What is it? What's it affect? Do you want low or high quench height? I always read about it in this forum, just blab about it, I'm intrigued.

 

Search for "quench" on "Advanced Tech" only. There are 51 threads, some with very good info.

 

Originally posted by Rippin92RS

What is it?
It's an area of close tolerance in the combustion chamber that get's "squeezed" when the piston comes up, forcing the fuel/air mix to the other side, promoting turbulence.

What's it affect?
The quality of the "burn", which has beneficial effects on efficiency, power and tendancy toward pre-ignition and/or detonation.

Do you want low or high quench height?
You want about .035-.040. Ask your builder for a specific recommendation based on your particular combination.

 

most is correct but one small detail was left out...factory the piston in .025 in the hole...and the other .010-.015 was the chamber....if you have your block ZERO decked then you have to work the chambers to get that .025 back....

 

Now I'm confused... what does the chamber have to do with this?

The piston is 0.025" in the hole, and the factory gasket is like 0.036"... yes, stock LT1's have a crappy quench distance of 0.061" on average.

Ideally you'd want a 0.015" gasket on a stock block, but integrity and head warpage can get tricky. Some go with the Impalla SS gasket which is ~0.020" I think. The SS gets you a tad more compression and a much better quench. The only catch is that it was designed for an iron block AND head combo, so some have talked about head leaks, although I've never known anyone with problems personally.

If you 0-deck a block (i.e. take it down to 9.000" deck height, from 9.025" LT1's use as stock), the ideal gasket becomes 0.040"... a bit more than the LT1/LT4 gasket.

I'm shooting for a 9.005" deck height on my 383 build up for use with a stock or FelPro gasket.

 

i'm semi confused about quench myself....
i'm probably wrong but isnt the quench area, the area between the head and block inside the bore of the gasket, that isnt covered by the gasket? this is because the gasket is wider then the bore of the chamber right?
and just for clarification, isnt the stock LT1 (aluminum head) gasket .049, Felpro .035-6, Impala .028?

what can optimum quench provide?


Steve

 

no, that volume IS used in calculating compression ratios, but it is not representative of the quench distance unless the piston is flush with the block (in stock form for example, the LT1 is 0.025" in the hole)

Typically, Small Block Chevy gaskets are all made with a 4.125" bore to accomodate a 400-block size. (easier to manufacture)... although you can go bigger with custom gaskets (if you have a need to do so, as in Rocket Block or Bow Tie )

I dug these up from the LT1 forum:

0.028" - Impalla SS (12553160) *some claim 0.029"*
0.039" - Fel-Pro (1074 LT1/LT4)
0.043" - LT4 (12551488)
0.050" - LT1 (10168457) *some claim 0.049"*

I recall that Mr.Gasket makes a 0.020" gasket, but the same reference to it claimed it had problems sealing.

Quote:

what can optimum quench provide?

better mixing of the chamber's contents can help resist knock and produce a small hp gain (from better average burn per cycle would be my guess). This allows a bit more compression to be run safely.

 

Quench is the compressed thickness of your head gasket + piston deck (.xxx in or out of the hole).


Chuck

 

thanks guys8)
so how do you figure out optimum "quench"? or is there an ideal amount for every piston engine?
say on a stock bottom end LT1, with heads that have been milled .010 using a FelPro gasket and chambers at 53.xcc's?

or if noone feels like explaining, maybe somewhere i can mess with calculations or something?
I'm guessing those head gasket thicknesses listed above are not compressed numbers? If not how do i get the compressed numbers?

Steve

 

milling the heads does not effect the quench. becuase the bottom of the heads is still the same place, it does increase compression. but shorten the quench distance and it raises compression.

quench is the distance from the pistion to the deck (while at tdc) and then from the deck to the head (gasket thickness).

if you raise the compression by milling the heads you will create the chance for predetnation. but lowering the quench area will up the compression yet help stop predetnation, becuase a big quench area say .060 holds alot of air and fuel that is not mixed very well. you will have pockets of rich a/f mixture and lean pockets as well. the leaner pocket will predetnate under pressure before the rich pockets but when the lean pockets detnate the hole thing fires. which makes a less effeicent engine. now lower the quench to say .040 and you have a smaller place for the for the air to stay under pressure. but haveing more air moving toward the spark plugs means that there is more turbulence in the combustion chamber, and the more turbulence the better a/f mixture, (less lean pockets of air) and you have a more constint a/f mixture through out the combustion chamber. this is why you can deck the block and raise compression and have less predetnation.

 

gotcha, thanks
where can crunch numbers to figure out if the FelPro gasket is the one i should use with my topend swap?

or does anyone have an equation i can use to figure it out for my
car?

Steve

 

im pretty sure those numbers are the compressed values...

you can just crunch the numbers in your head...if you wanted to use the fel-pro it would probably be best to have the block zero-decked for a quench of 039. with a deck height of .006 that would give you a quench of .045, which would be the maximum 'optimal' distance to go.

just add the deck height to the compressed gasket thickness and there you go...voila!

 

Let the noob give it a shot-

The combustion chamber only covers part of the piston top, the rest of the top of the piston is coverted by the bottom of the head. Where the piston is covered by the bottom of the head is called the quench area.

Here's how it works-

When the piston comes up to top dead center on the compression stroke, the air/fuel mixture between the quench area and the top of the piston gets squished out and it shoots into the combustion chamber. This mixture shooting into the chamber stirs things up a little in the chamber and helps insure a uniform mix and burn.

Having the piston get as close as possible to the bottom of the head increases this mixing effect, this jet of high speed mixture stirs thigs up real good. This when combined with a good chamber design gives a really good controlled burn which allows higher compression.

What to do? if you use a dished piston, try to find one that has a dish that matches the chamber shape, aka D dished pistons. Get the piston to go as close a possible to the head without hittting it.

This is one of the keys to high horsepower. There are people out there with some really strong motors who have found evidence of the piston lightly touching the head when they were freshing up their motors, needless to say they were maximizing the quench effect but they were also on the edge of destruction.

Make any sense?

 

Years ago Yamaha built a 750 Seca MC (I purchased one new in '83) that had a "sub-port" cast into the intake cc to increase swirl. This was a static mod to the head that hardly cost anything to manufacture. Yamaha tested their design and found an realized increase of 6-7hp on thier inline 4cyl. engine. Doesn't sound like much, but the bhp was only 84. That was about a 9% realized increase in hp! The engineers figured that the volocity of the charge past the subport was increased by a factor of 4. I always wondered why manufactures didn't copy this static design in head design.... Realize that this was back in ''83...

 

SERPENT99's post and some of the others cover it pretty well. Just to clarify a few points. Minimum quench for steel rods is usually considered to be ~0.035". That's to allow enough room for rod lengthening at operating temps, a little bit stretch in the rods, piston rocking in the bore, etc. The idea is that the piston hitting the head is a bad thing! Aluminum rods need another 5-10 thousanths clearance. Leaving possible piston to head interference aside, can the quench be too tight? I am not sure, but I believe that it can be. Just a gut feeling though, I have nothing to really back that up.

It's interesting that the stock LT1 has a lot more than 0.035". 0.049" gasket + 0.025" deck = 0.074" and it runs fine. I don't know what the quench distance is on an LS1, anyone know? I use 0.045" out of habit, it seems to work for me. My current combo is a 0.040" gasket and a 0.005" deck. As was stated, milling the heads does not decrease the quench distance. This is accomplished by milling the block deck, using a longer con rod or a piston with taller compression height, or using a thinner gasket.

Rich Krause