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post #1 of 10 (permalink) Old 08-02-03, 05:27 AM Thread Starter
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compression ratio

What would be a good compression ratio for a daily driven el xr8 with edelbrock performer rpm alloy heads(already have these). When i get it rebuilt it will also have an edelbrock performer manifold etc. Don't know what cam yet(any help would be appreciated). Would a stroker be a good option(330 or 347).thanks

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post #2 of 10 (permalink) Old 08-02-03, 06:35 AM
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With alloy heads I think 10 to 1 will be acceptable, maybe a little bit more.
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post #3 of 10 (permalink) Old 08-02-03, 01:15 PM
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Re: compression ratio

yeah, if you want to run pump petrol, what bossxr8 said.

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post #4 of 10 (permalink) Old 08-02-03, 07:17 PM
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mate strokers rule, check out the ford motorsport catalog for cams or call crow cams etc. they will give you good advise. it is easy to get lots of power out of the 5.0 L ( actually 4942cc's i think ) with a uni chip, extractors, gt 40 manifold and motorsport cam i got 160 rwkw.
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post #5 of 10 (permalink) Old 08-03-03, 06:02 PM
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Your actual compression ratio will change depending on the cam you choose. Most cam manufacturers will recommend a certain static compression ratio for any cam they make. The static compression ratio is the volume of the cylinder with the piston at BDC divided by the volume of the cylinder at top dead center.

The dynamic compression ratio (what the engine actually runs at) will not only depend on piston selection, head gasket thickness, head selection, etc. but also on the valves opening and closing. To figure what your engine will actually run at, you need to use the cam specs.

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post #6 of 10 (permalink) Old 08-03-03, 10:44 PM
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Re: compression ratio

Daily driven and with a milder cam you should probably stick to no more than 10:1, possibly 9.5. The only reason you could get away with 10:1 is the alloy heads. If you go to a bigger cam the upper limit for a daily driven car should be 10.2-10.5 dependent on overall condition etc.

Don't get caught running too much comp because then you'll end up pulling out too much timing to avoid detonation.

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post #7 of 10 (permalink) Old 08-03-03, 11:32 PM
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Re: compression ratio

'92BigBronco is 100% spot on here.
You need to chose a cam before working out an optimum CR.

AP-
Why will the use of alloy heads enable more CR? If the CR ends up the same, detonation will stil lbe a problem.
Are the chambers radically different in shape?

Rick.
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post #8 of 10 (permalink) Old 08-04-03, 02:22 AM
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10.1 max on pump fuel
unless you want to run some methyl benzine to up the anti

i have a 347,so i say 347 ALL THE WAY

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post #9 of 10 (permalink) Old 08-04-03, 11:47 PM
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Re: Re: compression ratio

Quote:
Originally Posted by Soxx
'92BigBronco is 100% spot on here.
You need to chose a cam before working out an optimum CR.

AP-
Why will the use of alloy heads enable more CR? If the CR ends up the same, detonation will stil lbe a problem.
Are the chambers radically different in shape?

Rick.
Aluminium provides a much faster heat transfer rate. Therefore, any hot spots, non-uniformities etc are reduced and so a slightly higher CR can be used. That's why aluminium pots are so popular with professional cooks!

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post #10 of 10 (permalink) Old 08-05-03, 04:23 AM
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Re: Re: Re: compression ratio

Quote:
Originally Posted by Aussie Pete
Aluminium provides a much faster heat transfer rate. Therefore, any hot spots, non-uniformities etc are reduced and so a slightly higher CR can be used. That's why aluminium pots are so popular with professional cooks!
I'm well aware of all that, however IME, it has made bugger all difference unless the head has some fancy chamber shape.

Rick.
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