462 HO

180 lbs. compression check

5 posts in this topic

I finally got a chance to do a check on my 400 with Cleveland 4V heads, a very healthy roller cam that smooths out at about 4000 rpm's.

I got 180 lbs. very close across all cylinders.

What is the likely compression ratio ?

 

Thanks.

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compression ratio is still in the mist, Intake Valve Close point determines the 'effective swept distance' or the the dynamic compression ratio

being that we don't know the intake valve close point we can't figure DCR and I'm not sure there's a reverse calculator to come up with the static CR either, you'd need to just plug away at punching in CR's until you find a match to your DCR & cranking pressure. the Wallace DCR calculator gives these results but you're missing the IVC

but 180 psi is pretty stout w/o being overboard, it should run on pump premium with a reasonable tune (ignition timing)

with a cam that smooth out around 4k (probably a fairly late closing intake valve) and 180 psi cranking says it does have some significant static CR,

just know way to put a number on it. good news is that now you know you're dealing with a 180 cranking psi motor :)

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Thanks, Tinman! I appreciate the input. Now I need to get the timing right and see what this motor will do.

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You really need to figure it mathematically. For example my 436 with a stout 13.5 comp. because of cam timing events has about 170. Cranking psi. Ive had 12.1 truck motors over 200 psi with tight rv style cam. 

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As a comparison my ancient nitrous Cleveland stuff (zero deck, TRW 12.5:1 pop-ups, 4VCC heads milled .080", and a decent Crane .630(ish) lift solid f/t cam installed straight up) usually had around 185-190 lbs cranking compression.

But my ancient "street" Cleveland stuff (stock deck height, flat-tops, 4VCC heads, and a tiny Isky .510 lift/302 adv dur hy f/t cam installed straight up) had about (IIRC) 160 lbs cranking compression.

As mentioned earlier cam timing plays a part in the overall "compression number" picture.

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