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Rb25/30Det

R32Abuser

By R32Abuser,
in Engines & Forced Induction

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R32Abuser Mentor

R32Abuser

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Something I am curious about. From where Im standing, I believe it may be one or a combination of:

a) Cams - As Cubes stated, the R32 RB25DE head causes the motor to ping easier than normal

b) Cam timing - Possibly issue with CAS, or base timing

c) Static CR (assuming the head is approx as Bl4ck32 stated) - the 9:1 CR would make the motor more succeptable to pinging than say an 8.3:1 motor. However, I dont see this as being the issue right now until we've ruled out timing. However, I have heard two VERY different values for the head cc measurement which has caused some confusion.

One thing to note is that the tuner had dealt with a Stagea RB25 Neo with similar/same pistons. Same symptoms. Put E85 in it and it was all good and made plenty of power.

Always options to consider...

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R32Abuser Mentor

R32Abuser

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As rolls said

207RWKW on the 7-8 deg of timing. AFR's were apparently spot on.

Been doing a few calcs here and there and all are coming back the same... Approximately 9:1 pending a few things.

The only thing I'm not 100% on is the chamber volume. Im 99% sure it is as per Bl4ck32/Cubes measurements at 62cc. That is unless there was a serious issue with the head being overheated earlier on in its life. I just cant be too sure unless I get it measured...

Anyone got any ideas on how much (an average value) they would take off a warped head to see it flat again?

JonnoHR31 Grand Master

JonnoHR31

Posted
Posted (edited)

I would go somewhere else and get a second opinion.I dont know how the motor was built but to be tuning it for full load on a 30 minute old engine seems a little odd to me. Please correct me if its only a base tune for the run in process that they are doing.

please explain how the engines ever gonna be in better condition to handle a thrashing than a few minutes after the rings have finished bedding in? 1000km run ins are useless

as for the head, it depends how badly it was warped but normally its not enough to affect compression by any signifigant amount. i've had my head faced 3 times now (its never been cooked badly though) and i'd be lucky to have gained 0.1 compression.

Edited by JonnoHR31
Rolls Grand Master

Rolls

Posted
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Yeah once the rings are bed in, change the oil and go for gold, never understood the process of running in a motor. Once you've bedded the rings and got any metal left over from the build out of the oil then what else is going to change? Nothing I hope!

R32Abuser Mentor

R32Abuser

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Again I will say it won't be an inherent problem with the the RB25DE head or cams specs.. my money is on the wrong pistons for the application.

Ive done a few investigations and by using online calculators and inputting the following:

6cc dome pistons (Confirmed many times via R33 RB30DET thread/Spool Imports)

1.28mm Head Gasket (0.05") (Cometic) (Confirmed via Spool Imports)

86.5mm Stroke x 86.5mm Bore

0 Deck height (From speaking to the builder, the deck height is actually below 0 deck height (decreasing compression!) exact value Im unsure of)

62cc combustion volume (Head type Confirmd by Cubes as being an R32 RB25DE head. Also, 4 different R32 RB25DE heads all cc'd to this value - so the only way mine may read less is if it had been seriously overheated and decked to get it straight again)

Standard pin height 1.280" (As confirmed by Spool)

Approximately 9:1 (probably less due to pistons being below deck height)

A few online calculators ask for teh HG bore. Without it infront of me I can only guess, but all in all, EVERY different calculator got approximately 9:1 Static CR.

Is there something im missing?

Edited by R32Abuser
bubba Grand Master

bubba

Posted
Posted

If deck height is below 0, wouldn't that increase compression??

I was more trying to make the point that the head and cams are fine.. there is no inherent problem with that type of head and cams that would cause this issue.

rob82 Mentor

rob82

Posted
Posted

Does the dyno plot look normal - like the cams are relatively in the right spot? If so that compression pressure is pretty much spot on.

My RB30/26 with CP 9:1 pistons was around 160psi +/-5psi - when I advanced the inlet 7degrees there was very little compression presure difference (maybe 5psi at most). This would suggest to me that your engine has the correct static compressure ratio of 9:1.

So many things to check before pulling the engine apart. Start by checking the CAS like I said.

R32Abuser Mentor

R32Abuser

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From all that I've read, and from thinking about it:

If the piston (flat section of the piston-not including domes/dish's) sits below the deck of the block, then the combustion volume when the piston is at TDC is larger compared to if the piston was sitting above the deck ("proud of the deck").

Correct me if Im wrong tho?

R32Abuser Mentor

R32Abuser

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Does the dyno plot look normal - like the cams are relatively in the right spot? If so that compression pressure is pretty much spot on.

My RB30/26 with CP 9:1 pistons was around 160psi +/-5psi - when I advanced the inlet 7degrees there was very little compression presure difference (maybe 5psi at most). This would suggest to me that your engine has the correct static compressure ratio of 9:1.

So many things to check before pulling the engine apart. Start by checking the CAS like I said.

Yup. Builder is slapping a different/known working CAS on it.

Taking it back to the dyno, checking if it knocks again, if so, getting a safe tune to do some k's on it. If not - great!!!

Thoughts?

KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted

Yup. Builder is slapping a different/known working CAS on it.

Taking it back to the dyno, checking if it knocks again, if so, getting a safe tune to do some k's on it. If not - great!!!

Thoughts?

Running in takes 20 -30 mins - get a proper tune and see what it can do.

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