Compression numbers

bigmoose

Well-Known Member
Established Member
Joined
Sep 18, 2007
Messages
2,257
Location
Kingston, RI
I'm ran a compression test for a potential buyer for my car. To me the numbers all look great but I was wondering what could explain a slight variance bank to bank?

My guess is timing differences between the banks but want to hear from the experts.

1-4 were 190-195
5 - 180
6 - 175
7 - 172
8 - 180

Test was done with all plugs removed, no fuel, open throttle body on a cold motor. Also used a $25 amazon tool.
 

SS EATR

Active Member
Established Member
Joined
Feb 22, 2011
Messages
903
Location
La Crosse VA
I would do a leak down test on the driver's side head, my guess would be you have some leak down there. That was my situation with similar compression test numbers anyway. It's not too terrible though, not like you need to be ordering bottom end parts immediately.
 

HPLouis

Well-Known Member
Established Member
Joined
Sep 27, 2002
Messages
1,708
Location
New York City
I have a question about this. I always read that if the test showed a 10% variation, it was OK. Isn't there a 12% difference between the highest (195) and lowest (172)? Is that bad?
 

DSG2003Mach1

Well-Known Member
Established Member
Premium Member
Joined
Apr 15, 2004
Messages
15,913
Location
Central Fl
I have a question about this. I always read that if the test showed a 10% variation, it was OK. Isn't there a 12% difference between the highest (195) and lowest (172)? Is that bad?

if you had 1-2 holes that were over 10% different than I'd be a little more concerned. The fact that the variance is more bank to bank is a different situation
 

HPLouis

Well-Known Member
Established Member
Joined
Sep 27, 2002
Messages
1,708
Location
New York City
IMG_1509.JPG


These were mine. I see a 7% difference between the highest and lowest it i didn’t hit as high of a number as you did


Sent from my iPhone using the svtperformance.com mobile app
 

SVTXTC

Active Member
Established Member
Joined
Jun 4, 2014
Messages
953
Location
Cincinnati
I have a question about this. I always read that if the test showed a 10% variation, it was OK. Isn't there a 12% difference between the highest (195) and lowest (172)? Is that bad?

it’s not good. I have seen 13k and 20k stock cobras that had bad heads (factory defect) showing similar results. Sometimes these results are from defects in the DA and DB heads. Usually head work and additional ARP 2000 head studs make this all go away plus the opportunity to upgrade while you are in there. Really good to catch this before you purchase a cobra and especially before you throw a larger blower on it.
 

4sdvenom

Never Enough!
Established Member
Joined
Dec 2, 2003
Messages
2,439
Location
Ft. Wayne, IN
I believe the OP’s difference is due to cam phasing variation from bank to bank. Is this a factory untouched motor or has there been work done?
If factory it’s probably just due to Ford’s timing tolerance variation between the 2 banks.

Numbers are pretty good nonetheless
 

bigmoose

Well-Known Member
Established Member
Joined
Sep 18, 2007
Messages
2,257
Location
Kingston, RI
I believe the OP’s difference is due to cam phasing variation from bank to bank. Is this a factory untouched motor or has there been work done?
If factory it’s probably just due to Ford’s timing tolerance variation between the 2 banks.

Numbers are pretty good nonetheless
Factory untouched.
 

DSG2003Mach1

Well-Known Member
Established Member
Premium Member
Joined
Apr 15, 2004
Messages
15,913
Location
Central Fl
I believe the OP’s difference is due to cam phasing variation from bank to bank. Is this a factory untouched motor or has there been work done?
If factory it’s probably just due to Ford’s timing tolerance variation between the 2 banks.

Numbers are pretty good nonetheless

this is my opinion as well.
 

Users who are viewing this thread



Top