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

Yes sir I am. I was still in HS and had no real clue about deck heights. You tend to remember your firsts though. I distinctly remember the pistons above the block as I was cleaning carbon off the piston tops out in my dad's driveway. I can't give you a dimension as I never had any reason to measure it at that point in time.
BTW, It was also my first "4 speed swap in" car as well, but that's a longer story!



After I read it in my manual I realized what that was all about.
It is also in the NHRA Engine Specs for Stock for 1969.
 
It is also in the NHRA Engine Specs for Stock for 1969.

Yes, exactly. One more piece of evidence. None of the factory engines were anywhere near blueprint spec.
 
O.K., So after all that I read, I still need a piston for my 68 440 with 906 heads! I want to "Quench" or "Squish", but
I don't want to use Hypereutectic. I feel like I'm juggling running chain saws!
 
O.K., So after all that I read, I still need a piston for my 68 440 with 906 heads! I want to "Quench" or "Squish", but
I don't want to use Hypereutectic. I feel like I'm juggling running chain saws!
I think you are in between a rock and a hard place then. As far as i know, basically two ways to get quench with a 440, closed chamber heads, either with a flat top or a d-dish to get the compression you want, or... quench dome pistons to fill the open chamber of a 906 head, and i think they are all hypers. I may be wrong about that, icon may have a forged quench piston, i dont know. Then there is always custom pistons, but i would probably go to a closed chamber aluminum head before i paid for custom forged quench pistons.
 
O.K., So after all that I read, I still need a piston for my 68 440 with 906 heads! I want to "Quench" or "Squish", but
I don't want to use Hypereutectic. I feel like I'm juggling running chain saws!

Sometimes you simply cannot have what you want.
 
Checked icon catalog on line. Looks like they have what they call a "step dish" forged quench piston...... but only for low deck strokers with rat motor pins. Oh well...... So, how do you feel about a 512?
 
I would use the Hyper's, except that I had forged pistons in the engine and the piston to wall clearance
is a tad too much for them. Don't want to bore any more, so I guess I'll put a set of flat-tops in with
valve reliefs. I went to 440 Source and they only have pistons with 0.990 Dia. pins. I have Eagle rods
with 1.094 pin holes. I guess I CAN'T get what I want. Oh Pashaw!
 
Late to the fight here, sorry.

With all other parameters equal ( ports, valve size, etc), open chamber heads flow better. Why? Because the valves, especially the intake, are unshrouded.

Closed chamber, or quench heads, are more detonation resistant, for all the reasons argued in the above posts.

When high octane gasoline is available ( I’m talking the old SONOCO 100) why worry about quench? Get the flow, IF you can get enough compression with the open chamber.

Rule of thumb: on a 350 ci engine, each point of compression is worth 25hp. If the gas is shitty, like today, gaining that point of compression may outweigh the flow gain from the open chamber.

426 HEMIs are designed open chamber because no one needed to worry about shitty gas, or emissions, and open chambers flow better.
 
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
 
I would use the Hyper's, except that I had forged pistons in the engine and the piston to wall clearance
is a tad too much for them. Don't want to bore any more, so I guess I'll put a set of flat-tops in with
valve reliefs. I went to 440 Source and they only have pistons with 0.990 Dia. pins. I have Eagle rods
with 1.094 pin holes. I guess I CAN'T get what I want. Oh Pashaw!
More shopping is in order. Ross, Diamond , Icon etc. I have a couple sets of Ross shelf flattop pistons with the mopar pins.
 
More shopping is in order. Ross, Diamond , Icon etc. I have a couple sets of Ross shelf flattop pistons with the mopar pins.
Theres another , too, that does mopar stuff, was founded by a guy who sold his previous piston company. Race tech? Or something like that . I'm sure someone here will have the right name.
 
I can get to RaceTech's site, but I can't shop or pull anything up! I Dunnow?
 
I can get to RaceTech's site, but I can't shop or pull anything up! I Dunnow?
I had the same problem when i checked. However auto tec, and racetec are the same company. Checked thru duck duck go, i found cnc motorsports that show a beautiful autotec forged flattop, 030 040 or 060 for $550. for a 1.094 pin, and stock stroke. Dont know if that fits your budget or not. I dont even know if thats a good price! At cnc's site just narrow the field by asking for the 1.094 pin.
Edit: racetec seemed to want to download their whole catalog, i didnt need that taking up space.
Edit: competion components has the same autotec for $528
Further edit: .030, 040, 055 not 060.
 
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I have to measure my deck height, and cc my heads before I pull the trigger. This post couldn't have come
at a better time. I learned alot from everyone about this subject. At this point price is not as important as
getting the right piston but don't get me wrong, I won't spend $700.00 or more. Who do these piston
manufacturers think they are? They mass produce them in minutes and then want a fortune. I'll make my
mind up in the next week or so and post my choice and reasons. Thanks again guys!
 
The autotec above says it has a 2.07 pin height, so .020 in the hole at blueprint deck heught of 10.725 . Let the compression ratio calculations begin! (Or .013, if you use 6.767 for rod length)
 
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