Author Topic: Quench question. (Read 3165 times)

HP2 · « **Reply #15 on:** January 03, 2008 - 10:37:49 AM »

Quote from: StRoKer on January 02, 2008 - 05:21:46 PM

personally I think people zero deck their block to get more compression.... however a zero deck and a .040 gsket is ideal quench...

Only with a closed chamber head. Most open chamber mopar big block heads have another .050-.080 in space in the chamber area. The last few I've checked were all over the place and there was very little consistency across the chambers. For this reason I chose to mill the chamber flat to get my quench distance, but then again, I had a significant quench dome on the pistons I was using that allowed this to work.

Swedefish · « **Reply #16 on:** January 03, 2008 - 02:05:39 PM »

Quote from: moper on January 03, 2008 - 07:44:12 AM

No, zero deck does a couple things. Like CP said again, the math is easier...lol. Second, there is less wasted space above the top ring (this area never burns and doesnt produce power. So the smaller it is the better) Third, the piston is designed for a certain height deck surface. Mopar factory maching is crap. If it was flat, it was good enough. That's why the "10.5:1 compression" ratings are a joke. It also has a side effect of keeping everything else correct when the decks are parallel to the crank and flat. When the decks were originally milled, they were cut on a milling wheel. Because it's a wheel, the center will always be cut deeper than the edges, as the milling head has to be angled, or the cutters will hit as they pass accross the surface and they may chatter. It's not much, typically in the .0015" range. But I've had blocks with decks where the center was .017" taller than the blueprint spec, one edge of one end was .024" taller, and the opposite corner on the opposite end was .029" taller. These had been "milled" during a "performance build". The RB wedge blueprint spec is 10.725 IIRC, and I think one out of ten or so I've used was even in the 10.72? area. Most are 10.74+ from the factory. So you buy a good forged piston, the deck is milled flat, and then put together, and your ) deck just went to recessed .015+. If you were building for quench, that would be a problem. Which is why every engine I do, regardless of size or output, gets the mains align honed, and the block square decked to the height I need. The better block equipment now uses the main bore centerline and the camshaft bore centerline to index the decks. Old millers use a machinists level and someone's eye.

When checking the align of the mains is there any tolerence accepted? I did the measure at the bottom of the seat and were it meets the main cap.
I can insert a .0019 gauge between a ruler and the 2:nd, 3:d and the 4th main seat. Otherwise its not out of round.

moper · « **Reply #17 on:** January 04, 2008 - 07:53:02 AM »

It's not so much out of round, as it may not be exactly 90� to the bell housing flange. Think of it as building a house on a hilly lot. First you have to level things, then form up and pour the foundation. Mess those two up, and the rest of the house will suffer over time, even if it does get built and someone moves in. The basic deal on a V8 is teh crank must be 90� to the bell's mating surface, the bores have to be 90� to that centerline, and the decks have to be parallel to that centerline. Out of round affect bearing crush and fit. Out of alignment with each other, or out of parallel with respect to the decks, means more stress on the crank and rods, harmonics that do weird things like torque convertor and/or bellhousing bolts loosening up, input bearings, pilot bearing, shifting and clutch problems, and it all translates to lost power output and shorter life, not even considering the effects on cylinder to cylinder compression ratios from the installed heights of the pistons. You cant measure that with a straight edge, and if you found .0019" shift from #1 and 5 to the three center, I would call that unacceptable. By factory spec it would be fine. I build as far beyond that as I can...lol. Laso, it is crutial that each bearing bore have zero taper accross the saddle and cap. Because the bearing will mimic the housing its in when torqued. Taper on teh crank is bad, taper on teh bearing is the same bad, and again, unless you have a dial bor gage, torque the caps, and then measure several points accross the bore, you dont know if it's tapered. I'd bet yours have some taper on at least #1, and that's why you are coming up with the three center ones being "out". In any case, it's $150 to correct. Why would you not spend $150 if your spending $4K+ on even a budget build? And as I said, the modern machines use the bell housing and the crank and cam centerlines to properly index the other operations. So if that is off, it makes it impossible for anything else to be "on" down the line.

Swedefish · « **Reply #18 on:** January 04, 2008 - 09:34:39 AM »

Thanks moper.

When I get in written, it all are so obiously, lol.

tactransman · « **Reply #19 on:** January 05, 2008 - 04:25:13 PM »

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 � 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

Author Topic: Quench question. (Read 3165 times)

HP2

Re: Quench question.

Swedefish

Re: Quench question.

moper

Re: Quench question.

Swedefish

Re: Quench question.

tactransman

Re: Quench question.