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

Kern Dog

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Did Ma Mopar use the quench heads in 1967 440s then step away from them for 1968 and keep open chamber heads until the end?

I hear people tout the benefits of quench. I can see their point but the 1967 440 Magnum and the 1968 440 Magnum had the same HP and torque ratings.

I am looking at using 906/452/346 heads on my engine for the Jigsaw car.
Even at zero deck, there is no chance of quench. I've read that you have to mill these open chamber heads about .120 to get a closed chamber. No thanks!

If quench isn't that important, where is the harm in leaving the heads uncut, the decks uncut and just assemble it and run it ?

4.35 bore
3.75 stroke
7 cc valve reliefs in the pistons
.025 deck clearance
.039 head gasket = 9.26 to 1. Seems like a comfortable margin for iron heads, right?
 
Did Ma Mopar use the quench heads in 1967 440s then step away from them for 1968 and keep open chamber heads until the end?

I hear people tout the benefits of quench. I can see their point but the 1967 440 Magnum and the 1968 440 Magnum had the same HP and torque ratings.

I am looking at using 906/452/346 heads on my engine for the Jigsaw car.
Even at zero deck, there is no chance of quench. I've read that you have to mill these open chamber heads about .120 to get a closed chamber. No thanks!

If quench isn't that important, where is the harm in leaving the heads uncut, the decks uncut and just assemble it and run it ?

4.35 bore
3.75 stroke
7 cc valve reliefs in the pistons
.025 deck clearance
.039 head gasket = 9.26 to 1. Seems like a comfortable margin for iron heads, right?

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
 
Quench is bad for emissions so the factory had to move away from it during the smog years. Once the engineers figured out EFI then quench came back as did a whole bunch of performance. But with a carb and a mechanical distributor the engineers hands were tied. Almost everyone went with open chamber heads in the early 70's and the performance dropped like a rock.
 
How much of the power loss was due to the huge drop in compression and catalytic converters? Ha ha, I know, unrelated and apples to oranges....Just teasing !
Again, I agree with the theory of quench, I'm just curious about how the 67 and 68 440s carried the same ratings. It would be interesting to see a side by side dyno comparison
 
Didn't the 915s have a smaller exhaust valve? Maybe the bigger exhaust valve in the 906s made up for the loss of quench? Also gas was better back then.
 
Didn't the 915s have a smaller exhaust valve? Maybe the bigger exhaust valve in the 906s made up for the loss of quench? Also gas was better back then.

LP 915's had 1.72 ex valves HP 915's had 1.81 ex valves same as 906's.... And adding 1.81's is an easy upgrade..

Correction...

1 Wild R/T said:
LP 915's had 1.62 ex valves HP 915's had 1.74 ex valves same as 906's.... And adding 1.81's is an easy upgrade..
Fixed

Thanks @BSB67
 
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How much of the power loss was due to the huge drop in compression and catalytic converters? Ha ha, I know, unrelated and apples to oranges....Just teasing !
Again, I agree with the theory of quench, I'm just curious about how the 67 and 68 440s carried the same ratings. It would be interesting to see a side by side dyno comparison

How long have you been playing with cars Greg? (Kidding). Manufacturers advertised specs weren't based on facts... Car salesmen are allot like politicians... They stretch the truth....
 
Quench. If you can get good quench, go for it. If you're building from scratch, silly not to plan for it. Other than that, it's overrated.
 
Wild, a correction, low perf 915's used 1.60 Ex, HP 915's used 1.74 Ex. The 1.81's are the upgrade for both 915 & 906's.
 
How long have you been playing with cars Greg? (Kidding). Manufacturers advertised specs weren't based on facts... Car salesmen are allot like politicians... They stretch the truth....

Wild, I agree, very few advertised HP ratings were "real", mostly advertising bull, or playing the sanctioning body "factor" game.
 
My friend that helped me out with my 512, builds race engines for a living. He is all about Quench, or squish as he calls it. I have no complaints whatsoever! I know my 512 was built as close as we could to maximize it!

I’d have to locate the paperwork on build to come up with specs on it. I can if interested.
 
When we build engines from scratch we do quench. However, most our builds are open chamber, we may back off the open chamber compression .3 vs a quench engine. But, we've built 10.5:1 iron headed open chamber engines that you can run 87 octane with all the timing in and never a sign of detonation...and 9.3:1 engines that would ping. Every part of the build is a factor. Most shops back off compression to keep the success rate up. Because some people just drive and then wonder "whats that rattling noise"...until it's to late....and blame it on the builder. I've seen owners 2 cheap even 2 try premium to see if it helps.:cursin: ...they expect it to run fine on whatever they put in the tank.
Some combinations work better with quench where others combos don`t seem to care. Sometimes you will see less detonation with quench and most of it likely will be from the need to run less timing to make power. 32-34 vs 36-38. As for hp gains quench may only increase hp in the single digits. How quench responds to the build IMO not the same on every build. I think quench usually gains, but how much it gains quantatively??? So use the open chamber and enjoy the car and built it knowing there is no quench.
You may consider a .020 head gasket for a modest bump in compression.
 
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426 hemis didn’t have quench and they ran ok!
:thumbsup:
 
I think you already answered your own question.

Are you assuming the 67 had quench just because it had closed chamber heads?
 
I seem to have lost track of what quench really means. What is it to the rest of you guys?
 
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1967 quench...Yeah...Am I wrong on that ?
 
WILD
thanks so much fo posting that piece from thre late john erb
guys go back and read it again
Back after the open chambers came out we were consulting on the problem of burned down engines in 440 transit bus applications- warranty rebuilds
Then finding motorhomes were burning up half way to Vegas
exhaust manifolds were glowing cherry red
we started welding up the chambers
Then getting custom quench dome pistons
We were Invited up to Carson City by John and the KB quench dome piston was produed
He had other good input from other excellent people-we learned some
The other fix was to ditch the stock cam and keep the valves on the seats as long as possible
lots of dyno time on both small and big blocks and other makes
on BBM EGT could drop 800 degrees
OH more free flowing exhaust helps
AnotherAdvantage is that motors are not as sensetive to advance or fuel (pinging)
Now power
past the point of max torque there is not as much of an advantage with race fuel
drag only car can run with open chambers but IMHO it will require better fuel
Rmember the TRW "turbo" piston?
 
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