Moparts
At what point is QUENCH not effective?
Posted By: Jjs72D
At what point is QUENCH not effective? - 06/28/13 09:56 AM
I have read many, many threads and posts but haven't seen this topic clearly defined.
Maybe it is a gray area and hard to determine?
Lets say you have a closed chambered Small block head with pistons .020 in the hole with a .039 head gasket. You have a .059 distance between the piston and the head. How effective is the quench? From what I have read, the sweet spot of quench is between .035-.045.
What if this engine has a spark knock issue due in part to the high compression ratio. If the .059 gap results in limited quench, would it be safe to assume that a thicker head gasket could be used to drop compression a 1/2 point without a penalty?
Jeff
I have read that lowering compression via thicker head gaskets can result in more spark knock because of lost quench. My question is:
If the engine is already out of the quench zone, would the thicker gasket help matters?
Posted By: gregsdart
Re: At what point is QUENCH not effective? - 06/28/13 01:08 PM
You would lose some benefit, but a lot of it is not there due to being at .059 already, IMHO. If you can, fix it right with setting the proper quench. Study what happened to the same motor when compression dropped from the factory back in the early 70s. That is a big clue as to what will happen to your motor. It all depends on what you want. Do you want it to run the best and spend the money, or do a quick fix and live with a motor that is down on torque? The other thing to consider is what cam you have. If it is bigger than stock, then reducing compression will be a double whammy. The motor will suffer even more loss, because your true compression will take a bigger hit. A total run down on what you are working with would help you get better responses also. There may be other options here, but we need facts to work with.
Posted By: MR_P_BODY
Re: At what point is QUENCH not effective? - 06/28/13 01:09 PM
I cant answer your question(I dont have the smarts
or the experience)but I would ask what fuel, timing,
cam and where its installed at.. also how hot do you
run the engine at and what plugs you run... yes your
correct that .040 seems to be the best point for it..
a thicker gasket can cause it to detonate even more
(just like the low compression engines can detonate)
Posted By: JohnRR
Re: At what point is QUENCH not effective? - 06/28/13 01:24 PM
I'm with the guys above, what is your combo, what timing , fuel octane and what's your elevation?
Posted By: Hot 340
Re: At what point is QUENCH not effective? - 06/28/13 01:30 PM
https://board.moparts.org/ubbthreads/show...rue#Post7600787 I asked this same exact question a few months ago. My conclusion was to err on the side of caution because how do you measure these clearances accurately when the piston rocks in the bore? And heat changes everything too. And so does the quality and material of parts.
Posted By: Jerry
Re: At what point is QUENCH not effective? - 06/28/13 01:37 PM
ideal quench is good at .040 or less. ultimately your trying to not allow room for the gas mixture to ignite. however, in real world driving applications your never really at the point of needing ideal quench. you may have to back your timing down a few degrees and you may lose a couple of hp. but are your really going to notice the difference? you might if your worried about your top speed or best performance all the time. most of us just want to drive our cars, and whether you have 580 hp or 560hp, you'd never tell by the seat of your pants.
Posted By: mbogina
Re: At what point is QUENCH not effective? - 06/28/13 02:05 PM
I agree that the ideal quench clearance is about .035, dependent on piston rock. The detrimental area is clearances of about .040 to .100, which generally leaves areas of combustion that are too small to efficiently ignite the mixture. Above .100 will be more efficient because the area is large enough to allow the flame travel to burn the mixture within a short enough time span.
Posted By: MoparBilly
Re: At what point is QUENCH not effective? - 06/28/13 02:06 PM
When you are spraying 400hp of Nitrous, quench is not effective, head gaskets aren't either.
Posted By: Twostick
Re: At what point is QUENCH not effective? - 06/28/13 03:05 PM
Quote:
When you are spraying 400hp of Nitrous, quench is not effective, head gaskets aren't either.
Funny. Too bad it's true. Although I would think having quench couldn't hurt.
Kevin
Posted By: Crizila
Re: At what point is QUENCH not effective? - 06/28/13 03:09 PM
Quote:
I have read many, many threads and posts but haven't seen this topic clearly defined.
Maybe it is a gray area and hard to determine?
Lets say you have a closed chambered Small block head with pistons .020 in the hole with a .039 head gasket. You have a .059 distance between the piston and the head. How effective is the quench? From what I have read, the sweet spot of quench is between .035-.045.
What if this engine has a spark knock issue due in part to the high compression ratio. If the .059 gap results in limited quench, would it be safe to assume that a thicker head gasket could be used to drop compression a 1/2 point without a penalty?
Jeff
I have read that lowering compression via thicker head gaskets can result in more spark knock because of lost quench. My question is:
If the engine is already out of the quench zone, would the thicker gasket help matters?
