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Old 11-26-2012, 02:14 PM
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Originally Posted by mouse77 View Post
Can i ask an honest question without getting flamed (im actually fine with being flamed), or banned, or whatever?

Whats the deal with quench here?

It seems every single post that has anything remotely to do with compression ratios, theres more than a few guys on here that are fascinated with "Quench"
Most actual engine builders call it "Squish" Which is only slightly less dumb sounding than Quench.
I will use "Quench" for everyone that loves that word, but when you read it please remember i prefer Squish.

Quench is a misnomer, because the whole idea of the quench area is not to "quench" the new beginings of the combustion process, it is to give it a head start. Everyone here obviously knows what comes next, as most of you have studied the 1/8th paragraph in Smokey Yunicks 200 page book where he breezes over it. And at the end of that small paragraph it reads (Quoting offhand, but you will get the idea) Quench/squish while important, is not THAT important, as long as it is not excessive one way or the other.

How did the magical unwarrenteed HEMI that blew up all the time, so they didnt give it a warranty, even run with zero quench?
How did honda make 250 plus HP out of the S2000 with, you guessed it, little to zero quench.
*Most* Dodge 340/360/440 Engines had like .100-.125 Quench. Im not kidding. They were so poorly machined and slapped together it was common to find pistons .040 and .050 in the hole, and a dished piston, and a dished head!. Any old guys remember the quench step piston? Ya, it didnt work so great. Twas still a stone.

Heres 2 engines, that would actually benifit huge from tightening up the quench, Flathead Fords and a Briggs and Stratton.

Quench, in racing engines is used to lower detonation. It can cool the piston. It can do alot of great things.
Under sustained WOT at high operating temperatures.
In your street car. Not so much. Idle around town, take it to 6000 6500 (woooo) once a week...

Quench is almost insignifigant in street engines, it is not even worth looking at 99% of the time.
And never mind you deck the block, buy a flat top, and run a performance type gasket, i can guarentee that thing is between .050 and .040 quench. You didnt just launch a nasa missle or finally reengineer the wheel, you decked the block a got a decent piston, and somehow you engineered your quench?

Now heres the kicker: Have any of you, even once, though about rod stretch when calculating your critical, cannot deviate, must have "quench"? Theres one guy going, "Ya i have!"
You my friend, are the smartest man on this site! The rest are going "Oh man, my quench is .0xx (depending on profile and material used) tighter when my cars actually moving down the street, my dreams have been smashed!

As for real performance/racing applications, if you are doing your homework, your going to depth mike the block/piston at preassembly to get your in the hole number. THEN you calculate in rod stretch, and bearing material, and oil film compression, and then you find out your actual gotta have quench number, after of course taking into the account that different kinds of pistons do grow at different rates when they are absorbing all the combustion heat, and that they dont just grow in diameter. Then you machine the block, AFTER adding everything up.

Now i see you guys arguing over .005 in quench.....
Now we take into account that your piston grew .002 up, at 6000 your rod has streched, for arguments sake, .005, you used a digital caliper instead of a $500 depth mike, you probably didnt measure TDC and piston rock correctly with a accurate gauge and a 24 inch degree wheel, you are probably at least .010 out on your static measurements!

And you all are telling me and everyone else on here how critical quench is, and how to check it?

PLEASE, keep it realistic fellas! Anyone can use Google and look like a genius. Anyone can memorize a Yunick, or how to build a small block chevy book (which are both outdated by 20+ years now, things have changed a bit in racing engines in 20 years)

All the new guys on here, are all wound up about quench, and swirl port heads, and pushrod length, and all sorts of crap that only really matters if you race your engine. Stick to the basics. Stop being so holier than thou with each other. Try and help someone get into the hobby, instead of confusing them with wild calculations and theory. Small block chevs have made up to 365HP with all of the stuff you guys call junk. Soft exhaust seats, "too wide" "too narrow" lobe centers, small valve springs, short dual plane intakes, with exhaust manifolds!!
Then i see posts where the guys got a stone asking about something stupid like coil bind with his 480 lift 116 centerline turd cam, that might make 250 hp and you all are desktop dynoing it at 344 hp, and "you gotta use an airgap intake with a port match precisly 2 inches into the head with vortecs and 1 5/8 headers ONLY, and a .037 quench and you gotta use plasma moly rings with a 800 finish on the cyls with a burnishing brush run at 400 rpm, and a 625 edelbrock with A5 metering jets......."

