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Rb26dett Bored To 87.5mm Or 88mm

johnnyt

By johnnyt,
in Engines & Forced Induction

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johnnyt Rising Star

johnnyt

Posted
Posted

hey guys

my engine machinist has told me that my block is already at 87mm and needs to be replaced or bored further.

what ive found from searching on the forums and the net is that wiseco do a 87.m piston and also a 88mm piston.

what i need to know from you guys is

1.what do you think about boring out to 87.5 or 88mm

2.would you use wisecos

3.what headgasket should i use with these oversize pistons (was going to use the tomei kit but they dont list a 87.5)

4.am i going to have a CR issue ?i cant find any info on the wisecos CR

thanks in advance guys

johnny

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https://www.sau.com.au/forums/topic/155682-rb26dett-bored-to-875mm-or-88mm/
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itbmils Proficient

itbmils

Posted
Posted
hey guys

my engine machinist has told me that my block is already at 87mm and needs to be replaced or bored further.

what ive found from searching on the forums and the net is that wiseco do a 87.m piston and also a 88mm piston.

what i need to know from you guys is

1.what do you think about boring out to 87.5 or 88mm

2.would you use wisecos

3.what headgasket should i use with these oversize pistons (was going to use the tomei kit but they dont list a 87.5)

4.am i going to have a CR issue ?i cant find any info on the wisecos CR

thanks in advance guys

johnny

I've used Wisco in my RB26 (87mm). They are 2 years old with no probs, pulling ~300awkw

BUT they are noisy - but that could also be a clearance thing with my build tho

johnnyt Rising Star

johnnyt

Posted
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Posted
Stockish power would be ok?

I would think you'd want to sonic test cylinder wall thickness to make sure there's enough meat there.

i understand that there may be a problem with the fact there is less meat in the walls but why do some of the big jap brands do some 60thou over and above pistons?

has anyone here heard of or seen a cracked rb26 cylinder wall from not having enough meat?

johnny

Denver Grand Master

Denver

Posted
Posted

You can safely bvore out a 26 to 88mm, but, its all down to how much power you intend to make, if your only looking at 350-400 you'll probably never have an issue, if you start pushing on it and go for 500+ then eventually, you might end up with a cracked block..

Age of the block is a factor here too, if its an older block from say a 89/90 32, it'll be stronger than a newer block due to the metal ageing/hardening up over time with the heat cycling..

Personally i wouldn't use wiseco pistons, or anything yank, they spec largeish clearances, which are all well and good in a nascar where you'll get enough heat into the thing so it expands to not rattle, the jap pistons spec clearances usually close to factory piston to bore requirements, mainly due to the makeup of the raw material used in there pistons, not expanding as much as the yank gear..

Price wise, if you get stuff from greenline.jp the jap gear is also about the same cost as the yank gear too..

  • Like 1
  • 7 years later...
$$slowmedown Mentor

$$slowmedown

Posted
Posted (edited)

Thanks Peter

Darton sleeves might be the best option then. As the moto goes, do it once, do it right...

It's a track only car and we are looking to push 600HP + at the flywheel with up to 30PSI of boost

I've emailed JHH Racing here in Bris to get their thoughts and provide a quote...

Edited by $$slowmedown
GTRPSI Mentor

GTRPSI

Posted
Posted

Partially grout fill the block to support the bores from flexing.

Its only the bottom inch to inch and a half, it wont effect cooling but will provide much extra bore strength.

We are 86.5mm on a RB30 block and not too concerned about it holding to 650Kw at all 4, remember our bore is taller with more room to flex and fail compared to a 26.

Id be more worried if it was a stroker as the rod stroke ratios of strokers tend to provide more side loading on the bores, with stock RB26 or 30 ratios they are as good as it gets to minimize side loads.

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