Compression test came back... What do ya think?
12-24-2009, 02:39 AM
#31
Registered User
Join Date: Dec 2002
Location: NYC burbs
Posts: 1,553
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by marcucci,Dec 24 2009, 12:52 AM
But hey, buy whatever you want. More business for people like me when you see your crap dyno numbers or stock Civics pull away from you at streetlights.
11past9, please do not put all your cards into what just this one person says.
12-24-2009, 05:45 AM
#32
Registered User
Better he believe me who knows what the compression on a lawnmower is vs any Honda with a CR over 10:1.
BTW, I know about on-spring valve compressors and own one but not that type. But hey, you know it all, so you probably knew that too.
11past9, I wasn't ragging on you but rather the myriad of posters who are recommending you buy a car that likely has issues. I highly recommend you have the car checked by an independent shop w/some experience with the S2, or have the dealer compare the compression numbers with a new car, or check the numbers on other S's. That right there should show you the difference.
For reference, here's what I recall from the last few I've worked on-
245 to 255 across the board: healthy
225 psi: badly pitted exhaust valves (resulting in about 12% cylinder leakage)
210 psi in cyl 4: badly pitted exhaust valves and some scoring of the cyl walls resulting in about 20% cylinder leakage
150 psi across the board: badly pitted exhaust valves and bent intake valves resulting in about 40% leakage
Rodney, I'm not sure where you get your attitude but I can take that, it's your facts you need to clean up.
BTW, I know about on-spring valve compressors and own one but not that type. But hey, you know it all, so you probably knew that too.
11past9, I wasn't ragging on you but rather the myriad of posters who are recommending you buy a car that likely has issues. I highly recommend you have the car checked by an independent shop w/some experience with the S2, or have the dealer compare the compression numbers with a new car, or check the numbers on other S's. That right there should show you the difference.
For reference, here's what I recall from the last few I've worked on-
245 to 255 across the board: healthy
225 psi: badly pitted exhaust valves (resulting in about 12% cylinder leakage)
210 psi in cyl 4: badly pitted exhaust valves and some scoring of the cyl walls resulting in about 20% cylinder leakage
150 psi across the board: badly pitted exhaust valves and bent intake valves resulting in about 40% leakage
Rodney, I'm not sure where you get your attitude but I can take that, it's your facts you need to clean up.
12-24-2009, 05:54 AM
#33
Registered User
Thread Starter
Join Date: May 2009
Posts: 108
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by marcucci,Dec 24 2009, 06:45 AM
Better he believe me who knows what the compression on a lawnmower is vs any Honda with a CR over 10:1.
BTW, I know about on-spring valve compressors and own one but not that type. But hey, you know it all, so you probably knew that too.
11past9, I wasn't ragging on you but rather the myriad of posters who are recommending you buy a car that likely has issues. I highly recommend you have the car checked by an independent shop w/some experience with the S2, or have the dealer compare the compression numbers with a new car, or check the numbers on other S's. That right there should show you the difference.
For reference, here's what I recall from the last few I've worked on-
245 to 255 across the board: healthy
225 psi: badly pitted exhaust valves (resulting in about 12% cylinder leakage)
210 psi in cyl 4: badly pitted exhaust valves and some scoring of the cyl walls resulting in about 20% cylinder leakage
150 psi across the board: badly pitted exhaust valves and bent intake valves resulting in about 40% leakage
Rodney, I'm not sure where you get your attitude but I can take that, it's your facts you need to clean up.
BTW, I know about on-spring valve compressors and own one but not that type. But hey, you know it all, so you probably knew that too.
11past9, I wasn't ragging on you but rather the myriad of posters who are recommending you buy a car that likely has issues. I highly recommend you have the car checked by an independent shop w/some experience with the S2, or have the dealer compare the compression numbers with a new car, or check the numbers on other S's. That right there should show you the difference.
For reference, here's what I recall from the last few I've worked on-
245 to 255 across the board: healthy
225 psi: badly pitted exhaust valves (resulting in about 12% cylinder leakage)
210 psi in cyl 4: badly pitted exhaust valves and some scoring of the cyl walls resulting in about 20% cylinder leakage
150 psi across the board: badly pitted exhaust valves and bent intake valves resulting in about 40% leakage
Rodney, I'm not sure where you get your attitude but I can take that, it's your facts you need to clean up.
12-24-2009, 06:24 AM
#35
Registered User
Engine temp normally only affects readings a few psi. No more than 10 for sure. Same goes for holding the throttle wide open while testing or doing the test "wet."
The engine I tested most recently that blew 255 psi, that test was done with the engine around 100F and throttle closed. Fuel wasn't disabled.
