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cranking compression question #1481768 08/08/13 09:50 PM 08/08/13 09:50 PM
Joined: Mar 2005 Posts: 3,145 Central NC gch OP master
gch OP master Joined: Mar 2005 Posts: 3,145 Central NC	On a low comp 440(75 model 8.2-1 advertised)what would be a good cranking compression number? The motor was cold and the cylinders dry.

Re: cranking compression question [Re: gch] #1481769 08/08/13 10:07 PM 08/08/13 10:07 PM
Joined: Nov 2003 Posts: 36,041 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,041 Lincoln Nebraska	I'd be comfortable with 140 give or take 10 either way & happy with 150 or more. Critical is that there are no low ones live every 24 hour block of time like it's your last day on earth

Re: cranking compression question [Re: RapidRobert] #1481770 08/08/13 10:55 PM 08/08/13 10:55 PM
Joined: Mar 2005 Posts: 3,145 Central NC gch OP master
gch OP master Joined: Mar 2005 Posts: 3,145 Central NC	The cylinders are all within 10 psi but the numbers are a LOT lower.I was thinking 120 at best with that low of a compression but all are between 80-90.

Re: cranking compression question [Re: gch] #1481771 08/08/13 11:03 PM 08/08/13 11:03 PM
Joined: Nov 2004 Posts: 843 Suffolk,VA I ireland383 super stock
ireland383 super stock I Joined: Nov 2004 Posts: 843 Suffolk,VA	I was thinking around 100ish. Have the head gaskets been changed anytime that you know of?

Re: cranking compression question [Re: gch] #1481772 08/08/13 11:41 PM 08/08/13 11:41 PM
Joined: Nov 2003 Posts: 36,041 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,041 Lincoln Nebraska	Quote: but all are between 80-90. It's in need of a rebuild live every 24 hour block of time like it's your last day on earth

Re: cranking compression question [Re: gch] #1481773 08/08/13 11:41 PM 08/08/13 11:41 PM
Joined: Jan 2003 Posts: 15,411 Omaha Ne T TJP I Live Here
TJP I Live Here T Joined: Jan 2003 Posts: 15,411 Omaha Ne	Quote: The cylinders are all within 10 psi but the numbers are a LOT lower.I was thinking 120 at best with that low of a compression but all are between 80-90. 80 to 90???? Ouch!!!! it will run but will have its tail between its legs, www.tandmautomotive-omaha.com

Re: cranking compression question [Re: gch] #1481774 08/09/13 12:31 AM 08/09/13 12:31 AM
Joined: Jan 2003 Posts: 31,049 Oregon A AndyF I Win
AndyF I Win A Joined: Jan 2003 Posts: 31,049 Oregon	I checked the cranking compression on my stroker motor the other day and it was 235 psi. And that is with a 280 at 0.050 camshaft. I can barely turn the engine over with a cheater bar.

Re: cranking compression question [Re: gch] #1481775 08/09/13 12:56 AM 08/09/13 12:56 AM
Joined: Jun 2012 Posts: 1,899 MYRTLE BEACH SOUTH CAROLINA E ek3 top fuel
ek3 top fuel E Joined: Jun 2012 Posts: 1,899 MYRTLE BEACH SOUTH CAROLINA	Quote: On a low comp 440(75 model 8.2-1 advertised)what would be a good cranking compression number? The motor was cold and the cylinders dry. 100 lbs. will work fine. you would be surprised what just a good valve job or a new timing chain would do. warm it up, pull all the plugs out, and spin it over 3-4 times to test. when you warm it up , run a little marvel mystery oil in it also then re-check it. a good fresh 440 with 8 -1 compression making 130-40 lbs. would run fine. if you are looking for real power , 9:5:1 or better and 175 + is a good starting point. if the engine has set up for a long time, while running it, pour a little diesel fuel [ about a quart untill gone] in the carb when it is hot and revved up some . this will free the rings / valves up .

Re: cranking compression question [Re: AndyF] #1481776 08/09/13 01:27 AM 08/09/13 01:27 AM
Joined: Feb 2010 Posts: 18,493 Granite Bay CA Kern Dog Striving for excellence
Kern Dog Striving for excellence Joined: Feb 2010 Posts: 18,493 Granite Bay CA	Quote: I checked the cranking compression on my stroker motor the other day and it was 235 psi. And that is with a 280 at 0.050 camshaft. I can barely turn the engine over with a cheater bar. Holy crap! Thats a RACE fuel engine for sure! I was at 190 in my 440/493. 10.7 static with the MP '509 cam.

Re: cranking compression question [Re: Kern Dog] #1481777 08/09/13 09:30 AM 08/09/13 09:30 AM
Joined: Mar 2005 Posts: 3,145 Central NC gch OP master
gch OP master Joined: Mar 2005 Posts: 3,145 Central NC	Motor/car has been sitting for 10 plus years but runs surprisingly smooth.Still has the cat converter lol. I was hoping for a little higher number so I could justify throwing some spare performance parts on it and making a rat rod/beater for fun.Pulling the heads is more $$$ than I want to put in to it. I drove it home on 13 year old tires and then found out the idler arm was about to fall off of it.lol

Re: cranking compression question [Re: gch] #1481778 08/09/13 09:36 AM 08/09/13 09:36 AM
Joined: Jan 2003 Posts: 25,200 Upper Midwest M MoparforLife Too Many Posts
MoparforLife Too Many Posts M Joined: Jan 2003 Posts: 25,200 Upper Midwest	Tell you what - It will run fine. All the cylinders are even showing me that it has pretty equal wear pattern. Doing a valve job (unless you have a valve leak) will do nothing for you. an even test like you have does not represent a leaky valve. A cylinder with a leaky valve most generally will have a pretty noticeable compression drop from the rest. Not an even reading like you have.