Address the quench first. There is no magic #. Tighter is better. .035' - .040" is safer. Address the detonation with fuel, ignition timing, cam timing, water.
Posted By: 383man
Re: At what point is QUENCH not effective? - 06/28/13 03:17 PM
I can tell you my 493 came out about .046 to .047 and I thought about decking the block a tad more as my pistons were about .007 down in the cylinder. Two other eng builders told me its not worth the worry to deck it another .007 so I went with it and it has worked great. I run 37 total on 92 pump with zero ping and it runs fine. Ron
Posted By: jcc
Re: At what point is QUENCH not effective? - 06/28/13 04:27 PM
Address the quench first. There is no magic #. Tighter is better. .035' - .040" is safer. Address the detonation with fuel, ignition timing, cam timing, water.
So my first assumption is the purpose of quench is to keep the mixture uniform in temp and maintain fuel/air mixture, and possibly cool relative hot spots in the chamber. And I freely admit we are not speaking F1/Nasacar here, but to move the amount of air that quench does, in 8 cyls, at 7K?, I bet it takes/absorbs a reasonable amount of horsepower to move all that air from a dead stop, really fast. But if it allows greater hp to be made, that offsets and exceeds the pumping losses, we then chase quench. Forgetting mechanical issues of quench, regarding rod stretch, growth, etc, it would seem there should be a magic quench goal for each engine combination. What that is, I have no clue.071
Posted By: BradH
Re: At what point is QUENCH not effective? - 06/28/13 04:31 PM
FWIW, the general rules of thumb I've heard for years re: quench are:
1. .040" is a good target (steel rod motor, not aluminum)
2. < .040" can be better until things like piston rock start to cause piston-to-head collision issues
3. > .050" is where the benefits start to diminish and...
4. at .060"+, you're probably getting no quench benefits
Posted By: Performance Only
Re: At what point is QUENCH not effective? - 06/28/13 05:11 PM
Quote:
FWIW, the general rules of thumb I've heard for years re: quench are:
1. .040" is a good target (steel rod motor, not aluminum)
2. < .040" can be better until things like piston rock start to cause piston-to-head collision issues
3. > .050" is where the benefits start to diminish and...
4. at .060"+, you're probably getting no quench benefits
Brad pretty much nailed it IMO.
check your cranking compression. Different engine combinations will tolerate more or less cylinder pressure depending on other factors. Cam, heads, etc. etc. Often times you can increase compression and quench at the same time and rid yourself of detonation issues in one fell swoop.
More info on your exact combination would help you get more detailed information to fix your issues. 
Posted By: polyspheric
Re: At what point is QUENCH not effective? - 06/28/13 05:27 PM
Everyone speaks, no one listens
Posted By: jcc
Re: At what point is QUENCH not effective? - 06/28/13 05:35 PM
So all? the benefit arises from the additional power obtained from the now lessened volume of quench area, and that the quench area no longer pre ignites from the shock wave, because its cooled by its close proximity to the piston and the head, and burns later, correct? Interesting.
Posted By: Crizila
Re: At what point is QUENCH not effective? - 06/28/13 05:36 PM
Quote:
Address the quench first. There is no magic #. Tighter is better. .035' - .040" is safer. Address the detonation with fuel, ignition timing, cam timing, water.
So my first assumption is the purpose of quench is to keep the mixture uniform in temp and maintain fuel/air mixture, and possibly cool relative hot spots in the chamber. And I freely admit we are not speaking F1/Nasacar here, but to move the amount of air that quench does, in 8 cyls, at 7K?, I bet it takes/absorbs a reasonable amount of horsepower to move all that air from a dead stop, really fast. But if it allows greater hp to be made, that offsets and exceeds the pumping losses, we then chase quench. Forgetting mechanical issues of quench, regarding rod stretch, growth, etc, it would seem there should be a magic quench goal for each engine combination. What that is, I have no clue.071
The #1 purpose of quench is to try and eliminate a second flame front. Then do what you said, which also helps to eliminate a second flame front. Since everyone likes .040', that makes it the magic #. 
There is a reason why the most common head gasket thickness sold ( for wedge motors ) is .039" - and it's because most aftermarket and race engines are built with "0" deck height - or close to it. So now that you have the "magic" quench #, I hope your build is just as magic. With pistons .020 in the hole at TDC, a little magic could be in order. 
Posted By: Bad340fish
Re: At what point is QUENCH not effective? - 06/28/13 05:40 PM
Ive seen a few good examples of good effort being put into quench and what happens when its not. I have seen two 360s very similar other than one being a quench motor and one not. The quench motor was a 10:1 deal and the non quench was in the 9s. The quench motor was able to run a good amount more timing with little problems with knock. The other motor constantly fought with knock and would put some race gas in so he could run the timing where it needed to be on the track. The quench motor was also about .75 faster in the 1/4 in a slightly heavier car. This was like 15 years ago so the details are a little fuzzy, it did however burn "quench is good" into my head for life.