As for what would make a motor blow those numbers- you could expect a 5-10 psi higher numbers if it was done warm (assuming this test was cold). More than likely the exhaust valves are starting to pit and the rings are starting to wear. The fact that all the cylinders are same says that it's an issue common to all the cylinders, so I would say probably higher-RPM use, poor maintenance (extended oil change intervals on a crummy oil) or possible FI used with bad tuning or lean operation. With those numbers I doubt that valves are bent but it's possible.
There's always the chance that the tech didn't do it right or his gauge had an issue, but if the dealer did it, that's unlikely.
For the cars/numbers I quoted, bent valves come only from over-revving the engine, usually by mis-shifting. Burnt valves or exhaust valve pitting comes with age (high miles, usually 100k or more on the S2k) OR used with forced induction and poor tuning (running lean). It's also possible to do this NA but most cars out there that have been tuned were done so w/FI and were not naturally aspirated.
The engine I tested most recently that blew 255 psi, that test was done with the engine around 100F and throttle closed. Fuel wasn't disabled.
As for what would make a motor blow those numbers- you could expect a 5-10 psi higher numbers if it was done warm (assuming this test was cold). More than likely the exhaust valves are starting to pit and the rings are starting to wear. The fact that all the cylinders are same says that it's an issue common to all the cylinders, so I would say probably higher-RPM use, poor maintenance (extended oil change intervals on a crummy oil) or possible FI used with bad tuning or lean operation. With those numbers I doubt that valves are bent but it's possible.
There's always the chance that the tech didn't do it right or his gauge had an issue, but if the dealer did it, that's unlikely.
For the cars/numbers I quoted, bent valves come only from over-revving the engine, usually by mis-shifting. Burnt valves or exhaust valve pitting comes with age (high miles, usually 100k or more on the S2k) OR used with forced induction and poor tuning (running lean). It's also possible to do this NA but most cars out there that have been tuned were done so w/FI and were not naturally aspirated.
12-24-2009, 10:36 PM
#36
i disagree. if your numbers are what they say they are. you cant put too much buying weight on the compression numbers alone. too many factors involved. What the compression test determines is wear according to the other cylinders, not what other s2000 tested under different conditions, atmospheric conditions,etc,etc. kinda like the dyno thing...only use it for tuning. compression test is supposed to be done at WOT and fuel pump fuse taken out.
255 seems like the top end of what a gauge would read and sounds like it was done wrong. 255-10(not WOT)-10(not Hot engine)-x(whatever the gauge was off/mechanic/real world circumstance)= what your test has shown(equal fine).
sure you could still have good numbers then the motor grenades a week later due to something else. dont put too much into the compression test.
To be comparing compression numbers against ones done on other days,cars, mechanics,etc, is like comparing dynos...pointless.
255 seems like the top end of what a gauge would read and sounds like it was done wrong. 255-10(not WOT)-10(not Hot engine)-x(whatever the gauge was off/mechanic/real world circumstance)= what your test has shown(equal fine).
sure you could still have good numbers then the motor grenades a week later due to something else. dont put too much into the compression test.
To be comparing compression numbers against ones done on other days,cars, mechanics,etc, is like comparing dynos...pointless.
12-25-2009, 03:43 AM
#37
Registered User
Join Date: Dec 2002
Location: NYC burbs
Posts: 1,553
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by starchland,Dec 25 2009, 02:36 AM
i disagree. if your numbers are what they say they are. you cant put too much buying weight on the compression numbers alone. too many factors involved.
12-25-2009, 06:21 AM
#38
This may not be a factor, but intuition seems to suggest that raw compression numbers may be affected by Density Altitude. Would the same car not have higher compression numbers at sea level than it would at 5000 feet?
12-25-2009, 09:02 AM
#39
I'm not sure how reliable these numbers are, but I found a site that gave these conversion factors for compression numbers at various altitudes.
0' = 1.0
1000' = .9711
2000' = .9428
3000' = .9151
4000' = .8881
5000' = .8617
6000' = .8359
7000' = .8106
8000' = .7860
So it seems that an S2000 that generated compression values of 250 PSI near sea level would probably do about 215 PSI at 5000'. What altitude is the dealership where the car was tested?
0' = 1.0
1000' = .9711
2000' = .9428
3000' = .9151
4000' = .8881
5000' = .8617
6000' = .8359
7000' = .8106
8000' = .7860
So it seems that an S2000 that generated compression values of 250 PSI near sea level would probably do about 215 PSI at 5000'. What altitude is the dealership where the car was tested?
12-25-2009, 10:15 AM
#40
Yeah, density altitude would have an effect on the compression test results. the less dense air you start with, the lower the cylinder is going to be able to compress it to.
And those numbers look right to me, I know off the top of my head that 5,000 ft is about 15 percent loss, so that looks good.
And those numbers look right to me, I know off the top of my head that 5,000 ft is about 15 percent loss, so that looks good.