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440 compression check #2250592
02/09/17 08:20 PM
02/09/17 08:20 PM
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wv
73bbroadrunner Offline OP
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Did a compression check on a 440 I just bought. It supposedly has 10.1 compression pistons 906 heads that have been milled 30 and the block has been zero decked. The cylinders are showing about 250 psi average.Not complaining but seems high to me. I think it has higher compression than 10.1. What do you all think? Thanks.

Re: 440 compression check [Re: 73bbroadrunner] #2250599
02/09/17 08:27 PM
02/09/17 08:27 PM
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Kirkland, Washington
Pacnorthcuda Offline
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Your cam might have (in fact if the 250 number is real it DOES HAVE) an early intake closing event.

Re: 440 compression check [Re: 73bbroadrunner] #2250600
02/09/17 08:28 PM
02/09/17 08:28 PM
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Maine
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jerseybud Offline
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What cam is in it?

Lots of variables here. 250 is pretty high

Re: 440 compression check [Re: 73bbroadrunner] #2250613
02/09/17 08:45 PM
02/09/17 08:45 PM
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wv
73bbroadrunner Offline OP
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mopar 484 purple shaft

Re: 440 compression check [Re: 73bbroadrunner] #2250622
02/09/17 08:54 PM
02/09/17 08:54 PM
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Oregon City, OR
Baxter61 Offline
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pull a head off and measure. while youre in there check the degree of the cam.

Re: 440 compression check [Re: 73bbroadrunner] #2250624
02/09/17 08:56 PM
02/09/17 08:56 PM
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Lincoln Nebraska
RapidRobert Offline
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agreed, that is very high. It'd be nice if you had a borescope to see whats in there. My HF unit was not cheap but it has came in very handy/saved my bacon several times.


live every 24 hour block of time like it's your last day on earth
Re: 440 compression check [Re: 73bbroadrunner] #2250633
02/09/17 09:08 PM
02/09/17 09:08 PM
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So. Burlington, Vt.
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fast68plymouth Offline
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Was the motor run just prior to the compression test?


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: 440 compression check [Re: 73bbroadrunner] #2250663
02/09/17 09:53 PM
02/09/17 09:53 PM
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73bbroadrunner Offline OP
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No I havnt ran it yet.

Re: 440 compression check [Re: 73bbroadrunner] #2250683
02/09/17 10:38 PM
02/09/17 10:38 PM
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Prospect, PA
BSB67 Offline
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check the gauge, or try another gauge.

Re: 440 compression check [Re: 73bbroadrunner] #2250685
02/09/17 10:41 PM
02/09/17 10:41 PM
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73bbroadrunner Offline OP
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I checked the gauge and it is ok.

Re: 440 compression check [Re: 73bbroadrunner] #2250689
02/09/17 10:48 PM
02/09/17 10:48 PM
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Kirkland, Washington
Pacnorthcuda Offline
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Originally Posted By 73bbroadrunner
No I havnt ran it yet.


Have you cranked it over with plugs in it? I'm thinking it might not even crank over very well without a great starter and battery.

Re: 440 compression check [Re: 73bbroadrunner] #2250703
02/09/17 11:06 PM
02/09/17 11:06 PM
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So. Burlington, Vt.
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fast68plymouth Offline
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Originally Posted By 73bbroadrunner
No I havnt ran it yet.


If it has been sitting for a while, it's very possible the lifters are no longer pumped up, which makes the duration at the valve much shorter....... And the compression test will read high.

If the 250psi had been observed just after the motor was run and warmed up, and you knew the gauge was accurate....... Then I'd say the cam was like a tooth off(advanced), or the motor is way over 10:1cr(as in waaaaaaaaaaay over).


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: 440 compression check [Re: BSB67] #2250720
02/09/17 11:30 PM
02/09/17 11:30 PM
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Posts: 1,235
Phoenix, AZ
Jjs72D Offline
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Originally Posted By BSB67
check the gauge, or try another gauge.


Yeah, I agree. I've seen them be in error before.
Has anyone ever seen an engine with these cylinder numbers run on even 93 octane unleaded? It seems to me an engine with 250psi would need over 100 octane to avoid knocking like 20 bill collectors at the door.

Re: 440 compression check [Re: Jjs72D] #2250822
02/10/17 01:54 AM
02/10/17 01:54 AM
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Lincoln Nebraska
RapidRobert Offline
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agreed, sumpin ain't right (& if it is, it is race gas city). Keep after it & keep us posted.


live every 24 hour block of time like it's your last day on earth
Re: 440 compression check [Re: 73bbroadrunner] #2250998
02/10/17 01:29 PM
02/10/17 01:29 PM
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CT
GTX MATT Offline
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That sounds like almost 100 PSI too much for that CR and cam, if you told me 150-175 I'd say it sounds right. That sounds like a 13.5:1 engine


Now I need to pin those needles, got to feel that heat
Hear my motor screamin while I'm tearin up the street
Re: 440 compression check [Re: 73bbroadrunner] #2251025
02/10/17 02:08 PM
02/10/17 02:08 PM
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So. Burlington, Vt.
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fast68plymouth Offline
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I don't know what kinds of parts the op has laying around, but if the motor has an adjustable valvetrain, or the op has some rockers kicking around, and some solid lifters..... You could pull two hyd lifters out, swap in two solids, adjust lash to about .003 lash, retest.

If it still tests stupid high(and you're absolutely sure the gauge is accurate.....then IMO, something needs to come apart to see what's what.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: 440 compression check [Re: fast68plymouth] #2251098
02/10/17 04:29 PM
02/10/17 04:29 PM
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dogdays Offline
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I agree with Fast68.

You are doing the compression check right, with all the plugs out.

You say average. What is the spread? Have you gotten the same result on more than one cylinder?

R.

Last edited by dogdays; 02/10/17 04:33 PM.
Re: 440 compression check [Re: 73bbroadrunner] #2251332
02/10/17 11:21 PM
02/10/17 11:21 PM
Joined: Mar 2010
Posts: 28
wv
73bbroadrunner Offline OP
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I did the compression check one plug at a time on all 8 cylinders. All cylinders were in between 248 and 265. The motor did set for a while on a stand before I put it in the car.I havnt ran it yet I am waiting on HP Exhaust manifolds to be ceramicoted. fast68plymouth sounds like you are on to something. Once I run motor I will check again and post results. Thanks for everyones input.

Re: 440 compression check [Re: 73bbroadrunner] #2251352
02/10/17 11:48 PM
02/10/17 11:48 PM
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Phoenix, AZ
Jjs72D Offline
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Exhaust manifolds on an engine that cranks that high?

Re: 440 compression check [Re: Jjs72D] #2251358
02/11/17 12:09 AM
02/11/17 12:09 AM
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wv
73bbroadrunner Offline OP
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Well, I didn't think it would crank that high. It shouldn't . I am trying to figure out why it is. I am hoping my exhaust manifolds will be alright with the motor I thought I bought.

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