Sr Compression Results (pics)

[wangan_cruiser]

i did a compression test on my sr. cold out of engine. i had couple of numbers. i read the fsm and it tells me 128 psi is the minimum and 150 psi would be the max for sr's and u need record the highest you can get. but im wonderin. i cranked the motor for more 4-5 times to get the max output. my question is whats the difference between crankin a motor 3 times against more than what the fsm says?


CYLINDER # 1
http://img.photobucket.com/albums/v224/neozmc24/SR20DET/DSC00004.jpg

CYLINDER # 2

http://img.photobucket.com/albums/v224/neozmc24/SR20DET/DSC00007.jpg


CYLINDER # 3

http://img.photobucket.com/albums/v224/neozmc24/SR20DET/DSC00005.jpg

CYLINDER # 4

http://img.photobucket.com/albums/v224/neozmc24/SR20DET/DSC00009.jpg

[SiI40sx]

damn 150 on a redtop!? thats a good ass motor...... mine is 130 :(

[adictd2b00st]

nice results :tup: and 3-4 cranks should do it!

i was pleasantly surprised to get 150 out of mine as well when i tested it a few weeks ago cold :)

[wangan_cruiser]

yes it looks too good to be true for a redtop. engine is been sitting for 2 yrs since the previous guy bought it. i wanted to make sure everything is cool before i drop her in

[ManoNegra]

Shouldn't need to crank it more than a handful of times, reading won't change much after. Redtop looks pretty healthy.

[aznrib]

So the motor does not have to be warm to have accurate reading for a compression test?

[sr20detconv]

Sorry for the thread hijack but my sr20 did 165,165,170,165.Higher than the max....?

[CarloSR]

The engine has to be in operating temperature.

http://img221.imageshack.us/img221/2927/compresionam3.png

[Bad40r7]

No it doesnt NEED to be. Colder compression numbers are normally higher than warm though, which are more accurate. Not by more than about 10 psi MAX though.

The engine has to be in operating temperature.

http://img221.imageshack.us/img221/2927/compresionam3.png

[adictd2b00st]

i always thought cold was lower? since everything isn't really "seated" by being warmed up?

[sirfallsalot243]

Compression tests all read differently, and each person will get different numbers based on a cold test, hot test, and the testor that theyre using.

The main thing to look for is an EVEN spread of numbers not varying in more than 10-15psi or so.

For example:

Good- 150-145-155-150

Bad- 160-155-150-125

[adictd2b00st]

yea definitly, uniform #'s are key !

[Gjohnson7]

Hey that's a lot better than my
156 - 30 - 157- 157

[wangan_cruiser]

Hey that's a lot better than my
156 - 30 - 157- 157



what happened to your 2nd cylinder? that shit is low

[wangan_cruiser]

i always thought cold was lower? since everything isn't really "seated" by being warmed up?


they were low at 1st then i had to cranked it more to get the highest psi i can get. thats why i asked whats the difference between the standard 3x crank against fully crank till u get the highest # u can get.

[brewster240]

compression is overrated.

[wangan_cruiser]

compression is overrated.


how is it being overrated? people are just tryiing to make sure the swap will be successful thats why they check for compression.

[slider2828]

Because it just tests the compression ring instead of all the other rings such as the oil ring... Leak down test oil ring, valve seats, compression rings, headgasket, all at the same time. But for me compression is ok if rebuilt, otherwise might wanna do leak down if you going to buy the motor.

[IRN]

as long as the numbers are relatively close you should be fine. i got 145 ish all across.

[Gjohnson7]

what happened to your 2nd cylinder? that shit is low


Yeah, I still don't know. Trying to figure out what it could be. I pulled the head and they did a vacuum test, which it passed. I did a leak down test before I pulled it and the air was leaking out the intake.

[reactor]

Alright, enough talk from the peanut gallery about what they have heard, think, and yadda yadda.

Here it is for you folks.

Compression tests are used to determine the overall status of the engines ability to compress air. Compression tests are supposed to be performed after the engine has reached operating temperature due to the fact that you "could" receive false low numbers on a cold engine, due to piston expansion, ring sealing, etc. Basically you are looking for abnormally low cylinders, cylinders that are abnormally high, variations between cylinders, and good cylinders. For the SR20DET engine, 128psi is the minimum reading you would like to see, 156psi is nominal cylinder compression (what it is in good condition), and no variation between cylinders greater than 14psi per the FSM. Also when performing the test you are supposed to note the cranking speed at which the engine is turning during the test and the altitude at which you are performing the test (although rarely ever does one need to do this). All the numbers listed are with the engine cranking at 300RPM. One last note is that when performing a compression test you need to have the throttle plate FULLY OPENED! You should crank the engine over between 5-6 times, there is absolutely no reason to go beyond this.

If your numbers are good, leave it at that, they are good. You can always perform another compression test to verify your results. If your numbers are higher (more than 10psi or so) you have excess carbon built up in your cylinders which raises the compression ratio of the engine, and therefore the compression numbers have been artificially altered. If your numbers are low (I'd say 135psi or so) you can follow up with a leakdown test to identify the source of the compression leak.

