Rb25/30Det

[R32Abuser]

Hi all,

So I have come to the culmination of my build and have hit a brick wall. Before I run through the problem, here is the spec. list:

Parts

R32 RB25DE head

RB30 Series 2 bottom end

RB26/30 CP Pistons 9:1 Static CR (CP pins, rings etc.)

Spool RB30 Rods to suit. ARP fasteners

ACL Race series bearings to suit above rods

Standard Crank. Blueprinted/Balanced/Crack tested etc

RB25DET Series II Oil Pump with extended drive "Snout" (Spool Imports)

GT3076R 0.82 A/R Garret Turbocharger (Standard oil/water lines)

Stiffer valve springs (unsure of brand)

High Energy Style Sump + Head drain (big f**k off fitting on the back of the head)

Standard valve train (Cams/gears/lifters etc)

Cometic Head gasket (Spool Imports)

GTR Waterpump

550cc Bosch EV14 Injectors

Nismo Fuel Reg (Adj.)

Nismo Engine Mounts/G-Box Mounts

Bosch 040 Fuel Pump

Nistune ECU Remap

Labour

Bore/Hone Block to suit CP Pistons

Deck Block

Grind/Blueprint Crankshaft

Balance Pistons

Micropolish Crankshaft

Balance Motor

Reconditioned Head

Modify/Weld/Machine Head

There is probably stuff I have left out but anyway onto the problem...

So it came to tuning the motor up today.

Car goes on the dyno, normal procedure run-in etc. Tune up starts, and the tuner finds a problem.

No matter what he did, he could put more than about 8 degrees worth of timing advance in the motor until it would knock/ping/detonate. Generally I was told that 20 degrees is about right for these motors.

Now there was several suggestions at this point:

1. Fuel - dropped the fuel in the tank. Replaced with 98 Octane BP Ultimate. Made no difference.

2. Faulty CAS/Timing sensor - Apparently nothing seems funky on this end of the spectrum so isn't something they think is wrong.

3. Static CR is too high - Pending a compression test (being done tomorrow).

4. Timing - Possibly the timing is out a tooth or two. Will check after the compression test.

Is there anything else every one can suggest?

With regards to the Stactic CR - I purchased these items from Spool Imports. They were quoted as the 9:1 CR Pistons alot of guys off here have used time and time again without any hassles. The only issue I see here is if the machinist as stuffed up somewhere and hasn't machined to suit the CP pistons. Has anyone else on here had any problems regarding these pistons? Is there anything anyone can suggest with regards to this portion of the build?

All help will be greatly appreciated!

Cheers,

David

[GTSBoy]

Do those pistons actually suit the non-turbo non-RB26 head?

[R32Abuser]

All three heads (25DE/25DET/26DETT) cc up around the 62-64cc mark.

Therefore there should be little to no difference in Static Comp. ratio between the three. Many have used these pistons in all 3 heads with no problems.

[Duncan]

what was the result of the compression test?

are you certain the cam timing is correct, and that the base timing is accurate? Is it making the right power for 20o or is it miles short?

[tridentt150v]

Does it run lean? What are the afr's like?

thinking it could be a lazy pump or FPR?

[Rolls]

Could dynamic timing from the cam cause this?

I've been told that I think it was 25de and det cams are the same overlap + lift etc, but one is offset by a couple of degrees and they usually dial it in with adjustable gears if using in a different motor.

I can't remember what the cams were that people were talking about, though when I was looking for a replacement exhaust one for my motor someone mentioned that, I'll see if I can dig up the reference.

Does it run lean? What are the afr's like?

thinking it could be a lazy pump or FPR?

David told me that the fuel pressure was sweet and the injectors were all flowing the same. Pretty sure it is a nismo FPR (stock with adjustment) and decent pump.

Edited July 16, 2011 by Rolls

[GTScotT]

+1 cam timing.

Check that its all TDC and if they are the DE cams as mentioned above might want to fiddle with some gears.

[rob82]

How did you test the CAS? Lock the timing at 20degrees and take it to 6000rpm and check how much timing variation you get any more than +/- 2degrees and its time for a new CAS or its time for a crank trigger setup.

BTW - nice setup. Looks like a well thought out combo.

Edited July 16, 2011 by rob82

[DVS JEZ]

Were the chambers in the head modified at all?

