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Author Topic: Compression test results help?  (Read 193 times)

Eggylshatch

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Compression test results help?
« on: May 17, 2017, 09:24:55 AM »

Engine is a b20z, so I think it should be the higher CR engine if its stock internals, 9.6:1 I believe. Bought it used from another guy years ago, supposedly a low-mileage JDM engine, but have no idear. I did a compression test just to check on the health because I'm planning to boost it.

Results:
  4    3     2     1
151 150 150 151

I tried putting a bit of oil down #1 and it bumped it to around 161. I tried two different compression testers. if it was shitty ring seal, wouldn't the oil bump the pressure higher? It doesn't seem likely to me that the numbers would all be so close if the engine was beat to hell enough for the pressures to be this low?

Am I doing something wrong? My battery is a little weak so the engine cranks more slowly maybe, but I let it go 12 cranks for each cylinder. I watched the gauge for about 10 sec each time, didn't seem to be losing pressure. Could there be lower CR pistons in there? Or is this just a saggy old bitch of an engine?
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Tim

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Re: Compression test results help?
« Reply #1 on: May 17, 2017, 12:12:59 PM »

seems real even to be beat.
did you hold the throttle open?
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Eggylshatch

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Re: Compression test results help?
« Reply #2 on: May 17, 2017, 02:01:02 PM »

seems real even to be beat.
did you hold the throttle open?

That's what I thought too.

I did hold the throttle open for the first test for sure, I might have forgotten to do so when I did it with the second comp. tester. I used mine first which looks a little rusty and beaten up from years of riding in the bottom of the tool box so I was a little skeptical. The second one I grabbed a rental from o'reilly auto parts. Maybe I should rent it again and make sure I didn't screw it up that time... Weird to get the same results for both though.

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ratcityrex

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Re: Compression test results help?
« Reply #3 on: May 17, 2017, 10:53:37 PM »

Cam timing? It's real even. If your rings were sloppy the oil would have bumped the comp up a bunch more there 10psi. I'm thinking the cam timing is funky. Off a tooth or something on the belt.
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New setup is old bottom end with a hype r head with gsr cams. built lsv with hx35 @ 26psi on pump gas
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Old Setup B18a1 296hp/289tq LEED Tuned 20psi on pump! http://www.youtube.com/watch?v=2Yj-Z90j4W4 
http://www.realhomemadeturbo.com/forum/index.php/topic,205.msg2437.html#msg2437

Eggylshatch

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Re: Compression test results help?
« Reply #4 on: May 18, 2017, 09:34:16 AM »

Cam timing? It's real even. If your rings were sloppy the oil would have bumped the comp up a bunch more there 10psi. I'm thinking the cam timing is funky. Off a tooth or something on the belt.

Hmm. I'll see if I can double check it. I had a cluster when I put it back together- it has adjustable cam gears on it and a crankshaft pulley off a b18a and it's missing the lower timing cover with the handy mark on it. So something could certainly be off
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Tim

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Re: Compression test results help?
« Reply #5 on: May 18, 2017, 12:00:53 PM »

there is a mark on the oil pump you can line up with the crank gear.
I can't remember if it coincides with anything on the pulley to make it easier now that its together.
either way its annoying when the cover is gone but not the end of the world.
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Eggylshatch

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Re: Compression test results help?
« Reply #6 on: May 18, 2017, 02:14:51 PM »

there is a mark on the oil pump you can line up with the crank gear.
I can't remember if it coincides with anything on the pulley to make it easier now that its together.
either way its annoying when the cover is gone but not the end of the world.

Okay that's good to know. I think when I did it last time I did the ole screwdriver down the spark plug well to see where TDC was in combination with the rough location of the pulley mark, seems a little imprecise though.
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Eggylshatch

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Re: Compression test results help?
« Reply #7 on: May 23, 2017, 12:52:44 PM »

Just realized what the problem is! I'm at 7,000 ft in elevation here in Flagstaff. The adjustment I found puts 150 psi at around 185 for sea level. The engine is now rated Good To Go  O0

Interesting way to think about the power lost at elevation. It will need more boost.
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Tim

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Re: Compression test results help?
« Reply #8 on: May 23, 2017, 05:23:13 PM »

damn that puts in perspective for sure
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92CXyD

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Re: Compression test results help?
« Reply #9 on: June 05, 2017, 05:27:57 PM »

Just realized what the problem is! I'm at 7,000 ft in elevation here in Flagstaff. The adjustment I found puts 150 psi at around 185 for sea level. The engine is now rated Good To Go  O0

Interesting way to think about the power lost at elevation. It will need more boost.

Same in my area 5200 ft altitude
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