View Full Version : Compression check?

mobius maximus
05-21-2013, 01:32 PM
Does anyone happen to know the correct pressure range for checking compression on a 350 indmar assault? Had my muffler blow up on me and wanted to make sure i didnt blow out any piston rings. Thanks guys!

05-21-2013, 02:13 PM
You don't actually need a figure. Just measure all of them. They should all be within about 10% of each other. If you have one that's 40% different or something like that you have a problem.

05-21-2013, 02:15 PM
I don't know the specs but, if memory serves, I did a compression test on my 2003 outback a couple of years ago and I think the reading was about 195 lb/sq in. across the board. They were all within 2 or 3 pounds of each other. I didn't dig any deeper than that as the motor was running fine anyways.

If you blew some rings, I would suspect one or two cylinders will be way off.

mobius maximus
05-21-2013, 03:10 PM
Awesome thanks guys. I was just searching the interwebs and i found a indmar manual and its saying nothing less than 100psi. And as you said kane, they should be within 10%.

Thanks very much guys. Ill repost if i find anything off.

05-21-2013, 03:55 PM
Within 10% of each other and you will usually find the lower readings on the rear cylinders. I would be concerned if the average was much less than 125. At 100, you are starting to lose a bit of power from the engine in blow by.

mobius maximus
05-21-2013, 06:29 PM
Alright awesome. So basically as long as the average pressure is above 125 and they are all within 10% of each other i should be good?

05-22-2013, 09:40 AM
I would not sweat too much if I was consistently 118 or so across the board either. Not all compression testers are created equal. You are looking for a bad cylinder not a weak engine here.

05-22-2013, 03:17 PM
I bought a 07 OBV and had the compression checked before I bought it and it was between 180 - 185 accross all cylinders...

mobius maximus
05-22-2013, 06:16 PM
Yea i did the check this morning and the lowest i got was 120 and the highest i got was about 150. Im thinking itll be alright. And according to the indmar manual its saying the minimun psi is 100 and the lowest recorded pressure should not be anymore than 70% less than the highest recorded psi.

Thanks for all the input guys. ill let yall know how she runs tomorrow.

05-22-2013, 08:58 PM
Cool, good luck.

05-23-2013, 11:19 AM
She's gonna run fine.