Rb25/30Det

[DVS JEZ]

depends on the piston height to start with. Cubes and i used rb25 weiscos at the time we did ours and had to deck the blocks to make the pistons sit flush due to the lower pin height.

Rb25 and 26 piston pin heights are different arent they???

[bubba]

Make a bit more sense now

[Bl4cK32]

Rb25 and 26 piston pin heights are different arent they???

i think so

[DVS JEZ]

Yep so that changes alot

[Rolls]

Yep so that changes alot

not if he confirmed they were below the deck height at TDC

[R32Abuser]

Rb26 piston compression height - 30mm

Rb25 piston compression height - 31.5mm

Rb30 piston compression height - 32.51mm

Do not quote them for accuracy

[R32Abuser]

In saying that,

If they are a 26 piston height on a 30 rod the assembly will sit lower in the bore compared to a 30 piston on a 30 rod. I.e lower compression.

Spool imports told me they should be approximately close to being a zero deck height with I'm assuming a 30 rod. Mine is definately sitting lower in the bore which would mean a lower compression ratio than designed.

If anyone can point me in the right directionif what I've said is wrong then feel free- I don't know much in this area!

[Cubes]

As per email I believe you mentioned when she first went on the rollers all appears well and then as she gets a bit of heat in to her power tumbles and she starts pinging.

Is the motor breathing? I vaguely remember you said you don't have catch can setup? Oil in the inlet is a bad thing - it causes detonation.

Ring gap? Loss of power as she gets hot could indicate this.

Valve springs, I know they have been replaced but whats the seat pressure and where's a dyno sheet so we can possibly tell if there's the old tell tale float signs. When I had valve spring issues as the motor warmed up she lost power and wanted to ping.

Thats a few more suggestions I can think off all though they typically mean.. Motor apart. :S

[Rolls]

Just out of curiosity why does valve float give it a tendency to ping, wouldn't it decrease dynamic compression?

[ido09s]

Fuel??? Is it getting hot... maybe the wiring to the pump?

Have they put a fuel pressure/flow gauge on the car to test it all out?

I would be getting a second opinion still on cam timing.... I have never built an RB30/25-26 in my years as a mechanic, but i seem to remember that there was somthing funky about timing the cams and, correct me if i am wrong, but you dont take to much notice of the timing marks as they basically shouldnt line up. If they do you have issues......

Edited July 29, 2011 by ido09s

[R32Abuser]

It has a Bosch 040 in it at the moment. Dunno bout wiring but I want this to be done aswell. Still tho, I wouldnt have expected it to cause this issue without giving symptoms of fuel starvation.

In terms of the fuel getting hot, Im not sure. Something to note and something else to try.

I want to get the motor re-timed. The builder said he has timed countless RB25/26 etc with no problems whatsoever using the same method. Also he rechecked the timing again (not sure on whether he took it all off and re-timed it).

We are chucking RB20DET cams in it to see if that makes a difference. Hence it will need to be re-timed anyway.

[R32Abuser]

Also,

am looking for a catch can setup just for good measure. Was always planning to have one setup anyway so now is the best time to do so.

[Rolls]

Hot fuel is no issue at all, if anything it helps atomisation.

[Bl4cK32]

Also,

am looking for a catch can setup just for good measure. Was always planning to have one setup anyway so now is the best time to do so.

ive got a kit here i can sell you i bought, but never needed to use.

[R32Abuser]

ive got a kit here i can sell you i bought, but never needed to use.

Expect a SMS

[Cubes]

Just out of curiosity why does valve float give it a tendency to ping, wouldn't it decrease dynamic compression?

Unsure. :S It would definitely reduce dynamic comp.

Mine had severe inlet floating, as boost was increased and she got all warm the onset of float would begin.

Maybe the exhaust gets pushed back out in to the inlet or something contaminating the charge.

I did have her backfire through the inlet once or twice, as it would drop to idle it would be running on what sounded like 5.

The idle would then smooth out as the hydraulic lifter would bleed down. Was nasty, a set of springs fixed her all up though. No damage done as it was rectified fair quickly.

