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With all the fanfare about quench, why then.....

wyrmrider, many thanks for your last post. It confirms my observation of 906 vs 915 heads in my drag car. I ran both versions with the same level of porting and the same short block, open headers. No significant performance difference between the 915 & 906. 12.0 CR using 110 race gas. Thanks Bill
 
It'll run better with no quench with full timing/low compression than it will with reduced timing/too high compression with quench. The power level between 9.0-1 and 10.0-1 is roughly about 3%. So at 500hp your talking 15hp.
Doug
 
Isn't quench about efficiency?
 
Isn't the quench built into the piston dome?
Mike
I don't think the Hemi design is a very good use of quench but the valve/port angle is very efficient and makes up for the lack of quench. THey talk about that a bit in the article I posted above.
 
Isn't the quench built into the piston dome?
Mike

12.5 pistons have valve clearances machined on the domes. Top has a flat to clear plugs, if using an extended reach.
 
Ok, my memory is going... LOL... I'm not sure if it's drug & alcohol related or just all the years but the memory is going... 1.74, 1.81 what is .070 amongst friends... What ever the case, 1.81's drop in with minimal machining.... So do 2.14's on the intake side....
 
Ok, my memory is going... LOL... I'm not sure if it's drug & alcohol related or just all the years but the memory is going... 1.74, 1.81 what is .070 amongst friends... What ever the case, 1.81's drop in with minimal machining.... So do 2.14's on the intake side....

I know the feeling!! I switched to the 2.14/1.81 combination on my motors shortly after DC started selling them. They work real well with the pocket porting. I did update some 516 heads to the 1.74 ex for customers many years ago. Bigger valves do work in BB's.
 
12.5 pistons have valve clearances machined on the domes. Top has a flat to clear plugs, if using an extended reach.
Yes but, since the quench area is around the perimeter isn't the clearance between the dome and chamber tight enough to perform the quench action?
Mike
 
Good thread Kern :thumbsup:

2286 flat tops, .050 in the hole. 452 stock heads. Sum 6401 cam. No quench, runs strong as far as I'm concerned.
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It'll run better with no quench with full timing/low compression than it will with reduced timing/too high compression with quench. The power level between 9.0-1 and 10.0-1 is roughly about 3%. So at 500hp your talking 15hp.
Doug

You didn't say it, but for clarity, ......and you will not be able to go up one full point in compression solely because of adding quench.
 
1967 quench...Yeah...Am I wrong on that ?

The 67 piston is about 0.085" in the hole. No quench and not really fixable without a different piston. And a 68 - 69 piston, still no quench (0.050" in the hole). The six pack piston, or six pack like piston with a 2.06"-ish compression height is the only reasonable way to get quench with the 915 head. Then the compression ratio will be very high.

That said, for an iron head motor, the 915 will always be my first choice if new pistons are going in
 
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You could build it that way & it should be fine...
Back in the day 915's were a known quick easy upgrade, you would feel the difference and that was on engines with the piston so far down the hole that it wasn't quench, it was compression.... Quench is just a bonus... Kinda like using an MSD without using an MSD...

This article is well written & explains it better than I ever could....



