My friend picked up a cheapie compression guage from AutoZone this weekend to test a van he just bought that's not running properly. I figured, what the hell, lets test my D16Y8 for fun.

Background:

The motor has 105K on it, been maticulously maintained with full synth changes every 3-5K. When I removed the valve cover at 90K, the top end was so clean, you would have a tough time beleiving that it wasn't factory fresh or a rebuild.

Pulled the FI, Fuel pump and IGN Coil fuses, and run the test. I got 145 150 150 147. I was pretty happy with the consistancy. Get home, check the helms, and it said min. was 135, max variation 28. So now I'm thinking those are pretty crappy numbers; but maybe I did something wrong.

I checked this link:

http://www.c-speedracing.com/h...t.php

And it says to be at WOT, which I did not do. The spec in the helms said that the numbers should be from 250 RPM (I'm assuming that's the starters speed) with wide open throttle, so I guess I did the test wrong.

So my question is, if I was to retest at WOT, would my numbers be higher? I'm not exactly sure how having it at WOT would affect the test. Can anyone enlighten me?

CLIFFS:

Did compression test, numbers low. Was not at WOT while testing; would this yeild higher numbers if I did, and why?

 

how many times did u crank it over per cylinder?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blackeg &raquo;</TD></TR><TR><TD CLASS="quote">how many times did u crank it over per cylinder?</TD></TR></TABLE>

I cranked until the guage didn't go any higher. Probably about 10, I wasn't counting really.

 

hmm, never knew about that open throttle idea, i have done it without putting the pedal down and gotten good numbers. its interesting though, i will try it next time.

 

those # are alright for stock compression, i wouldnt be concerned at all.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lohatch &raquo;</TD></TR><TR><TD CLASS="quote">those # are alright for stock compression, i wouldnt be concerned at all.</TD></TR></TABLE>

Really? I've seen some people posting about getting #s in the 180's.

The minimum was 135 according to the Helms, so that freaked me out a bit, since I'm only 10psi away from that figure.

 

its much more about consistency than it is about how high the comp is, for a motor w/ that much milage then its normal for comp to not be what it was, but as long as its consitent then your good.

 

dip your finger in some oil and wipe on the rubber Orings before you install the comp tester. do each cylinder 3 times and average them. if they are still a little low and you want to feel better put a little oil in each cylinder. waaalaaa your 180 but seriously i wouldnt worry about it a lot. if you want it to be fresh, rebuild it.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lohatch &raquo;</TD></TR><TR><TD CLASS="quote">dip your finger in some oil and wipe on the rubber Orings before you install the comp tester. do each cylinder 3 times and average them. </TD></TR></TABLE>

I was going to try that next, hoping for a better seal.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lohatch &raquo;</TD></TR><TR><TD CLASS="quote"> you want to feel better put a little oil in each cylinder. waaalaaa your 180 </TD></TR></TABLE>

Nice, I just want to be able to say I've got factory fresh specs

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blackcivic95 &raquo;</TD></TR><TR><TD CLASS="quote">its much more about consistency than it is about how high the comp is, for a motor w/ that much milage then its normal for comp to not be what it was, but as long as its consitent then your good.</TD></TR></TABLE>

I figured that was the case. But I'm just trying to predict the longevity of the motor. I'd like to keep it going without any money (besides maintenance) until I get my dedicated race kaa; then I was going to b00st this baby.

I figured the way I took care of it, it'd be set to go. Now I'm thinking if I should be saving up for a rebuild. I guess I just wanted to have justification for all the money / maintenance / **** retentiveness went into this thing since I've owned it.

Oh, and BTW: Thanks all so much for the replies

 

i wouldnt worry about it. little boost will solve everything

 

I think being at WOT when doing the test may make a difference.

Your testing the compression of air in the cylinder. If there is less air to begin with then you may get lower numbers, being WOT allows more air pass into the cylinders.

