SideStep

Two questions for those in the know...

1. Is quench important when building a low compression (7 to 10cc dish) engine to be used with a super charger???

2. Is there a preferred type of head gasket for boosted applications? MLS or Composite type???


As usual thanks for any advice or input...

DeltaT

iTrader: (5)

Quench is always important. Most people, nyself included, seem to be using a MLS gasket from FelPro, Cometic or GM.

Jim

SideStep

How do you keep a tight quench when you have large/deep dish pistons??? What is the optimum quench for a boosted application???

hellbents10

iTrader: (10)

They key is to get a piston that has the dish in the same area as you combustion chamber on your head. It should be flat in the same area that your head is.

DeltaT

iTrader: (5)

Right. To add to what hellbents10 said, the quench area in a combustion chamber/dished piston combo are the flat areas outside the dish, and the part of the chamber that is 'blind' to the piston. If these match nicely, your quench area is optimized. In the most modern 2-valve setups, there's actually a double quench - that small area between the valve seats on the opposite side from the sparkplug - if it has a nicely matching piston you will get some quench action from there as well.

The whole idea of quench is to have an area that gets very tight (.060 - .025" depending on your rod material and piston clearances) at TDC (but doesn't hit of course) and literally squirts the fuel/air mixture sideways to induce turbulence and a good mixing of the entire fuel/air mix in the chamber.

Most people try to get it in the .040-.030 range. Loose is bad, but too tight (if it ever makes contact) is very bad.

Jim

SSblack98

iTrader: (8)

How bad is a .060" quench on a 8.5:1 turbo engine?

I know it is not optimal but wondering what the side effects may be at around 15-17psi.

engineermike

The Neon SRT-4's have .340" quench. Here is a pic of TDC:

http://www.sportcompactcarweb.com/pr.../photo_11.html

TTAWD

I don’t think it’s as big of a deal as people
make it out to be.

If some one would build a motor and change
only the quench to see what would happen
it would be nice.

Don’t hold your breath.

brad8266

iTrader: (23)

Its important and the changes from different quench would mostly relate to resistance to detonation. Tight quench aids in fighting detonation. I run ~.034 quench at about a 12:1 compression ratio and I have no knock issues running more advanced timing as well.

The powers differences wouldn be large but the ability to fight detonation may change a lot in a blown motor by varyind quench area.

stevieturbo

I havent a clue what mine is....

GM MLS gasket at circa 0.050" compressed. My pistons are flush with the top of the deck I think...dont recall actually measuring.

I guess that makes my quench poor ?

8.7:1, as much as 19psi at 7000rpm on pump fuel with no detonation issues whatsoever.

LS1's seem to be quite good in that respect.

engineermike

Quench is one of those things that in theory and in practice, improves power. However, people tend to get carried away, thinking that quench MUST BE .035 - .040. There was a dyno test a while back in one of the magazines where it improved power by 10 - 15 hp. It's sorta' like the whole 4/7 swap thing. People swear that you need it to make big power, because alot of class racers use it. The fact of the matter is that it's worth <5 hp on a 650 hp engine. We'll never see the difference, but in highly competitive classes, every little bit counts.

Mike