Jump to content
SAU Community

Recommended Posts

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...

  • Replies 146
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Posted Images

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?

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

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!

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

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.

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.

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?

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?

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.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Similar Content

  • Latest Posts

    • Don't even try to run it on the stock ECU if you're going to have the boost controller bring boost above ~10 psi. I've already told you that. If you use the Nistune ECU, you will need to CAREFULLY read the available documentation for Neo tuning, and read some threads on the Nistune forums, to discover the various things you have to do to prevent the ECU from going bananas when the boost is too high. The is a table associated with th boost sensor that must be modified to prevent it from shitting the bed. This is just one of the things that you will need to do to the tune in Nistune, because the Neo turbo ECU will be expecting to see a number of things (such as the TCS) that are not there, and you have to block the DTCs on those. It is totally not surprising to me that you are having the problems that you are, but the solutions to these problems have been known for >15 years. So just get it done.
    • Hi. Sry iam not a mechanic and iam not at the car atm so i dont know 100% but they told they measure those and even try to change those. AFM they have two. Coils are new a they have my old one too. Plugs too. ECU...we have 25 NEO stock and Nistune 25 NEO.   But i dont know if any one those could be the problem and why/if/what can cause this, Only thing they did not check is fuel...but that walbro 255 is new(like 1,5 years)... That fuel pressure gauge idk...but i let them know Any suggestions?   EDIT: how can they know if it is like you say he ECU pull power when it reaches a specific boost level that is too high? Tha car has boost controler
    • Can you clarify what you mean by boost cut, do you mean it misfires both when under load (driving) and when stationary and out of gear? Or does the ECU pull power when it reaches a specific boost level that is too high (boost control issue)? Does it occur at idle with no throttle? When you say "the ECU is OK", what ECU is it and why do you think it is OK? Have you used the NEO ECU, and if so do you have a MAP sensor attached? Same for the AFM, why do you think it is OK? Do you have any way to put a fuel pressure gauge on it (even just a mechanical one between the fuel filter and fuel rail)?
    • Hi.. Just another problem. So maybe you can help. I(my mechanic) done swap from my RB20DE NEO to RB25DET NEO. Everything is OK but we have a boost cut. Coils/Plugs are ok...AFM is ok. ECU is ok. I have Walbro 255 but it "changed" sound few months ago(you can hear it ouside) you did not hear that when it was new(maybe faulty?) Sooo...what now? What can cause this boost cut? It is even when you standing still...
×
×
  • Create New...