I often wonder about the stroker 4.0 in my jeep. I built it in a hurry and didn't put forth any effort into quench etc. I just followed a canned recipe for a budget stroker motor. Its mid 9s compresion and fights detonation with premium fuel in the warmer months. I often wonder how much power and efficiency I left on the table by not going the extra mile and putting some effort into quench. I was however in a time crunch as it was my daily driver and I blew the motor up(ingested water).
Posted By: 383man
Re: At what point is QUENCH not effective? - 06/28/13 06:38 PM
[The #1 purpose of quench is to try and eliminate a second flame front. Then do what you said, which also helps to eliminate a second flame front. Since everyone likes .040', that makes it the magic #.
There is a reason why the most common head gasket thickness sold ( for wedge motors ) is .039" - and it's because most aftermarket and race engines are built with "0" deck height - or close to it. So now that you have the "magic" quench #, I hope your build is just as magic.
With pistons .020 in the hole at TDC, a little magic could be in order.
That is the truth as quench helps fight having more then one flame front. Thats what causes detonation is 2 flame fronts collide and cause the knocking which is bad for the eng mechanical contition. Here is what one of the good eng books I have says..........The closeness of the cyl head to the piston and the relative coolness of these metallic surfaces cause heat to be extracted from the end gas so the tendency for detonation to occur is quenched. Knocking results when the end gas temps go to high and the end gas explodes before the flame front reaches it. Ron
Posted By: Leon441
Re: At what point is QUENCH not effective? - 06/28/13 11:46 PM
My small chamber W8 468 CID nitrous combo had huge compression. We installed a dish piston with. Lost so much compression the engine was down on power. Then installed a.032 head gasket and power came back and the rings ran cooler.
My 421 with same heads and flat tops was also high on compression. It made great power over a broad range.
My Durango RT needed a rebuild. I cut a bunch off the block to develop quench as this thing detonated terrible. Raised compression at least a half a point. Well it spark knocks more now. So win some loose some.
Race engines like quench. Nitrous engines love it even more. In my experience. But, the Durango said I was full of crap.
So who knows. Two out of Three I will build quench in future builds.
Posted By: dogdays
Re: At what point is QUENCH not effective? - 06/29/13 05:57 AM
The whole topic of "quench" give me hives. The name is all wrong, it was called that by someone who didn't understand what it really does.
The subject is properly called SQUISH. That's what Sir Harry Ricardo called it when he developed it and actually patented the idea back around 1919.
If you understand about flame travel it'll help. If the mixture isn't moving around much, the actual flame travel is on the same order of magnitude as piston speed. That's slow. While the slow burn is heating the contents of the combustion chamber, the fuel in the farthest out places is turning into compounds that self-ignite much more easily than the original fuel. So how to get the mixture to burn quicker?
By bringing two surfaces together very closely, a high speed jet is expelled and physically mixes the flame through the chamber. Thus the burn completes faster than the knocking compounds can form.
So the good idea is speeding up the burn. The wrong idea is that somehow the surfaces are "quenching" the knock. But it is the speed that the burn is completed that makes the difference.
If one could get the piston to come within 0.001" of the head every single time it would be better.
Check out
www.theoldone.com for more.
R.
Posted By: Jjs72D
Re: At what point is QUENCH not effective? - 06/29/13 08:59 AM
Sorry if I led you guys down the wrong path. I've been contemplating a 360 with a 4" crank and I'm trying to understand as much as I can before buying any parts.
I have read about guys dealing with spark knock and how quench helps reduce the risk of it. I am interested in learning from experienced engine builders so I can make as few mistakes as possible. I've read through a few books including "How to rebuild your small block Mopar". Those books don't delve into aluminum heads and strokers though and that is where I need the help.
The reason I mentioned the .020 number for pistons in the hole was that I read that number in a thread somewhere. The .039 is a common thickness for the Fel Pro head gasket.
I understand that quench is important, I just was curious about the approximate distance where it becomes a NON issue.
Thanks to all. I hope that you don't feel that your time was wasted. I just want to learn this stuff!
Jeff
Posted By: gregsdart
Re: At what point is QUENCH not effective? - 06/29/13 11:55 AM
I don't think you wasted anyone's' time. That is what we are about. Helping each other get better performance. With a clean sheet, you can put together a REAL stout peace, given the time to glean all you can from this web site and others. For some very interesting reading that goes deeply into what happens in the combustion chamber, get a copy of David Vizzards book Porting cylinder heads. There is a wealth of knowledge there.
