Great place to start learning CJ, and never too late to start!

You asked about quench area... Look at the very top pic in this topic; it has a RED zone... now while the red zone was me just messing around with a paint pen, THAT IS the quench area. The formal definition is the distance between the piston at TDC and the Head area that you see in red. As noted before this can be in the range of 0.030 to 0.045.

The pics are here.
http://www.bulltear.com/forum/viewtopic.php?t=726

A lot of people will spend numerous amounts of $$$$ on engine parts, and bolt in/on stuff, but they do not devote adequate respect to the heads. When I say heads, let‚Äôs assume this to be the Intake Runners, Combustion chamber, and Exhaust runners.

Porting is the process that makes the Runner area physically LARGER, in both height, and width. Usually this is for high performance and high RPM engines, as they want to flow as much air in as quickly as possible. For lower RPM usage, let‚Äôs assume under 5K, if you make the runners TOO large, it will slow down the travel time of the gasses, and thus you will never feel the effects of the porting until the upper RPM band.

Polishing, as I believe it to be limited to this, is not only porting the runners, but also giving them a smooth finish, sometimes to the extend of a chrome finished look. The stock heads have pits, and large air obstructions, which will create turbulence in the air flow in the runner. Some will argue that this is a good thing, and to be honest I have nothing to dispute against leaving the runners stock.

Now to discuss the level of polishing, let me first explain where and why I am taking my runners to the level that I am. I am going to a brushed aluminum look, with a slight rough finish. For the lower RPM that I am trying to work around, I do not want huge ports that would slow down air velocities. The same idea is true for guys who run exhausts that are too large in diameter, but we‚Äôll get there another time.

The reason for not polishing the intake runners is because of the necessary properties of fuel. Gas, 93 octane, will not burn in the liquid state. The carburetor transforms the liquid into a fine vapor, which needs to stay vaporized. With a cleanly polished surface, the air/fuel mix will not mix and ‚Äútumble‚Äù with enough chaos, to stay mixed. However any time that you can eliminate an obstruction in the way of air flow, either from mixed matched gaskets, or protrusions in the runner, or chamber for that matter, will increase air velocity. The protrusion will not only disrupt the air flow, but it will also create a void and a drag effect.

Another good thing to do is to measure the volumes of the runners, after the head is assembled with valves. You want the volumes of all Intake runners, on both sides to be equal.

With regard to the exhaust runners anything you do will be better than stock, anything from removing imperfections, to all out polishing. The exhaust isn‚Äôt that critical, to where you need a specific volume, or surface, you just want the gasses to get out.

*Contrary to this idea I have a thought that I will be soon to post on a topic here, for critiques and perhaps a new idea MC 😉 *

That almost covered it with runners, and now we can move on to combustion chambers. The idea here is to create chaos in the chamber, while minimizing or elimination of hot spots. The stock castings have many imperfections which impede the flame front, and are prone to hot spots. These hot spots can turn red hot, and ignite the raw air/fuel mix before the spark plug.

After smoothing out the rough casting, you need to cc the heads, through using a Burette and a sheet of Plexi-glass. Making sure each combustion chamber is of equal volume is of great significance. Each chamber, if of equal volume, will yield a smoother and more equally balanced explosions and forces. There are some schools of thought out there that recommend swirling the combustion chamber. I still have yet to read up on this, and learn how I want to customize it to my engine.

I want to keep as much reflective surface on the valves, Combustion chamber, and Piston top for a few reasons. 1) To reduce if not eliminate carbon build up, and 2 to physically reflect heat in the combustion chamber, such that it stays in the chamber, instead of being diffused into the head and piston. Now I should also say that the cylinder walls should not be polished, unless they are silicone lapped. Mercedes does silicone lapping, even read in their technician‚Äôs manual one time that if they cylinders are not properly silicone lapped, the pistons will seize in the block. Now how‚Äôs that for ingenuity, and tight tolerances! Anyone know where we can get our AMC engines done this way. But anyway, the machinist will hone/cross hatch the cylinder walls accordingly, and make sure to inform them whether you have cast rings or molly rings for this makes a difference in the way they are cross hatched.

CJ, you have a great place to start with your information search, and a plethora of knowledge amongst the group! Feel free to ask any questions, or IM me any time, I‚Äôd be glad to help anyone out.

Best regards,
Mike M
Charlotte, NC