What squish clearance is the piston to head?

What thickness headgasket?

[R32Abuser]

DVS Jez

Head has been left standard besides a reconditioning.

I am in the process of finding the specifics out with regards to the machinist (squish, deck height etc etc) and will have more answers tomorrrow/tuesday. Head gasket

I BELIEVE is 1.2mm - But Im not 100%. Im talking to Brad from Spool Imports today to check all of this and to brainstorm what the problem could be.

Rob82

Im unsure how they tested the CAS as I was not there. However, I suggested the CAS could have been a problem but they replied by saying that if that were the case they would have been getting funky readings/timing all over the rev range (which they weren't apparently).

Problem is, If we do lock in 20 deg timing and take it to 6000RPM it will PING/KNOCK its head off and possibly cause damage. Something which I dont want to do. I will be suggesting the CAS sensor/assembly having an issue again.

Thanks, the setup is pretty much identical to Cubes RB30 setup. In fact, it is his turbo which is bolted on the side of my motor I got to drive it between the tuners and the builder/assemblers. Made 207RWKW with 7-8 degrees worth of timing but still feels SOOOO responsive!

GTSt Scott

I agree. Many have used these pistons with no issues. Seems strange to see all of a sudden for the pistons to be an issue without anything else being changed.

Duncan

Will know the results of the compression test on monday I would say. Pity I dont have the car here to do it all myself.

I will be updating this thread as soon as I know more.

Tridentt150V

AFR's Im unsure of. I will ask this come monday, but Im sure that the tuner would have mentioned something if there was a large issue in this area.

Cheers for the replies! I will keep updating with as much news as possible to try and pinpoint the issue...

Edited July 17, 2011 by R32Abuser

[R32Abuser]

Spoke to assembler today...

Compression test still yet to be done

AFR's were apparently spot on. So besides the pinging nothing is too suggestive!!!

[Guilt-Toy]

make a run at 20deg, as soon as it knocks switch the engine off, take the spark plugs out and check which cyl's are knocking, all of them? or just 1 or 2?

how do you know it is knocking? are you hearing this? or is he looking at knock count in consult?

[R32Abuser]

I was told that it was audible knocking. Not off a sensor, but the sensor was indicating that the motor was knocking.

Ill run this by the tuner/assembler. Cheers Guilt-Toy.

Ill update as soon as I know anything more.

[ido09s]

I was also going to ask a few questions re screamer pipe, piston clearances etc as these things can send the knock on the ECU off prematurely but if it can be heard in the engine bay or seen coming out the tail pipe that puts my theory to bed.

Dont take this the wrong way, but is it an experienced guy listening to the motor? Is it really pinging? or is it an engine noise they are mistaking as pinging? Can you see it out the tail pipe? normally a puff of black smoke....

[DVS JEZ]

RRR

What spool pistons? Hope theyre not for rb26 head and ur running rb25 head as below

Rb25 head cc's a 54 ish and rb26 is 64 ish. Thats an extreme increase in comp.

So chances are u have too high a comp ratio

[ido09s]

Sounds like you have found your problem then

[wolverine]

RRR

What spool pistons? Hope theyre not for rb26 head and ur running rb25 head as below

Rb25 head cc's a 54 ish and rb26 is 64 ish. Thats an extreme increase in comp.

So chances are u have too high a comp ratio

I am pretty sure only the neo heads cc up in the low 50's.

[tridentt150v]

I thought the DE ones did as well?

[R32Abuser]

RRR

What spool pistons? Hope theyre not for rb26 head and ur running rb25 head as below

Rb25 head cc's a 54 ish and rb26 is 64 ish. Thats an extreme increase in comp.

So chances are u have too high a comp ratio

You sure? The RB30DOHC thread quotes:

"Three heads can be used for the twin cam conversion.

• RB26DETT Head

• RB25DE (R32) Head

• RB25DE/T (R33) VCT Head

All three heads cc up around the 62-64cc mark."

Im not taking it as gospel, but that a fair difference in cc stated in the thread as opposed to in the actual head. In any case, the engine builder/assembler should have cc'd the head to check this!

[Rolls]

neo rb25 heads are meant to be smaller than r33 rb25 ones, perhaps that is where he is getting that figure from.