Quench Vs Piston To Head Clearance

[805moparkid]

so im stumbling on these two. i under stand quench is best tighter than .065" but ive read people going south of .030. then i read .055" is minimum piston to head clearance to allow for any rod stretch.

any help? this is such a newbie question lol :newb:

 

[CPMotorworks]

so im stumbling on these two. i under stand quench is best tighter than .065" but ive read people going south of .030. then i read .055" is minimum piston to head clearance to allow for any rod stretch.

any help? this is such a newbie question lol :newb:

It will vary with the application, bore size, stroke, piston rock, rod material, and RPM. Average Street/race engine with steel rods 4" bore .035-.050" is safe and effective.
Aluminum rods .060"+.

 

[805moparkid]

It will vary with the application, bore size, stroke, piston rock, rod material, and RPM. Average Street/race engine with steel rods 4" bore .035-.050" is safe and effective.
Aluminum rods .060"+.

quench or piston to head clearance?

 

[Cudafever]

give your definition of piston to head.
And quench.

Right or wrong, it will help us answer your question better.

 

[805moparkid]

give your definition of piston to head.
And quench.

Right or wrong, it will help us answer your question better.

uh well, piston to head clearance is the closest area of the head and piston in relation to each other

i dont know how to describe quench other than its goal is to contain the mixture for a better and more efficient burn

 

[rumblefish360]

First, let's get distance set up. You start to loose the effect of quench when it is greater than .055, or as I'm told. Getting it tighter is a good thing. It does how ever depend on the rod material. A steel forged rod is pretty standard and can get to .035 easy enough. But an aluminum rod will stretch a little more. Take not of the rod manufactures suggested limits.

Now you seem to have Piston to Head clearance OK.

Quench. Imagine a flat top piston set at zero deck height. Now, picture a Edelbrock head. You know the chamber is small and some of the flat area sits over the cylinder bore.
When the piston comes up close to the head, this becomes the quenched area. (High sqush area) this small area pushes the air and fuel out and into the more open area of the head.

This last instant of piston travel shoving the air and fuel out help create that last instant rumbling of the fuel, it also acts like a false compression increase. It's because of that last instant where the quenched area is so small it is like a quick turbulent fuel increasing the pressure in the cylinder.

A typical gasket used is a .039 Fel-Pro. This is a safe amount to run. I've gone tighter where the quenched area doesn't get carbonized. This is better.

 

[Cudafever]

Rob summed it up well.

If it is a open chamber head,( like early 340/360 heads) you don't have a quench possibility and is why the original 340s got away with a piston, that pop up above the deck.

Closed chamber heads are Quench potential heads.

A quench head will resist detonation much better then a standard head. Given the same compression.

 

[kennygene]

Subscribed and learning...

 

[rnaz]

The Magnum R/T heads are a good quench head with a flat top piston set at zero deck. That's what I'm running in my stroker right now.

 

[805moparkid]

ok im just give some variables and you guys can fill in the blank.

if you have an open chambered head but the piston has a step to act like a closed chambered head wouldn't that give you quench?

Rumble
First, let's get distance set up. You start to loose the effect of quench when it is greater than .055, or as I'm told.

what area are you measuring the quench from?


Getting it tighter is a good thing. It does how ever depend on the rod material. A steel forged rod is pretty standard and can get to .035 easy enough.

.035" meaning .035" of head gasket or .035" to the largest volume area of the head? or??

But an aluminum rod will stretch a little more. Take note of the rod manufactures suggested limits.

yea understood the aluminum will stretch more.


this seems to me to be two terms that are either directly related or are the same thing. Rumble whats a minimum piston to head clearance (flat top with flat closed chamber head)??

 

[RustyRatRod]

In a quench engine, piston to head clearance is the quench distance. According to the United Engine web site, for an engine not using aluminum rods, .035" is optimal quench distance. The easiest way, imo to set up quench is to zero deck the block to a given piston and use the head gasket to determine quench distance. That's how I have my 383 machined. I determined what my deck height needed to be for zero, got my machine shop to mill it there. now when I assemble it, all I need to do is choose a head gasket with the appropriate compressed thickness and go. Even though mine is a domed piston engine, it still has a quench pad and as long as I use a closed chamber head, I will have a quench dome engine. Though some say a quench dome engine is not as effective as a flat top quench, I have spoken with United Engine in depth about it and their dome design actually promotes quench. I didn't know that was possible, but if you look at the dome on the KB400, it kinda gives itself away.

