Hey guys, i have spoken to many people about this but i am getting several different answers. im getttin gready to bore out my engine (420a) and i need to know what size to take it out to. what im looking for is apx 300whp, at apx 20lbs of boost. ALL im looking for here is a size, i've been told .020, .030, .200, .040 all i want is the max size i can safely take it out and where to get the forged pistons to match them. thanks

 

due to the way engines work, over time the cylinders become sort of egg shaped. you bore out an engine as much as you need to when rebuilding to return the cylinder to a perfect circular shape, you dont bore out an engine to gain desplacement/power. whoever builds the engine will bore it as little as possible to fix it. the more you bore it, the less it can be rebuilt in the future.

 

.25 is is about the bigest you really want to go .30 can be acomplished but is more of a risk. If you are looking for size get it resleaved with a stronger sleve that can hold .30-.35 with no major problems now .40 most macineast will tell ya at this point in time you need to reseleve it.

 

thanks DSM, i didn't know that (still new lol) i guess that's what im lookin for, i'll just get it done about .02 or .03 then. thanks.

 

420a isant sleved....

Dsm is right the info that i had was wrong, the most you can bore it over is .020 When the block was made its orginal intentsions was for it to be a daily driver so they did lots of little things to make it better, like a incorapeted a bead plate in the blocks desgine to reduce noise and vibration. One thing that they did was make the block thinner then nessicary to reduce the weight of the fat *** car. The block is actually lighter then the 420a tranny.

 

you sure it is not sleved because when i had my motor apart it had sleves in it. and depeneding on wear of block you can go .25 with no problems but it is best to consult with a macinest to make sure that it will be safe to do so.