A
Anonymous
Guest
Will someone please explain this phenomenom to me? How do you figure it and what exatly does it do? Does more quench mean better performance and flame travel? Thanks ya'll.
A
Anonymous
Guest
As a general rule the more quench the better.
Take your head and turn it over so the chambers are facing you. Now draw a circle around the head gasket to show the cylinder wall. The flat area that is in the circle but not part of the chamber is the quench area.
This flat area of the head and the flat area of the piston coming together in very close proximity (.035-.050) is the quench zone. The .035-.050 distance from the piston to the head is the quench distance.
We call it quench the Brits used to call it mechanical octane. What it does is to send a shock wave into the chamber causing extream turbulance. This causes a fast burn of the fuel and air mixture. This in turn allows an engine to run with less ignition lead timing and is more octane tollerant.
I have read that the difference in terms of compression can be 1 full point, but I think a half point is more realistic.
You have heard of Zero Decking a block. This is when the piston comes exactly to the top of the block, not obove or below. Then the quench distance is set be the compressed thickness of the head gasket, about .035.
There are other factors that come into play on the compression distance. Such as the RPM range of the engine and the materials (aluminum rods) and clearances of the engine.
On a very high RPM engine with aluminum rods the quench distance will be around .055 or more. But the dynamic distance, the distance at racing RPM, will be much less than that.
In general, if your engine has quench it will have more power and get better mileage than an engine that does not have quench.
Hope it helps,
John
Take your head and turn it over so the chambers are facing you. Now draw a circle around the head gasket to show the cylinder wall. The flat area that is in the circle but not part of the chamber is the quench area.
This flat area of the head and the flat area of the piston coming together in very close proximity (.035-.050) is the quench zone. The .035-.050 distance from the piston to the head is the quench distance.
We call it quench the Brits used to call it mechanical octane. What it does is to send a shock wave into the chamber causing extream turbulance. This causes a fast burn of the fuel and air mixture. This in turn allows an engine to run with less ignition lead timing and is more octane tollerant.
I have read that the difference in terms of compression can be 1 full point, but I think a half point is more realistic.
You have heard of Zero Decking a block. This is when the piston comes exactly to the top of the block, not obove or below. Then the quench distance is set be the compressed thickness of the head gasket, about .035.
There are other factors that come into play on the compression distance. Such as the RPM range of the engine and the materials (aluminum rods) and clearances of the engine.
On a very high RPM engine with aluminum rods the quench distance will be around .055 or more. But the dynamic distance, the distance at racing RPM, will be much less than that.
In general, if your engine has quench it will have more power and get better mileage than an engine that does not have quench.
Hope it helps,
John
MandarinaRacing
Famous Member
What happens with dished pistons???? Why do some engines use them and some don't ?
Alex
Alex
A
Anonymous
Guest
Alex, engines that have fully dished pistons, like many DOHC 4-bangers, don't have any quench at all. Dished SBC pistons generally are only "half" dished, with their dish on the side away from the head's quench area.
Floridaphatman":1mb32unj said:
From what Im reading quench area forces the air and fuel in the trapped areas to rush back into the chamber and disrupts the rushing flame front which in effect slows the flame front and the slowing and the turbluence of the two onrushing masses would promote more complete burning and the speed of the onrushing flame front, ineffect comtrolling the burn front.
If I have this correct then it would seen that a custon designed dished piston could "direct" the air fuel being squeezed from the quench areas into areas where you get the best mixing and control, in effect increasing power.
A
Anonymous
Guest
The quench (old texts call it "squench") band is pretty important on these I6 engines, even more so with crummy gas (aka low octane numbers). It controls the burning flamefront by pushing the unburned charge into the burning fireball, reducing the progress of the flamefront toward the cylinder walls. This effect reduces knock and smooths the power pulse.
If the quench band's height is too much, no effective charge movement occurs. If it's too thin (on decked blocks) then the RPM will be limited before 'rod stretch' at high RPM causes contact between piston crown and head. However, before the RPM limit is reached, the performance will be better.
Ford carried the quench band technology to it's extreme in the mid-1960s "FCP" series of FE engines. These 410/428 CID engines had wide, thin (.006") quench bands and deeply-dished piston crowns to contain the flamefront almost completely while it burned. The resulting increase in low-end torque and efficiency ushered in the era of 2.5:1 ratio differentials in Lincolns and Mercurys of that time, getting up to 20 MPG out of the 410 and 428 engines at highway speeds. These engines were RPM-limited to 4000 max, though, with a tricky reverse-advance distributor mechanism that sharply reversed the spark lead above 4k. Hot-rodders who changed distributors to get around this limitation paid a high price in crankshaft damage.
Most hi-RPM motorcycle engines use quench technology to reduce the "droop" in power between the low-end torque peak and the high-end HP peak, which is considerable in small-bore, hi-strung engines. The most common arrangement is the flat-topped piston with the much smaller diameter, semi-hemi head chamber, often with 2 spark plugs. Opening up the quench distance in these engines causes them to fall 'flat on their face' in the all-important midrange power area.
Which brings us to the FoMoCo 200 family. With log intakes, these engines are low-to-mid RPM power curve types, due to the intake system. Because of this, the quench band is very important for improving gas mileage and torque above 1800 RPM (aka HP). This translates to a peppier response at highway speeds, which we all would like..
If the quench band's height is too much, no effective charge movement occurs. If it's too thin (on decked blocks) then the RPM will be limited before 'rod stretch' at high RPM causes contact between piston crown and head. However, before the RPM limit is reached, the performance will be better.
Ford carried the quench band technology to it's extreme in the mid-1960s "FCP" series of FE engines. These 410/428 CID engines had wide, thin (.006") quench bands and deeply-dished piston crowns to contain the flamefront almost completely while it burned. The resulting increase in low-end torque and efficiency ushered in the era of 2.5:1 ratio differentials in Lincolns and Mercurys of that time, getting up to 20 MPG out of the 410 and 428 engines at highway speeds. These engines were RPM-limited to 4000 max, though, with a tricky reverse-advance distributor mechanism that sharply reversed the spark lead above 4k. Hot-rodders who changed distributors to get around this limitation paid a high price in crankshaft damage.
Most hi-RPM motorcycle engines use quench technology to reduce the "droop" in power between the low-end torque peak and the high-end HP peak, which is considerable in small-bore, hi-strung engines. The most common arrangement is the flat-topped piston with the much smaller diameter, semi-hemi head chamber, often with 2 spark plugs. Opening up the quench distance in these engines causes them to fall 'flat on their face' in the all-important midrange power area.
Which brings us to the FoMoCo 200 family. With log intakes, these engines are low-to-mid RPM power curve types, due to the intake system. Because of this, the quench band is very important for improving gas mileage and torque above 1800 RPM (aka HP). This translates to a peppier response at highway speeds, which we all would like..
Just to provoke some further thought on this subject, consider what happens in a flat-head engine, otherwise known as an L-head. I have a small collection of old Popular Science and Popular Mechanics magazines dating from the 1940's and 1950's. One of them has an article about testing a Hudson Super Six, in which they discussed the relative merits of the L-head design versus the overhead valve engines. One of the alleged advantages of the L-head was the fact that it had superior turbulence in the combustion chamber, resulting in more efficient burning. Another old term for quench is "squish area", which I find to be more descriptive of what is actually happening. The Hudson that was being tested had factory twin carbs. I sure wouldn't mind owning one 
Lazy JW
Lazy JW
