hello, once again i am looking for advice. My question is should i use stock cast aliminum pistons or hypers? i should be making around 420fwhp and 440ftlb and about 9.3:1. I was originally going to go with the hypers but the machinist keeps trying to convince me that they are going to crack. i dont plan on spraying right now but if i did i wont go over 125 shot. So what do you guys say? thanks again for your input.

 

Hyper pistons are stronger than cast pistons. You should only have a problem with hyper pistons if you have knock from detonation. On the other hand, if you have detonation, cast pistons won't hold up much better anyways.

That being said, the next step up from hypers is forged and those are $$$.

 

If you're making 400HP then plan on spraying it, hyper is "entry level", and most people would recommend forged.
Speed pro has forged pistons that are cheap like borscht, if we're talking flat tops.

 

hey guy ive seen 650 horse small blocks with hyperutectic pistons in them ,you must understand that all hypers are not created equal some are better than others ,as for nitrous having forged pistons is a myth ,weve sprayed cast stock gm and for pistons key here is to retard timing enough and have plenty of fuel going to that solenoid ,hypers also have tighter cylinder wall clearances which is good for piston ring life ive got a 350 horse 355 with solid cam that runs kieth blacks claimer hyper piston and havent had any problems ,besides forged pistons are noisy when you start them ,long live hypereutectics ----------bigzeke355cid92bird

 

The problem with hypers with PA applications is two-fold:

1) They are more brittle than cast or forged pistons.
2) They transfer heat to the top ring more than cast or forged.

Cast pistons with PA isn't all that uncommon. They have their limits, and above a certain power level they won't be strong enough to hold together - that's when you go forged. But, 400 HP NA and 125 shot aren't going to be over that limit as long as they are good quality pistons, and you don't go lean.

Still, I wouldn't go hyper with a PA application if you are still in the build stage. Go forged if possible, cast if the budget really won't allow forged (but, if you're considering PA, "budget" should be the last consideration in parts choice).

 

Well, thanks for your advice. I dont have the money to go forged so i guess i am going to go with the hypers and hope they dont do me wrong.

 

Gap the rings wide. Very wide.
Then you won't have to worry about them getting the heat, expanding and butting solid.

 

how wide approx? i dont want to do it to wide. This is my first complete engine build. thanks again

 

i believe KB recomends .023-025 on thier hypers for a NA... they come with a chart depending on induction/app and bore. you can go pretty big on the top ring and see no ill effects while going to small will be very disapointing...