Posted By: 383man
Re: At what point is QUENCH not effective? - 06/29/13 01:02 PM
As Dogdays says one of my books does call it Squish and sometimes if you read enough about it you wonder if all the engineers who design the engines all agree on the Quench/Squish therory. I found it is easiest for me to just remember that when you think about Quench to remember its about if more then one flame front comes about and flame fronts collide. Ideal is one nice flame front and anything that helps that helps fight eng knock. And of course ideal quench is about .040. It was pretty basic for me as when I built my 493 which of course is the Mopar wedge eng I wanted to build a simple zero deck flattop piston eng with a wedge combustion chamber and a .040 head gasket for perfect quench. After I decked my block and fit everything I was about .005 off as my pistons came out about .007 down and it was close enough for my setup. But it is easy to build a good quench bigblock Mopar wedge when starting from scratch. Just shoot for .040 quench and dont worry if you totally understand its therory. And this is never a waste of time because know matter how matter times this board talks about quench it seems everytime I always learn more about it. I agree with what Brad posted that after .050 you start to loose the quench effect. Ron
Posted By: JohnRR
Re: At what point is QUENCH not effective? - 06/29/13 02:35 PM
Well the good thing is you haven't built it yet so you can buy the parts you need to get things right. I don't know what you plan on using for pistons but you should contact one of the board members that is a Diamond WD to choose which piston you want , if it's a shelf stock piston you can go semi custom for a small up charge and get it with the pin move and possibly a small D dish to give you a pump gas friendly compression ratio and take advantage of SQUISH
Posted By: MR_P_BODY
Re: At what point is QUENCH not effective? - 06/29/13 02:55 PM
Quote:
Well the good thing is you haven't built it yet so you can buy the parts you need to get things right. I don't know what you plan on using for pistons but you should contact one of the board members that is a Diamond WD to choose which piston you want , if it's a shelf stock piston you can go semi custom for a small up charge and get it with the pin move and possibly a small D dish to give you a pump gas friendly compression ratio and take advantage of SQUISH
That was the nice thing about dealing with Diamond..
they changed the pin height for $35 a set and will
do other changes for cheap.. so you end up with a
semi custom piston from a shelf blank
Posted By: jcc
Re: At what point is QUENCH not effective? - 06/29/13 03:26 PM
Quote:
The whole topic of "quench" give me hives. The name is all wrong, it was called that by someone who didn't understand what it really does.
The subject is properly called SQUISH. That's what Sir Harry Ricardo called it when he developed it and actually patented the idea back around 1919.
If you understand about flame travel it'll help. If the mixture isn't moving around much, the actual flame travel is on the same order of magnitude as piston speed. That's slow. While the slow burn is heating the contents of the combustion chamber, the fuel in the farthest out places is turning into compounds that self-ignite much more easily than the original fuel. So how to get the mixture to burn quicker?
By bringing two surfaces together very closely, a high speed jet is expelled and physically mixes the flame through the chamber. Thus the burn completes faster than the knocking compounds can form.
So the good idea is speeding up the burn. The wrong idea is that somehow the surfaces are "quenching" the knock. But it is the speed that the burn is completed that makes the difference.
If one could get the piston to come within 0.001" of the head every single time it would be better.
Check out www.theoldone.com for more.
R.
So with this explanation, does that also mean because of a "faster burn", timing can be dialed back?
I was mentioning to 383 last night a question about thermal coatings interfering with the heat absorption based on the earlier explanation of the nearby surfaces cooling the fuel air mixture preventing pre ignition. Seems to me if coating reject heat from being absorbed by the piston, etc, the coating would also retard heat being absobed from the mixture.
Posted By: dOoC
Re: At what point is QUENCH not effective? - 06/29/13 03:58 PM
OK ....who makes the best piston with the least amount of "rock" ?
Posted By: d-150
Re: At what point is QUENCH not effective? - 06/29/13 04:25 PM
shorter the piston the more rock you will have,like stroker pistons,also where does flat top pistons and flame travel without squish fit into engine building .
Posted By: MR_P_BODY
Re: At what point is QUENCH not effective? - 06/29/13 04:27 PM
Quote:
OK ....who makes the best piston with the least amount of "rock" ?
Probably KB... they tend to run the closest piston to
wall clearances but they arent the strongest
Posted By: 383man
Re: At what point is QUENCH not effective? - 06/29/13 04:30 PM
Quote:
Well the good thing is you haven't built it yet so you can buy the parts you need to get things right. I don't know what you plan on using for pistons but you should contact one of the board members that is a Diamond WD to choose which piston you want , if it's a shelf stock piston you can go semi custom for a small up charge and get it with the pin move and possibly a small D dish to give you a pump gas friendly compression ratio and take advantage of SQUISH
These are the D-dish pistons I use to have 10.6 pump gas friendly comp on my 493 with the 75cc EZ heads and still have good quench. Ron
Posted By: dOoC
Re: At what point is QUENCH not effective? - 06/29/13 04:42 PM
Quote:
Quote:
OK ....who makes the best piston with the least amount of "rock" ?
