built 6-bolt ross/eagle compression ?

[eclpsegsx12]

i have a 6-bolt bored .30 over with ross pistons, eagle rods, decked ect.....

compression is 8.5:1

im running a 4-layer mitsu MLS, ss valves, si manleys and comp race cams.....

what SHOULD my compression be at each cylinder...motor has 1500-2000 miles on it...its not as high as i think it should be....

its about 150-145 across the board which seems a little low to me...

yes, the motor what fully warm, and the throttle was open when i cranked on it.....

im thinking about re-ringing it over the winter because im pulling the motor again anyways....what do you all think?

THANKS

 

[Mirage2LTurbo]

I blew 210 in all four on 9:1.

 

[eclpsegsx12]

what rings were you running?

hmmm....if i do get it re-ringed....what should i do about making sure its tuned on startup and to drive around on to break it in....i want to make SURE i do this right...also, i have the AEM and its tuned roughly on my setup now pretty decent, enough to do some 3rd gear pulls on it but i need to upgrade my fuel lines first

 

[1fast97gsx]

I had the ross / eagle combo in my old motor ( which had a few problems as well ), but my compression was about 170 in all 4.

 

[Black94TSI]

I always go by the adage that if your numbers are all very close you don't have anything to worry about. There are so many different variables when it comes to cranking compression that it's impossible to compare numbers from car to car.

 

[gritsak]

i agree with the above stament..when there is one or two cylinders way of then you have something to worry about.

also, try another gauge...maybe that one is reading low.

 

[eclpsegsx12]

any reccomendations of gauges? ill try to pick up a craftsman, any other brands?

 

[1fast97gsx]

not really ... I just got a cheapo pep boys guage and it works fine.

 

[TD05HTalon]

since your shortblock is built do you have anything done to the head like upgraded cams? I remember a post before about compression tests and some people with big cams couldn't get very accurate readings and they seemed low due to the valve overlap. I wouldn't worry about the compression reading as long as your not burning any oil and all 4 cyls are even.

 

[eclpsegsx12]

the head is built also.....comp full race cams, si/manley's, SS valves, vicron seals

 

[Hooptytalon]

any reccomendations of gauges? ill try to pick up a craftsman, any other brands?

Don't buy a cheap compression tester!
I tested my compression a few days ago first with Harbor Freight(POS from Taiwan R.O.C.) Compression Gauge...it came up @ 120 psi :thumbdown , I tested again with a Mac Tools tester and I got a solid 150 psi, then to verify I tried a Snap On(this was @ school)...150 psi again. Don't buy shitty tools

 

[turbodagain]

The longer intake duration on your cams , is reducing your dynamic compression ratio at low rpm and easpecially at cranking speeds. Your intake valve is held open significantly longer after BDC than stock . At such low speed the air doesnt have enough intertia to stay in the cylinder as the piston is moving up., so it comes back out through the intake valve, reducing your compression reading. At high rpms when the air has alot of inertia, this actually helps full the cylinder, thus the high rpm, gains of big cams. Use a search engine to find more about this subject. Search for Static compression vs. DYnamic compression.

 

[eclpsegsx12]

Ya, that would make sense! Well, sears only has an actron tester and thats the one that i have now and have dropped numerous times....hmmm....where to buy a mac,snap on?

 

[drivemusicnow]

... to see if its the rings do a "wet" test... if it raises the compression, you have a problem, if not you're fine... don't spend 50$ on a mac/snap on tool you don't need.
(how thick is the 4 layer gasket compared to stock?)

 

[Turbo 2g awd]

I have a Ross/Eagle 6 Bolt built by Slowboy, 8.5:1. Cometic Head Gasket and their Stage V Head with 272 cams. I have 175psi across all cylinders.

Did you crank it 4-5 times or did you crank it say 6-8 when it peaked? My results were with 6 cranks(thats where mine peaked), WOT, and a battery charger on the battery.

 

[eclpsegsx12]

i checked it with a good compression tester, no battery charger(i should have though as my cranking wasnt fast) and warmed up....it did around 170 across the board...so i figure with a battery charger and cranking it more, it would yield more psi than 170

 

[sb7775]

when trying to figure out the compression of a built motor ther is a formula. u can't just can think its the same because u have 9-1 pistons and because u have 180 in all cylinders that its correct because its not. a true 9-1 i belive should be 190 plus. i don't have the paper work in front of me but its something like bore-stroke-dish(piston)-cc of head and gasket thickness. there is a calculator at ross pistons.com that i use all the time when building a motor, its under the calucators take a look at it and plug in all your numbers and the only one u will have left is the head gasket thickness, measure a stock(.0051 i think) or any gasket to get a starting point then change that number a hare up or down and watch the compression change. when u get the compression your looking for call cometic and give them the number u came up with and tell them what its for and they will cut u the gasket u need. hope this helps, its kind of a pain in the AS# but its the right way. thanx steve