I ordered a set of Mahle -16cc dish tops for 6" rods to get the compression on my zero decked 383 around 11:1. Didn't know when I ordered them that they have a round shaped dish with just a 1/2" wide squish band around the perimeter of the piston top that comes up close to the head. Wondering if anyone has any experience with this configuration compared to a standard type dome with a squish surface that matches that of the head (and a dish that matches the combustion chamber).
Just wondering if the smaller squish area might affect the compression tolerance?

Thanks, Michael

 

The "D" shaped dish is pretty standard. With 11:1 and a mild cam you should have no worries about detonation as long as the tune is good and you keep your cooling system maintained.

 

Don't know if I made it clear, the dish is not D shaped but is round. It covers the entire top of the piston except for a roughly 1/2" wide band around the outside.

Thanks, Michael

 

sounds like they sent you blower pistons. most high compression pistons are either flat or slightly cut in. if it's dished all the way aroudn it's likely a low compression piston...just means you need to add a power adder

 

Gotcha - Have not used dished Mahles yet for a SBC, but have used them for 4.6L 4V fords and they did have the round dish which is standard for those motors because of the chamber shape.

That is the way nascar pistons are dished....so I would assume that they have done the R&D and found that it will promote a better burn and more even distribution of the air/fuel...hense a good thing.

 

Thanks for the info. The NASCAR reference makes me feel a lot more comfortable and gives me a idea of where to research it further.

Later, Michael

 

Not a good thing unless ya got 30-35CC secret shape chambers in the heads like I have been told they were running.

 

Hey 1racerdude, is that speculation or would you happen to have any useful info about this dish configuration and compression ratio on pump gas?

Thanks, Michael

 

Figure it out.
Ya need less than 9.0-1 DCR.With no quench ya need less than that. Get a reverse dome piston like ya should have done in the first place. Flat tops will be too much with your tiny cam.

How's that for usefull.

 

The "sStandard" dish for production 2V heads is a "D" shape. You do see the circular dish used on 4V heads. Typical SBC heads are designed to have a "squish" area where the flat part of the piston crown and the adjoining flat area of the head are in close proximity. How did you decide on that particular piston?

Rich

 

I wouldn't worry about the shape, it's actually a good design.

Bret

 

My Probe SRS pistons have a round -12.8cc dish.

Dean

 

I used the Mahle -26cc pistons and they are great so far. I have absolutely NO knock retard except for on shifts, just like it's supposed to be. I even made the knock retard MORE agressive than stock - the exact opposite of what everybody else does! The plugs look great. There's NO blowby, either. I am running about 10 psi non-intercooled boost. I have the meth-water injection, but did some tuning w/o it for a base tune, and no problems yet. I am running pretty cold plugs, too. This was a home-built engine, and I am really happy with how it runs.

About 1300 miles on it so far. We'll see how they hold up in the future. I know there are tougher blower pistons out of tougher material, but these seem great for a mild blower build thast sees a lot of street duty. No piston slap - good quality rings also. We'll see if I can break them at the track this fall...

 

Out of curiosity, what CC are your combustion chambers?

 

Haven't cc'd the chambers, I'll be doing that and equalizing them tomorrow or Monday. They were milled about .005" and have had a very small amount of metal removed, should be pretty close to the stock 54 cc's.