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What should my cyl compression be??

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Old Aug 30, 2011 | 10:14 AM
  #1  
IROCtheThird's Avatar
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From: Northeast CT
Car: '89 IROC-Z
Engine: LSx
Transmission: T-56
Axle/Gears: 3.42
What should my cyl compression be??

I put together a fresh motor at the end of the season last year, 355, 9:5:1, RHS heads, HSR, Comp Cam, etc, probably has less than 1,200 miles. I lapped the valves myself and had my machinest check them after, and I used summit rings with a moly top ring. I checked compression cold and got 150# across the boards. I havent checked it hot yet but I have a couple friends telling me this to low even for a cold reading. Any input? Thanks.

James
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Old Aug 30, 2011 | 04:47 PM
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From: batavia ohio
Car: 1992 z-28
Engine: 383 stealthram
Transmission: auto
Axle/Gears: 4.10
Re: What should my cyl compression be??

do a search on the internet. my sites out there to determine your comp. ratio
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Old Aug 30, 2011 | 05:30 PM
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From: 51°N 114°W, 3500'
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
Re: What should my cyl compression be??

150# is about average. The amount of cylinder compression from an engine depends on a lot of factors including cam grind. Anywhere in the 130-180 range is normal. If they were all around 100#, I would be concerned.

A leakdown test is a better indication of a problem with the cylinders.
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Old Aug 31, 2011 | 10:04 AM
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old z mzn's Avatar
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From: batavia ohio
Car: 1992 z-28
Engine: 383 stealthram
Transmission: auto
Axle/Gears: 4.10
Re: What should my cyl compression be??

read the post wrong 150 is in okay. like alky said leakdown test is the best test
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Old Aug 31, 2011 | 01:16 PM
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IROCtheThird's Avatar
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From: Northeast CT
Car: '89 IROC-Z
Engine: LSx
Transmission: T-56
Axle/Gears: 3.42
Re: What should my cyl compression be??

Ok, I wasnt to concerned about, I was actually pretty pumped to the same number on all 8, just had alot of friends telling me it was low for a fresh motor. A leakdown test will be on the future agenda anyway. Thanks for the input guys.
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Old Aug 31, 2011 | 05:46 PM
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old z mzn's Avatar
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From: batavia ohio
Car: 1992 z-28
Engine: 383 stealthram
Transmission: auto
Axle/Gears: 4.10
Re: What should my cyl compression be??

yes it's great to have everything consistent. I like your build. what you think of the pro torker heads.
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Old Aug 31, 2011 | 06:01 PM
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IROCtheThird's Avatar
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From: Northeast CT
Car: '89 IROC-Z
Engine: LSx
Transmission: T-56
Axle/Gears: 3.42
Re: What should my cyl compression be??

I havent had the car dyno'ed yet so I'm not sure what it makes exactly, but for the tune its on and the small 170cc intake runners the pro torkers have it runs real strong. They've been on the market for over 2 years now and I still cant find any flow numbers for the specific ones I have though.
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Old Aug 31, 2011 | 07:34 PM
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AlkyIROC's Avatar
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From: 51°N 114°W, 3500'
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
Re: What should my cyl compression be??

If you can't find useful head flow data from this page then you have very odd heads.

http://users.erols.com/srweiss/tablehdc.htm
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Old Sep 1, 2011 | 04:13 PM
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From: Northeast CT
Car: '89 IROC-Z
Engine: LSx
Transmission: T-56
Axle/Gears: 3.42
Re: What should my cyl compression be??

They dont have them, mine are p/n 12402 which are just the "early sbc Pro Torkers". All I see on there list is the vortec Pro Torkers. I think I've actually seen that list before. I call RHS every couple months and all I get is "we're working on getting all or heads benched"
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