408 Piston Dish

[Kern Dog]

It is an interesting design.

 

[Newbomb Turk]

It is an interesting design.

It is. It don’t make sense to me when I first got my eyes on them.

I suppose you can stick the deck out out of the bore but the bottom of the piston is the wrong design for open chamber heads.

 

[mbaird]

He’s right. It’s NOT an open chamber piston. It’s designed to be zero deck with a dish.

Like I said, the outer ring that’s lower was done so they didn’t have to make the dish deeper.

When you say he are you referring to the techline guy ?
If the quench pad is supposed to be at zero deck my machinist really fucked up ! Maybe I will take my old pistons and rods in and if they are above deck I will know he did the damage . I really dont want to spend my LA roller block on this issue . And if milling the quench pads down to zero deck puts my quench vs static compression out of whack I guess he will have to find another magnum block .

 

[Kern Dog]

Years ago Dwayne Porter mentioned this design.
I had detonation issues and when I told him the pistons I had, he asked if I knew any good local machinists. He spoke of having about 2/3 of the pistons milled approximately .040 while leaving the top 1/3 alone.

 

[mopowers]

They probably mean the outer edge around the step should be zero deck..while the pad is positive.
Anything with a raised quench pad is designed for an open chamber head. All the others that are flat top zero deck or maybe positive .019- .024 ' like a 340 kb243 ...can be used for the closed chamber head and adjusted with a head gasket.
Your shop needs to equalize all the rod lengths, the stroke on the crankshaft if it isn't already then properly Square the block up based off the four corner measurements of 1,2,7,8 rods n pistons. Mock up is always involved as foar as im concerned

Turk's right. The quench pad is the surface that's meant to be zero decked. It's not designed for open chambered heads.

 

[fishmens67]

is the wrong design for open chamber heads.

It's the wrong design for open or closed chamber heads.
What are the benefits for such a design, please explain

 

[fishmens67]

I had detonation issues

My exact thought with that design.

 

[mopowers]

@mbaird - Did your machinist tell you how much he took off the decks? Sounds like he fucked up. Could you use a thick gasket to compensate?

 

[mbaird]

@mbaird - Did your machinist tell you how much he took off the decks? Sounds like he fucked up. Could you use a thick gasket to compensate?

He said .012 but I have asked him what the deck height is several times and he has never given me a direct answer . I told him to check the deck when I dropped the block off and even stopped by to tell him not to take any more than necessary…. He said it was being decked as we spoke ( assistant did it) because it was porous and asked me if I used distalled or tap water… . Then today he told me they decked it because the center was low…. Hmmm… I picked up on that right away .

If I run a gasket thick enough to give me .039 quench I might end up with 8:1 compression.
And my intake will probably not line up . Then I have to consider how close my rings will be to the deck ???

 

[mbaird]

It's the wrong design for open or closed chamber heads.
What are the benefits for such a design, please explain

The benefit as I understand it is that the quench forces the air/ fuel into the chamber which keeps the fuel atomized and creates a smaller area for the flame to propagate. My concern is not so much for maximum power but rather detonation resistance on pump gas . Power is just a side benefit.

 

[mopowers]

If I run a gasket thick enough to give me .039 quench I might end up with 8:1 compression.
And my intake will probably not line up . Then I have to consider how close my rings will be to the deck ???

Why would your compression be that low or your gaskets not line up? I'm not suggesting it's the best method, but you'd essentially be replacing the removed block material with extra gasket height. The top ring on the Icon 745 pistons is 0.272" under the top of the piston so ring land height shouldn't be an issue.

 

[XFX]

Here is one in action. In this case with a long stroke. Over 4 inch.

 

[33IMP]

I have a set of Ross pistons with almost the identical piston top shape. They are designed to give a moderate cr for a big block B1 stroker. Compression pad near zero deck, stepped dish and a "generous" valve relief.

 

[MOPAROFFICIAL]

Turk's right. The quench pad is the surface that's meant to be zero decked. It's not designed for open chambered heads.

You're not comprehending what I said...and thats ok. Carry on.

 

[furrystump]

I ran that piston, the highest section was not proud of the deck. Blueprint used or uses that piston. I know that the flat top version I replaced it with sits .010 in the hole on the same block/rods/crank so my deck height is a bit tall? If yours does sit way proud, something off.