220psi Compression on 331 sroker with stock 58cc heads, too high? - Mustang Evolution

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Old 07-17-2012, 06:28 PM   #1
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220psi Compression on 331 sroker with stock 58cc heads, too high?

Im wondering if maybe my cam is not installed properly?
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Old 07-17-2012, 06:53 PM   #2
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dude that is way high. i would figure something out before you put boost to it. at that high of pressure you already need higher octane fuel. maybe you should find a compression ratio calculater and type in your specs to see what ratio you have.

what makes you think this is caused from the cam?
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Old 07-17-2012, 06:55 PM   #3
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The cam is the only thing different. It also could've been the stuck valves or something.
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Old 07-17-2012, 07:03 PM   #4
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maybe the stuck valves. the pistons are different right?
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Old 07-17-2012, 07:03 PM   #5
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I did the test also with this oiling lifter problem.

---------- Post added at 07:03 PM ---------- Previous post was at 07:03 PM ----------

Yeah, they are all new.
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Old 07-17-2012, 07:04 PM   #6
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if the exhaust valve werent opening then that could account for the high number.

you had that in every cylinder?
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Old 07-17-2012, 07:05 PM   #7
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Yeah pretty much 200-225
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Old 07-17-2012, 07:08 PM   #8
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Cam should not have anything to do with high compression. What is your comp ratio. What are the other cylinders reading? If cam was out of time then your readings would be lower since the valves would be open during comp stroke
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Old 07-17-2012, 07:13 PM   #9
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I don't know the ratio. Compression was 200-225 on all cylinders. This is a new motor and I have oiling issues and some of my valves are staying open when the lifters collapse.
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Old 07-17-2012, 07:21 PM   #10
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if the motor was cold it could also make the readings high.
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Old 07-17-2012, 07:21 PM   #11
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Only ran for a minute
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Old 07-17-2012, 07:23 PM   #12
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your sticky valves could be the problem. but hard to say if all the valves stuck the same being they were all within 25 lbs.

still wouldnt hurt to check the CR though
http://www.csgnetwork.com/compcalc.html
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Old 07-17-2012, 07:45 PM   #13
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According to DSS it should be 10.75 to 1
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Old 07-17-2012, 07:53 PM   #14
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thats pretty high for a boosted motor. it maybe alright if you keep the boost low, but most people dont recommend it. i would run 93 octane and low boost. then when you decide to upgrade the heads i would get 64 cc combustion chambers.
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Old 07-17-2012, 08:02 PM   #15
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yup
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Old 07-17-2012, 08:05 PM   #16
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you watching king of the hill to? "yup" lol
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Old 07-17-2012, 08:08 PM   #17
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Not at the moment
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Old 07-18-2012, 08:26 AM   #18
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Re: 220psi Compression on 331 sroker with stock 58cc heads, too high?

With a CR that high you are going to have to be very diligent about monitoring and preventing detonation. Maybe consider a thicker head gasket to lower the compression a bit if possible. Also use some really good head studs if possible.
I wouldn't get too concerned over the cold compression test.
You need to get it running and go through a few heating and cooling cycles, then check it with the engine hot.
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