I have twin 1998 merc 350 mpi's and am thinking about changing the rockers to crane golds. anybody aware of the stock size and what the largest i could go to is ? motor builder says if i increase intake's by 1 size and leave exhausts alone would notice a slight increase. any truth to this ?

Small blocks come stock with a 1.50 ratio. I don't think that going to a 1.7 would make any noticable change in performance.

One thing about stock rockers is between stamping variances,flexing(especially with stiff springs) the ratio of 1.50 ends up more like 1.45.If you jump up to the 1.65's it wil increase your net lift approx .045 thou-Example-.450 cam turns into a .495 lift cam. Your cam will also act approx 1/2 size bigger,your .002 duration won't change but your .050 duration will(valve will be open the same amount a few degrees earlier that it used to be open at .050 lift). Unfortunatly,if your using stock springs and your cam is already .450-.460 lift adding the .045 would be too much for the springs AND like checkmate 454 said, you won't gain enough power to really see a difference,Smitty

1.5 is stock
1.6 is standard cheater ratio
1.65's are starting to need some grinding in the pushrod slots if you're running a lot of cam.

Normal rockers and a better cam would be a far better choice.

I'd look at doing cam, lifters and rockers all at the same time if you want to notice something big. Go with a hydraulic roller and some roller rockers. Nothing wrong with the Crane Golds. Just make sure that your springs are setup so that everything works together.