Quench Pads ?

[SkylineUSA]

I ran into this term today when I was reading up on detonation. What are quench pads?

I know about quench, opt .025-.035. Any more than that you get det probs, any closer than that, your pistons try to shake hands with your heads.

[MustangRoadRacer]

It's an urban legend.
like full service gas stations or the RIAA.

[SkylineUSA]

That's just it, it was used in a lot of different engine articles. Not just the Ford ones either.

[MustangRoadRacer]

I was kidding.
I found this in an article, It should help.

"Quench, or squish area is typically the flat area on the top of the piston that's almost level with the top of the block deck. It must have a corresponding flat area on the deck surface of the head to qualify as quench.
If you look at a combustion chamber, you will usually see these flat areas, and they will have the volume of the actual combustion chamber between them. When the piston is compressing the mixture, as the piston nears the head, the flat areas on the head and piston come together and force the mixture from those areas to "squish" into the chamber, where the spark plug and burning mixture reside, so you achieve a more complete burn.
The quench area also runs cooler than the rest of the chamber / piston. These lower temperatures are where the "quench" comes from.
When properly designed, the quench areas can have a tremendous effect on the quality of combustion, and allow higher compression ratios, and due to this they are considered "artificial octane" by scientific types.
Bottom line is "properly designed, quench is good".

[SkylineUSA]

Yep,

Got it. Quench is good Any higher than .035 its prone to detonation.

[SkylineUSA]

Correction, higher than .045 is prone.

[Mendari]

Originally Posted by SkylineUSA

Correction, higher than .045 is prone.

I'm a little retarded, is 0.045 the distance from the piston to the head at Top Dead Center?
Also, I've seen pistons with tiny pits around the circumerence of the piston head. What are they for?

[90Stangjc]

what do you mean "the piston with the tiny pits"? I think your talking about so the valves wont hit the pistons, maybe?

[SkylineUSA]

check out the picture of the combustion chamber on these heads:

http://cgi.ebay.com/ebaymotors/ws/e...item=2455255904

If you will notice the combustion chamber is not perfectly round (all though the pistons are). I believe the quench pads would be the area of the head that is an extension of the mounting surface that protrudes over the piston. It is that area that comes very close to the piston and sends the shockwave through the rest of the combustion chamber and helps fight detonation.

THe limits of how close you can push the piston to the head deck is a multitude of factors. Quality of rod. Typical Oliver will streatch .004" at RPM. A high end aluminim can streatch as much as .020 depending on length.

Amount of and type of material in piston crown. Hyperutectic pistons will expand about .003. TRW forged domes can have as much as .010 expansion (thick heavy pistons)

Then there is the amount of rock to consider, them TRW's require .006 to .008 skirt clearance. A lighter better piston will assmeble with much less, and have less room to rock at TDC and change the clearance measurement.

LASTLY quench affect is not a static number. The slower the engine the tighter the squeeze has to be, the higher the RPM the greater the shock wave above the piston, the less tight the assembly needs to be.

For engines in the 6000 to 8000 RPM quench assembly at .035 is effective. Slower than 6000 RPM you should look at pushing it a little tighter....

If its a high winder then you can leave a large gap and still have effective quench.

And all that said.... I have a friends that has a 9000 RPM engine, and its assembled with a .026" quench.

[351wStang]

Thats interesting, but now that I think about it I completely understand. Thanks for the info Skyline. I love learning new things, especially when they are in-depth motor things . I had never even heard of quench before now, and I thought i was fairly knowledgable about motors. I feel like I picked the brain of a genius after reading all that lol. It was really interesting.

[SkylineUSA]

[351wStang]

Any other interesting topics of the day?? LoL.

[SkylineUSA]

We could into timing events? Lift and duration are so over rated

[351wStang]

Ooo.. Timing. As in the effects of advanced timeing? I bet hot spots can get pretty nasty with quench. But, ya i'd like to learn more about predetonation. And yes lift and duration are very over-rated. People think they know how to get alotta power out of a car and make it streetable if they go low duration and high lift. Theres more to a cam then how much you can make your valves move and keep good vacumm at the same time. Also how about lobe seperation and scavenging? Thats something I have always wondered about. Lets see where we can go with this?