 

[RustyRatRod]

ok im just give some variables and you guys can fill in the blank.

if you have an open chambered head but the piston has a step to act like a closed chambered head wouldn't that give you quench?

Yes. But it is much more difficult to set quench up in that manor. Since the combustion chambers are rough cast and not finished machined, like the quench pad on a closed chamber head, it is much more difficult to get the quench distances equal cylinder to cylinder.

Rumble
First, let's get distance set up. You start to loose the effect of quench when it is greater than .055, or as I'm told.

what area are you measuring the quench from?

Quench is measured from the area opposite the dome or valve reliefs. The "flat" part of the piston to the quench pad of the head. An open chamber head is not considered a quench head since it has no quench pad. Read my response above.


Getting it tighter is a good thing. It does how ever depend on the rod material. A steel forged rod is pretty standard and can get to .035 easy enough.

.035" meaning .035" of head gasket or .035" to the largest volume area of the head? or??

Meaning .035" quench distance. From the flat part of the piston to the quench pad of the head. Yes, quench dome pistons are made and they will turn an open chamber head into a quench head, but it is very difficult to get it right. Again, refer to my first response.

But an aluminum rod will stretch a little more. Take note of the rod manufactures suggested limits.

yea understood the aluminum will stretch more.


this seems to me to be two terms that are either directly related or are the same thing. Rumble whats a minimum piston to head clearance (flat top with flat closed chamber head)??

Again, .035" with iron or steel rods is about it. As I said, quench distance and piston to head distance are one in the same, whether it is a quench engine or not. Since even in a non quench domed piston engine, the flat part of the piston will hit the head before the dome will.

 

[805moparkid]

In a quench engine, piston to head clearance is the quench distance. According to the United Engine web site, for an engine not using aluminum rods, .035" is optimal quench distance. The easiest way, imo to set up quench is to zero deck the block to a given piston and use the head gasket to determine quench distance.

this assumes you have a chamber not like out slants correct? but would have to be like this?

That's how I have my 383 machined. I determined what my deck height needed to be for zero, got my machine shop to mill it there. now when I assemble it, all I need to do is choose a head gasket with the appropriate compressed thickness and go. Even though mine is a domed piston engine, it still has a quench pad and as long as I use a closed chamber head, I will have a quench dome engine. Though some say a quench dome engine is not as effective as a flat top quench, I have spoken with United Engine in depth about it and their dome design actually promotes quench. I didn't know that was possible, but if you look at the dome on the KB400, it kinda gives itself away.

well that makes sense as if you "filled" the open chamber portions of the chamber you could basically mock a closed chamber head.

so all in all quench=piston to head clearance though they have different reasons for each number depending on rod material and piston/head design.

 

[RustyRatRod]

Wherever the piston would contact the head FIRST if you pushed it up the cylinder into the head is quench distance, or piston to head distance, regardless of the type head you have. MAYBE the only exceptions would be pistons with grossly exaggerated domes that would hit the head before the flat opposite the dome. I think those situations are few and far between. They would not be able to have quench, period.

 

[805moparkid]

Wherever the piston would contact the head FIRST if you pushed it up the cylinder into the head is quench distance, or piston to head distance, regardless of the type head you have.

hmm ok. so if you had the head deck milled (clean up) then had each chamber (like that flat in a slant head) milled for a given depth. then you could have a step piston built to get some quench

 

[RustyRatRod]

hmm ok. so if you had the head deck milled (clean up) then had each chamber (like that flat in a slant head) milled for a given depth. then you could have a step piston built to get some quench

Sho nuff. But to me, it would be easier to run a zero decked flat top (like the KB239) and mill the head to a closed chamber. The slant heads have enough meat to do that, I believe. I believe you could even angle mill the head, to remove more material from the flat section of the chamber with no ill effects.

 

[FJRdoc]

I'm trying to learn as much as I can on this subject for my first engine build. My 1970 340 engine has the original open chambered cylinder heads. I intend to use them on my rebuild. I understand that because they are not closed chambered I won't have quench possibilities. What can I do with the stock heads to reduce potential detonation?