We talk about pushrod length for hundreds of pages, and then most of you are running stock rockers or chinese summit rockers that are deflecting all over the place, why??
Do you have a jesel state of the art rigid valve train to warrant .117 longer custom pushrods? or will .125 do if you are using a 510 hydraulic piece of junk with lifters that compress .020 and blow all of the measurements and hours of theory out the window???

Sorry about the rant. It went longer than i expected, I couldnt take it anymore. If I dont get banned, i will try to help more, in practical ways without all the big word voodoo i see so much.
Geeze, I take 4 days of vacation and the wheels come off!

Squish and quench are two (2) different functions of the same part of the combustion chamber. This part exists in wedge, hemi, and pent chambers just in a different configuration. It also exists in the Ford flathead which would never have lasted into 1953 without it; it just looks different when you look inside of one. For a wedge the squish/quench step is on the side furthest from the spark plug. For the hemi and pent chamber it is a circular ring around the outside diameter. For the Ford flat head and the Briggs and Stratton it would be the extreme close closure of the piston to the cylinder head, because the valves are off in an anti-chamber beside the bore which makes a long and difficult chamber to design.

Both Ford and Chevrolet tried putting the squish/quench "wedge" into the piston in the MEL and the W motor while using a plainer surface to the head, neither worked as well as desired. While the Ford Cortina and other small bore Euro designs worked pretty well. Goes to show that bore diameter has a say in the outcome so hard fast rules will head you into problems.

Smokey skims a lot of subjects, while wanting to make money from his books, he really wasn't looking to add competition on the track, so there are a number of technical issues he leaves the reader with just enough information for them to be dangerous to themselves and everyone nearby.

Letís take Squish and Quench functionally apart, they are two different things happening at different times but produced by the same parts.

1) Squish---this happens as the piston is rising and ignition has not happened but will soon. Squish ejects the mixture from the distant side of the chamber regardless of shape (flathead included) toward the spark plug. It is intended to do two things to the mixture; first is to breakup remaining fuel globules into a fine mist and mix the air and mist into a homogeneous brew for a fast and complete as possible burn; the second event in Squish is to place as much molecular density as possible before the spark plug, this increases the likelihood of the spark actually starting a fire that also spreads quickly through the higher density of molecules than would be there in a more open chamber.

2) Quench---this happens at the end burn as the piston is passing over Top Dead Center and starting down the bore. Once ignition occurs the temperature inside the cylinder raises very high, thus in accordance with the Gas Laws so does the pressure. As the temperature and pressure increase, the yet to be combusted mixture ahead of the flame front is pushed into its self-ignition zone. The best example of this are the videos made of a home fire as it progresses in a closed room where combustible gases collect along the ceiling as the contents of the room burn. At some point the temperature and pressure along the ceiling come to the self ignition point of those gases and they just suddenly explode. A similar thing will happen to that mixture on the far side of the chamber as it gets hotter and more pressurized from expanding because of that heat. Suddenly it just explodes sending an even higher pressure wave to slam back into the flame front. So what to do involves Quench, which is nothing more than an area, the same area that did the Squish function nano-seconds earlier is now a place where there are two large surfaces that have a very small volume of mixture trapped between them. Lots of surface and little volume allows the surface to sink the heat out of the trapped mixture keeping it cool enough and lower the local pressure as a result to where the explosion of detonation is less likely to occur.

Since modern unleaded pump gasoline pump fuels cannot be doped with unlimited amounts of lead to push resistance to keeping the end burn from self-igniting, there has been a significant return to the Ricardo chamber to mechanically extend the octane of available fuel. Engines of the late 1950's through 1970 exhibit small and often sloppy degrees of squish quench as you the consumer could just buy more octane, if it pinged on 100, you bought 110. Today this option doesn't exist at least on the street, so we have to do a better job of design and manufacture which you see stating to happen in the mid 1980's as the manufacturers turn from add on gadgets to a systems integration approach to design to solve the problems of emissions, improved mileage, and increased power.

I'll offer a picture of a graph that is the output of the same engine in back to back dyno runs with the only change being an 18cc circular dish piston for an 18cc D dish piston. This because of the difference in dish shapes changes the amount of surface area in close proximity during squish and quench. The D dish has more activity than the circular dish. The big effect is to fatten the torque and power curves from midrange up to equality around the peak RPMs and the D dish carries its power fatter and longer into the rev range over the point of peak horsepower.

Bear with my I'm having quite a time getting old data into something that can be trasfered into here using this new Windows update.

Attached Files
File Type: doc Round to D dish.doc (72.0 KB, 87 views)
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