Compression, duration, etc.

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Oct 1, 2001 | 05:25 AM

kameleon

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Compression, duration, etc.

Ok, what is the benefit of a higher compression ratio? And what is stock compression on the 4.9L I6?
Also, on a cam what does all the numbers mean? When i ordered my crane cams cam it was because it was the only one I knew of besides a "wolverine blue racer" which I had never heard of before. The duration on the crane cams cam was something like 262/270 I forgot the lift and other stuff. I guess this is "better" than stock because I saw a difference in performance. But what is the stock lift and duration? What is the benefit of longer duration (in trucks that is

). I know this is alot of questions, but I am kinda new to this "hopping up" a I6 engine. I appreciate your help and answers to these questions.

D. Brooks

Oct 2, 2001 | 10:15 PM

Herman

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Compression, duration, etc.

Lift is how far the valve will be pushed open, (actually how high the lifter is pushed) duration is for how long the valves will be held open, overlap is how long the intake and exhaust will be open at the same time. Very important to match your intake and exhaust to the cam for the best performance. The higher lift and longer duration cam allows more fuel to enter the combustion cxhamber. The higher compression ratio means you get more push, for a slightly longer time out of each stroke. Herman

Oct 3, 2001 | 06:04 AM

kameleon

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From: USA

Compression, duration, etc.

So since I have an aftermarket/high(er) perfomance cam I should change my compression? What should be stock for that old of an engine? Would I benefit more making it a higher compression engine or would it be best left alone unless I want to re-ring and piston it? And last, would a more "radical" cam do me any better?

Thanks for the help.

D. Brooks
kameleon25(No Email Addresses In Posts!)
1980 F-150 "Flare side" Custom
4.9L I6
Offenhauser DP 4bbl intake
Edelbrock 600cfm Elec choke carb
Dynomax standard series headers
Crane Cams PerformerMax 270H? cam
Borg Warner T-18 (that will pull the titanic)
9" rearend (not sure of ratio)
I Love My Truck!

Oct 3, 2001 | 02:50 PM

jwtaylor

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Compression, duration, etc.

If your motor is in good shape as in a compression test has been done and is close on all cylinders then bump the compression. Pretty easy to do and I think that getting it to 9.5:1 would be safe as far as daily driving. Just have to get a machinist to mill it and check the valve to piston clearance to be safe but I think this would be ok. If it is stock now then you probably have a mid+ 8:1. Someone will jump in an verify this I am sure. I don't know if you were asking this or not but you don't necessarily have to have a new cam to bump compression but you do have to have one to get the most benifit from it. You could take $500 and just put a 100 shot through it. Ha ha. Good luck

Oct 3, 2001 | 10:19 PM

Herman

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Compression, duration, etc.

If I was going full out, rather than raise compression, I think I would try a supercharger. (not easy, but very effective) We have a lot of mountains here. Herman