Question for 340King

[Speedy#1]

I did a search on KB PISTONS and on page5 they talk about Quench area and how it relates to power and performance,now every one knows that milling the head will raise the compresion but milling the deck will allso raise the compesion and will get you closer to a .040 quench area.O K now on the /6 ,the piston sit's .140 down from the deck for example would just milling the head be a bad thing to do? Will reducing the cc's on the heads change any thing beside the compresion? would stock pistons work o k ?

[340king]

Well Speedy, you always ask good questions. I must first tell you that I have never worked on a /6, but it really doesn't matter for the questions you have asked.

The cylinder head design has a lot to do with the matter of creating quench. Most Mopar engines have an open chambered or non-quench head. Some, like the 273 Commando and the big block 915/916 headed engines used a quench chamber. The quench chamber uses a flat surface inside the chamber area that reduces the chamber volume. This flat surface forces the gases out of the area between the head and the top of the piston when the piston is operated at a close tollerance. Milling the quench chambered head does not move the flat mating surface (the portion inside the chamber) any closer. Milling only reduces the volume of the open or domed portion of the chamber.

In non-quench heads, milling the head increases quench. This is because the open or domed portion of the chamber gets closer to the flat mating surface. This also decreases the chamber size, increasing compression.

Now, just milling the head is not a bad thing to do. You just have to keep in mind that you may only be reducing the chamber volume while doing this. In the case of the .140" below the deck piston height, milling the head(s) will really not affect the quench. Even though the domed portion of the head is getting closer, the quench remains virtually unaffected. Now as we get the piston closer to the deck, we begin to see the benefits of milling.

I like having my pistons come close to the cylinder head(s). It causes a little more turbulence in the chamber just before firing. I like turbulence inside the chamber. It can resuspend any fuel that has formed droplets on the surfaces in the quench area. It also can reduce the inherent temperature differences found inside the chamber by mixing the air/fuel more.

Are your stock pistons down the hole .140"? If so, you might be able to increase the output of the engine with a better quench setup. All things being equal, a flat-top pistoned-quench headed engine is more efficient than a domed piston open chambered engine. Most naturally aspirated high output race engines use some form of quench cylinder shape.

The quench chamber shape does have its drawbacks though. It is usually worse at valve shrouding. They may be worse at heat retention or having hot spots. The coarse cast dome has a greater surface area that helps to gather and disipate heat. The usually sharp transition from the flat mating surface to the domed chamber is a prime area for hot spotting. Efforts to reduce the valve shrouding and the hot-spotting should be considered in the final product.

I hope I have covered everything you needed here. If you can achieve quench at a reasonable cost do it. Can you get by without it, yes.

[Speedy#1]

Thanks 340King ,those are the answers to the questions i was looking for,i figured you would be the person to ask ,now i know what i need to do and hope it don't cost to much!!