I am sure this has been covered but a search yeilded nothing anyways
will gsr pistons and rods fit in a b18b motor if so how much will it change the compression and is it worth doing.

thanks in advance

 

They pistons will fit, but the rods won't. Put the GSR pistons on the LS rods and you'll end up with a bit more compression (not sure how much though).

 

if you want the GSR pistons and rods to fit in a B18B, you will also a GSR crank and it should be fine.

 

will I have to do anything special to fit the pistons on the ls rods

 

As everyone already said, use both the B18C rods/crank and you'll be fine... Whatever pistons you use is up to you, but DON'T put PR4 (LS) pistons back onto the B18C internals, you'll just be dropping your C/R as the GSR crank has 1.80mm less of stroke which intern increases your rod ratio from the LS' (1.54) to the GSR's (1.58)... If you're trying to gain compression and you're still running the nonVTEC (PR4/P75) cylinder head I would say just stick with the LS internals and swap pistons (P73-A0/00, PR3, P30, or PCT's) would all be a nice bump up for you... I just wouldn't waste my time with stock GSR slugs, it's not all that big of an increase... Just my $0.02

 

cool thanks