a 268 cam in my 383 with about 8.8:1 compression. im not so sure on all of the specs but i think the cam is the "comp cams" and if i was smarter when i got my motor i would have gotten all the specs to go along with it. but do you guys know what compression ratio i could go up to safely (pump gas) without running into valve clearances? would upping compression be wise to get more power right now? im sure you need to know everything else my motor has but i'd thought i'd ask first before listing....thanks in advance

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Old 02-19-2003, 11:31 AM
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Is this a Chevy small block that you've stroked to a 383? If so, then where did you get your 8.8 to one compression figure from? I very cheaply built up a 383 using cast flat top pistons and smog big chamber heads. The compression is 9.4 to one. My cam is a SSI 214/224 which does not have as much duration as your Comp Cams(?)268 cam does. I cannot run the auto on regular gas but it will run fine on medium grade. So I would say you are safe with at least as much compression as I'm running. However, it's important to note that I live at 2000' above sea level so that will make a modest difference in the true compression ratio. Incidently, how are you planning on modifying your compession ratio? In reality, a 8.8 to one 383 small block can be made to run just fine. A high lift short duration cam is just the ticket that will turn that old Chev into a barn burner that will run on regular gas and you won't have to worry about piston to valve clearance and all of the trouble of changing the compression ratio. Good luck
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Old 02-19-2003, 02:40 PM
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with that little cam dont get compression too high or youll detonate. The only real way to check actual piston to valve clearance is to clay the pistons and do it manually. You must have a huge dish and some 76cc heads to get 8.8:1 man, are you sure about your current compression?? I have a calculator if you give me you head cc and the piston dish cc ill figure it out for you
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Old 02-19-2003, 02:49 PM
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I've got a 383 with a Comp Cams XE268 and I'm running close to 10:1 with flat tops. The cam lift is in the .490 range for the intake and a little less for the exhaust. The only problem arose when a valve guide seized and held an intake open, but that's a freak accident. I have to use premium gas. As above, I would recheck your compression specs, 8.8 sounds a bit low.
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Old 02-19-2003, 04:41 PM
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My 383, with 76 cc heads and TRW forged flat tops had 9.4 to 1 compression so 8.8 to 1 with dished pistons would be reasonable. Had no problem with pump gas but was not running that big a cam.

Trees
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Old 02-19-2003, 09:05 PM
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ya thats the thing, im not sure what exactly my compression ratio is.....i wasnt smart when i built my motor (still aren't ) so thats the only number i recall the guy saying about compression, i could be wrong.....damn i wish i knew
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