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AP2 Compression Test prior to turbocharger

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AP2 Compression Test prior to turbocharger

 
Old 08-04-2018, 07:18 AM
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Default AP2 Compression Test prior to turbocharger

Hey all, I've read a number of 'compression test results' posts but couldn't find enough info to compare to my somewhat odd results. I bought my 2005 S2000 in March 2017 with 146,600 miles. I've done all the normal maintenance since (some of it twice) since it had no service records. This included new spark plugs but i didn't have a tester at the time. Since then, I've added about 2,000 miles, only about half of that being highway, and I've done a few autocross events as well. It now has 148,500 miles. Car feels strong overall, but wanted to start upping the power past basic bolt-ons so picked up a GReddy turbo kit. I wanted to cover my bases before boost, so I started with a compression test which I expected to be mundane because the car feels perfectly fine throughout the rev range.

Followed the Stickied DIY - engine idle to bring up operating temp for ~7 minutes. Pulled the fuel pump fuse and all four spark plugs were removed. I own a Shankly tester from Amazon, ~$25 so not exactly top-tier but it works. Started at #1 (front of car), checked it once, then two tests each on Cyl 2-4, then circled back around at the end to validate Cylinder 1 to account for variations. 8 tests in total, 2 per cylinder. Both tests per cylinder were consistent withing 2psig.

Summary: Cyl 1: 208, Cyl 2: 195, Cyl 3: 190, Cyl 4: 179
Link to test/results and spark plug photos. Imgur Link to Photos

As far as evaluating the results, I've seen that consistency is most important. Even if it was 180psig across all four cylinders that's preferable to variations like 220/220/160/220. I've got 210/200/190/180. Considering it's a cheap gauge, they could all be higher or lower, but using the same gauge for all cylinders means that cylinder integrity is effectively dropping as i move to the back of the engine. I know the 'minimum range' is something like 130psig for an AP2, and that 180 on it's own isn't inherently awful. That said, I want to add in up to 10psi of boost (even if only from a T518z), so I want to get some outside feedback since it's a higher-mileage motor.

Thank you!


Updated: Leakdown tested: Cyl 1/2/3/4 at 15%/20%/20%/30%...i think? Full details below on August 5, 2018 (US Central Time)

Last edited by Dwnfrce; 08-05-2018 at 02:16 PM. Reason: Updates
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Old 08-04-2018, 09:00 AM
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It gets thrown around a lot and I don't know who came up with "consistency is key" because its not. If you had 180 across the board, that top end is toast. Having 180psi will put you in the neighborhood of a 40-50% on a leakdown. If its just one or two cylinders down this badly , other than being down on power compared against another s2000s, you won't notice much a difference. If the rings are leaking, a lot of the times it will blow the dipstick up from all the crankcase pressure.

Either way, you need to fix the issue before you starting dropping $$ on performance because it will be wasted.

Assuming you did this comp test with the throttle wide open and preferably the airbox off...You need to do a leakdown to see if its your valves or your rings that are leaking.
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Old 08-04-2018, 09:59 AM
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Thank for the feedback. I did do the test at wide open throttle, but i have a comptech intake installed (not the stock airbox). I'm not sure if that would have any impact or not.

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Old 08-04-2018, 11:18 AM
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I would say those are typical numbers for a motor with 146k miles on it. My motor with 36k never had 240 across the board and I have been boosted for 3 years. Minimal oil burning as well. I think you should be ok on a greddy kit.

i always checked for consistent numbers.
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Old 08-04-2018, 02:17 PM
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Im with umair. Might as well run the kit and see how everything runs that way if and when engine gets rrplaced you can rest assured all is well. When was the last time the valves were adjusted? If you have the exhaust manifold off you can run a cylinder leak down test and easily hear if the exhaust valves are letting air through and contributing to loss of compression.
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Old 08-04-2018, 03:13 PM
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I had them adjusted last summer, and it's the only thing I haven't done myself. I asked for Intakes: 0.008in, Exhuasts: 0.010. The tech said everything looked fine during the adjustment.

It's a used greddy kit, so i had planned to drop in the injectors and emanage to make sure the base tune was in the range without boost before putting the turbo into the mix. I'll pick up a leakdown tester and see how it goes.
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Old 08-04-2018, 06:08 PM
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Originally Posted by Dwnfrce View Post
I had them adjusted last summer, and it's the only thing I haven't done myself. I asked for Intakes: 0.008in, Exhuasts: 0.010. The tech said everything looked fine during the adjustment.

It's a used greddy kit, so i had planned to drop in the injectors and emanage to make sure the base tune was in the range without boost before putting the turbo into the mix. I'll pick up a leakdown tester and see how it goes.

i highly recommend getting an AEM for tuning. You will probably get tired of the power the greddy kit produces pretty quickly.

AP1chief is a good guy for your tuning needs. He is pretty active on the forums.
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Old 08-04-2018, 06:43 PM
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Originally Posted by umair View Post
i highly recommend getting an AEM for tuning. You will probably get tired of the power the greddy kit produces pretty quickly.

AP1chief is a good guy for your tuning needs. He is pretty active on the forums.
I expect I'll want to move to stand alone at some point, but for now I'm more worried about the basics. Thanks for your feedback on the compression issue
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Old 08-05-2018, 02:14 PM
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Updated with Leakdown Test.

I picked up a Pittsburgh tester from Harbor Freight. I followed a write-up (not video) to try and get it done quickly, but came across confusing results. I had everything on the engine installed with the exception of: the spark plugs (obviously), the dip stick, the radiator cap and a return hose on the intake manifold. That way I could effectively check for leakage through the intake valves, piston rings or cylinder head. The last being the exhaust valves but that was by elimination.

I carefully put a long 3/8" extension down the Cyl 1 spark plug tube with my left hand to rest gently on the piston, and had my right hand on the 19mm ratchet on the crank pulley. I turned the pulley and guided the extension with my hand until the extension reached it's peak and was no longer climbing on the up stroke. I attached the leakdown tester and Cyl 1 and it was around 15% leakdown with some bubbles coming out of the intake manifold. I expected it to be decent since the compression test was 208psig. No bubbles through the radiator cap or traces of air at the dipstick hole.

Then, expecting that Cyl 1 and 4 hit top dead center (TDC) at the same time, I moved the leakdown setup to #4, but it was severely leaking (over 60%) not only through the intake manifold but also through the Cyl 3 hole (although from the piston chamber or the crank case vent, i couldn't say, but i'm assuming the case). I was surprised it was so bad, but recorded it and moved to set Cyl 2 at TDC. It came our around 20%, so I moved to Cyl 3 and it was leaking horrible. I figured something was wrong, so I moved to Cyl 4 again and adjusted the positioning for it to be at TDC and it was more reasonable at 30% (not good but expected from a compression of 180 psig). So again, because i thought 4 and 1 should be TDC at the same time, i moved back to 1 that had done well before but it was awful. Last I moved back to Cyl 3 again after 4 and adjusted it to TDC and hit 20% similar to Cyl 2.

So i'm thinking the ratings would be Cyl 1/2/3/4 at 15%/20%/20%/30%, but am a bit confused at the results of paired cylinders 1-4 and 2-3. Maybe due to the inaccuracy of "True TDC" since i didn't have the valve cover off? Thoughts?
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Old 08-05-2018, 02:28 PM
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You must have done the leak down test out of order. The order is 1-3-4-2 like the manual says. Make sure your engine is warmed up and try again.
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