Bloody "precious" RB engines!

[blind_elk]

If you want to save the cash as you don think you will ever be making the number to justify forgies, then what are a set of new GTR pistons worth from Nissan?

Maybe not such a bad idea, Roy.

Just having a look at the ACL cattledog, These are the differences:

RB25 crown = 11.5cc dome

GTR crown = 16.3cc dome

RB25 comp height = 31.3mm

GTR comp height = 30.3

(What's "comp height"? is it like pinion-to-crown distance, or something?)

And GTR pistons are slightly lighter (RB25 = 442g, GTR = 428g), although I'll probably be getting the rods and pistons balanced anyway.

ACL piston drops C/R on the RB25 from 9 down to 8.5

Another possibility would be a 1mm overbore and fit VG30DETT pistons (9cc dish, 32 mm comp height, 8.5 CR)

[GTRgeoff]

Mmmm, I seem to recall that the GTR crank has a longer throw, but a lower compression ratio and the rods are the same length. So, using the standard 26 pistons would in effect lower the 25 CR even more then the standard 26 CR unless the combustion chamber is significantly different.

All too hard anyway. The back has been upset again so the brain isn't functioning properly.

I also recall the 26 pistons and rings came to about 900 bucks.

Greg what are the ACL pistons retailing for? Never knew they did RB's.

Anyway, I don't in anyway recommend reducing compression ratio. Sorry I'm not much help right now.

[blind_elk]

Well, I finally got the engine out and disassembled. It pooped the ring land around #2 ring in #2 cylinder, broke the ring, and (lightly) scored the bore.

I'm still in a quandary about replacement pistons. I still don't know whether to go to the expense of forged, or fit standard Nissan replacements and just keep the car away from the racetrack (build a dunger for competition).

The guy I'll get to re-assemble the engine says he would go straight to forged since the opportunity is there. But it's not his money that's paying for them. Others say Nissan pistons should be capable of withstanding the power output (180 Awkw). I'm really confused, and I can't proceed with all the machining and balancing until I get the pistons.

Please help.

[Roy]

Well if the Nissan pistons are still fetching $900 with rings etc, then i would throw the extra bit of money at it and get forged pistons. Get them 40thou oversized if the bore has been scored a little. It will mean an extra $1000 by the time you factor in the extra for the pistons, the machining and chemical wash and gasket etc...but doing tings once takes the pain out of cars... a rule i dont always abide by:(

Have you considering just getting another RB25, perhaps a NEO??? You could probably sell your RB25 for approx 1k (if not complete then crank and rods to an RB20 owner looking for a cheap stroker kit, the head to a member of the RB30 crowd etc)

Just ideas that you may have already seen the shortcomings off ...i dont know:)

[blind_elk]

Have you considering just getting another RB25, perhaps a NEO??? You could probably sell your RB25 for approx 1k (if not complete then crank and rods to an RB20 owner looking for a cheap stroker kit, the head to a member of the  RB30 crowd etc)

Just ideas that you may have already seen the shortcomings off ...i dont know:)

I don't know if they make the NEO in 4WD (maybe the Stagea has one?). But this is a Stagea engine anyways, which cost me nearly $4G in the first place. Not sure I can go another $4G, although the rebuild is probably going to be close to that anyway.

Just don't like the idea of trying to sell off the bits - still trying to sell the 2 RB20s I've got cluttering up the garage (much to the distaste of "she who doesn't really need to be obeyed").

Thanks for the thought anyway. I'm investigating pricing for some ACL forgies - will let you know how that goes.

[blind_elk]

$950 + GST for ACL Hyperlite forged pistons - sounds pretty good to me.

(FYI - Arias from Rocket around $1300)

[acsplit]

It was in the tuning. ! i won't elaborate any further but detonation is early tuning stages are a feature of some peoples tuning abilities.

and i have many reasons why i believe it was the tune but i won't go into it on a public forum.

Again bad luck greg but sped the $$ on the forgies if it is gonig to be tuned correctly and you won't ever look back

cheers