 

[805moparkid]

I'm trying to learn as much as I can on this subject for my first engine build. My 1970 340 engine has the original open chambered cylinder heads. I intend to use them on my rebuild. I understand that because they are not closed chambered I won't have quench possibilities. What can I do with the stock heads to reduce potential detonation?

im no smallblock guy but I think there is a step piston like rusty and and were talking about from KB. I know they have them for the 440's, we have them in my dad's motor. if I recall they called them D steps

 

[RustyRatRod]

I'm trying to learn as much as I can on this subject for my first engine build. My 1970 340 engine has the original open chambered cylinder heads. I intend to use them on my rebuild. I understand that because they are not closed chambered I won't have quench possibilities. What can I do with the stock heads to reduce potential detonation?

Limit your compression to about 9.2:1 and run a camshaft with a relatively late intake closing event.

 

[moper]

I think most of this has been coevered but in bits and peices. My own input...

The piston to head clearance is the mechanical distance between the piston top and the chamber bottom. For any engine build.When we talk about quench tight is best but like was said - a lot of variables go into what's "perfect" vs what may not work or what might hit.
The the proximity of the head and piston create the condition for what's called "squish". That's the forcing of the intake charge from the dead space of the chamber over to the valves and spark plug. That does some good stuff: it cools the surfaces of the head and piston, it re-suspends liquid fuel that may have come out of suspension during the intake cycle, it packs the area around the plug and exh valve where it will more readilly ignite, and if effectively lowers the volume of available space the expanding (ignited) gasses have which in turn puts more force on the piston and crank during the initial flame kernel/front development.
That first thing - the cooling affect - that's what "quench" really is. It's not the distance, it's to cooling. The tighter the "quench distance" (or piston to head) the more cooling there is and the more effective the detonation suppression. Obviously the larger the distance, the less cooling, the less mixing, and the less detonation resistance there is. Beyond about .045 or so there isn't much happening.

Getting into specifics of certain applications - An as-cast surface is far from smooth. Any roughness or texture adds volume that reduces the quench effect. Add in the additional volume of the radius of the cast chamber & the space built around the edges of the quench dome of the piston and you can see issues. With a rough open chambered surface and quench dome type piston there is a less defined direction of movement. There is more squishing, but it's more chaotic accross the entire bore width of the chamber and less centered on the direction we want.
Think of it like this - Assume we have a perfect 2'x'2 box. Drop a 1'x2' piece of plywood so one edge of the 1' width edge hits first and then it falls flat into the box (covering 1/2 the floor of the box). The air basically gets squeezed out from the edge that's on the ground, towards the edge that is falling. Now drop a 10"x23" log in there on one side of the box. There is some air that will follow that path and go towards the open 1/2. But a lot will just whoosh around the log too.

I build engines designed to maximize quench. I have built one using the Kb quench domes (a 440). It requires a tremendous amount of work to get any really strong quench effect vs a flat top/closed chamber design. The deepest chamber has to be found on each bank. they all have to be equalized to that depth either by hand or (preferably) by milling to get a flat surface perpendicular to the deck surface (BTW - some chambers are twisted in the castings too so one end of the same side's deeper than the other.) The block is decked to a known height. Pistons and rods are mocked up and each cylinder is checked because some varience in stroke and rod length is normal especially in factory parts. Then you decide on a gasket thickness, then remove the pistons and mill them to get every hole the same hieght so they have the same quench distance. It's blue printing taken to it's next level... and the effect even if you get it perfect is not as good as it would be with flat tops and closed chambers.

Getting it right is important, and there are huge benefits especially in the game of running real pump gasoline and making big power and long service life.

 

[jeffromopar]

wow good stuff guys . thanks

 

[4spdragtop]

Ok, yes reviving an old thread lol. But while doing research on quench for my 340 build, it looks like stock 340 X heads can't be used to measure quench?

 

[rumblefish360]

Why?

Quench is the distance between the piston and the head.

 

[4spdragtop]

With my 340 build i got to thinking about quench and did some reading.
Am I right that due to x heads being open chamber heads that quench is a non factor?
Piston sits .034 outta the hole, I'm thinking Felpro head gasket .038 compressed thick and quench area is 0.080" "deep"

Why?

Quench is the distance between the piston and the head.

 

[rumblefish360]

Am I right that due to x heads being open chamber heads that quench is a non factor?

How could it be a non factor unless there is none?

Piston sits .034 outta the hole, I'm thinking Felpro head gasket .038 compressed thick and quench area is 0.080" "deep"

Take some clay and soften it up in your hands to place on the piston top. Install the head gasket and cylinder head and tighten and torque to spec. Remove, measure the clay. Take this measurement against minimum piston to head distance spec.

Do you have pictures of the piston and it installed at top dead center? Is the head chamber stock? Has the head been milled?