Probably KB... they tend to run the closest piston to
wall clearances but they arent the strongest
Does Diamond have a piston design that can be run with less p2w clearance ?
Posted By: MR_P_BODY
Re: At what point is QUENCH not effective? - 06/29/13 05:01 PM
Quote:
Quote:
Quote:
OK ....who makes the best piston with the least amount of "rock" ?
Probably KB... they tend to run the closest piston to
wall clearances but they arent the strongest
Does Diamond have a piston design that can be run with less p2w clearance ?
That I cant say... you would have to talk with them...
they are close to me so it was nice to deal with them
and when they had them done I just drove over there
and picked them up... plus I know the owner and see
him fairly regular at a car club thing.. if I can
find another 340 block I'm gonna start another engine
build for my Rampage.... but it might end up as a
stroker 318... still unknown... but I'm running out
of 340 blocks unless I start putting sleeves in them
Posted By: dogdays
Re: At what point is QUENCH not effective? - 06/29/13 06:16 PM
With regards to timing, good question! Yes, If the squish is working right, the engine needs less spark lead for max power. A happy byproduct is that less negative work is done (piston compressing an expanding mixture) so, more positive work is done, meaning more power.
That is one of the main reasons the later cylinder heads make both, more power and better mileage.
R.
Posted By: dOoC
Re: At what point is QUENCH not effective? - 06/29/13 06:53 PM
Quote:
Does Diamond have a piston design that can be run with less p2w clearance ?
That I cant say... you would have to talk with them...
they are close to me so it was nice to deal with them
and when they had them done I just drove over there
and picked them up... plus I know the owner and see
him fairly regular at a car club thing.. if I can
find another 340 block I'm gonna start another engine
build for my Rampage.... but it might end up as a
stroker 318... still unknown... but I'm running out
of 340 blocks unless I start putting sleeves in them
P-guy ... do you have an email addy for your guy ....I could drop him a note later today and he could digest it at his convenience on Monday.
ANOTHER point on max-squish ... the less "open area" beyond the combustion chamber gives more swirl to the AF mixture THUS a better and more complete burn.
ONE of my projects that could definately use-this would be my 413 motorhome moder ...with those goofy heads. HUGE CC closed chambered head design ... 100 PLUS CC's ... so a +.010 deck piston with a slight dome with a fire-slot would be in order IMO .....
Posted By: Crizila
Re: At what point is QUENCH not effective? - 06/29/13 07:12 PM
Quote:
Quote:
Quote:
OK ....who makes the best piston with the least amount of "rock" ?
Probably KB... they tend to run the closest piston to
wall clearances but they arent the strongest
Does Diamond have a piston design that can be run with less p2w clearance ?
Pistons, like many of the race parts we buy, are application specific. Those that "push the envelope" on their builds To gain the HP edge, run on the edge. Example: Tight piston to wall clearance is good. Those pistons are usually cast with a high silicone content - minimal heat expansion. They are not as strong as forged pistons and very intolerant to detonation. ( don't ask me how I know ). They also require large ring end gaps. For low performance applications they are the choice. Building a 600+ HP motor, you will want to go forged.
Posted By: moparniac
Re: At what point is QUENCH not effective? - 06/29/13 10:21 PM
Quote:
I agree with what Brad posted that after .050 you start to loose the quench effect. Ron
My engine is .051 - .024 in the hole and .027 HG 11.89 to 1 static and 8.2ish to 8.8ish dynamic depending on altitude with a cam with an intake closing at 73 ABDC and cranks at 170ish summertime DA and around 180ish cooler weather with a jump box on the battery.(probably why my car is such a dud) Would a thinner HG help me out some? I think so.How I got my piston in the hole value I raised the piston out of and got true TDC with and indicator, I then put the indicator with a deck bridge on the side of the piston close to the wall rocked the piston to the high side then to the low side in the bore and divided by 2 and came up with .024. piston is a diamond with .0065 piston to bore / -19.3cc
hope any of that made sense 
Posted By: emarine01
Re: At what point is QUENCH not effective? - 06/30/13 02:39 AM
Quote:
Everyone speaks, no one listens
I will listen....
Posted By: Cab_Burge
Re: At what point is QUENCH not effective? - 06/30/13 02:48 AM
Posted By: Brian Hafliger
Re: At what point is QUENCH not effective? - 06/30/13 03:09 AM
Quote:
I have read many, many threads and posts but haven't seen this topic clearly defined.
