apex2112

How much if any of the benefit of ideal .035/.045 quench height is lost with dished pistons vs flat top pistons?

WE TODD DID

iTrader: (2)

You will still have quench with a dish piston.

Che70velle

iTrader: (6)

To optimize the effects of setting up an ideal quench distance, a flat top piston and wedge shaped chamber (not a hemi) is always going to work the best. A flattop piston will push the combustion wave (due to effects of quench) toward the center of the chamber and spark plug, more so than a dished piston. Quench AREA is a major contributor in efficiency of a well setup chamber design. Flat tops have more quench area than dished pistons.
The overall purpose of setting up an ideal quench is having enough quench area to cause turbulence in the chamber. Turbulence in the intake runner or port is always a bad thing, but chamber turbulence is uber important in efficiency and allowing you to make the most potential power with the least amount of timing.
A hemi engine has vey little to no quench area, but makes up for it with a better flowing port layout and overall better flowing design (more potential to make power) than a wedge setup...at the cost of needing more overall ignition timing.

G Atsma

I learned here! I have a Tahoe with LM7, and wondered, come overhaul time (maybe top end only) how much difference it would make using a .040 head gasket and milling about .020 which SHOULD net about a 10:1 CR. I think this should be able to use 87 regular gas, as the Gen IV 5.3's are mostly around 10:1 and use regular. Is this on the right track?

psicko

I don't think that's 100% true. More quench area turns into more crevice volume where air/fuel mix isn't getting burned. Having too much is as bad or worse than too little. A dish is better than a flat top in that respect, especially with small chambers.

psicko

I was just with a buddy of mine earlier this month in his Tahoe with the 6.2L as he was datalogging on different fuels. Bone stock engine and tune and it was seeing KR on 87 during cruising. He says it went away with 89 though.

omc8

iTrader: (7)

For those of you that feel you need mid grade 89 . This is what I do , I alternate one tank of regular , then premium . In my state premium is still 93 .By doing this I get a higher average octane level at a cheaper total cost. In my area midgrade is 30 cents more than regular. But 93 is only 20 cents more than 89 . Premium 93 has considerably more detergents also .The 50/50 mix is 90 run it down to 1/3 tank premium and your still at 89

Che70velle

iTrader: (6)

Crevice volume refers to the area on top of the rings. Some of the most powerful N/A engines ever built have ridiculously small chambers (35 to 40 cc’s) and flat top pistons. Can you elaborate more on your reply please?