What is Quench

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Wyrmrider

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good question Richard
actually several related issues
First is quench as in quench the fire
Which is moving two cold surfaces (the piston and head) so close together that fire, detonation is not supported
Here the amount of fuel mixture is also made so small that there is not much to burn
David Vizard recommends .030 for a tight piston/ steel rod motor
I've gone lower than that on smaller bore motors

The second phenomena is "squish"
where the gas between the piston and head is squirted out into the combustion chamber as the piston come up to TDC
Usually this just promotes turbulence that gives better burn and allows somewhat less timing lead
but it can be directed for swirl or tumble if you want to get sophisticated
You can have too much of a good thing and blow out your fire
we had to reduce the squish pad on a blown alcohol motor
The challenge on open Chamber Mopars is the part of the chamber away from the spark plug
how to get it to quench
Speed-O-Motive and TMS Propane Performance welded up the chambers until we got KB to make the relatively inexpensive KB pistons (I also used custom forged pistons Nick Arias understood the problem first)
Note the two quench pads on the new Hemi from
Maximizing Cylinder Head Compression Ratios for More Power - Part 12
see also The Power Squeeze
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Google was my friend on this one...
While the terms “quench” and “squish” are often used interchangeably by many manufacturers, quench and squish are not the same thing, nor are they produced by the same set of conditions. The Society of Automotive Engineers (SAE) has defined squish as the gases trapped between the piston dome and head that are ejected across the combustion chamber at high speed by the near-collision of the piston dome and head, causing turbulence and mixture homogenization. For our purposes, if the squish area is too close, there is a pumping loss and if the area is too far apart there will be lower squish velocity and less turbulence.

Quench on the other hand, is the ability to lower temperature of the end gases trapped between the piston dome and head by conduction. This prevents a second flame front from igniting the air/fuel mix prematurely. Members of the SAE acknowledge that for motors with 3.5” to 4.5” cylinder bores, a quench distance of 0.035” to 0.040” work well and result in near zero clearance due to thermal expansion, rod stretch and piston rock-over.
 
good on ya Gary
Vizard also says .100 to .125 is the worst
what is a stock Mopar open chamber...
and the BBM spark plug location (except 361-413 Trucks and Motorhomes )
is THE WORST
 
Good posts fellas.

Running a distance of .030 or less will require good parts as old or sub par parts will stretch a bit and smack a piston into the head. So! Novice builders beware! Don’t go hay wire on super close clearances!
 
My dilemma was that I was running the stock magnum piston with a 5cc dish and EQ closed chamber head.
I decked the block to bring the compression up and used a .028 gasket which left me with around .038 between the piston edge and head but the dish area was considerably more ( dont recall exact depth of dish) so I wonder how that effeects my squish ?
 
you still have some on the back side of the chamber where it is needed most
that shape is much better than a round dish and a round dish is better than nothing even if it's only a few hundred thou
much better than an LA
I'm having the same deli ma with my future magnum rebuild

and you do not want tight on large bore short skirt hard large clearance forged pistons where piston rock is a given
 
rumblefish360 said:
Good posts fellas.

Running a distance of .030 or less will require good parts as old or sub par parts will stretch a bit and smack a piston into the head. So! Novice builders beware! Don’t go hay wire on super close clearances!
Click to expand...
Agreed 1000%. The local circle track guys here go down to .025" and that is with detailed measurements. I'd keep typical builds up at .035" and not worry if it got up to .045". For a long term street motor, wear on bearings and pistons (with more consequent piston rock) will allow the gap to close up over the very long term.

Garry in AZ said:
While the terms “quench” and “squish” are often used interchangeably .....
Click to expand...
Raising hand... guilty as charged!

So am I the only one who remembers the TRW 'quench dome' pistons that were made for certain open chamber heads in the 70's? Probably not made for Mopars, I am now thinking.

mbaird said:
My dilemma was that I was running the stock magnum piston with a 5cc dish and EQ closed chamber head.
I decked the block to bring the compression up and used a .028 gasket which left me with around .038 between the piston edge and head but the dish area was considerably more ( dont recall exact depth of dish) so I wonder how that effeects my squish ?
Click to expand...
Good question.. I have always assumed that if you get around 1/2" or more of squish width, you are good, but that is just an assumption based on nothing but my imagination... Don't you get some from both edges?
 
I got started on the old TRW "TURBO" pistons for the SBC with the D shaped cup
Milled D Cups in the 6 pack pistons to same shape with the closed chamber heads
On the Quench domes- were they not some of the ones that shrouded the spark plugs on BBC, Cleveland etc
I remember cutting fire slots on some but can't verify the name
also lots of those back then did not have the deck high enough requiring more than usual bloc decking
Bitched at KB about this at first
 
The recent 360ci I put together has 0.024-0.029" quench height with '302' heads.
11,3:1 cr, 208-210 psi cranking compression. XE256 CompCams.
Daily driven engine. No ping (LPG).
Won't rev over 5k.
 