Maybe it is a gray area and hard to determine?
Lets say you have a closed chambered Small block head with pistons .020 in the hole with a .039 head gasket. You have a .059 distance between the piston and the head. How effective is the quench? From what I have read, the sweet spot of quench is between .035-.045.
What if this engine has a spark knock issue due in part to the high compression ratio. If the .059 gap results in limited quench, would it be safe to assume that a thicker head gasket could be used to drop compression a 1/2 point without a penalty?
Jeff
I have read that lowering compression via thicker head gaskets can result in more spark knock because of lost quench. My question is:
If the engine is already out of the quench zone, would the thicker gasket help matters?
Answer is NO, the thicker head gasket won't help until you get the piston at least .120 away from the head.
Quench range is .045 or less, or make sure the piston is .120 away or more. This is much more important with compression in the 10:1 range and less important below 10:1.
Brian
Posted By: Clanton
Re: At what point is QUENCH not effective? - 06/30/13 03:10 AM
Quote:
Everyone speaks, no one listens
I went to your web site and read about quench.
Posted By: Jjs72D
Re: At what point is QUENCH not effective? - 06/30/13 03:12 AM
Those pistons with a heart shaped dish are interesting. Looking at some old engine books, there is no mention of that or anything like it.Of course, the books were 20 years old. These pistons look like newer designs. The raised/flat portion is designed for Quench, right? I saw another piston design somewhere that had a raised section and a stepped down section. 1/3 was raised, 2/3 was stepped down at what looked like at least .060-.080 lower. Seems like the same principal at play. I'd think as long as a safe amount of meat was left to support the rings, you'd get a lower/safer compression ratio while maintaining quench.
Thanks guys. I enjoy learning about this stuff!
Posted By: dodgeboy11
Re: At what point is QUENCH not effective? - 06/30/13 09:18 AM
Quote:
So with this explanation, does that also mean because of a "faster burn", timing can be dialed back?
I was mentioning to 383 last night a question about thermal coatings interfering with the heat absorption based on the earlier explanation of the nearby surfaces cooling the fuel air mixture preventing pre ignition. Seems to me if coating reject heat from being absorbed by the piston, etc, the coating would also retard heat being absobed from the mixture.
In a word, yes. Some of the people I learned from are big believers in mirror polishing over coatings. Whether one is better than the other, I do not know or really even care. Reflecting the heat back into the combustion area helps push the piston down rather than being absorbed by the cooling system. Because there's more heat it burns faster so less spark lead is needed for ideal burn. Less spark lead and the engine doesn't fight itself quite so much and it frees up some power.
Posted By: JohnRR
Re: At what point is QUENCH not effective? - 06/30/13 11:58 AM
Quote:
Those pistons with a heart shaped dish are interesting. Looking at some old engine books, there is no mention of that or anything like it.Of course, the books were 20 years old. These pistons look like newer designs. The raised/flat portion is designed for Quench, right? I saw another piston design somewhere that had a raised section and a stepped down section. 1/3 was raised, 2/3 was stepped down at what looked like at least .060-.080 lower. Seems like the same principal at play. I'd think as long as a safe amount of meat was left to support the rings, you'd get a lower/safer compression ratio while maintaining quench.
Thanks guys. I enjoy learning about this stuff!
2 different pistons designs for 2 different cylinder hears .
the D dish is used in a stroker application with a closed chamber head , you get the flat as close to zero deck as needed so you can build quench(squish) and the dish helps lower the compression.
The other piton with the small D shaped dome is for use with an open chamber head, The D dome makes the piston APPEAR to be a flat top in an open chamber head but it requires machining of the open chambers of the head to make them flat and uniform across the head because as cast they are anything but.
I had diamond do this one with a D dome AND a dish for a build I speced for a friend a couple years ago, the piston was a lot more affordable that one would think.
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Posted By: emarine01
Re: At what point is QUENCH not effective? - 06/30/13 04:40 PM
Different engine combos require different quench specs, my alu rod small block has .058 quench cold, if I run .055 quench the piston just kisses the head over 7500 rpm, I would think I have reasonable quench with the engine hot and running in its power band 5 to 7k & not so good @ cold idle.
Posted By: 383man
Re: At what point is QUENCH not effective? - 06/30/13 04:44 PM
These are the KB quench dome pistons for the open chamber head to try and get quench. I was mocking these up in my old 440 as I know some are in the wrong cylinders here. I used them in my old 440 with open chamber 906 heads to get quench in the open chamber and as John stated they are alot of work getting the combustion chambers right and close to equal. I had to do alot of grinding but in the end it had an average quench about .043 to a worst of .048. Much better and easier to build a flattop piston closed chamber head eng. I used these because money was tight and I used what I had laying around for my old 440. But when I built my 493 from scratch I went with the closed chamber head zero deck (or very close) setup. Ron
Posted By: Jjs72D
Re: At what point is QUENCH not effective? - 06/30/13 06:47 PM
Ron, I saw a picture in the current issue of Mopar Muscle that showed a Sport Fury with pistons like the ones in your picture. The raised area looked similar. They also wrote that the intended goal there was to close up the distance for quench when using an iron head, open chamber design.
