Done a compression test on my S14's KA24DE. . .

[Jagstang]

Alright so today I done a compression test on my 1995 240sx KA24DE, and the engine has 190,xxx km's (118,371 miles). As for the numbers...

1st cylinder got 190 PSI
2nd cylinder got 205 PSI
3rd cylinder got 190 PSI
4th cylinder got 205 PSI

As you can see, there's a 15 PSI difference from each cylinder. . . Is that safe? I heard that the maximum each cylinder can exceed on an S14 KA is 15 PSI, and that's exactly what I have. . . So should I be worried?

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Secondly, today we also done an engine compression test on Asoomal's 1992 KA24DE which has 310,xxx km's (192,625 miles). And as you can see, his engine has a lot of KM's and the numbers he got were very very very surprising. . .

1st cylinder got 180 PSI
2nd cylinder got 179 PSI
3rd cylinder got 180 PSI
4th cylinder got 179 PSI

As you all know, S13 KA's come with 180 PSI stock from factory, so how is it possible that his S13 still has brand new compression when it's quite old?

Let me know, cause if that's not normal, I'll have to return the compression tester for another one, and redo my car's compression tests.

Help would be greatly appreciated, thanks in advance.

[gigabit240]

Why wouldn't it still have good compression? Im kinda worried about your car though... The compression seems a little high? I think... I'm not sure if its different for s14's

[whyteboi]

when most ppl do compression on an s14 it always seams alil higher than s13, idk mayb something different in the rings from the factory

[Jagstang]

Why wouldn't it still have good compression? Im kinda worried about your car though... The compression seems a little high? I think... I'm not sure if its different for s14's

The compression on the S14 from factory is 220 PSI (as opposed to the S13's 180 PSI). . . So my car is fine in terms of wear etc. . . But what about the 15 PSI difference from each cylinder?

[motoman399]

well 220 is not the factory psi. i copied this right out of the 95 240sx FSM

[Jagstang]

well 220 is not the factory psi. i copied this right out of the 95 240sx FSM

That 179 compression is not the factory rating, it's the average over time. . . If you look on wiki, it states that the 94-98 240's have a compression of 9.5:1, while S13's have 9.0:1. . .

So as you can see. . . 9.5>9.0 So that's why S14's have a higher compression.

[motoman399]

all ka24de's had a compression ratio of 9.5:1 none came with 9.0:1. and you stated that 94-98 240's had the higher compression, but s13's didnt. 94 is an s13.

the stock compression pressure for a 240sx is 179 from the factory. thats not the average over time. the fsm doesnt work like that. what if someone tested it right from the factory? and the fsm said 179 but they pulled 205... see where its not adding up. they give you the specs from the factory and then what the lowest is they want to see.

[asoomal]

Probably meant late 94...his S14 was made in April 1994 btw.

You sure they didn't bump up the compression for the S14's?

[motoman399]

im like 95% sure. they use the same pistons for 240sx ka24de's

[IanS]

Unless you are having driveability issues, then you are most likely fine. General rule of thumb, for any engine, is 120 PSI to run, and no more than 25 PSI difference between any 2 cylinders.

You may have a slight imbalance in actual power production between cylinders, but nothing should be noticeable. If you have a consult port, and access to a proper scanner, you could try running a cylinder balance test. This will tell you if the difference is enough to throw the ECU off, but my professional opinion is that you should be fine.

What prompted the compression test?

[Jagstang]

Unless you are having driveability issues, then you are most likely fine. General rule of thumb, for any engine, is 120 PSI to run, and no more than 25 PSI difference between any 2 cylinders.

You may have a slight imbalance in actual power production between cylinders, but nothing should be noticeable. If you have a consult port, and access to a proper scanner, you could try running a cylinder balance test. This will tell you if the difference is enough to throw the ECU off, but my professional opinion is that you should be fine.

What prompted the compression test?

Curiosity is what made me test it out. I was always interested in knowing the compression on my engine. But I might just replace the compression gauge, because if you haven't noticed. . . On both my car and Asoomal's 240, every 2nd cylinder was the same. . . SO I think their may be a problem with it.

But yeah, my engine runs amazingly. . . It purs like a brand new engine, idles well, and has amazing power. But yeah, the 15 PSI difference does worry me a bit.

[IanS]

But yeah, my engine runs amazingly. . . It purs like a brand new engine, idles well, and has amazing power. But yeah, the 15 PSI difference does worry me a bit.

I wouldn't worry about it, really.

What are you going to do about it anyway, tear down and rebuild the engine for no gain in performance or reliability?

It is not a problem unless it deteriorates. How would the engine have been if you had never checked it?

[Jagstang]

But yeah, my engine runs amazingly. . . It purs like a brand new engine, idles well, and has amazing power. But yeah, the 15 PSI difference does worry me a bit.

I wouldn't worry about it, really.

What are you going to do about it anyway, tear down and rebuild the engine for no gain in performance or reliability?

It is not a problem unless it deteriorates. How would the engine have been if you had never checked it?

Well, my future aspirations is to turbo the engine, and if the compression was great all around. . . I would be pretty happy. But I guess that all changed now.

But then again, I guess I have to rebuild it to handle the turbo in the first place, but still

[RustspecS13]

The high/uneven compression could be from carbon build up. If you drive slow and easy, carbon easily builds up and collects in your intake manifold, on your pistons etc etc.

I would do a through seafoam cleaning and that should help with all that build up- if its not your gauge. Maybe do a comp check out of order?

~Alex

[gigabit240]

Probably meant late 94...his S14 was made in April 1994 btw.

You sure they didn't bump up the compression for the S14's?

It was made for the 95 model year. Just like my 92 was made in july 91

[gigabit240]

Well, my future aspirations is to turbo the engine, and if the compression was great all around. . . I would be pretty happy. But I guess that all changed now.

But then again, I guess I have to rebuild it to handle the turbo in the first place, but still

No not necessarily. Unless you're looking at throwing down past like... 270-280 hp, then you can probably just boost the stock internals.

Check the KA-T forums