Quench?

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cuda67

cuda67

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Alright, I'll be the dummy for the day. I have heard the term, quench, when reading about engine builds. I'll cop out and admit, I haven't got the slightest idea of what quench is, what it does or if it just means you guys are thirsty.

Don't all of you laugh at once and don't beat me up too bad. I am about to start a build, in the next couple of months, and I want to learn as much as possible so I can make you all proud. I have asked for help and a couple of guys on this board have offered their expertise, I just don't want to wear them out with every little question I have. I will come to the board to ask about stuff and I know that I'll get good answers. Now, what is quench? I have only done or helped with a couple of stock rebuilds but I have never heard of, quench.#-o
 
That's my question too! Spoke with a friend yestedya, he said it refers to theway the falme combusts on an engine with zero deck and closed chamber heads. I think!.
Lets hear from those who actually know please:profilel:
 
Quench is what you get when the piston is less then .060" from the combustion chamber. The fuel-air mixture is squeezed out at high velocity from the areas where there is quench and helps to prevent pre-ignition and promotes a fast even burn.

On an open chamber head, quench is very difficult to achieve due to the manufacturing (casting) variances and rough surface of the chamber, plus the difficulty of finding a piston that would match the chamber perfectly. Some quench may be achieved around the edge of the combustion chamber where the chamber is smaller than the bore.

Compare the above to a Magnum or aftermarket small chamber head with a flat surface that extends well within the bore making it easy to achieve quench with a flat top piston. With a quench distance of .040", a compression ratio of 10.5:1 can be acheived on regular pump gas if the rest of engine is built to take advantage of it.

Engines with lots of quench also don't need as much spark lead as do open chamber no quench engine builds as the mixture burns more quickly and evenly.

Here's a great article to read:

http://kb-silvolite.com/article.php?action=read&A_id=39
 
Ramcharger, you are a silver tongued devil! Excellent explanation! I have found that .025 quench clearance makes the best power; not hard to do with a zero deck height. Still praying for a good job to come your way! I think you would make a great TEACHER!!!
Pat
 
PFogel said:
Ramcharger, you are a silver tongued devil! Excellent explanation! I have found that .025 quench clearance makes the best power; not hard to do with a zero deck height. Still praying for a good job to come your way! I think you would make a great TEACHER!!!
Pat
Click to expand...

Thanks Pat!

I'm too chicken to get that tight but I know people who have. :-D Still trying to get that "Elusive Job". I hope something pops soon. :)
 
Jack, you'll have to fly down here and tell me what mine is........ I ain't got the slightest.

By the way, when I know the answer, what do I do with it? (Please have mercy on a blithering non engine-building idiot....!) :sad11:
 
I certainly understand your fears! You have to have the best rods. In my 331" SBC in my S/G Vette, I ran that squeeze using Manley Pro Pistons that we custom domed (looked like melted sherbet) with gas ports, .043 moly rings .100 down from the deck. I used Childs and Albert aluminum rods and just loved them. This was an engine used to seeing in excess of 10,000 rpm leaving the line and on the 5-speed shifts. We checked the stuff every two weeks. Even after 50 runs that clearance did not tighten! I used to check it by "laying on hands" on each end of the heads at start-up because if any thing was wrong, you could feel it. I saw Jenkins do the same thing! The engine also used studs everywhere and dead soft solid copper head gaskets to handle the 14-to-1 compression. That engine had the first sheet metal intake on it that I totally made for myself. That little engine powered the Vette to 9.40s at 146 mph. It was bad to the bone. It was on the cover of the June, '82 issue of Popular Hotrodding and featured full color on the centerspread.
Pat
 
Tom, it's not what you do with it. It's what it allows you to do. Like run cheaper gas. Good quench also lets you control the flame travel therefore letting your engine run more effecently. (sp?) More horsepower/torque is the benifit.
It's not that hard to figure out. An easy example is my engine. I have flat top pistons at zero deck. I also have magnum heads, they have a smaller combustion chamber than open heads like J's. So if you sat my heads on the block, the piston would be touching the closed part of my combustion chamber. That would be zero quench. I used .045 head gaskets, so the result is a quench area of .045.
I hope that makes sense.

Jack
 
I use .030-.035. The wider the distance, the less effect you have. Once you pass .050 it's not doing anything anyway. I know race engines that go to less than .025 with steel rods and tight pistons. But no way with aluminum, especially with any real rpm.
 
Excellent info and discussion here, fellas. I, too, have heard the term 'quench' thrown around for a few years without totally understanding it. So, to get back to basics, the concept was developed to propagate the flame front in a way with very high speed movement of fuel/air mix away from the squeezed area and toward the spark plug.

Now, I suppose that this will not necessarily produce ideal flow through the combustion chamber. I might be barking up the wrong tree here, but I learned about the science of combustion many moons ago as it related to huge radial aircraft engines with hemispherical combustion chambers. Of course, the aim of design of those engines was not so much to produce horsepower as to produce torque so as to spin humongus props without the tips going supersonic. Those engines had very noticeable valve overlap.

So, is a high quench head mostly designed to avoid detonation?
 
Well if it makes you feel any better I just got finished building a 69 340(still on the engine stand) and I don't know what quench means. Though I did quench my thirst with more Fat Tires and Molsons than I should have.
 
quench is kb 191s with a 0 deck. i spent a year of spare time massaging a set of heads to chambers within a few cc,s of each other and only a .035 piston to head clearance with 2.02s and 1.60s had to sink the seats and valves and rework the rocker geometry. if i had it to do over instead of 13 to 1 i,d go 10 to 1 with o deck flattops. growing up i always heard people bragging about popups so i had to have some.
 
