Quench................Worth It Or Not?

[toobroketoretire]

The need for a quench has been fiercely debated for over 50 years. Is a quench worth it or not? I know a quench is very necessary on 2-cycle engines but it has never been proven to be a big advantage on 4-cycle engines. If I were going to earn my living drag strip or track racing where every single horsepower counted I would try to run a minimum quench. But as my '71 only sees highway miles at 2500 rpm or less I'm not going to ruin my engine block to achieve a maximum quench unless a maximum quench is PROVEN to be a BIG advantage for a street engine. The modern HEMI doesn't have much of a quench nor does an open chamber big block nor most of today's modern engines.

Your thoughts?

 

[kpic]

In engineering terminology; quench height is the distance between the flat part of a piston and the cylinder head @ TDC.
Quench or the flat area of a piston creates turbulence of the charge which theoretically pushes the charge area towards the spark plug. By doing so, it reduces the possibility of unburnt fuel during the combustion cycle. BTW, not all piston designs have a flat area.
Quench, AKA squish, is out of the control of end users because we buy pistons and do not design them.

Basically, quench is about .038" to .043" with street engines. The values are subject to tolerance analysis, head gasket compressibility, and RPM.

As a former engine designer; I do not recall the so-called fierce debate you mentioned as the distance is all numbers. Point is, you read something and are guessing or fishing for what you are clueless about.

 

[toobroketoretire]

Quench....................Worth It Or Not?

Thank you very much for explaining what we already know; the definition of "quench" and how it's achieved. The point I'm making is modern engines don't seem to be using this uh "necessary" technology. The early HEMI had zero quench and the open chamber big blocks had very little and engines using dished pistons have diddly squat. Which make me think quench is not worth the effort achieving it. I would certainly not machine the deck of a good street engine block when quench has never been proven to be an advantage. I would think the combustion "event" would be over before the quench position is even reached because a flame travels awfully fast. I would also think quench would be about as necessary as adjusting hydraulic lifters "hot and running" as so many ignorant fools do.

 

[Vettehead Mikey]

Without making the slightest effort, I visited my favourite brewpub* yesterday where I experienced my own personal quench. Then I got back into my summer beater where the engine had 8 more quenches of it's own.



*for Mac- Old Mill at Ashton

 

[Mac]

Without making the slightest effort, I visited my favourite brewpub* yesterday where I experienced my own personal quench. Then I got back into my summer beater where the engine had 8 more quenches of it's own.


*for Mac- Old Mill at Ashton

I haven't explored out that way yet... Maybe I should take a drive on the weekend?

Mac

The Old Mill At Ashton (Ashton Brew Pub)

 

[bill81vette]

I got my quench at the local grocery store!!!!
Thank goodness for beer!!!!

Sent from my XT1080 using Tapatalk

 

[toobroketoretire]

Quench....................Worth It Or Not?

I don't think quench is an important factor because none of the world's engines seem to be using that uh "technology". It seems as though the most important technologies being used right now are dual overhead cams with variable timing and direct variable-timed fuel injection. Oh yeah, and turbocharging.

 

[kpic]

Thank you very much for explaining what we already know; the definition of "quench" and how it's achieved. The point I'm making is modern engines don't seem to be using this uh "necessary" technology. The early HEMI had zero quench and the open chamber big blocks had very little and engines using dished pistons have diddly squat. Which make me think quench is not worth the effort achieving it. I would certainly not machine the deck of a good street engine block when quench has never been proven to be an advantage. I would think the combustion "event" would be over before the quench position is even reached because a flame travels awfully fast. I would also think quench would be about as necessary as adjusting hydraulic lifters "hot and running" as so many ignorant fools do.

Answer: It depends on the shape of the combustion chamber. BTW, A Hemi isn't a Corvette engine; perhaps you are at the wrong forum

I apologize as you sounded as if you didn't know and for that matter you sound as if you still don't.

Click the links and see the pretty pictures with a flat area?

