We have actually two arrangements that I am going to pass around. One will only allow you to unscrew this just so far because we have put in a stop here at the 3-percent point, and that is this one. The other one allows you to unscrew it just as far as you want to go back and forth. You will see that it has a tapered screw adjustment here and you can just unscrew this and it does not make any difference beyond a certain point; you can go up to 3 percent and no further. Everybody is happy. (Refer to fig. No. 5.)

Mr. CHESEBROUGH. Mechanics like to move things, and they have to do this to be able to make them happy. So we have made this so that

they can be happy but they are not going to do anything to the idle mechanism.

Mr. HEINEN. Here is what I believe is the finest representation of the degree of meticulous detail that spells out success in this kind of operation. Here we have two throttle bodies and you see that they are identical except for two little holes that are located at this point and this point. (Refer to fig. No. 6 on p. 570.) We wondered if the location of that breathing hole made any difference at all so we went all around these blades. We put, I think it was something like 35, different holes in them, and we did this for several carburetors.

For this particular one, we came up with the fact that if you move the hole from this location to this location, you get a nine-part-per

million gain in hydrocarbons so we incorporated that. (Refer to fig. No. 6.) There are many, many studies of this type, and I obviously have not time to go into all of them here.

Now I do want to get into the other type of study. These are mostly directed toward better distribution. This group of studies that I am going to show you is directed toward the problem of burning as much as possible of all of your hydrocarbons. The process here is to avoid any places where hydrocarbons can hide. This is what we call quench

space.

In this area, you do not have a flame front. There are good reasons for doing this. However, from the point of view of exhaust control.

this is very harmful. So, the effort that we are making in modifying these combustion chambers is to eliminate these dead spaces. See, this area is a dead space; it has something of the order of sixty one-thousandths of an inch of clearance between the piston and the cylinder head here and that is just not enough room for the flame to progress. (Refer to fig. No. 7 below.)

Mr. BOGAN. Just a little thin slice.

Mr. HEINEN. So, this particular combustion chamber shows two steps that we studied. This was the tapered quench area and we reduced the hydrocarbons like something from 245 to about 232 parts per million going that far. Then we decided to completely undercut by another sixty one-thousandths and we moved down to something like 218 parts per million and this is the shape that we finally determined to pursue.

The gaskets, themselves, which I have here (refer to fig. No. 8), illustrate another part of this same process. Now, this is a perfectly good gasket from a power point of view, from an endurance point of view, from any other point of view that you care to mention. However, it did allow a small space between the block and the cylinder head so we filled in this small space with these little ridges that you see here. For our troubles we got an improvement of something like from 245 to 220. A very worthwhile move. So we incorporated that in the engines that did not have this fully tapered gasket.

Finally, Harry mentioned that some of these things involved rather substantial problems. Here is what we did to one of our six-cylinder engines the 170-cubic inch. (Refer to fig. No. 9.) We undercut it