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Old 04-22-2004, 11:20 AM
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Ben,
I understand where you are coming from and I am not taking it as an argument.

Let me see if I can put it another way, If you don't have a quench (anything above .050 or so), then the charge is not going to be forced (squished) to one part of the chamber (usually towards the spark plug). This will invite uncontrolled burns to start. It is not only the shape of the top of the piston that matters but, it plays a big role. With a "dog bowl" dish there is no quench (no flat part on top to create a squish), so in this case it doesn't make a big difference but, this is also the reason "D" dish pistons are a better choice. The same could be said for open or closed chamber heads.

So basically a good quench controls where in the combustion chamber the charge will be, and with this you can control "when" it is ingited. Since the squish will cool the cobustion chamber as the charge rushes across the top of the piston the benefits are two fold. Now with your example of a large quench I don't think it would matter what the shape of the piston is, because you really don't have a quench effect anyway. The piston is not coming close enough to the head to create a squish, so you will have a "lazy" charge just waiting to be ignited by the first available source (hot carbon, etc...) since it didn't cool the combustion chamber there is even more of a chance for hot spots and uncontrolled ignition. As you can see it is a cycle and chances of pre-ignition and detonation are increased as the quench gets loose.

Now if you run high octane race fuel this would be less of an issue, even though you would make more power with a tighter quench (IMO) but, you won't have as big of an issue with the detonation.

To answer your question about the difference in the flat top .105 down and the D dish .010 down. While you will have the same 86cc's of volume, it is "where" the volume is that counts. With the flat top (.105 down)a lot of the volume will be spread out over the whole piston and all over the chamber. With the tight quench and the d dish the same 86cc's of volume is in one specific are (right next to the spark plug) and HOW it gets over to that area is the advantage, It is forced/squished over to that side. This is the effect we are looking for.

While K-star has/had a friend that ran a HUGE quench and "got away" with it, I don't know what the combination was/is so I really can't comment. If I had to guess I would say he had open chamber heads for one. Was this a street car running on pump gas? What was the compression? Seeing that it was a 14-71 blower on it I would say it was not a pump gas engine. The blower would also have a very "active" charge. Even at that how do we know if it was detonating or not? If he filled up with 91 octane what do you think would have happened?

I am looking at this from a street driving perspective, drag/race cars get away with a lot of things that will not live on the street or pump gas. So make sure we are comparing apples to apples. Last I remember you planned on running pump gas, correct? If not then you may be able to get away with that wide quench but I still say power will suffer.

Royce
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