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Rb30 Crank At Rb26 Block

Supra2000

By Supra2000,
in Engines & Forced Induction

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  • 2 weeks later...
Supra2000 Contributor

Supra2000

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My friend

if I use RB20 Crank at RB26 block what will happen is any one tried, As you know the conrods is short and I think it will give me high RPM but the problem with stroke is low.

Please I need your advice.

mark99 Contributor

mark99

Posted
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Have a look about 6 months ago.

Guy did it, wouldnt go into much detail so its safe to assume one of two things

1. He was talking shit

2. Is cost a lot of time, and money and probably isnt worth the effort

Plus, when a 26 crank works just fine, not sure why you would bother

1. i wasn't talking shit

2. It took a fair bit of time, i was looking at trying to see if i could do it and have it commercially viable, and for me it was worth the effort.

The reason to not just use a 26 crank, is because almost with out exception no matter what your application, more capacity will be better.

I did it by offset grinding the rod journals down from rb30 size to rb26 size, taking a little bit of stroke out as i went down. Final stroke was 83.2mm. i used standard length Eagle rb26 rods, i rebushed them to 22mm gudgeon pin size (but you can leave them at 21mm pin if desired) . Then used custom forged pistons. Yes the rod to stroke ratio ends up fairly poor. But it doesn't seem to to have any serious adverse effects on the engine. The car has low mounts, runs pulp, 18psi, makes 406rwkw, pulls hard from 4000, and pulls harder than an under sexed school kid from 5000 through to 8800. The engine revs freely and smoothly, and is sweet all the way through to the just short of 9000rpm rev limit. There is also counter weight modification required.

Ill be the first to admit, a longer rod to stroke ratio is better, and the the OS is an awesome bit of gear. But for me it was just time, so it was certainly worth it, who wouldn't want 2.9L? It worked out that i can do the cranks finished ready to go for $2500 dollars, this is nitrided, and with a crank collar fitted. Standard rods will not clear the block, so you need an aftermarket rod like an eagle or crower, and then of course custom pistons. So all up it works out a lttle cheaper than say an HKS stage 1 kit, but most people like brand names, so i've only had a little interest.

Hope that helps, feel free to ask any questions.

skybarge Community Regular

skybarge

Posted
Posted
My friend

if I use RB20 Crank at RB26 block what will happen is any one tried, As you know the conrods is short and I think it will give me high RPM but the problem with stroke is low.

Please I need your advice.

instead of using an RB20 crank, use 2x SR20det cranks, cut one cylinder off each and weld them together, it'll allow you to rev upto round 13000rpm...

Supra2000 Contributor

Supra2000

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instead of using an RB20 crank, use 2x SR20det cranks, cut one cylinder off each and weld them together, it'll allow you to rev upto round 13000rpm...

how I can cut the cylinder and make it who can make it properly it will not fit will.

Shane_954 Enthusiast

Shane_954

Posted
Posted

You will need to bake the crank in the oven for 45 minutes on 180deg to make sure the araldite cures properly, that way you can reliably rev it to 13000rpm. Also use rb20 pistons so you have plenty of piston/bore clearance. Might rattle a bit but it wont sieze. Be sure to run an 85w/140 oil, the thin stuff can sometimes cause the araldite to lose its grip, cant rely totally on the electrical tape to hold it together.......

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