Expect a SMS

Run two catch cans stealth style

Block the PCV still run a pipe to it but with a black T piece that runs a hose down through to a catch can under the inlet manifold.

Cut the metal standard pipe that usually runs to the std turbos AFM to turbo inlet pipe, bend it towards the block a little, attach a hose and in to a catch can.

I've got a pic or two of my old engine bay how she was setup then if you like. Depends if having it stealth is what your after.

[Rolls]

might have been diluting the intake charge with exhaust super heating it perhaps.

[R32Abuser]

Unsure. :S It would definitely reduce dynamic comp.

Mine had severe inlet floating, as boost was increased and she got all warm the onset of float would begin.

Maybe the exhaust gets pushed back out in to the inlet or something contaminating the charge.

I did have her backfire through the inlet once or twice, as it would drop to idle it would be running on what sounded like 5.

The idle would then smooth out as the hydraulic lifter would bleed down. Was nasty, a set of springs fixed her all up though. No damage done as it was rectified fair quickly.

Run two catch cans stealth style

Block the PCV still run a pipe to it but with a black T piece that runs a hose down through to a catch can under the inlet manifold.

Cut the metal standard pipe that usually runs to the std turbos AFM to turbo inlet pipe, bend it towards the block a little, attach a hose and in to a catch can.

I've got a pic or two of my old engine bay how she was setup then if you like. Depends if having it stealth is what your after.

Im buying a catch can off Darren. Just need a second one to suit.

Im going for stealth so that would be perfect. Im planning on sanding the one I get from Darren, painting it matte black, then mounting it low.

Pictures would be perfect Joel. If you just send them in a reply to the previous emails I've sent you that would be great

Also, any other pictures you've got would be great! Be good to see your buildup if your willing to let me see?

Still got the old girl? Did you end up going GT35/40?

[R32Abuser]

Just doing some light reading of the R33 RB30DET Thread (all 350 odd pages of it!!!)

GTRNUR stated this:

This is the wrong way to build the engine. The RB25 pistons have a lower compression height than the RB30 pistons, so they will be down the block about 0.5mm. The pistons have an 14cc dome on the top of them too. Assuming you deck the block to 0 thou you would have a cr of around 9.8:1, possibly higher if you have the head skimmed to make it dead flat.

Not machining the block to 0 thou deck would give you a little more chamber volume but this would also make the engine more prone to detonation as the sqush pads in the head are way too far away from the squish area on the pistons to make the combustion chamber efficent.

The ideal engine has a 0 deck height and a 0.040" (1mm) head gasket. Then set your desired CR using dished pistons after having your head cc'd. Using RB30 pistons gets you close to 8:1 depending on your head cc.

You should read the PDF file, it covers the options for piston choice.

And Sydneykid said:

Hi Joel, I like it when the guys go and do their own research. It's much better than me telling you stuff, that you will forget tomorrow. If you do the work, you may not remember the answer, but you will always remember how to find out if you do forget.

The answer is that the optimum squish zone will result in improvements in Economy, Emissions, Performance and Response. Because there is a much higher chance for the fuel and air to burn completely. Since it takes out some unburnt fuel, it also improves the bore lubrication (no washing) and therefore engine life.

One of my favourite quotes comes from RaceTech Inc;

"On many engines, a squish or quench area is used to negate combustion in certain areas to avoid knock. By having a matched area where the piston and combustion chamber come in close proximity at TDC, the gasses are kept cool enough so that they will not ignite until the piston has moved down the bore and cylinder volumes are increasing. This keeps the rate of pressure rise below the knock limit. Some people are dismayed when they install a thicker head gasket to lower the CR and have knocking worse than before. This is because they have negated the designed-in quench effect. A large squish area also tends to promote increased chamber turbulence which is important for mixing and power at high rpm."

There is plenty of other squish zone reading around, a couple of guys in the US wrote a mega thesis on it a few years back. Do a search, it's there somewhere.

Potential issue with my motor being below 0 deck height?

Edited July 29, 2011 by R32Abuser

[DVS JEZ]

Did he Measure the squish area?