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compression numbers for a b235?

11K views 12 replies 7 participants last post by  Harvey's Autohaus 
#1 ·
when I got home from blowing my turbo up, I put the compression tester in, and I got 210psi across the board.
for 9.3:1, it seemed a liiiiiiiittle high.

can anyone confirm what the compression numbers SHOULD be for the b235?
This could come in useful for anyone that's told to "do a compression test", but doesn't know what to look for, or expect.


Thanks!

-Craig R.

(again, for the archives)
 
#3 ·
A better head design can get more air than the others

9.3 compression only is a static measure.
A B235 head is one of the most efficient out there so can cram more air inside the head. More air leads to higher PSI readings even if the nominal compression remains constant. This ignores the turbo as compression would only be measured with the engine cranking but not running.
 
#4 ·
I just rebuilt my ’02 9-5 Aero engine that had 90,000 miles, used JE pistons & rings.
I checked the compression after I had 1000 miles on it and they all read about 181 or 182 psi. I Let it crank 7 times each cylinder.

That’s about what they read before I tore it down. I cant find what WIS says they should be. John at JZW who did my ECU said the numbers were great. But I thought they would be higher.

I lightly ported my head intake and exhaust. I hope I didn’t screw it up after reading what dudethe9-5isfast wrote.
 
#6 ·
I just rebuilt my '02 9-5 Aero engine that had 90,000 miles, used JE pistons & rings.
I checked the compression after I had 1000 miles on it and they all read about 181 or 182 psi. I Let it crank 7 times each cylinder.

That's about what they read before I tore it down. I cant find what WIS says they should be. John at JZW who did my ECU said the numbers were great. But I thought they would be higher.

I lightly ported my head intake and exhaust. I hope I didn't screw it up after reading what dudethe9-5isfast wrote.
Its the consistancy that you look for and not the actual number so much. Anything above 170 is pretty good and if you had one down more than 10%, this would indicate a problem.

The actual numbers can vary by temperature and other variables. I had one motor in a 9k that really screamed, it was fast its entire life, the compression numbers only measured 160, 161, 160, 159. The motor used no oil, ran very strong and sounded very quiet as well.

John
 
#5 ·
It made no sense to me.
The in-cylinder pressure should be constant. There's a service range. between x, and y psi. 185ish sounds good. I think I remember my galant being somewhere around 195psi, and that was 9.5:1.

No worries, though. the car's fine in my case. it was a dead gt17, not bad rings.
no more smoke... ever.

thanks, guys.
 
#7 ·
when I got home from blowing my turbo up, I put the compression tester in, and I got 210psi across the board.
for 9.3:1, it seemed a liiiiiiiittle high.

can anyone confirm what the compression numbers SHOULD be for the b235?
This could come in useful for anyone that's told to "do a compression test", but doesn't know what to look for, or expect.

Thanks!

-Craig R.

(again, for the archives)
I have heard of numbers in the 190+ range and I think that is not unheard of and would consider if it was cold, warm, hot. The consistancy seems very good and its hard to think too much compression is possible with stock pistons and head gasket. I would think decking the head would increase it a smidge, but not that much.

I think you are golden,

John
 
#9 ·
Well, this is all stock. t7 head, t7 cams.
I'm amazed that the WIS, or any other manuals don't have a service spec.
Almost any other car would have the info.

I do appreciate the feedback, though.
my assumption is that the 210psi is from hot/fully expanded block/pistons/rings.
I have not done cold readings, yet.
 
#11 ·
Static Compression...8.8-1....9.3-1.. 10.? what ever like my Econo 93 2.3 has "36mpg" Meens Nothing. Its About "DYNAMIC" Compression. Take the Fuel and Spark Away and What do you have? An Air Compressor for an engine. Why Aircompressor theory? When you time your Aircompressor For DYNAMIC Compression "LIKE NICK SAID" The VALVE TIMING Dictates What the Actual DYNAMIC is Not the Static Ratio. Do a Comression test on Any Old Exotic. Or American Car with a radical Cam. The Numbers are all over the Place. Some High Some Low, ALL GOOD if it has any Kind or Radical OVERLAP.
 
#12 ·
guy... I know.

As a car rolls off the factory floor, in it's factory trim, it's got to have certain values.
I can't imagine that if a car rolled off, and it was 140psi across the board, they'd say "meh, they're all within 10%, it's cool"

There HAS to be a factory service range.
I don't need a lesson in cam timing, lift, duration, and overlap.
I know all about it.

follow this link.
http://www.geocities.com/dsmgrrrl/FAQs/compression.htm
At the bottom, there are VERY specific numbers listed.
Maybe you'll get what I'm saying...
 
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