RB26 Compression Results.

[cbileske]

Cyl 1 - 120PSI
2 - 125PSI
3 - 115PSI
4 - 120PSI
5 - 120PSI
6 - 115PSI

This was done with the engine cold, so the numbers might not be 100% true, but gives a good idea. I added some oil to each cylinder and the numbers hit 150+.

I have JE 86.5 pistons in a rebuilt engine, with JE proseal rings. I talked to a JE guy and he told me that the rings are hard to break in. I Also have came across a bunch of mixed info on the web, that says you multiply your compression ratio by 14.7 to get your PSI your aiming for. so 8.5 x 14.7 = 124.95PSI, doesnt seem right at all.

My guess is that all the piston rings didnt seal and that is the cause to my misfire. I have probbly 5000km on the rebuild.

[cortexx]

I bet the Cross hatching left by the honing process was not done properly , what oil were you using ? Should really use basic mineral oil , not synthetic for break ing it in.

What gap did your rings have ? If it was too large you'll get similar results to what your having!

[cbileske]

I cant remember what the piston ring gap was, everything was built to the proper tolerances. The cross hatching was done properly as far as I know. I have not switched from
Regular 10w40 oil yet.
Any one else use the je piston rings?
I might pull it apart in the near future since I have access to a hoist and full shop at work. Might stick to driving the r6 and driving the duramax this summer.

[gtrjon]

man thats shitty to hear. i would look into the je rings more. those numbers are pretty low but they are consistant. something doesnt seem right. did you build it yourself?

[cbileske]

The bottom end was built by a machine shop. I assembled everything else. Put head on, turbos on etc. Ran awesome to begin with, progressively had more and more
Intermittent misfiring. Now it seems to start and have a constant misfire all the time. All the ignition components
Have been checked or replaced. Yeah too bad the numbers wernt that consistent at about 40psi more. I will try and find another compression tester to retry the test.

[cortexx]

Do a compression test when warm , using different metals for high performance rings means different than normal gaps . The gap may be a bit big when cold until it heats up and tolerances change then it might be ok.

Do you have a cam in your workshop ? take out the plugs and scope the bores looking for glazing . This indicates improper running in procedures or a badley prepared bore.

ANother thing , when you were running it in did you load the rings properly ? This is done by varying engine speeds with lots of periodic WOT driving.

Driving down the highway at 70klmh at a constant speed is bad.

If that is the case , take it out on some quiet roads and drive it like you stole it , lots of slow downs followed by lots of hard acceleration. Also , consider dumping a can of seafoam into your oil , fuel tank and pour whats left into your intakes. this will clean out gummed up rings , makes one hell of alot of smoke too . dont drive it near any cop stations until it's cleared out.

[evilgtr]

Why do you think there is something wrong with your engine ? A RB26 with aftermarket cams can be around 120psi across the board depending on your overlap. My engine brand new was 128psi across the board and is still bang on those numbers after 2000km's.

[Oakville]

evilgtr makes a good point. wow, never thought about that

[cbileske]

No cam. As far as I know, will take a look. I did vary the load when breaking it in. Pulled some hills etc. It's midfiring pretty bad right now, you think taking it out and running it hard is a good idea? I was told that changing the gap to total seal rings with a gapless top ring would be the way to go. Hoping that a re-hone/re-ring will get it going good again. Is there anything else that could cause the low psi on all 6 cylinders. I'm pretty certain it's rings tho since the oil caused the compression to increase.

[evilgtr]

Your issue isnt ring related IMO. If your engine has a misfire and adding fluid increases the cylinder compression my first area of concern would be a bent valve or cam overlap. Iv melted enough turbo engines (some on purpose) to know that when you have a pressure going into your crank case you will know it and there will be a constant smoke stream following you. How thick is your headgasket ? Did you have your valve train and head inspected when it was off ? Anything you altered that isnt stock will affect your compression. In extreme situations race engines will be built with target comp numbers in the low 120's to handle alot of boost. I was expecting 125-140 and I fell somewhere in the middle and Im happy with it. Im running a strong 520whp at only 16psi and Im right around 130psi.

Tell us more about your misfire ? how much boost are you running ? stock coils ? plugs ? plug gap ? any smoke from the exhaust ?

I wouldnt take it out and abuse I would trouble shoot your misfire then go from there but pushing a hurt engine is like racing a horse with a broken leg. Start by removing your ignitor and cleaning the connections,make sure the ground loop is grounded properly when hooking it back up. Check your coils next,then plugs. if everything checks out in the ignition move to the fuel, check your injectors and pump and fuel pressure.

I bent the exhaust valves in a RB26 I had which gave me low compression in that cylinder. A wet test revealed that. It wasnt smoking but would blow big fireballs when shifting over 5000rpm due to all the fuel being dumped in and not having proper a/f ratios so fuel wasnt igniting properly and going into the exhaust

[cbileske]

I have tomei pon cams in the engine, head gasket is a tomei metal gasket 1.2mm, this thickness because of the head being resurfaced alitle and the block as well. The head was fully inspected, new valve guides were installed. The compression makes big jumps on the tester making me think it isn't valves.
New split fire coils, new coil harness, new ems harness, new fuel pump, all cylinders getting fuel, tried different igniters, plugs gapped at .08, have used iridium and standard coppers. It wasn't smoking but now it is smoking out black a little and seems to be leaking out unburnt fuel out the exhaust. (will have to double check that's what it was). New o-rings on all injectors. No boost controller installed, but the restrictor is out so it hits around 1.3bar peak. Garrett 2860-5 turbos. Mafs have been cleaned.

[M13]

you cleaned your maf but have you tested them? resolder or try known working maf's.

[evilgtr]

Have you had your cams degreed ? I seriously doubt you have a ring issue your compression isnt a worry. Sounds like you have covered almost evey angle, when you remove the plugs after a drive do they all look exactly the same ?

The last thing is your tune, what ecu are you running ? Are you able to data log and have your tuner analyse the data ? If your a/f's arent on target that may be why you are experiencing the misfire when you try to load up the engine.

For the record Im running pon cams with a 1.3mm head gasket so very similar. Iv had my cams degreed from Cam at lightspeed so there is a slight overlap which is why Im lower compression. I cant give you exact specs on my cam setup but I do know Cam called tomei directly to get the specs the cams need to be degreed to. GTR-DAD had just got his cams degreed to and the dyno results verified this was extremely beneficial.

Your situation is tough since you already tried almost everything, if you can though I would suggest a data log and look for flaws inthe tune maybe its a combination of timing fuel boost. Either way I wouldnt push the motor anymore of you might find your self pulling the donk out again.

[cbileske]

I'm running the stock ecu still, I want to upgrade that, but not until the misfire is sorted out. I will try resoldering the mafs. I'm not sure what having your cams degreed is. I'm in the okanagan, not sure if there is any shops in this area that are familliar with the rb26. The plugs all look decent except one. The a/f is lean when idling, last year it was always right around 14.7ish(idle).
When I was checking the coils, it seemed like the #2 cylinder wasnt firing, so I swapped the coil and plug from a working cylinder and it still wasn't firing. Have volts at the harness, and fuel cause that plug was wet.

[evilgtr]

So you have all those parts and your trying to run the stock tune ??