D-dished pistons vs. stock dished sbc 350/383

[jonsjunque]

Putting together a marine sbc, piston choices are for low compression.

Is there much performance difference between the d-dish versus the stock dish ?? (round dish with 4 valve reliefs)

As I understand quench, it is desired to have the piston top mirror the heads chamber . ( using Vortec or Vortec type heads)

The d-dish is definitely mirror-like and the stock piston is not.

How do you achieve/measure quench with the round dish?

Also, forged versus hyper is another question I have, particularly for marine use.

thanks, john

[Alan Roehrich]

Yes, there is a performance difference between a reverse dome and a plain dish. In order to see all of the gain, you need to set your piston to deck clearance to zero, and use a head gasket around 0.042" thick.

With a full round dish, you don't achieve squish/quench. Not in any really significant manner.

You can run hypereutectic pistons in marine applications. I prefer not to, as "lake gas" is often of even more questionable quality than regular pump gas.

Even if the compression ratio is as much as a full number higher, the detonation resistance gained by using a reverse dome piston and zero deck clearance will make up for it, provided you don't do anything else to create a problem. In other words, you'll be no more likely to see detonation at 9.5:1 compression with proper deck clearance and a reverse dome than you would be at 8.5:1 compression with a full dish and excessive deck clearance. The engine will run better, and cooler, as well as having lower EGT, with the higher compression. It will need less timing advance as well.

[jonsjunque]

I was thinking that too.

So, those under a grand stroker kits are leaving some HP on the table.

Thanks again, john

[Alan Roehrich]

Yeah, they are leaving both power and reliability on the table.

Were I building a "383" for a boat, I'd be using an Eagle crank and 6" rods, and an AutoTec reverse dome piston.

I'm building a similar 406 right now, although not for a boat.

[ProPower engines]

X 2 on the 6" rod combo.
All the marine 6.2lt engines we do are done that way. With a more limited cyl. head for the application the run way better and have a smoother power curve. The comp. ratio should not be higher then 9to1 as mentions marine fuel also has ethanol add to is an detonation issues with higher comp. will be seen. I try to limit the total timing at full advance under load to
28-30 deg's max

[novadude]

On this topic... Does anyone make a 12cc reverse dome piston for a 350 besides KB? Seems like most -12cc 350 pistons are full dish.

[ProPower engines]

I believe that mahle has a piston in there power-pak line
I think KB's icon series does as well. If you are looking for a hyperutectic you may be SOL.

[af2]

From what I have seen the 2 VP KB pistons are a "D" shape.

[Alan Roehrich]

On this topic... Does anyone make a 12cc reverse dome piston for a 350 besides KB? Seems like most -12cc 350 pistons are full dish.

AutoTec has several between 11.0cc and 13.0cc for 3.48" stroke with 5.7" and 6.0" rods, and 3.5" stroke with 6.125" rods. They have std, 0.020", 0.030", 0.040", and 0.060" over sizes, and the 6.0" rod and 6.125" rod pistons also come in 0.035" over size.Those are 4032 alloy forged pistons, with 1.5mm, 1.5mm, 3.0mm rings, 0.927" x 2.70" x 0.150" pins (130 grams), with round wire locks.

AutoTec sells only directly to engine builders, they do not sell to catalog stores or warehouses. The guy who founded JE owns AutoTec, I met them at the PRI Show and got set up as a dealer.

[jonsjunque]

Can a machinist do a job on flat top or even domed forged pistons and make his own dished pistons?

Are domed pistons hollow under the dome above the piston pin boss? i.e., not enough material left after removal for dish?

A set of dished pistons/ forged are $600-800!

john

[loudandproud]

A set of dished pistons/ forged are $600-800!

john

Pay to play?

[Barry_R]

Devil's advocate here

At the OE level it would not cost anything more to do a "D" dish than it does for a round one.
Why is it that virtually all of them frequently go to a round/spherical dish these days?

[Keith Morganstein]

Can a machinist do a job on flat top or even domed forged pistons and make his own dished pistons?

Are domed pistons hollow under the dome above the piston pin boss? i.e., not enough material left after removal for dish?

A set of dished pistons/ forged are $600-800!

john

The KB / Icon forged pistons are more affordable (and a good piston for many applications).

[DCal]

Devil's advocate here

At the OE level it would not cost anything more to do a "D" dish than it does for a round one.
Why is it that virtually all of them frequently go to a round/spherical dish these days?

Barry, I realize you said OE but unless the d-dish is forged or cast into the piston it is a lot more expense. For instance, we have 7 different double-radiused tools depending on dish requirements. That's two machines and a spare in the toolroom for a total of 21 tools. plenty spendy in my book.
We get a fair amount of spherical dish jobs and they require modeling time-more expense. So I will not try to talk anybody out of a round dish on a lathe.
Nice seeing you at PRI btw

[Alan Roehrich]

Can a machinist do a job on flat top or even domed forged pistons and make his own dished pistons?

Are domed pistons hollow under the dome above the piston pin boss? i.e., not enough material left after removal for dish?

A set of dished pistons/ forged are $600-800!

john

No, they do not cost nearly that much.

Send me an email or a private message.