Wyrmrider said:
On the Quench domes- were they not some of the ones that shrouded the spark plugs on BBC, Cleveland etc
Click to expand...
Yes, I know first hand for the 351C quench domes. Those ones I had (still have) had fire slots cast in; you know how that works: it became a 'feature'. Boy, I am glad someone remembers these! I was getting paranoid LOL
 
quench is when I press on the gas commin outta my butt and make it a lot louder than it could have been.

Use the search feature. It's all been discussed before. Here's a quick explanation. Quench is squish, but with direction. Simplest explanation you'll ever see.
 
Why would we need to use search if there's no question here?
It's an informative topic.

The propane fuel system is rated to about 300-some hp and the cam isn't a high revver.
I've had it up to around 4300rpm on the street on occassion, but 5K with this setup would be a stretch.
 
BigBlockMopar said:
Why would we need to use search if there's no question here?
It's an informative topic.

The propane fuel system is rated to about 300-some hp and the cam isn't a high revver.
I've had it up to around 4300rpm on the street on occassion, but 5K with this setup would be a stretch.
Click to expand...

Because my whole post was a funny. lighten up Francis.
 
RustyRatRod said:
quench is when I press on the gas commin outta my butt and make it a lot louder than it could have been.

Use the search feature. It's all been discussed before. Here's a quick explanation. Quench is squish, but with direction. Simplest explanation you'll ever see.
Click to expand...
Squish is when Rusty presses too hard and it becomes solid
 
Building for quench takes a lot of detailed measuring and machining. In all cases there's value to building for it. But it
s not always enough value to make it worthwhile. Building for it with any open chamber Mopar head is just that: a cost-prohibitive waste of effort.
 
not cost prohibitive if you are buying pistons anyway
actually building an open chamber mopar is a waste of time- high rpm race only where you have to and can use race gas excepted
 
moper said:
Building for quench takes a lot of detailed measuring and machining. In all cases there's value to building for it. But it
s not always enough value to make it worthwhile. Building for it with any open chamber Mopar head is just that: a cost-prohibitive waste of effort.
Click to expand...


I agree. Ain't no way I'm going to believe once you get to ~.050ish the rest is just picking the poop out of the fly pepper.

Guys get all whacked out about quench and then use valve notches that are too big, rings that are too thick and everything else.

If I'm at .050 quench and have the compression I want I leave it. If everything else is correct it is no more prone to detonate than anything else.

I've been doing this **** since 1980 and even with the piston .080-.100 down the hole I couldn't get them to detonate if you have the correct plug, a decent timing curve and a tune up in the carb that wasn't dumb as a bowl of soup.
 
RustyRatRod said:
quench is when I press on the gas commin outta my butt and make it a lot louder than it could have been.

RRR don't you mean queef ! LOL

Use the search feature. It's all been discussed before. Here's a quick explanation. Quench is squish, but with direction. Simplest explanation you'll ever see.
Click to expand...
 
I feel responsible for starting this mess but it's a good conversation. After reading through this thread I still don't know whether I could explain "quench" but I tend to think along the lines of common sense and not about all those formulas and mathematics. I think a closed chamber is pretty efficient especially as long as the piston isn't a foot below the deck at tdc. Keep the compression reasonable (9-9.5/1) and rock. When I had my heads done at Radar's shop, Woody polished the chambers, port marched and opened the ports and shaved them to minimum cc according to the book specs. (63cc if I remember correctly) I ended up with 9.68....static ratio and have no issues with detonation. I liked what he did and it works.
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Quench and squish is better explained in terms of two strokes, except it's not exactly the same. You change the width of the squish band on a two stoke and it affects power. I've seen guys fault mill a 2T head, up the compression and lose power. The squish band was too narrow and it no longer matched the pipe and port work.

Quench in a 4 stroke isn't nearly as critical. In fact, the testing we did only showed enough power gain that you could say the power came from the raise in compression.

That's why I don't get worked up over it. Especially with Chrysler open chamber heads. They are not nearly as bad as most people think and are miles and miles ahead of the junk **** chambers Chevrolet used on their stuff from the same era.
 
My take on it is ether build for it or don’t worry about it. YR is right about it when he said everything else is in the state of tune. And everything needs to be tuned not just the carb.

It is easier to build a zero deck flat top piston (+ or - in conjunction) with closed chambered heads and set the distance up with the gasket. (In conjunction with the pistons deck height) to achieve what your looking for.

This is what I have been doing the last few rounds. The current crop of closed chambered aluminum heads makes this almost to easy not to do. IF anything, it is getting harder to find a piston (forged or not) for low compression with the closed chambered heads for small cams and super charging efforts.

The effects of a good quench engine are good and best used in a nice high performance engine ready to rock and roll. Otherwise, it isn’t all that when your not taking advantage of it.

Again, ether build it with quench or don’t worry about it.
 
A couple years ago I built a 500 inch 440, it has BM aluminum rods ross flat top that came out of the deck .010 and closed chamber aluminum heads. All the parts cme out of a new build my friend bought, everything was set up wrong and the block was junk so we got a block rings bearings and .080 Cometic SS head gaskets, broke it in and he put it in a 67 notch, it ended up with 11.1 cr and runs on pump gas and it's a hand full on the street, last week he broke his custom 727 so waiting for him to pull it to see what happened.
 
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