How much Quench is enough?

[Anonymous]

Hi everyone,

I was wondering, is there a percentage of the total bore area that the Quench area should cover?

I have been looking at a lot of pistons and heads and some have a very small quench pad. Others have a quench area that covers about a third of the bore. Still some just have a quench ring.
I looked at Richard Fuelings site and his quench areas are huge, covering half of the bore area.

Is this just simply a case of, The more the better?

John

 

[StrangeRanger]

On the Ricardo flathead Sir Harry used nearly the entire area of the piston as quench. the combustion chamber was located over the valves wth just enough of the piston top involved to begin motion. It was a VERY efficient flathead. My "best" guess is that your quench area is limited by your fuel. Increasing the quench area necessarily raises your CR unless you hog equivalent crunks of metal out of the chamber. That is going to limit how far yuo can push things.

 

[Anonymous]

[No message]

 

[Anonymous]

Here's a couple of pics off my website you can use,

1980 head:

1966 head:

If the pictures dont show up, heres the link to my page,

http://www.inlinepages.com/~inlinefever ... tions.html

1980 head is around 62 ccs, and the 1966 head is around 50 ccs. These are off the 200-250 ci engines

Later,

Doug

 

[Anonymous]

[No message]

 

[Anonymous]

So you would say that, with in practicle limits, the more quench the better?

Or is there a point where there is nothing to be gained by more quench area?

John

 

[CZLN6]

Howdy John and All:

I've been reluctant to weigh in on this one because there are so many variables, but, Yes, generally a higher ratio of quench to bore is better for promoting turbulance and enhancing combustion.

One of the most hurtful variables on our engines is the small diameter of the bore and its effect on valve size and shrouding. Some of the "experts" recommend valve clearance from the chamber walls equal to the valve lift. With stock valves of 1.69" and 1.38" and a performance cam with a lift of .400" would require a bore of 3.87". Ours starts at 3.68"

Another is trying to get a .030" to .040" deck clearance with modern composite replacement head gaskets. If deck clearance grows much beyond this range much of the good quench effect is lost anyway.

The round shaped dish in the piston is more hurtful than the shape of the combustion chamber. On one hand a dished piston makes more power then a flat-top or domed piston in a wedge shaped combustion chamber engine, all else being equal. But at the loss of quench ratio? It would be a ton better, for bore to quench ratio, if the shape of the dish mirrored the shape of the chamber. No such piston is available. YET!

Yes, a higher quench to bore ratio is better, but must be balance with other factors and variables.

Adios, David

 

[Lazy JW]

Here's a dumb question, but I just gotta ask; It has been mentioned in various threads that the thicker "modern" composite head gaskets make it difficult to get the quench area tight enough. What about setting up the deck height with the piston slightly ABOVE the block, maybe .010"-.020"? Obviously, we don't want the rings to get too close to the top, but I doubt that .020" would cause any trouble there. One thing that I can think of would be the sharp piston edge creating a hot spot. Has anyone done this on purpose? Thoughts?
Joe

 

[Anonymous]

An 0.040 gasket and a 0 deck is perfect. popping the piston just slightly out of the hole if you're running a thicker gasket is fine so long as the compression ring doesn't pop out once everything is up to normal operating temperatures.


-=Whittey=-

 

[Anonymous]

True, pop-up for quench (up to 7/16") has been used since before WW2.
Try to keep the top ring 1/16" down in the hole because the higher wall temperature will de-temper it and warp it.

 

[Anonymous]

"Some of the "experts"

To whom do you refer?

 

[CZLN6]

Howdy Panic and All:

Easy panic. This is 'sposed to be and informal forum. Smokey Yunick's book comes to mind- I'd have to look up references to be definitive.

It seems I read a similiar guidance in one of your tech papers. Could that be? They are very good and helpful. Thanks for the resource.

Adios, David

 

[Anonymous]

I've seen figures both above and below that; walls opposite well-functioning swirl ports can be closer without loss. My intention was to use a "safe" figure for V8 with large bore size (3.6"-4.3") , but of course it can't be universal. The Chrysler "poly" motor (318, etc.) is especially frustrating because the intake valves are very close to the bore edge, but are still too small - sound familiar? On these relieving the wall is easy, because there's only so much you can remove!
Jerry Branch did some nice work on quench on the Harley Evo motor about 20 years ago.
Turns out that there is a very delicate balance where on one side the exhaust flow is restricted and power drops, on the other the motor becomes very octane/temp/spark advance sensitive. Leave it closed: power falls. Cut it back: knocks. Distance was critical to less than .060" (3.5" bore, 4.25" stroke).

 

[Anonymous]

Hi. been lurking for a while, and for some reason the board recently asked (forced) me to sign up. no loss.

Anyways, about quench area, Jim Feuling designed a cylinder head/combustion chamber that used up to 55% of the bore area as quench, with a tiny little 'peanut' shaped combustion chamber, smaller and very efficient valves, and a central spark plug. these things would handle 12.5:1 on 87 octane.
and just bolting them on to a BBC or 460 would give 100lb/ft more torque.
so, basically, more is better until you get so small that you have no place to put the valves.

Ern

 

[Anonymous]

I'd bet the flathead Ford boys would side with Ernie, here.

 

[Anonymous]

thanks. now if I could just get one in cross-flow form for the 4.9...'
and a turbo. but i think he may have sold the licensing to Ford for his patents. dammit!@#

 

[Anonymous]

Whittey and I debated this topic briefly in another thread last fall while I was deployed, and I am happy to say that having returned home and reread those sections of Ricardo, that I was completely bass-ackwards in my recollection.

It turns out that even in very slow turning, very low compression engines, the use of effective quench can make as much as 20% difference in the CR an engine can stand before detonation sets in. That's an enormous variance, and goes a long ways towards explaining how Feuling could get such performance improvements out of otherwise "modern" heads for the 454 and 460. It would be most interesting to see before and after results of adding quench to (especially) a later lo-po turd-head engine like the 1980 head Doug shows above.

 

[Anonymous]

Whittey and I debated this topic briefly in another thread last fall while I was deployed, and I am happy to say that having returned home and reread those sections of Ricardo, that I was completely bass-ackwards in my recollection.

That's what I like to hear


-=Whittey=-