I agree with others that the numbers are good across the board and I would't be worried about it. Besides what can you do about it? Nothing really.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EX_AutoXer &raquo;</TD></TR><TR><TD CLASS="quote">My friend picked up a cheapie compression guage from AutoZone
</TD></TR></TABLE>

I would suggest to you that your results may be somewhat lower than you were hoping for, for this reason alone. I've seen significant variations between different makes of gauges. Your readings being almost perfectly equal across the board is the best indication that your engine really is healthy. Test it with a quality gauge and you'll probably get better numbers.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lohatch &raquo;</TD></TR><TR><TD CLASS="quote">i wouldnt worry about it. little boost will solve everything </TD></TR></TABLE>

Damn straight! At least that's what I'm hoping anyway

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by flood &raquo;</TD></TR><TR><TD CLASS="quote"> Besides what can you do about it? Nothing really. </TD></TR></TABLE>

I just wanted to know if I would have to prepare to do something eventually, or just keep running her (which is what I'll be doing).

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 00Red_SiR &raquo;</TD></TR><TR><TD CLASS="quote">
Your readings being almost perfectly equal across the board is the best indication that your engine really is healthy. Test it with a quality gauge and you'll probably get better numbers.</TD></TR></TABLE>

That's what I thought. I'm going to try and track down a better guage and see what happens.

Thanks again everyone

 

Redo the test and your numbers will definitely come up. I forgot to hold the throttle open and I hit 150 or so, holding the throttle open I hit 210. It makes a difference.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by spoonek9 &raquo;</TD></TR><TR><TD CLASS="quote">Redo the test and your numbers will definitely come up. I forgot to hold the throttle open and I hit 150 or so, holding the throttle open I hit 210. It makes a difference.</TD></TR></TABLE>

Thanks! That's great to hear from someone who's done this. I'm still having trouble figuring out how this would make any difference, but as long as my motor is healthy, it's fine by me

 

It's like trying to breathe through a straw with the throttle closed. The air is there, but you just can't take it in fast enough. Remove the straw, open the throttle, and the air flows without a problem.

More air in the cylinders equals higher compression.

I'll take a guess and say your numbers will be 180-190. Let us know.

I suck when it comes to explaining things BTW.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by spoonek9 &raquo;</TD></TR><TR><TD CLASS="quote">It's like trying to breathe through a straw with the throttle closed. The air is there, but you just can't take it in fast enough. Remove the straw, open the throttle, and the air flows without a problem.

More air in the cylinders equals higher compression.

I'll take a guess and say your numbers will be 180-190. Let us know.

I suck when it comes to explaining things BTW.</TD></TR></TABLE>

Your explanation made sence, because how are you supposed to compress air in the cylinder if the TB is closed and can't pull any in on the intake stroke.

So on your advice, I went back to my friends garage for a retest. Pulled all the plugs, FI fuses, and went WOT while cranking; and I got 210 on cylinder 4 I'd say that was pretty healthy compression.

That was the only cylinder I was able to test though, because the damn test guage broke while it was still screwed in. The hose started spinning on the threaded fixture in the spark plug hole. After about 2 hours of messing with it, we were able to get a fine threaded easy out to bite enough to get it out, after pulling the hose completely off. Then that cheap piece of crap tester and cut up hose quickly made it's way to the dumpster.

Anyway, since the test was so consistent at 150 psi when I did it wrong, I'm just going to assume that I would have gotten 210 across the board.

 

That should make you feel better. Sucks that your compression tester broke off in your head though. Glad we could help!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by spoonek9 &raquo;</TD></TR><TR><TD CLASS="quote">That should make you feel better. </TD></TR></TABLE>

Absolutely!

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by spoonek9 &raquo;</TD></TR><TR><TD CLASS="quote"> Glad we could help! </TD></TR></TABLE>

Thanks again, you guys rock!

 

ive had 180 across the charts before... the highest ive ever gotten was 210 across the chart with a mini me motor i built cx block with a y8 head... ive never did a compression test on a motor that had numbers under 175...