"What is the most, exact precisely defined occurrence in all piston engines? It isn’t ignition timing, combustion, crank indexing, or valve events. It is Top Dead Center. You can’t build an engine with an error at Top Dead Center because TDC is what everything else is measured from. Spark scatter, crank flex and cam timing can move, but TDC is when the piston is closest to the cylinder head in any one cylinder. The combustion process gets serious at Top Dead Center and about 12 degrees after TDC, most engines want to have maximum cylinder pressure. If maximum cylinder pressure occurs 10 degrees earlier or later, power goes away. Normal ignition timing is adjusted to achieve max cylinder pressure at 12 degrees after TDC. If your timing was set at 36 degrees before TDC that is a 48 degree head start on our 12 degree ATDC target. A lot of things can happen in 48 degrees and since different cylinders burn at different rates and don’t even burn at the same rate cycle to cycle, each cylinder would likely benefit from custom timing for each cylinder and each cycle. Special tailored timing is possible but there is an easier way—“Magnificent Quench”. Take a coffee can ½ full of gasoline burning with slow flicking flame. Strike the can with a baseball bat and you have what I would call a “fast burn”, much like what we want in the combustion chamber. The fast burn idea helps our performance engine by shortening the overall burn time and the amount of spark lead (negative torque) dialed in with the distributor. If you go from 36 degrees total to 32 degrees total and power increases, you either shortened the burn time or just had too much timing dialed-in in the first place. If you have really shortened the burn time, you won’t need so much burning going on before Top Dead Center. Now you can retard timing and increase HP. Did you ever have an engine that didn’t seem to care what timing it had? This is not the usual case with a fast burn combustion but an old style engine with big differences in optimum timing cylinder to cylinder will need 40 degrees of timing on some and others only need 26 degrees. If you set the distributor at 34 degrees, it is likely that 4 cylinders will want more timing and 4 cylinders will want less ( V-8). Moving the timing just changes, which cylinders are doing most of the work. Go too far and some cylinders may take a vacation. Now what does quench really do? First, it kicks the burning flame front across and around the cylinder at exactly TDC in all cylinders. Even with spark scatter, the big fire happens as the tight quench blasts the 32 degree old flame around the chamber. Just as with the coffee can, big flame or small flame, hit it with a baseball bat and they are all big instantly. The need for custom cylinder-to-cylinder timing gets minimized with a good quench. The more air activity in a cylinder you have the less ignition timing you are likely to need. When you add extra head gaskets to lower compression you usually lose enough quench that it is like striking the burning coffee can with a pencil. No fire ball here and that .070-.090 quench distance acts like a shock absorber for flame travel by slowing down any naturally occurring chamber activity. A slow burn means you need more timing and you will have more burn variation cycle-to-cycle and cylinder-to-cylinder, result more ping. Our step and step dish pistons are designed not only to maximize quench but to allow the flame to travel to the opposite side of the cylinder at TDC. The further the flame is driven, the faster the burn rate and the less timing is required. The step design also reduces the piston surface area and helps the piston top stay below 600 degree f (necessary to keep out of detonation). All of our forged pistons that are lower compression than a flat-top are step or step dish design. A nice thing about the step design is that it allows us to make a lighter piston. Our hypereutectic AMC, Buick, Chrysler, Ford, Oldsmobile and Pontiac all offer step designs. We cannot design a 302 Chevy step dish piston at 12:1 compression ratio but a lot of engines can use it to generate good pump gas compression ratio. Supercharging with a quench has always been difficult. A step dish is generally friendly to supercharging because you can have increased dish volume while maintaining a quench and cool top land temperatures. You may want to read our new design article for more information. ".

By John Erb
Chief Engineer
KB Performance Pistons

Posted that article several years back....not sure if it's still on the site or not tho. I've read several articles about quench and that one was one of the easier ones to understand....at least for me lol
 
The 67 piston is about 0.085" in the hole. No quench and not really fixable without a different piston. And a 68 - 69 piston, still no quench (0.050" in the hole). The six pack piston, or six pack like piston with a 2.06"-ish compression height is the only reasonable way to get quench with the 915 head. Then the compression ratio will be very high.

That said, for an iron head motor, the 915 will always be my first choice if new pistons are going in
Got a 440 now with 516 heads and a .050 down piston and the CR is 10.3-1 with a steel shim gasket.
 
Got a 440 now with 516 heads and a .050 down piston and the CR is 10.3-1 with a steel shim gasket.
Yep, that sounds about right. I had one similar. Small cam too. No running that on pump gas.

Does yours run on pump gas? If so, what cam and timing curve.
 
So the only gain seems to be from compression, not actual flow.
 

I don't think the Hemi design is a very good use of quench but the valve/port angle is very efficient and makes up for the lack of quench. THey talk about that a bit in the article I posted above.

Take the information in my link above with a grain of salt I guess. One of the self professed experts on FABO says the guy doesn't know his *** from a hole in the ground (so to speak). Getting tired of all the F-king experts and of all the false information on the internet. Rant over! Drive through. (sorry, wound a little tight right now)
 
I guess I could have avoided that tangent had I titled this thread WEDGE Quench !
 
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