Posted By: WO23Coronet
Re: At what point is QUENCH not effective? - 06/30/13 07:18 PM
Quote:
Quote:
Does Diamond have a piston design that can be run with less p2w clearance ?
That I cant say... you would have to talk with them...
they are close to me so it was nice to deal with them
and when they had them done I just drove over there
and picked them up... plus I know the owner and see
him fairly regular at a car club thing.. if I can
find another 340 block I'm gonna start another engine
build for my Rampage.... but it might end up as a
stroker 318... still unknown... but I'm running out
of 340 blocks unless I start putting sleeves in them
P-guy ... do you have an email addy for your guy ....I could drop him a note later today and he could digest it at his convenience on Monday.
ANOTHER point on max-squish ... the less "open area" beyond the combustion chamber gives more swirl to the AF mixture THUS a better and more complete burn.
ONE of my projects that could definately use-this would be my 413 motorhome moder ...with those goofy heads. HUGE CC closed chambered head design ... 100 PLUS CC's ... so a +.010 deck piston with a slight dome with a fire-slot would be in order IMO .....
MPI (or the artist formerly known as Doc Fiberglass) are those 413 industrial heads a closed chamber or open? To cut the cc's down you could get them spray welded (I think Dr J's performance does this)
Posted By: MR_P_BODY
Re: At what point is QUENCH not effective? - 06/30/13 08:00 PM
P-guy ... do you have an email addy for your guy ....I could drop him a note later today and he could digest it at his convenience on Monday.
No I dont... next time I see him I will get it
Posted By: HotRodDave
Re: At what point is QUENCH not effective? - 07/01/13 05:55 AM
Quote:
My small chamber W8 468 CID nitrous combo had huge compression. We installed a dish piston with. Lost so much compression the engine was down on power. Then installed a.032 head gasket and power came back and the rings ran cooler.
My 421 with same heads and flat tops was also high on compression. It made great power over a broad range.
My Durango RT needed a rebuild. I cut a bunch off the block to develop quench as this thing detonated terrible. Raised compression at least a half a point. Well it spark knocks more now. So win some loose some.
Race engines like quench. Nitrous engines love it even more. In my experience. But, the Durango said I was full of crap.
So who knows. Two out of Three I will build quench in future builds.
Thats interesting, I just built a 318 magnum for my 98 Ram long bed ex cab truck and towing a 1/2 ton chevy in the heat today did not result in any detonation. I basically did a totally stock rebuild except zero decked the stock pistons and ran a .039 gasket. After CC ing everything I come up with 10 to 1 compression and a stock cam for some really high cylinder pressure for iron heads (165 PSI). The R/T had overly agressive ign timing. You might try retarding the crank sensor position by slotting the bolt holes and moving it to the center of the block.
Posted By: Von
Re: At what point is QUENCH not effective? - 07/02/13 05:06 AM
My experience with quench, which will most likely be remedial in comparison to most of the responses, but may help somebody?
In my experience...quench even at .055-.060 is beneficial. Motor in my car right now is 9.7 comp with .055ish quench. I did have a Comp XS282S cam in it, was in at 110. Cranking compression was around 150. I ran the motor on 87 quite a bit, flogged it pretty hard. Never heard any audible rattling. Pulled motor out, swapped heads and cam. Pistons showed no signs of detonation. Now have 9.8 compression, but with cam that holds IV open a few more degrees. Tank has 89 in it right now and the other day it was 90 degrees and humid, no rattling.
Same shortblock (more or less) with a MP 292 cam, compression at 10.25ish. Quench around .055-.060. Ran on 91 without any audible detonation. Pistons showed no signs of detonation.
Now...10.15 shortblock without any quench (open chamber heads, .045 gasket, etc). Cam was a 259/259 solid. By the info I have been able to find for the MP292, intake valve closes a tick later with the 259 cam compared to the 292. This motor would lightly rattle on pump 91 on a hot humid day. When heads were pulled, #1 and #5 show signs of detonation. Not bad, but they for sure saw detonation. All other pistons look fine...
So...in my experience.. quench matters, even if not at the optimum clearance.
