J 98ta

iTrader: (3)

How thin is it 'safe' to run a head gasket with 0" deck clearance ?

Motor:

6 liter Iron Block
3.62 x 4.03 " - 369 ci
Forged dish pistons - 28cc
Milled heads - 60cc chambers

I am going to be running N/A this year, and am trying to gey any compression I can get back. I have been told .035 " should be ok ? Car is street strip 60/40. 65-6600 max rpm A4. I plan on ordering a custom set of Cometic's soon.

Thanks !
'J 98 TA

Shinobi'sZ

I think what you are referring to is the minimum quench area. If you have 0 deck with a .054 MLS Head Gasket your quench area is .054 which is a little large for Natural Aspiration. I think most of the hi power NA cars quench (squish) area is between .030 and .040. I am sure somebody will chime in with there setup..this tends to be a common question on this board and the FI board.

I see that you have a dish piston motor...if you go to West Coast Racing Cylinder Heads website you will see a 7 sec. Acura NSX drag car...I don't think he runs any head gaskets at all. If the quench area is the relationship between the top of the piston and the chamber then you will probably not have to worry about running a .010 thick head gasket..I don't know what the lift is on your cam..but you should check Piston to Valve Clearance anyway. How much are your heads milled..you could mill the them .040..use standard small block chevy valves, and shorter pushrods with a thin head gasket an regain compression. Lots of work....wouldn't it be easier to just throw a Turbo or Supercharger on that car and boost the hell out of it??????

J 98ta

iTrader: (3)

Thanks for the reply. I did a search on quench, and found .035-.040 seems to be what to shoot for.

Thanks again.

'J

Shinobi'sZ

.035-.040 is usually for cars with 0-.007 deck height...you have a 28cc dish piston that is not a flat top and gives you extra room between the top of the piston(valve area) and the top of the chamber ATDC. You could probably go with .020 and be OK. Or like I mentioned mill some more off the heads.

J 98ta

iTrader: (3)

I thought the deck height 'out of hole' # was supposed to be subtracted from the compressed head gasket thickness to achieve the quench #. ?

Piston looks like this : http://j.cz28.com/02-14-04_2228.jpg
sorry for real poor quality pic......

I think there is supposed to be room for rod stretch IE > or = .035" at the outer edge of the piston.

Thanks,
'J

dano73327

The dish on the piston doesn't really have anything to do with it because there is always a rim around the dish as well as a quench pad on the piston top. This is the flat part of the piston that matches the deck surface of the head that covers the rest of the cylinder that the chamber doesn't cover. .020 quench is inviting disaster. Unless you had some killer carrillo rods and lightweight pistons I wouldn't even consider running less than .038 just to be safe and no more that .045 to keep detonation under control. With good GRP aluminum rods and light pistons we open the quench up to more like .055 because of the way the aluminum rods stretch at speed and grow when heated. Oh and the quench clearance is the deck clearance, either in the hole or out of the hole or zero deck plus the compressed thickness of your head gasket. Oh and milling the heads has no effect on quench clearance.