Rebuilt Rb25 Problem

[al_r33]

Hey people,

I recently got my rb25 rebuilt about 5000km ago & we have now found out that there is a very big problem with power output etc.

I recently got a PFC installed & the best we could achieve was 138rwkw on .7bar with the following mods

forged piston set 20tho

gtr rods

arp conrod bolt set

race series main bearing set

bigend bearing set

nissan gaskets

nissan cam belt

pfc

fmic

3.5inch full exhaust

avcr (.70 Bar)

cai

stock turbo

stock injectors

Now the problem is not with the tune as we put it onto the dyno before the pfc went in and the best it got was 111rwkw on stock boost! so the was a gain of 27rwkw at the end with the pfc installed., the tuner said that it could have an extremely high static compression ratio or another issue.

so then we thought it was a turbo issue but we pulled it off yesterday & the turbo is fine! which means there something wrong in the motor! we did a leak down test & compression yesterday and these are the results

leak down test: this was done with the car not being started in 2weeks so its dead cold!

1 cld: 7%

2 cld: 5%

3 cld: 5%

4 cld: 5%

5 cld: 9%

6 cld: 6%

compression test: also done cold

1 cld: 120psi

2 cld: 115psi

3 cld: 125psi

4 cld: 125psi

5 cld: 117psi

6 cld: couldn’t do 6 as oil started going everywhere

so the were the results & we still don’t have a clue on what the problem could be! the compression test come up really low but couldn’t that be caused by a low compression ratio?

I guess if any one has had this problem or could shed any light on it that would be good.

Sorry about the crappy post but im not really mechanically minded!

Cheers

Alan

Edited September 6, 2006 by al_r33

[R31Nismoid]

could be a poorly calibrated dyno?

boost reference is invalid, its less than .7bar possibly?

umm...how come oil went everwhere from cyc 6?

That doesnt sound right at all

Check the timing, if the cams where touched, cam belt is on correct etc etc

[r33_racer]

why is your cold compression so low? The temperature doesnt affect it too much...its whether its wet or dry that affects the compression dramatically. But that compression should be around what 160-170. What thickness headgasket did you put in it, std nissan one 1.2mm?

atm my money is on the low compression.

[al_r33]

i dont know why oil started going everywhere as the motor has heaps off\ parts of it atm!

the dyno is okk as i took it to another one just to see & they bascailly come up the same!

the cams were check and come up fine!

if its low compression how do you fix that?

Cheers

alan

and as for the headgasket i was aware that it was a std one!

Cheers

[Cubes]

More importantly not why but where was the oil coming from?

My Rb30det stone cold with 0.040" piston bore clearance was from memory high 150's after a 10degree night. All pots were to my suprise exactly the same with only one (cyl 5) being 1psi down. That was after ~20,000km's.

[r33_racer]

I just pulled down my rb25 for a rebuild...and when i was checking the compression, i accidently left the oil feed line hanging above cylinder 6....and after checking the first 5 cylinders oil pressure had built up enough to ooze out and straight down no.6 spark plug...well 165 across the board then 240 odd in no.6 lol. First thing i thought of that maybe they did the same thing...however the oil feed on a std turbo is a steel line, so yeh...not sure on that one.

Cubes why do you have such large clearance? What was the spec sheet clearance for your Wiesco's?

[Cubes]

The spec sheet on the wiseco pistons stated 0.0040" (from memory) for 24+psi or race.

Sorry I missed a 0 in the previous post.

I went a little overkill in the clearance department but suprisingly it only ever so slightly slaps (not noticable to the untrained ear) when cold.

[al_r33]

so does it sound like my motor is stuffed?

the car still feels very strong & pulls decent enough even thow its only got a 138rwkw

[T04GTR]

that is very low power. and thats some pretty huge leakdown aswell.

ps. arp dont make bolts for rb's people stick vg30 ones in them (abit dodgy)

umm. are you sure the cam TIMING is corect. is the vct working or jammed?

how often do you need to empty the catchcan?

why was ir rebuilt?

is you cat rooted from the old motor filling it with oil?

[Al]

Drop the exhaust, b4 the cat and do another dyno run. Keep an eye out on the boost levels, as these can skyrocket if the exhaust was stuffed.

For a fresh rebuild those figures seem very poor.

How good is the reputation of the person that rebuilt the engine?

[r33_racer]

The spec sheet on the wiseco pistons stated 0.0040" (from memory) for 24+psi or race.

Sorry I missed a 0 in the previous post.

I went a little overkill in the clearance department but suprisingly it only ever so slightly slaps (not noticable to the untrained ear) when cold.

haha yes 4 thou sounds better, i thought fark 1mm clearance..something not right there. Yeh we ran 0.0020" with the cp's and no conrod oil squirters just relying on splash and shes fine, no slap either.

al_r33 what clearances were run with the forged pistons that were put in? And do you have the spec sheet that came with your forgies? Maybe the clearances are way too sloppy and thats why your compression is shitty, power shitty and blowby in excessive amounts??? if thats occurring?

Edited September 6, 2006 by r33_racer

[al_r33]

well that’s the thing the guy who did it knew his sh*t that’s why I found it hard to believe that he built a bad motor!

I don’t have a catch can!

the exhaust was replaced after the rebuild as with the other parts!

the guy who check the cam timing said it was spot on!

so I dunno what’s going on with it!

Cheers

Alan

[Al]

Still suggest to drop the ehaust and test. Unless you are certain the exhaust has a proven high flow record.

[Adriano]

My money is on low compression, maybe rb30et forged pistons, which would have to add up to about 7 to 1

[FATGTS-R]

What have other peoples leakdown percentages been after a rebuild?

When I bought my GTSR(Circa 1987), I got a leakdown test done before purchase and it averaged about 12% across the board which the mechanic said was reasonable for the kms listed on the odometer which stated 130k.

Now for a 5,000km engine to show leakage as high as 9% isnt that a bad sign?

What was the run in procedure? Maybe its a case of the rings having not bed in correctly?

[al_r33]

i bascally drove the car for 1500km on no boost & no higher than 3500rpm.

can anyone suggest how you would fix this sort of problem if the compression is too low?

[Faid]

Dude you have a big problem. from what i see here t think it is that the dude that built your engine used to big clearances, causing exessive blowbyand loosing compression. i did the compression test yesterday on a friends GTST R33 S2, with a stock engine and it gave me about 165 psi on all cylinders, it was so good that all were in 1% of each other. the problem i see here is that your engine is pooooooorrrly assembled, have your tuner pull the engine off and take off the head, make him check the piston to bore clearance, the only soultion i can give you if the clearances are to big is that your have to re bore re hone and put bigger pistons in again. 138 kw is even lower than stock, so id advise to check your engine again. i wish i could live in aussi and be of assistance but cicumstances state that i have to give my advice from the other side of the planet

[al_r33]

thats the thing i cant do f*ck all because he moved to qld!

[Al]

i bascally drove the car for 1500km on no boost & no higher than 3500rpm.

can anyone suggest how you would fix this sort of problem if the compression is too low?

Even though i really don't think this has caused any problem, i beleive the problem lies with a poorly built engine , this method of bedding in an engine is not the best.

If i get my engine rebuilt, i will be loading the boot with heavy items (40kg bags of cement), to add load. Drive normally as if you are trying to conserve fuel. Then every 200-300km give it a quick strong squirt. An engine is best bedded with varying loads.

[SECURITY]

i was told to accelerate quick till 4000 when taking off, then take it easy after that.

and my motor is running beautifully