Pontiac 400 Pistons

I have 2 sets of pistons, for my Pontiac 400 engine. One set has 4 valve reliefs ,and the other set has 8 valve reliefs. What's the difference ?

 

4

 

A lot, I would guess. One is an aftermarket set for a hot rod or racing engine..The other is a rebuilder or replacement item.
Probably other differences too.
Of course Lloyd is correct, given the limited amount of info ;-)

 

How's about pictures of the piston tops????.. one of each piston will do....

 

Loyd your math skills are amazing. Your really wasting your talent on fire fighting and pushing sand paper.
And I don’t believe I’ve ever come across Pontiac 8 valve relief pistons. Pics or part number would help.

 

He may have a set of these.....

https://images.app.goo.gl/QNGxAw9QELtwsuY16

 

Thank you

 

Those are garbage.....

 

Wonder what the reasoning is behind those?

 

Interchange with 2 and 4 bbl heads.....

 

Or….maybe running 2x4 intake

 

Nice try, but you forgot he said "set" of pistons. So, 8 in a set means 4x8 = 32(for 4 relief pistons) & 8x8=64(for 8 relief pistons); Then subtract: 64-32=32
Your answer is 32. @Lloyd's paint & glass gets an "E" for effort.

 

The 8 valve relief pistons were made for both early (389) and later model (400) valve angles. 2 barrel 67 400's had the earlier 20 degree valve angle like a 389. Every 4 barrel 67 400 and later model 400 (both 2 and 4 barrel) will use the later model 14 degree valve angle. Those 8 valve relief pistons are cast and sit way down in the hole and lower your compression. I have seen some that the edge is beveled on to lower your compression even more. They usually sit around .050 down in the hole. I would not use them.

 

Yep! The Ford high output 5.0L engines from '87-'91 were factory equipped with TRW forged pistons....

 

This is the correct answer.

 

So if they are standard you bore the 389 .060

 

Nothing wrong with a set of 455 L2359 TRW forged for a street or Bracket engine. They are 4 eyebrow, multi-directional , of course. Don't know the 400 number, off hand.