Chevy pistons:
chevy pistons - Google Search

LS1:
chevy pistons - Google Search

LS3:
chevy pistons - Google Search

LS6
chevy pistons - Google Search

Point is, you aren't a mechanical engineer and everyone here knows it.

 

[toobroketoretire]

Wikipedia

Google "Quench" and read what Wikipedia has to say about it. And as the quench happens so late in the combustion event I see little need for a quench. It's like closing the barn door after the horse has escaped.

 

[Vettehead Mikey]

Google "Quench" and read what Wikipedia has to say about it. And as the quench happens so late in the combustion event I see little need for a quench. It's like closing the barn door after the horse has escaped.

Now we know where you got your 'engineering degree'.

I searched wikipedia and couldn't find any definition of quench as applies here. Can you give us a link or copy/paste?

 

[Tom Bryant]

Here's something I found at the Crankshaft Coalition.

Quench

 

[kpic]

Now we know where you got your 'engineering degree'.

A crackerjack's box?

Or highly imaginative fingers on a keyboard? In either case, it is all baloney.

 

[Peer81]

So what it the answer to the question? Yes I see a lot of funny stuff and kicking but none that even try to give an answer...
As I see it when you drive normally your volumic efficiency is much lower then at WOT. I think quench will only do his part when you drive at WOT.
I don't remember in which book I've read that you can also bump the compression a little with a good quench distance but it would be nice to see on a back to back dyno what a good quench distance will do for engine output (also at part throttle).

Greetings Peter

 

[kpic]

When individual engine tolerances are considered, there isn't an exact answer. The distance between the big end and small end of a con rod varies. As a V8 has 8 tolerances plus the tolerances between the piston pin and the top of the the piston plus the tolerance between the crankshaft axis and 8 rod journals.. The list goes on and on.

Summary

Experimental evidence is given which indicates that wall-quenching of the combustion reaction occurs in an internal combustion engine. The apparent quench distances observed are in agreement with the quench distances calculated from burner data at approximately the same pressures and temperatures. In addition, the observed quench distances are of the right order of magnitude to account for the unburned hydrocarbons found in the exhaust gas of automobiles operated in the range of full throttle and road load.

Flame quenching at the walls of an internal combustion engine

It is not only full load or WOT; it is road load which is less than WOT.

As usual, the so-called claimed distances do not consider manufacturing tolerances. The little +/- numbers on the drawings of all the parts in a ststem, There is no such thing as all these Xs have a tolerance of +/-0.

Toobroke... An engineer wouldn't be checking Wikipedia of all places. An engineer's professional life is all engineering and numbers.

 

[Peer81]

I understand but for an experiment you can take a bottom end first dyno it for example with 72cc heads. 10:1 compression and ideal quench distance. After that rework the same head in 64cc model to match the 10:1 compression with a bigger quench distance. Same dynamic compression, etc etc. Then you can see as close as possible the effect quench has. Maybe a good idea for a new hotrod magazine youtube episode.

Greetings Peter

 

[toobroketoretire]

Quench....................Worth It Or Not?

The brilliant factory engineers who design engines have never felt "quench" is an important factor so why would you? Do you suppose the need for quench in 4-cycle engines is a just a myth?

 

[Tom Bryant]

I can't imagine any powertrain engineer would be designing a combustion chamber and piston top to match it and not consider every possible variable; quench being one of them. How do you know this?

Tom

 

[kpic]

I designed engines for 20 years. Knowing the volume sets the CR; so if no one pays it any attention, how would they know the CR?

Here it is, short and sweet:
"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."

Toobroke..
As usual, ignore it for a few days.

 

[toobroketoretire]

I suspect the need for "quench" is just another of the dozens of Chevrolet small block myths that have been started by well meaning not very bright people.

 

[toobroketoretire]

Quench....................Worth It Or Not?

I have read about several people running ZERO deck clearance and thinner head gaskets so their pistons actually TOUCH their cylinder head at high rpm's. All of this for the sole purpose of getting maximum quench which has never been proven to accomplish anything. Heck, if they're that desperate for a bit more performance they would be better off forcing their behemoth wives to go on diets.