Re: cranking compression question [Re: MoparforLife] #1481779 08/09/13 10:01 AM 08/09/13 10:01 AM
Joined: Aug 2009 Posts: 1,318 Ohio J jlatessa pro stock
jlatessa pro stock J Joined: Aug 2009 Posts: 1,318 Ohio	Just a thought, are you cranking with the carb at WOT? Joe

Re: cranking compression question [Re: jlatessa] #1481780 08/09/13 10:27 AM 08/09/13 10:27 AM
Joined: Mar 2005 Posts: 3,145 Central NC gch OP master
gch OP master Joined: Mar 2005 Posts: 3,145 Central NC	I had my mechanic do it because I am lazy. I will have to ask him.

Re: cranking compression question [Re: gch] #1481781 08/09/13 11:15 AM 08/09/13 11:15 AM
Joined: Jan 2006 Posts: 8,162 USA 3 360view Moparts resident spammer
360view Moparts resident spammer 3 Joined: Jan 2006 Posts: 8,162 USA	I have never understood it but 100 psi minimum is the cranking compression listed in the official Dodge Ram 1995 Field Service Manual specs page for the 488 ci/8L iron V10 which is a spec of 8.4 to 1 static compression and has a quite modest duration camshaft.

Re: cranking compression question [Re: 360view] #1481782 08/09/13 11:25 AM 08/09/13 11:25 AM
Joined: Jan 2006 Posts: 8,162 USA 3 360view Moparts resident spammer
360view Moparts resident spammer 3 Joined: Jan 2006 Posts: 8,162 USA	167 psi on a warm engine with a shot of oil in each cylinder throttle bores propped fully open starter turning crank at 300 rpm 75 degrees F 700 feet above sea level is what the PerformanceTrends Engine Analyzer 3.2 computer software estimates the cranking compression should be on the fourth stroke of the piston when the camshaft specs for a 1995 488 iron V10 are entered

Re: cranking compression question [Re: 360view] #1481783 08/09/13 11:35 AM 08/09/13 11:35 AM
Joined: Jan 2006 Posts: 8,162 USA 3 360view Moparts resident spammer
360view Moparts resident spammer 3 Joined: Jan 2006 Posts: 8,162 USA	178 psi cranking compression is what the EA 3.2 estimates for the 1969 Mopar 440 V8 This a an example engine that comes with the program. Specs are filled in by the author of the software Kevin Gerten, an ex-Ford engine development engineer. Static compression is 10 to 1 Intake Valve timing: centerline 113 degrees duration at 0.050. 214 open at 0.050 -6 degree btdc close 40 degrees abdc gross lift 0.447 inches SAE conditions HP on 93 octane AKI gasoline 309 horsepower at 4200 rpm 410 ft-lbs at 3200 rpm 0.497 lbm/hp-hr BSFC at 2200 rpm

Re: cranking compression question [Re: 360view] #1481784 08/09/13 12:06 PM 08/09/13 12:06 PM
Joined: Aug 2005 Posts: 11,543 chicagoland,usa B buildanother I Live Here
buildanother I Live Here B Joined: Aug 2005 Posts: 11,543 chicagoland,usa	I don't think the o/p stated how many hits of each cylinder were utilized for his findings. I go about 4 cycles which gets you close enough. Some folks have said they just bring it around once and that won't work as the first spin has to fill the gauge-hose etc.

Re: cranking compression question [Re: buildanother] #1481785 08/09/13 12:49 PM 08/09/13 12:49 PM
Joined: Jan 2003 Posts: 2,931 P Paul_Fancsali master
Paul_Fancsali master P Joined: Jan 2003 Posts: 2,931	That engine is a 7.5 comp at best 90 psi is plenty after not being run and sitting Drive it some add some sea foam and bet it will be over 100 Those engines new barely cranked 125 psi If they are all even it alone change the timing chain get a cam that will help it out Comp 260 series comes to mind

Re: cranking compression question [Re: Kern Dog] #1481786 08/09/13 04:45 PM 08/09/13 04:45 PM
Joined: Jul 2006 Posts: 4,179 California mickm master
mickm master Joined: Jul 2006 Posts: 4,179 California	Quote: Quote: I checked the cranking compression on my stroker motor the other day and it was 235 psi. And that is with a 280 at 0.050 camshaft. I can barely turn the engine over with a cheater bar. Holy crap! Thats a RACE fuel engine for sure! I was at 190 in my 440/493. 10.7 static with the MP '509 cam. the new engine is 210 on every cylinder, and runs fine on 91. but i guess 25 more is a lot. same thing for me, tying to turn it over with a breaker bar is an exercise in upper body strength.

Re: cranking compression question [Re: mickm] #1481787 08/09/13 06:57 PM 08/09/13 06:57 PM
Joined: Sep 2004 Posts: 6,906 IL, Aurora A ademon master
ademon master A Joined: Sep 2004 Posts: 6,906 IL, Aurora	205psi on 93 pump, they run so nice with hi cranking pressure !!!

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