Fishbreath, in hemispherical engine's heads, the quench area is actually 100% over the piston. It is the same with pent roof combustion chambers and applies to 348 and 409 Chevies and the old 430 Lincolns. The wedge chamber became popular in production because it was easier to cast and machine. All the old Chrysler hemi chambers were 100% machined! Holding the exhaust valve open longer helped to scavenge and "sweep" the chamber of foul residual combustion products. Buick did the same thing effectively with their "nailheads". The quench area, say in a 340, is like "taint"...it's that flat spot on the piston not included in the main squeeze of the combustion chamber. As the piston approaches TDC, whatever fuel/air volume is in that tight squeeze (quench) area between the piston deck and the head is eliminated from most of the flame travel...thereby "quenched". Material in that small clearance volume is forced out into the flame front at high speed and promotes combustion. This is the advantage many see in the wedgie over the hemi. I hope I didn't muddy the waters. The tighter the quench area, the higher the static compression ratio and the higher the dynamic compression ratio as well. Just how much timing a tight quench engine likes is dependent upon a lot of variables. I still say nothing beats a hemi because the quench area IS over the entire dome with the plug firing near the center and nothing interferes with flame propogation. Look at the hemi valve angles and sizes! Nothing feeds on fuel and poops gases better than the hemi design! Todays better alloys have helped to reduce the weight of a high compression hemi piston. Top fuel pistons are really heavy slugs with really thick domes and flat tops and they are tuned "down in the hole". I've seen the tops of these pistons CONCAVED coming out of Don's last Top Fuel car!! The smart hemi racers do all they can to get as light a piston they can get with as big a dome as they can get with the least amount of compression height (center of pin to lowest part of deck). The power stroke on a normally aspirated hemi never bothers a piston even with dykes rings mounted way up but if that piston has a big compression height, the connecting rod feels it really big time at TDC on the exhaust stroke! It's like you tied a rope to a cinder block and swung it around like you were the crankshaft and then stopped it at one point and tried to "instantly" change it's direction. It will try to pull your arm out of its socket! That's what a rod feels with a heavy piston on the end at TDC on the exhaust stroke.
Pat
 
Thanks, Pat, that is a great concise treatise on combustion chamber design. From a purely theoretical power production standpoint, is it better to have instantaneous combustion throughout the entire combustion chamber or to have a moving flame front type of combustion event? (Of course, this is purely theoretical because there is no pracitcal way to get instantaneous complete combustion inside the chamber - does a diesel engine have an instant combustion event or does it ingite in a "hot spot" and propagate from there?)
 
cuda67 said:
Alright, I'll be the dummy for the day. I have heard the term, quench, when reading about engine builds. I'll cop out and admit, I haven't got the slightest idea of what quench is, what it does or if it just means you guys are thirsty.

Don't all of you laugh at once and don't beat me up too bad. I am about to start a build, in the next couple of months, and I want to learn as much as possible so I can make you all proud. I have asked for help and a couple of guys on this board have offered their expertise, I just don't want to wear them out with every little question I have. I will come to the board to ask about stuff and I know that I'll get good answers. Now, what is quench? I have only done or helped with a couple of stock rebuilds but I have never heard of, quench.#-o
Click to expand...



Well, lets see, there was a time I had no idea what that was ethier, and so I asked around the lunch room at work. No one else knew. (No real surprise there.) So I did the only thing I could think of.

I called Summit racing and asked the guy. What the heck, it was around 3:00 am on a Tuesday I think it was. I got a 15 min. explanation and left the phone happy and greatful and, LOL, just a bit smarter than the lunch room at work.
 
Fish, you can't have instantaneous combustion because the flame kernel will always start from a plug/ignition source if everything is working right. Also why many Hemis now have dual plugs. Nissan did it in the 80s on the 2400 series engines for that reason. The burn will be the fastest, best controlled, and most complete, when the mixture is tubled just prior to ignition, and the unburnt volume is the smallest. Why is controlled faster better? Because you can time the burn and the pressure spike much more precisely so less ignition lead is neede, less total timing, and less energy is wasted on developing heat as the piston is not located at the most best point in it's travel until 17-20° past TDC. This is for maximum leverage applied to the crank throw upon firing. That's why small-chamber pump gas strokers dont like total timing much more than 30° if everything is working right, and many dont like over 28° total. The quench distance allows a lot of good things to happen in the running cylinder, and the results are more power from less fuel at lower rpms. All from paying attention to detail during the initial design and machining of the package.
 
Thanks, moper, that sure makes sense. I can see how a progressive combustion can aid the power stroke. It amazes me that engineers can time the sequences so precisely in such a rapidly moving rotating assembly.

I am trying to remember what my dad told me about flying the Lockheed Constellation in the old days. Being a Flight Engineer, he would monitor a device on his panel that actually showed the flame propagation inside the combustion chamber. He would control/fine tune the condition by adjusting mixture and timing, if I remember correctly.
 
I saw siomething on the History Channel about that (WAYYYY before my time...lol), and yeah, they "tuned" the engines manually on the last piston powered planes. Altitude will change the burn, and even now, the guys running Avgas, are using a fuel that's not formulated for sea level use...lol. It's hard for me to visualize it in real time. It's easier saying "slow" vs "fast" but we're talking hundreths of a second. It's easy to "freeze frame" the motions and angles at any one degree. It's entirely another to map out a burn characteristic.. but they do. Must make for a long day...lol.
 
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