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Re: ENGINE COMPRESSION CHECK- COLD?
[Re: Labratt]
#1086513
10/01/11 11:20 PM
10/01/11 11:20 PM
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Joined: Dec 2009
Posts: 20,622
in a cattle trailer down by th...
Guitar Jones
Paddle faster! I hear banjo music!
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Paddle faster! I hear banjo music!
Joined: Dec 2009
Posts: 20,622
in a cattle trailer down by th...
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Quote:
Does anyone know what the difference in P.S.I. would be checking a cold engine...as opposed to one that's warmed up,like it should be? I did a check on my 440 this afternoon,without first warming it up!  My average was 185psi. Thanks in advance!  Randy 
If it's still fresh there won't be much difference. As a general rule I only use a compression check to determine the state of health of a cylinder when compared to the others. Otherwise a leak down test is a much better tool.
"Follow me the wise man said, but he walked behind"
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost coming soon!
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
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Re: ENGINE COMPRESSION CHECK- COLD?
[Re: Labratt]
#1086518
10/02/11 12:49 AM
10/02/11 12:49 AM
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Joined: Jan 2003
Posts: 6,591
Canton, Ohio
Sport440
master
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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Randy, with those intake numbers your installed at a 104 ICL if that cams on a 110LSA, witch I think it is. Its a comp cam, they make 90% of thier cams with a 110 LSA.
Being a solid with lash its going to close about 4* earlier and with a 10.2 comp, I think it should be more in the 165 to 170 max psi cranking range.
Mopar 65, your cranking psi of 185 is in the ball park for a 11.1 combo with your roller cam 264 @.050 Maybe 5 psi high or so, or not. IMO
No software or math here, just some basic comparisons to past builds. I think 68 Lar has a software program to fairly accurately predict cranking PSI based off of Compression and a IV closing point.
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Re: ENGINE COMPRESSION CHECK- COLD?
[Re: Labratt]
#1086519
10/02/11 12:52 AM
10/02/11 12:52 AM
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Joined: Jan 2003
Posts: 6,591
Canton, Ohio
Sport440
master
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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Quote:
WHAT HAPPENED TO THE FOLLOWING POSTS???  
Mopar65, Bailed I guess! Maybe he didnt want to Hijack
He responded to you and then asked me a question.
I answered you both, in my last response
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Re: ENGINE COMPRESSION CHECK- COLD?
[Re: Labratt]
#1086522
10/02/11 01:11 AM
10/02/11 01:11 AM
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Joined: Jan 2003
Posts: 6,591
Canton, Ohio
Sport440
master
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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Quote:
Mike..the cam is actually ground on a 108 LSA...installed at 105. I'm going to pick up Mike's gage early in the week,and see what I get with it! If I do have 11:1..maybe I shouldn't have Jeff mill them.  Thanks!
Randy I did a quick run on some estimated numbers of your engine and came up with a 10.1 comp.
I used
.001 below deck
4.34 bore
84cc combustion chamber
6cc PV
4.5 gasket bore
.038 gasket thickness
3.75 stroke
if this is close to accurate your comp is about right. 10.1 - 10.2
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Re: ENGINE COMPRESSION CHECK- COLD?
[Re: Labratt]
#1086525
10/02/11 11:30 AM
10/02/11 11:30 AM
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Joined: Oct 2007
Posts: 4,205
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,205
New York
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You can't use the .050" IVC point.
Boffin Emeritus
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Re: ENGINE COMPRESSION CHECK- COLD?
[Re: Crizila]
#1086526
10/02/11 11:40 AM
10/02/11 11:40 AM
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Joined: Jan 2007
Posts: 3,695
nc
emarine01
master
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master
Joined: Jan 2007
Posts: 3,695
nc
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My small block runs around 200/205 cold 220/225 hot with 12 to 1 @ a solid roller 260@.050 106/106, Engine is 4.5 years old with around 500 passes, The only real difference I saw compression testing is when we went to 16 vdc, It makes pressure on the 3rd bump
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Re: ENGINE COMPRESSION CHECK- COLD?
[Re: Labratt]
#1086527
10/02/11 02:58 PM
10/02/11 02:58 PM
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Joined: Jan 2003
Posts: 6,591
Canton, Ohio
Sport440
master
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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Quote:
Mike,Todd's build sheet says the pistons are .008 in the hole @ TDC..Fel Pro 1009 head gasket,with compressed thickness of .039..volume as 9.9 cc's. The cam at that time was a Scott Brown solid with 252/244 duration,with a 112 LSA,and ICL of 107. He's got the CR listed as 10.211. How much,if any..would this Comp cam change the "original" compressional ratio,when he put it together? Thanks for ALL your responses,Mike! I REALLY appreciate!   Forgot to mention that the bore is actually a .040 over...4.360"
Cheeze, with those numbers the comp comes in even lower to about 9.75
There will be no static change difference in compression between the two cams. Just a dynamic change.
The diiference in the static compression numbers between mine 9.75 and Todds 10.2 can be just the use of a diiferent calculaters.
Jeff is right about not being able to use the .050 numbers to accurately figure cranking comp. But to have a true 185# with a 9.8 to 10.2 comp with a 260* @ .050 cam is far enough out that I suspect a guage problem.
Lets see what Mikes gauge reads. You do have a SQ cam with fast ramps, but I doubt they are closing soon enough to net you that 185* psi.
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Re: ENGINE COMPRESSION CHECK- COLD?
[Re: Labratt]
#1086533
10/03/11 02:54 AM
10/03/11 02:54 AM
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Joined: Jun 2005
Posts: 793
Utah
topbrent
super stock
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super stock
Joined: Jun 2005
Posts: 793
Utah
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Quote:
Brent,do these seal as well as the Fel-Pro's? What manufacturer? Thanks!
Great seal and an easy compression bump without the milling your heads.
A light coat of wet silver spray paint or copper gasket spray and you are good.
Mopar Performance $21.95
http://www.summitracing.com/parts/DCC-4286754/
There are also more expense Cometic and MrGasket MLS gaskets available in the ~.027 range
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I don't remember you telling me to use a different gage! 
I'll have to borrow P-Body's..and re-check it! 
What should it ACTUALLY be,given my compression,and duration? 
You can also use it to check the general health of your motor if you have a comp. test history - I do a test about every 30 - 35 runs. You gotta do the test EXACTLY the same each time. Cold, throttle open, 5 pumps, and cranking rpm is critical. I do one bank and then recharge the battery for about 10 minutes before I do the other bank. Also as stated, I have seen guages vary as much as 15 psi. Doesen't matter much as long as you use the same gauge. I also suggest you stick with a cold test. Hot just throws in another variable that's hard to control. JMHO.
randy i would send them to jeff or dawayne and them do there thing to them.Mopar65 
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