i was discussing quench with a fellow on another board and he made the following statement, i was wondering if it is true or not...he was trying to find a thick gasket to knock down his CR a tad and i was telling him about keeping an eye on his quench.

and he had this to say...

"I would normally worry about that, but my custom JE pistons have a full face -30cc dish, and the TFS-R heads rotate the valves out over the middle of the bore effectively doing away with a "quench" pad or chamber. Plus with a forced induction motor the air/fuel charge will be forced into the chamber faster and will help keep the fuel atomized, which is what "quench" promotes. I feel it will be fine. "

 

If the pistons are already dished all the way across I don't think he had much quench going on to begin with. Probably will work just fine.

 

The idea of quench is to get the deck surface of the head that is over the chamber to not have air/fuel mixture near it. Even a dished piston that big still should have good quench. Basically quench is used to keep the air/fuel charge closer to the plug and away from hot spots in the motor to reduce detonation and increase power. It's important in any type of motor.

Bret

 

this is what he first said that got my attention..."I still have to buy a set of .078 cometics to get my compression down below 9:1"

his block isnt zero decked either. i was just thinking that it is ALOT of room between the two!

 

How's a dished piston ever going to produce the desired quench results, regardless of head gasket? You hear people spec'ing everything out to get around .040-.045 so that it does any good to begin with. A heavily dished blower piston is going to have WAY more room than that under the head even if the head gasket was 0.0000" thick.

 

so, you wouldnt even try to get the top of the piston (not the dish) close to the head?

 

This just sounds to me like the standard blower addage, just add more boost for more power. (The reason NA motors appeal to me because HP is a function of combination not how fast I can turn the blower, but that's just me.)

Obviously the first thing you think is I need less compression for more boost, but detonation is always going to relate to any combustion process.

Here is a post I googled that has the same question going on at the same time as yours......

My personal opinion on why it would be done on a OEM motor is more to do with cost and the fact that the motor is not pressing the limits of detonation and boost levels on a certain octane level.

Bret

 

I have and always will use 'd' shaped dished pistons in my own engines (to keep the effect of squish/quench), rather than a salad bowl dish.

I would also kick my own *** before installing 'down in the hole' pistons.

Bret, alot of forced induction guys have the 'just add more boost' mentality, but there are those of us who are after high efficiency too

 

INTMD8- I also run d-dish pistons on my blower motor. Same reason you said. I LIKE efficiency, if there's efficiency to be had. You can bet I spent a little time making sure I had .045" clearance between the flat part of my d-dish pistons and the head.

The reason I don't lose sleep suggesting otherwise in this case is as you describe- not much point when you have "salad bowl dish" pistons. Like moving the moon 20 feet further from the Earth. Not going to make much difference.

 

When I do a blower motor that's how I like to think of them too. It's still a system, and when you put down stupid numbers like yours obviously it's working well!

Bret

 

That 632 "Smith" talks about is insane.... twin 91mm turbos and making 1700hp at only 12psi? Wow I wonder if one of those would fit in a 95 camaro....

 

its a shame that link is only one page long...

i guess my main question is this part... "the TFS-R heads rotate the valves out over the middle of the bore effectively doing away with a "quench" pad or chamber. Plus with a forced induction motor the air/fuel charge will be forced into the chamber faster and will help keep the fuel atomized, which is what "quench" promotes"

are both of these statements true?

 

Obviously, somebody doesn't know what quench is or what it does or how to get it,Judging from the original post and what he had stated to him by someone else. I'm not sure if he is running a "HEMI" but not on a CHEVY.
If he was running a full circle dish he would still have a quinch area. But that would be a funny looking head with no quinch area or combustion pad,That thing got a"HEMI"
Quench is important in any engine if you want to meet that engines capability.
They run their best when the piston just ticks the head.

 

lol...so i guess ill tell him he doesnt know what he is talking about then!

 

Quench or squish is used to develop turbulence as the piston approaches TDC. The main benefit of this turbulence is not necessarily fuel atomization (which may have already been optimized by tumble), but rather gross mixing in the chamber which leads to a faster burn time. Better propagation of the flame kernel due to the turbulence means less timing advance required, less work required on the compression stroke, and more controllable and consistent combustion with less detonation taking place.

-brent