Built KA24DET compresion a little low?

[TD or Not TD]

My friend has a built KA24DET. i did a simple compression test on the car and the break down is this.

Cyl.1-116psiCyl.2-116psiCyl.3-112psiCyl.4-109psi

The cars engine specs are:

Crower 264 camssupertech valvetrainarias forged 8.8:1 pistonsPauter rods1mm Cometic head gasketJGS turbo man.T3/T04 turbo.

the motor is brand new and has only about 200miles on it so i know the rings arent seated compleatly but i was wondering if this seems a bit low.

my CA18DET was pushing 150-160psiour friends SR20DET was 150's

The piston ring clearance was in spec along with the cam to shim clearance.

one of my questions would be with the higher duration cams would it be bleeding off some of the compression(also causing a lower vacuum at idle)?

the car runs and idles perfect has good power i am just concerned with the #'s


Modified by TD or Not TD at 4:58 PM 6/10/2007

[TD or Not TD]

Edited: its 8.8:1CR not 9.5 i corrected it.

[Florida240sx]

Give it another 300miles and check again. Smoking any?

[teambuiltnissan]

is your cam timing correct?is your injector cam be leaking ?

who built your head, or who built it.. Iknow the who builts ka24 engine and does really ****ty job.

my motor has 100 miles on it and about 155-160 all the way across, with crower V3 cams.

do the leak down to see where the air coming out of

[Florida240sx]

Usually they are around 150-160. With lower cp pistons

[TD or Not TD]

The car doesnt seem to smoke at all, the timing marks were right on when it was put together. i guess we'll have to test it after we run it for more miles.

[Chezedik]

What does your vacuum look like?

[TD or Not TD]

its approx 15-16psi vacuum

[Florida240sx]

Cams are off then, should be -20 or you got a leak somewhere.Although I've had IC pipes popped off before and still had perfect vacuum lol

[Chezedik]

Do you leak oil or coolant? If not, then you prob just have a cam off. I would do a leak down test to know for sure.

[TD or Not TD]

Well we checked multiple times on setting the timing marks up right because last time the bolt for the center sprocket stripped and replaced it and it was off when they put it back together. now me and him checked it over multiple times so i dont think its off. but we would have to take the front of the motor apart to check everything out

[Chezedik]

What is leakdown?

[scole]

Stupid question but did you go to full throttle while doing the test?

[TD or Not TD]

we tried it both ways on one cylinder.... it was like 2-3psi difference

[Chezedik]

Tried what both ways? Have you done a leakdown test?

[TD or Not TD]

checked compression with the TB open and closed.

and i dont quite know how to do a leakdown test so no i didnt try that yet.

[CoupedUp]

You put the 1st cylinder at TDC. Put a fitting into the sparkplug and on the other end have a T with a Pressure Gaauge and a quick realease fitting for an air comppressor and pump the cylinder up to 150-160 PSI. Then let it hold the PSI. I cant remember what PSI drop is permittable over a minute or 5 minute periods. But if it drops VERY fast and you have no leaks and or smoke, id Agree the timing is off.

[WDRacing]

Is the car warm when taking the compression reading? If so, pour a cap full of oil into the cylinder and retest it. If the numbers jump up, then you have a bad ring, ring land or scratch in the cylinder.

But they are off across the board, so it's somthing very simple I'm sure of it.

[TD or Not TD]

i beleive we are going to take the motor out and check the rings, he wasnt sure when he put the rings on if he might have possibly put the rings in wrong(ei wrong side up) so we are going to probably tear it down. i put 60psi of compressed air into the cylinder and it was blowing right into the crank case.... BAH!

[Chezedik]

1) Do a leakdown first. That will rule out a lot of dynamic problems like valve seals and rings.

2) Typically low numbers on all cylinders indicate incorrect cam timing, but you need to do leakdown to be sure that you did not need to overbore and put in pistons that were too small.

EDIT: If vacuum is low, but not bouncing around and idle quality is good, and you are not smoking, but compression is low, keep an eye on gas mileage and report, but you are probably fine. BTW, sorry WD for the run-on, it was just part of one long thought.

[TD or Not TD]

idle quality is fairly good, it pulls about 17-18 vacuum at idle. we lined the timing marks up on the crank pulley also with a screw driver on the piston to make sure it was TDC(or close to) and it was right on. we checked the cams and they seem to be correct as well. but thats without taking it apart.

the car made 260whp and 335lbs of torque at 17psi recently so i beleive it is 100hp shy of what it should make. this was also tuned by a local guy which seem to have done a fairly good job. A/F was 11.8-12.3ish

Also like i said above i put 60psi of compressed air(from the compressor) into the cylinder (with half of my craftsman compression tester w/ the valve removed)

[Florida240sx]

Car pull to redline?Sounds like cams are off. When mine were I made 191ftlb and 167hp at 8psi air fuel ratio was perfect.Power dropped off after 4000rpms.Car was perfect at idle and felt fast.... Once I fixed my cams I was stuck in my seat... And I could burnout with ease when they were messed up.

[TD or Not TD]

Yeah we are going to check it out, i think we need some really good detailed pics of what everything is supposed to look at, and diagrams. i found some online ill have to find them again.

[Chezedik]

If they are off vacuum is looking pretty good. What was the leakdown percent when you shot air in?

[TD or Not TD]

we just tried putting air into the cylinder, we didnt actually do any tests. he is going to buy an actual tool to do the leakdown test i beleive.

he called Ivan from AMS and he asked what cams they were, crowers or brian crower cams. he wanted to know because he said the ones that are in the "black box" made a car they tested make no power more or lose power. something to do with how the lobes were made i am not sure. this is what my friend with the KAT informed me of.

so he is going to put his stock cams in and see if that makes a difference.

[PapaSmurf2k3]

Cams are off then, should be -20 or you got a leak somewhere.

he said he was at ~-15 PSI. I think you are thinking mmHg, or inches HG. Most guages read vacuum in HG, not PSI.

[Chezedik]

he said he was at ~-15 PSI.

That is my biggest pet peeve! Vacuum can NEVER be read in PSI. Vacuum is not a force, but rather a lack of force, so it can never be expressed in terms of a force. The only ways it can be expressed is in how much it will move a given material in a tube or in absolute pressure. That is if you have 20 inches of vacuum, you have about 10 pounds absolute pressure. But it will almost always be expressed in kilopascals.

As far as your leakdown test, this will be the nail in the coffin. I expect that you either have very wide duration cams that need to be re-timed, or they are off. This seems obvious by your TQ, but the leakdown will tell us for sure.

[TD or Not TD]

ok dont get too far off track, when i said 15-16psi i meant inches of vacuum(when he asked how much vacuum it was pulling). which im sure it was obvious thats what i was refering to but sorry if you guys got confused.

the stock 91 cams are back in now and its going to get shimmed tomorrow and check it then....

[Florida240sx]

I know how a boost gauge reads. vacuum should be 20.

[Chezedik]

Try not to get offended, people just can't express that correctly and it bothers me. If you think that I am talking only at you, then take that for what it is.