You always start off with a compression test first. If your numbers are good then there is absolutely no need to perform a leakdown test. A leakdown test is only needed when compression problems are indicated by the compression test. A leakdown test is performed to identify the source of the compression leak. When performing a leakdown test, first start by removing piping connected directly to the throttle body (intercooler pipe/intake pipe) and setting the throttle wide open, have all spark plugs removed, remove oil dipstick, and take off radiator cap. Set the piston you are currently testing on TDC on the compression stroke and start test. Once leakdown test is connected to the cylinder and compressed air is entering the cylinder, you need to make sure that then engine does not move from TDC. If air comes out of the throttle body, intake valves are leaking compression. If air comes out of the exhaust, exhaust valves are leaking compression. If air comes out of the dipstick tube, compression rings are leaking compression. If air comes out of the radiator neck, the headgasket is leaking compression. If air comes out of an adjacent cylinder, the headgasket is leaking compression between the two cylinders. NOTE: these are all the common issues, cracks in cylinder walls, holes in pistons, cracks in cylinder heads, can cause some of these also.

[wangan_cruiser]

Alright, enough talk from the peanut gallery about what they have heard, think, and yadda yadda.

Here it is for you folks.

Compression tests are used to determine the overall status of the engines ability to compress air. Compression tests are supposed to be performed after the engine has reached operating temperature due to the fact that you "could" receive false low numbers on a cold engine, due to piston expansion, ring sealing, etc. Basically you are looking for abnormally low cylinders, cylinders that are abnormally high, variations between cylinders, and good cylinders. For the SR20DET engine, 128psi is the minimum reading you would like to see, 156psi is nominal cylinder compression (what it is in good condition), and no variation between cylinders greater than 14psi per the FSM. Also when performing the test you are supposed to note the cranking speed at which the engine is turning during the test and the altitude at which you are performing the test (although rarely ever does one need to do this). All the numbers listed are with the engine cranking at 300RPM. One last note is that when performing a compression test you need to have the throttle plate FULLY OPENED! You should crank the engine over between 5-6 times, there is absolutely no reason to go beyond this.

If your numbers are good, leave it at that, they are good. You can always perform another compression test to verify your results. If your numbers are higher (more than 10psi or so) you have excess carbon built up in your cylinders which raises the compression ratio of the engine, and therefore the compression numbers have been artificially altered. If your numbers are low (I'd say 135psi or so) you can follow up with a leakdown test to identify the source of the compression leak.

You always start off with a compression test first. If your numbers are good then there is absolutely no need to perform a leakdown test. A leakdown test is only needed when compression problems are indicated by the compression test. A leakdown test is performed to identify the source of the compression leak. When performing a leakdown test, first start by removing piping connected directly to the throttle body (intercooler pipe/intake pipe) and setting the throttle wide open, have all spark plugs removed, remove oil dipstick, and take off radiator cap. Set the piston you are currently testing on TDC on the compression stroke and start test. Once leakdown test is connected to the cylinder and compressed air is entering the cylinder, you need to make sure that then engine does not move from TDC. If air comes out of the throttle body, intake valves are leaking compression. If air comes out of the exhaust, exhaust valves are leaking compression. If air comes out of the dipstick tube, compression rings are leaking compression. If air comes out of the radiator neck, the headgasket is leaking compression. If air comes out of an adjacent cylinder, the headgasket is leaking compression between the two cylinders. NOTE: these are all the common issues, cracks in cylinder walls, holes in pistons, cracks in cylinder heads, can cause some of these also.


this is the exact answer what im looking for. thanks for the time and explaining things

[jspaeth]

Because it just tests the compression ring instead of all the other rings such as the oil ring... Leak down test oil ring, valve seats, compression rings, headgasket, all at the same time. But for me compression is ok if rebuilt, otherwise might wanna do leak down if you going to buy the motor.


That doesn't make it "overrated", just not fully conclusive.

[JVD]

Lucky! My last comp test went like this.

Cyl 1: 145
Cyl 2: 149
Cyl 3: 148
Cyl 4: 25

I LOL'd... then cried.

[wangan_cruiser]

^^ holy shit. i would too!

[Harbe]

Lucky! My last comp test went like this.

Cyl 1: 145
Cyl 2: 149
Cyl 3: 148
Cyl 4: 25

I LOL'd... then cried.


put a can of Restore in it and call it a day

[mifesto]

on a warmed up engine , this car im seriously considering buying came up with 145 145 135 135.... still contemplating if i should still pull the trigger.... compression test is really killing me... should it even be a deal breaker? the number spread was good for mine and variances in tests can also effect it... arg

[GSXRJJordan]

Reactor said it very well - you're looking for uniformity. When performing the test, make sure you're holding the throttle plate open while someone else cranks the engine ~5 times. If you get uniformly low numbers, try adding a half-cap of oil through the spark plug holes, waiting a minute, and testing again - if that gets you much higher numbers, just know that your piston rings are a little old. If not, you could have valve issues, and a leakdown test will help you identify them.

About mifesto's motor - are those numbers warm or cold? If you let the motor come up to temp (thermostat opens, etc), then you get those numbers, I'd say your head gasket could be on its way out, but you're OK for the moment. If those are cold numbers, test it warm and see if it changes ('split' head gasket could get worse when the car's warm).

[mifesto]

GSXRJJordan... yeah when the owner did the SR swap, he did metal gasket. also seldom here and there he would raise the boost to 18 psi, it made me think it would raise the head slightly since he doesnt have arp studs.

also nissan says if two cylinders are low and together, it can be the head gasket.

[mifesto]

by the way, metal gaskets can slightly reduce compression... no?

[GSXRJJordan]

Most metal gaskets actually lower compression, because they're slightly bigger than stock (1.2mm is > stock, by a hair). Only the .9mm gaskets (that barely anyone gets) would raise compression on stock pistons.

It's not the boost itself that'll "raise the head"/fuck with stock head bolts, it's the power. 18psi on a T28 is ~250hp, 18psi on a GT3071 ~350hp. There's a big difference. That being said, stock head bolts (as long as they're not re-used) are very good.