Welcome to moparts

Moparts Tech Archive

Motor General

What is quench?

I know what the compression ratio is, but what is quench? how do you adjust it?

I plan on doing a 425-450hp build up of my 383 in about a year or so, and one thing I'm going to do is increase the compression...right now its only 8.0:1 I was thinking of 10:1, is that too high for a pump gas, street (hard driven street) car? would I still be able to get close to 425-450 with 9.5-ish compression?

Quench - When the piston is compressing the mixture, as the piston nears the head, the flat areas on the head and piston come together and force the mixture from those areas to "squish" into the chamber, where the spark plug and burning mixture reside, so you achieve a more complete burn.

The quench area also runs cooler than the rest of the chamber / piston. These lower temperatures are where the "quench" comes from.

When properly designed, the quench areas can have a tremendous effect on the quality of combustion, and allow higher compression ratios, and due to this they are considered "artificial octane" by scientific types.

With some careful planning you should be able to run 9.5-10:1 on the street and make 400-450HP pretty easily. I have seen some strong 383's and seen them spank some much more notorious engines. How streetable do you want it? What heads are you planning on using? And of course, what's your budget?

The only drag about 383's is not as many companies make shelf stock pistons for them. It looks like TRW, Keith Black and Venolia are the only companies stocking decent pistons for the 383. The good news is it looks like a lot of them offer something that will get you right around 9.5:1. Of course custom pistons are always an option, but they co$t $600+ with pins. I would get the lightest piston I could afford, do the mandatory machine work on the block / rods, port the heads and do a nice valve job (or bolt on some Edelbrocks!!!) and use a cam similar to the Comp Cam High Lift 275, 231/237 @ .050 .525" lift. That combined with the right induction system will get you where you wanna be.


Back to Tech Index
Tech Index