25 Crank In 30 Block

[Ahmetm7]

Hi new to this but would like to know if this sorta build is possible? Would be handy to know if it is possible or if I'm just wasting time

Edited January 27, 2013 by Ahmetm7

[StevenCJR31]

what are you trying to achieve by attempting this?

[blk94r33]

Or did you mean a RB30 crank in a RB25 block?

[AngryRB]

Or did you mean a RB30 crank in a RB25 block?

i think the idea is to have the rb30 capacity but able to rev like an rb25?

im interested to know too, the shorter stroke does sound less exciting.

[r32-25t]

That doesn't work if you shorten the stroke you decrease the capacity and you basically end up with a tall block 25

[mad082]

yes it could be fitted, but it won't run. the rb30 bore is the same diameter as the rb25, but the stroke is 13.3mm longer, so the piston will be 13.3mm lower at TDC than with the rb30 crank. so the compression with me drastically lower than standard (you'd have higher pressure in your tyres than in the combustion chamber). of course you could overcome this with aftermarket conrods (expensive), but then all you would end up with is a rb25 with a taller block (won't have 3L capacity) and no VCT. so you would spend a heap of money to make a stock rb25 worse than stock

[Ahmetm7]

Thanks guys just an idea but wasn't to sure as to how it would work. Always tryin to find something different

[mad082]

sometimes it's better just just follow others and go with what is tried and tested

[blk94r33]

A 30 crank in a 25 block would be interesting in terms of keeping the same engine appearance engine number etc, but the cost of machining along with custom rods and pistons would kill the idea quickly.....

[mad082]

using a 30 crank with a 25 head has been discussed on this forum before (many years ago though). then general consesus was that, other than the cost, it would be a bad idea as the conrod length to crank length ratio wouldn't be very good, reducing torque and increasing the chance of breaking conrods, etc, because at 90 degrees ATDC the conrod is going to be at more of an angle than with the stock (longer) conrod, meaning it has much more sideways load on it