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What happens if i put a b25 crank in a b23?
Posted: Mon Jul 31, 2017 2:16 am
by Matto323
Hey all im not the greatest when working out compression ratios and cc's etc but im looking at lowering compression on a m20b23 motor. I noticed the b25 motor has a slightly shorter stroke then the b23. Im not sure if its in the pistons, rods or crank but i was wondering what the cc's and compression ratio would be if i used a stock b25 crank in a stock b23. Does anybody know?
Re: What happens if i put a b25 crank in a b23?
Posted: Mon Jul 31, 2017 9:24 am
by Speedtouch
The 325i crank would give a cubic capacity of 2.262 litres (2262cc) in an M20B20/23 block, compared to the 2316cc of an M20B23 (i.e., 54cc less).
Not sure what the CR would be - somewhat lower than the M20B23 one, obviously, seeing as the M20B25 crank stroke is 75mm compared to the M20B23's 76.8mm, a 1.8mm shorter stroke.
Re: What happens if i put a b25 crank in a b23?
Posted: Mon Jul 31, 2017 9:30 am
by reggid
2262cc, approx 8.8:1 CR
Re: What happens if i put a b25 crank in a b23?
Posted: Mon Jul 31, 2017 9:31 am
by steve_k
what you really want is the b23 crank in the b25 block, gives a cc of 2554 like the early hartge h26 & early alpina c1 (iirc).
Re: What happens if i put a b25 crank in a b23?
Posted: Mon Jul 31, 2017 9:53 am
by Speedtouch
Yes, but the OP is aiming for a turbo conversion on his M20B23.
Re: What happens if i put a b25 crank in a b23?
Posted: Mon Jul 31, 2017 10:02 am
by steve_k
Speedtouch wrote:Yes, but the OP is aiming for a turbo conversion on his M20B23.
oops didn't see that bit
will teach me not to skim read
Re: What happens if i put a b25 crank in a b23?
Posted: Mon Jul 31, 2017 10:18 am
by reggid
just tune it properly or use a thicker gasket