VTC_CiViC

Well for those of you who are not familiar with my "freak" as I lovingly call her, my '99 GS-R has always been... well... odd. It all started back when I first bought her in Sept. '01. One of the first things I did after bringing her home was giving her a head-to-toe look over including a compression test. This is when the 'oddity' surfaced, you see, as healthy a motor as it seemed to me, the numbers didn't add up. I don't remember exactly, but it was something like:

160-220-200-220...

I added a little oil to number 4 and it shot up to 300+psi damaging mycompression gauge in the process, so I wasn't sure if it was just a freak occurance or the #2 and 4 cylinders were truly low on compression. Either way for the next 2 years the car would perform flawlesly. Never once smoked, never consumed oil, plugs never showed a sign of oil burn-off. Infact, at a local dyno she put down a relativley amazing 161.5whp.... that's a '99 GS-R with a CAI and nothing esle! Shortly before taking the plunge to the darkside, I wanted to recheck the compression numbers to record any loss in performance over time. Did another comp test and it was worse!

130-210-170-210

Again, not a single sign of any oil consumption, and this car has always been faster than "normal" both at the track and on the street. I dismissed it as a problem with my compression tester (even though it works flawlessly on every other car I've used it on) and went on with boosted life.

Fast forward to tonight. The car is going for it's Hondata installation and tune tomorrow. So in an effort to make sure she's 100% ready, I changed the plugs, oil and gave her a valve adjustment. Well, something happend in the doing because just for the hell of it, I decided to give her one more shot on the compression gauge.....

240-240-240-240

.......whoa. Therein lies my question. Has anybody ever seen such a drastic change in compression with a simple valve adjustment???? Now before you all go and blame the tool, let me stress it again that I've used this gauge on pleanty of other cars including my Civic doezen of times without error, so this is just plain weird!

Is my car possesed or what?

Drew Peacock

My mechanic reccomends when doing a comp test if you get crap numbers the first time to restart the car take it for a blat then try again. He say's sometimes you can drop some carbon or whatever which could hold one of the valves open which of course will give you lower compression readings for that cylinder. Nice numbers now let see the dyno figures

SiRkid

260? you sure it has stock pistons in there?
when you add oil even if the piston is ok the comp goes up ..at least thats been my experience(which is weird)
260 is hella high though .

VTC_CiViC

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SiRkid &raquo;</TD></TR><TR><TD CLASS="quote">260? you sure it has stock pistons in there?
when you add oil even if the piston is ok the comp goes up ..at least thats been my experience(which is weird)
260 is hella high though .</TD></TR></TABLE>

Actually I edited that, it was 240 not 260

S2KP

thats crazy and awesome!

rjardy

Sounds about right, if the valves are not fully seated at the top of the compression stroke, that would yeild low numbers, do to the escaping compression. Glad you got it dialed in there, and yes your car is a freak. And you may be to


Rob

intekragsr

if your valves werent seating, then the compression tester needle would just drop slowly in pressure due to the leak....right?

ATS*Mark

your car is a siko

Charlie Moua

iTrader: (3)

hahah like owner like car..... both amaze me at times. LOL

well I have never heard of that trastic change in compression#, since you stat that she has always been running strong ect w/out problems. I know most of the time before and after valve job compression should only change by 5-10psi at max.

I don't see why it would change so drastically unless your valve was waAAAAy off on both sides but than again you should of heard it tapping or somthing weird like that.

Tinker219

perhaps onces the valvetrain gets rolling at higher RPM, it was enough to "seat" the loose valves well enough so that compression wasnt lost, therefore thats the reason your car has alwasy run well. Congrats on some killer compression numbers! (me who is at 80, 50, 70, 35 LOL)

VTC_CiViC

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tinker219 &raquo;</TD></TR><TR><TD CLASS="quote">perhaps onces the valvetrain gets rolling at higher RPM, it was enough to "seat" the loose valves well enough so that compression wasnt lost, therefore thats the reason your car has alwasy run well. Congrats on some killer compression numbers! (me who is at 80, 50, 70, 35 LOL)</TD></TR></TABLE>

Yea I kinda 'assumed' something along those lines as well because I just can't think of much esle lol.. oh well, off to the dyno she goes!!

racerxadam

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by intekragsr &raquo;</TD></TR><TR><TD CLASS="quote">if your valves werent seating, then the compression tester needle would just drop slowly in pressure due to the leak....right?
</TD></TR></TABLE>

most compression testers have a check valve in them so that the gauge will read the peak since last reset.

Muckman

iTrader: (2)

I agree with turbozxi, deposites can land on the valve seats causing a slight leak. It wont prevent the engine from running and once its heated up it will probably burn off or get crushed by the valve. This can cause alot of inconsistent compression/leakdown test results.

SuperTeg95

Did you adjust your valve to the minimum spec or the max. spec? I am very interested in knowing which would yeild higher or lower compression #s.

What valve clearance did you adjust them to??

D-Man

the new oil would bump the comression up too

green_GSR

Well, valve lash affects valve lift and duration. So I guess if your valve lash is out of spec and the lash is different for each cylinder, then each cylinder gets different valve lift and duration. Hence you have inconsistent compression readings.

vha27

definetely wrongly adjusted valves wont seal, to much valve lash and theres ticking along with poor performance, over adjusted, no valve lash, will never let the valves seal thus all that compression just being blown either out the exhaust or back into the intake tract

SuperTeg95

so the minimum spec would yeild lower compression numbers and the max. spec would give you higher compression?

VTC_CiViC

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SuperTeg95 &raquo;</TD></TR><TR><TD CLASS="quote">so the minimum spec would yeild lower compression numbers and the max. spec would give you higher compression?</TD></TR></TABLE>

Backwards.. and mine were adjusted .006 In / .007 Ex

EH2LS

umm

when u do a compression test, motor has to be hot.

when u do a valveadjustment, temp has to be sub 100 deg F.

did u wait, or do comp test, vadjust, comp test?

ur lash specs and comp test results could be skewed if u did

VTC_CiViC

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Response &raquo;</TD></TR><TR><TD CLASS="quote">umm

when u do a compression test, motor has to be hot.

when u do a valveadjustment, temp has to be sub 100 deg F.

did u wait, or do comp test, vadjust, comp test?

ur lash specs and comp test results could be skewed if u did </TD></TR></TABLE>

Valve adjustment was done on a dead cold motor, comp test done the day after on a freshly flogged motor