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Old 03-02-2015, 11:46 AM   #1
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Default Less than ideal compression numbers

1....Dry:130.....Wet:159
2....Dry:140.....Wet:174
3....Dry:118.....Wet:152
4....Dry:118.....Wet:144

Test done on 03 engine, stock 10:1 pistons, dead battery but jumpered to a running vehicle so decent but not perfect voltage, spark plugs all removed, throttle body no installed.

Engine has not run since Sept 2013, so safe to say it was not warmed up for the test.

Going to boost it anyways, but any thoughts on these numbers? They jumped up a lot with one cap full of oil into each cylinder. I'm guessing rings are either ****, or maybe just reading low since no oil to seal it up from sitting and cold numbers too.

Thoughts? Just thought if this, if I run 30 PSI boost that will get my numbers up about where they should be!
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Old 03-02-2015, 01:09 PM   #2
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Pretty low, but if it sat for so long, cylinders were bone dry.

They all went up roughly the same amount. I can't believe that's all due to rings. It would have to be nearly identical wear. Most times you see an outlier, with the rest normal.

Boost that sucker, and keep an eye on oil consumption.
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Old 03-02-2015, 01:18 PM   #3
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if it's dead cold and has been sitting a long time, might not be too bad. I'd re-check once you've used it a bit and when it's warm
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Old 03-02-2015, 01:26 PM   #4
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a motor sitting that long could have a lot of time based crap going on. run it in, let the rings clean out some of the gunk and test again.
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Old 03-02-2015, 01:29 PM   #5
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If those numbers don't improve with some runtime (like an hour of runtime at most), I wouldn't put 30psi through that motor. The blowby will be unmanageable.
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Old 03-02-2015, 01:33 PM   #6
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Thanks guys! This shortblock will be used to test the new setup/learn how to tune a SC'd car, then I plan to pull it and put my new shortblock in. But I'll do a comp test after an hour or so as Andrew said and see if it improves. This motor ran strong/no oil consumption or smoke before it sat.
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Old 03-17-2015, 08:57 PM   #7
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Quote:
Originally Posted by Savington View Post
If those numbers don't improve with some runtime (like an hour of runtime at most), I wouldn't put 30psi through that motor. The blowby will be unmanageable.
Well I got about 1hr or so of idling on it, and redid the test since I had to pull the plugs anyways.

Did a compression test while the plugs were out. Hot test throttle open dry numbers. 01+ engine.

Cylinder..... PSI
1..........180
2..........181
3..........179
4..........167

Looks like something is going on with cylinder 4, it's down a bit compared to the others. Not 100% sure (can't find spec, anybody know it?) but pretty sure a VVT motor should test higher than 180, like 210 or so right?
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Old 03-18-2015, 05:22 PM   #8
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I hate compression tests. They don't tell you anything of value. Buy a small-bore leakdown tester with the proper restrictor orifice for a ~3.3" bore and do a leakdown test so you can actually figure out what's going on. Don't use a HF tester, they are junk. Google "FAA Leakdown Procedure" for more info.
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Old 03-18-2015, 05:24 PM   #9
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I have a cheapo leakdown tester, but it's not here in TX. It is definitely junk anyways.

I'll have to see if I can find a good one for a decent price. What leakdown tester do you use Andrew?
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Old 03-18-2015, 05:58 PM   #11
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Thank you sir! I hate to spend the coin right now, but I may do it anyways. If I do, I will definitely post up the leakdown results.

But for now, considering the numbers came up a quite a bit with an hour of idling, I'm guessing it's at least OK to boost it for a while. I don't know what's going on with hole 4, but I don't think it's catastrophic whatever it is that's causing to read a bit lower than 1-3.

Curious though, shouldn't they all be around 210 not 180?
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Old 03-18-2015, 06:39 PM   #12
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I put little weight behind the actual numbers. They will vary from gauge to gauge, especially if you're using an HF tester or something similar. The difference between #2 and #4 is borderline alarming, though, and there's clearly an issue with #4. I would not put 30psi into that motor.
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Old 03-18-2015, 07:29 PM   #13
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It's a 30 dollar autozone tester, probably junk I don't know.

I agree there's something going on with cylinder 4. I'm not planning to boost on this motor very long though. It's basically just to shake down test all the stuff I made and learn how to tune a SC'd car and get the WI setup up and running. Once that's done, this motor comes out and new shortblock goes in. But for sure, I'm going to do a leakdown test before I pull it, as I want to know what is up with cylinder 4 for sure.

I'm going to check the head out while it's off anyways to see how everything is holding up as I did all the head work on this motor, so who knows maybe something is up with the head on cylinder 4. Leak down will tell me, I'll do it before I pull this motor.

Still, I think as long as blowby is manageable, I should be able to boost it enough to get it tuned decent. I may actually retest it one more time, as now I've actually driven the car vs just letting it idle for about 1hr before I did the test above.
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