Boring out rb25

[sweetr33]

Was wondering if anyone knows how far u can bore out an rb25det block before u reach the unsafe mark? IE. 89mm bore etc? Is the rb26 and rb25 cylinder bore the same diameter its just the stroke that makes the difference in capacity? Just curious as to how far u can go b4 overheating may be an issue due to not enough meat between cylinders or even cracking the block may be a drama? any help is appreciated

[N I B]

88mm is the max but only for lowish power.Use 86.5 max for huge power engines.

25-26 - are all 86mm bore.

[sweetr33]

why use smaller diameter cylinder for high performance engines and a bigger cylinder diameter for smaller hp? and is 400rwhp in the 88mm category or 86.5?

[N I B]

The block is strong enough to handle 400rwhp at 88mm,when you get into the 600rwhp the block will start to crack.

[sweetr33]

ok thanx steve, thats good to know. I wont be reaching 600rwhp ever, i have no intention of heading any higher than 450. thanx for ur replies

[T0nyGTSt]

But can I ask this...

With all these big bores - where da fark do you get pistons?

It was my impression that 87.5/88mm pistons is about as big as it gets.

Unless you want custom Cossies

T.

[sweetr33]

to be honest i havent found that out yet but i dont see why there would be a drama, a mate of mine has gtr crank n rods in his rb25 and he got big diameter pistons, bigger than 88mm.