Posted By: Jjs72D
Re: At what point is QUENCH not effective? - 07/02/13 07:35 PM
It seems that while a larger quench distance may not be optimal, you'd still get some benefit from the mixture being shoved/forced from the tight side of the chamber to the valve/spark plug side. That sort of movement would mix & blend the air and fuel better than an open chamber design, right?
Posted By: hemidup
Re: At what point is QUENCH not effective? - 07/02/13 08:04 PM
How important is quench/squish with a dished piston?
Posted By: JohnRR
Re: At what point is QUENCH not effective? - 07/02/13 08:18 PM
Quote:
How important is quench/squish with a dished piston?
Posted By: titan
Re: At what point is QUENCH not effective? - 07/02/13 09:01 PM
And With A Flat Top Piston, .100 Down, Would The Burn Be Better With Open Chamber, Or Closed Chamber Heads?
Posted By: MR_P_BODY
Re: At what point is QUENCH not effective? - 07/02/13 09:17 PM
Quote:
And With A Flat Top Piston, .100 Down, Would The Burn Be Better With Open Chamber, Or Closed Chamber Heads?
With the piston down .100 you want the smallest chamber
you can get... its still gonna be a lazy burn..
a swirl port chamber would help it burn better/quicker
Posted By: Jerry
Re: At what point is QUENCH not effective? - 07/02/13 09:36 PM
ultimately preignition works just like it sounds. areas where heat and pressure can build will per ignite the mixture before the flame front from the spark can burn through it. so there are two ways to counteract this problem. 1. is to have zero quench, have such a large gap that you don't get hot spots and not localized areas of high pressure in the chamber. 2. is to have ideal quench and then you basically smother the preignition because there is no room for the fire to start. just like covering a carb with a rag to smother flames. same concept. so in terms of your dish piston and the one thats down in the hole .100, you effectively have zero quench. and in order to maintain no preignition you want to use an open. is this good for performance? Nope, but you don't have any spark knock either. in reality if your using a closed head on a piston deep in the hole you won't have any quench anyway either so it won't matter.
now with a dished piston there are some dished pistons that have a quench dome built in for running either open or closed chamber heads. these are setup ideally for lower compression in boosted applications while trying to maximize the quench. obviously option 2 with quench is better than option 1 with no quench at all.
there is alot more to this, and i can keep going, but i'm getting tired of typing.
Posted By: Jjs72D
Re: At what point is QUENCH not effective? - 07/02/13 09:58 PM
Nice explanation, Jerry. makes sense.
Posted By: Rapid340
Re: At what point is QUENCH not effective? - 07/02/13 10:37 PM
An actual running quench height up to about .060 can be useful.
As it goes from above .060 to around .090 a quench area can actually reduce power because little to no effective quench is realized yet combustion is inhibited in increasing volumes.
.090 is a typical number going from my memory but will vary based on percentage of total quench area.
Posted By: WO23Coronet
Re: At what point is QUENCH not effective? - 07/02/13 11:11 PM
What about in a big open chamber like a Gen III HEMI? There really is no spot for end gases to hide, I imagine it helps that the plugs are centrally located. And the chambers must be efficient cause the Gen III's like around 24 degrees of timing for max power
Posted By: Jerry
Re: At what point is QUENCH not effective? - 07/02/13 11:22 PM
thats correct. on the hemis with a centrally located spark plug, the entire chamber is the quench zone. there is no pad so to speak for these engines. the comments above are more for the wedge head engines where the plug is located on one side of the chamber taking the flame a long time to travel across.
Posted By: Crizila
Re: At what point is QUENCH not effective? - 07/03/13 12:07 AM
Here is a blower piston ( 8.9:1 ) with a quench area for a closed chamber Magnum head. Zero deck and .040" MLS gaskets gives .040" quench area. FYI, if you are running an open chamber cast combustion chamber head and a raised ( above deck ) piston in the quench area, measure carefully! The piston quench dome often has to be cut and the combustion chamber quench area can very due to casting irregularities. You will surely ( and don't call me Shirley) need to know your head gasket compressed thickness.
Posted By: Big Squeeze
Re: At what point is QUENCH not effective? - 07/03/13 12:14 AM
Quote:
When you are spraying 400hp of Nitrous, quench is not effective, head gaskets aren't either.
In big nitrous hits, quench is too effective...motors make more power without quench and a few more degrees timing than with quench and low timing (that's what chamber softening is all about)...and without quench there's a bigger tuning window for timing.... 
Also, if you're spraying 400hp of nitrous on a 400hp motor and the long block/head gaskets would hold 800hp naturally aspirated, it will still hold 800hp when spraying...what kills head gaskets is detonation....
What's amazing is how good a motor runs while its detonating while being sprayed... 
I started using the close alloy pistons years ago in NHRA legal stocker motors I was building, .004 to .0047 Piston to wall clearances at 70 F 
