Ok guys I posted this in LS1 tech but have goten 0 responses I am getting ready to build a forged LS2 for a TT turbo application. So heres the dilema quench is very important in these engines, given the choice to build the same compression ratio using either a full dish or a reverse dome which is better and why.

My thoughts are a reverse dome will have better off boost driveabilty, since the burn should be more complete with a optimum quench area. Under full boost I would think the either will perform just fine and the full dish may have advantage in strength but am uncertain. I have heard from various engine builders that say it does not make a difference Thoughts anyone??

Les

 

Blue00rdstr had a set of full dish Mahle's and blew it up almost immediately. Myself, I have Ross reverse dome and haven't had any issues in 30K--primarily road track and hard canyons. Both these motors are 346's on 91 pump FWIW. Personally, I would lean towards the reversed dome for better quench and to minimize detonation especially under boost (but since I didn't stay at a Holiday Inn last nite I may not be completely up to date ).

 

Thanks I am leaning very heavily toward the reverse dome as well but just would like as much info as possible before proceeding.

Les

 

my forged short block built for boost made by wheel to wheel is a dished piston setup

 

I had a set of Mahle, very similar to his, and mine ran perfectly....

I highly doubt his pistons were to blame.


Maybe this is a stupid question....can you explain the difference between a reverse dome, and a dished piston ?

IMO a reverse dome, is a dish.

Or are you referring to a dish, as a specific shape cut into the piston ? as opposed to a simple...well dish shape ?

 

There are a number of articles which talk about what quench does. I would search for quench and draw your own conclusions. However all the top brand pistons (JE, Diamond, etc.) are reverse dome, and you would do well sticking to what tuners and others on the forum have learned.

Reverse dome pistons leave the quench area intact, which was designed in to help prevent detonation; it creates turbulence in the combustion chamber to prevent lean areas and hot spots. When the piston nears the top of the stroke at high speed, it goes from 3.622" to within 0.40" of the cylinder head quench surface. Now take that 'clap' area away (use a dish) and you have one less thing which prevents detonation. The other reason for the quench area is to cool the area furthest from the spark plug. The burn mix starts where it's sparked, and a second flame front can't start in the quench area.

Dish pistons also remove reinforcing material from the valve notch area; take a look at failed LSx pistons and this is where the failures start.

Full dish was not the only contributor to the early failure I experienced. There are were two other factors; (1) I requested thermal coated pistons and the vendor assured me they were coated (didn't mention they were simply graphite coated), (2) I requested 'stronger than the previous Diamond pistons' and they also referred to W2W use of Mahle, however Mahle alloy is silicon/aluminum similar to stock brittle pistons, and not the zero silicon alloy used in other forged pistons. Mahle alloy is more prone to piston land breakage than the more durable alloy used by JE or Diamond or others.

 

Mahle makes some great turbo pistons. When W2W built my motor they called JE and Mahle to see who could get me pistons quicker. JE was able to deliver quicker at that time because Mahle was backlogged because of one of the race series they sponsor.

I wouldn't be afriad of running either brand.

 

As I say, I ran Mahles see below, for almost a year. This was on a 346, stg 1 heads, 230/236 cam, and of course my YSi at circa 16psi at 6000rpm. This was on 9.1:1 CR, pump fuel only.
The car ran perfectly at all times, and performed ok.





Im sure Im not the only person to have run them with success either. I would find it extremely difficult to apportion the blame of detonation to a piston. Even when I stripped the engine down to go 382, the Mahles were in excellent condition.

From my own direct experience, LSx's really dont seem that badly prone to detonation in the first place.
The reason stock pistons fail, is down to detonation. They arent the cause of it though. Some designs and materials may be a little more resilient when faced with detonation, but at the end of the day, it can kill any piston.

If you are detonation free, within reason, there is little reason why any half decent piston shouldnt give a reasonable service life.


I also ask again, what do you guys see as a "dish" and a "reverse dome"

To me, a reverse dome and a dish sound like exactly the same thing.

These are my current pistons, custom made by Ross. I didnt specify dish shape, this is just what they supplied me with.



Ive had no trouble with detonation on either setup.

 

Dished would be the picture at the top. Dish, is as in a full diameter pocket.
Reversed Dome, would be like the bottom pic, is like a domed piston, but reveresed into a pocket. It will match the combustion chambers opened area. This will give a squish as a flat top piston.

 

Thanks guys I think I am going with the reverse dome I want to keep the quench area intact.

Les