i have been slowly been aquring parts to build a bigblock gsxr750, the plan was/is to use a short stroke top end ( long stroke =70mm bore short stroke=73mm bore ) on a long stroke bottom end, using a spacer plate under the barrels to take care of the diffrence in the stroke/hight of the two motors.
However, suzuki in it wisdome have made it a lot harder to do than just put a spacer plate under the borrels of the short stroke motor and away you go with 815cc motor. No they have used diffrent sized rist pins in the pistons to stop us from doing this, the long stroke motor has 18mm pins and theshort stroke has 19mm pins.
So something is not going to fit obviously, so the next thing to work out is how to get around this problem, (THERE ARE SEVERAL WAYS AROUND THIS PROBLEM WITH THERE OWN PROBLEMS AND MERRITS ) first thing i considered was to have the conrods bored out to it the bigger pins, but this was the least desirable way to go for several reasons, the two main ones are that i have to dissasemble the cases to do so and that it will make the conrod weaker around the pin area.
The second way around this is to get a set of custome pistons made for it, which is proberly the best way but cost and lead time were factors that i considered, (i didn't research this much as i have another plan) what i have found out is that wiseco will charge extra for costom pistons reguardless of how they do it, but apprantly JE will not chare you extra if they can use a blank that they use for another pistone IE if they use the short stroke piston and only bore the pin out to 18mm instead of 19mm which is not a bad way to go.
The third (and this is not to say that they are other ways around this ) is to use pistons from another motor that will suit the application on the motor that i am trying to put together,
after many hours on the net and downloading catalogs then cross refrencing them i have found that there are a few diffrent options avalible to use but only one that uses 73mm pistons, the others use bigger pistons which is ok if you want to bore the barrels out (BY THE WAY A MAX OF 76MM OR 3MM OVER SIZE IS RECOMENDED UNLESS YOU ARE GOING TO USE AFTERMARKET LINERS TO SUIT THE LARGER PISTONS) so back to the knowledge, Kawasaki 1996-2003 ZX7R's use 73mm pistons and have 18mm rist pins, ( in the wiseco catalogue they use the same pins for both the suzuki and kawasaki )so this is the option that i am most likly to use as i can get of the shelf parts, also the kawasaki pistons come in oversize pistons as well so if a rebore is required it can catered for.
now for the other pistons that will suit this application are GSX1100E 1980-83 (18mm pin) and are availble in 74mm 75mm 76mm 78mm 80mm 83mm pistons, however as you can see you will need to bore your barrels out oversize to use the smallest pistons avaible
Ok now i have found suitable pistons ( i am going to be using the ZX7R or ZX7RR pistons ) i no have to work out how much IF any diffrence there is in pit to piston top hight ( i know that there is on the ZX7R and ZX7RR pistons ) to that of the suzuki ones, how ever this is not a problem as such as a spacer plate has to be used to compensate for the extra stroke of the long stroke motor. the ZX7RR has a shorter hight between the pis and top of piston so it might be of advantage to use it i don'know untill i get the specs of both the pistons and check them out to see which will best suit my applications
So that is how things stand at the moment, i will keep you informed of progress as i go.
if you have any questions i will try to answer them for you and if you have any information it would be appricated.
Cheers Clive.
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