Rb26: Max Bore Size?

[gtrtech]

Hello to all,

What is the maximum bore size you can safely take a RB26 block out to?

Are 88mm pistons the largest you can go?

Cheers

Edited July 1, 2006 by gtrtech

[GTRsean]

Seems 87mm to 87.5 pistons is the max you would dare to go in general due to cylinder wall thickness/cracking esp for xtra boost, mods etc.

Anyone elses opinon?

[amosite]

Grex and tomei as well as a few other companies offer an 88.5mm kit.

[SECURITY]

Seems 87mm to 87.5 pistons is the max you would dare to go in general due to cylinder wall thickness/cracking esp for xtra boost, mods etc.

Anyone elses opinon?

im sure ceramic coating of the bores and pistons etc will help reduce the strain caused by heat if you wanted to go over standard size.

[GTRsean]

Sleeving the cylinders could get more life out of block if it's scored too bad etc?

[amosite]

Yes, you can get them sleeved if bad enough..

A mate of mine badly damaged his block, apparently the culprit was was a split fuel reg vacuum line causing a lean mixture and melted piston and badly scored block.

It was bored to about 88mm, then sent away for sonic testing which came back fine. He was quoted about $2400 for Grex 88mm pistons but ended up getting a set of rods and 88.5mm pistons locally for $3K. Cost a little more then off the shelf pistons as they had to be custom made.

They got it sonic tested again just to be sure and the engine builder built the rest of the engine for no more then 2 bar. This sounds about right as the more meat you have, the stronger the block.

From what I gather, its not really the bore that is the weak part in the RB26 even at 88.5mm. Its the bottom of the block which can twist on big hp engines above 900 hp. This leads to bearing failure. Apparently its the length of the engine?!

I think JUN also make an 88mm piston but they are special order only, probably super expensive and 3 months from order.