Cometics, .040 or .045?

Reply Subscribe

Thread Tools

Search this Thread

Apr 3, 2007 | 09:15 AM

chuckyt1

Thread Starter

11 Second Club

iTrader: (33)

Joined: Apr 2006

Posts: 1,008

Likes: 0

From: Chicago Area

Cometics, .040 or .045?

Going to order my head gaskets today. I was told, by a very reputable sponsor, that .040's on a stock short block would be a little tight. That you would have to be very careful with the .034 quench because of the loose tolerances.

Anyone had any problems with the .040?

The difference between SCR/DCR is 11.4/8.43 for the 040 and 11.25/8.32 with 045. But I've read the the ideal quench is .034.

Any thoughts, comments or suggestions on which ones to use?

Tried searching - all I get is a white screen...

Apr 3, 2007 | 09:17 AM

brad8266

TECH Senior Member

iTrader: (23)

Joined: Aug 2005

Posts: 8,797

Likes: 0

From: Watertown, NY

yeah .040 is a bit tight for a stock block. The .045 would probably be a better choise.

Apr 3, 2007 | 09:50 AM

Xtnct00WS6

TECH Fanatic

iTrader: (8)

Joined: Jan 2005

Posts: 1,429

Likes: 2

From: Sterling VA

I've seen .040 recommended a lot because of the DCR, but I wanted to play it safe and got a .045 and didn't look back. The DCR is a very important element of the combo and I'd think you'll be fine with a .040. However, PTV clearance could become an issue if you have aftermarket valves, and a lot of duration in your cam.

Apr 3, 2007 | 09:52 AM

brad8266

TECH Senior Member

iTrader: (23)

Joined: Aug 2005

Posts: 8,797

Likes: 0

From: Watertown, NY

.040 is more recommended more for the quench not the DCR.

Apr 3, 2007 | 09:55 AM

KONG

12 Second Club

iTrader: (4)

Joined: Oct 2006

Posts: 300

Likes: 0

From: Chesapeake, VA

For an unmilled head the .040 Cometic is perfect. I run them and have no problems.

Apr 3, 2007 | 10:38 AM

chuckyt1

Thread Starter

11 Second Club

iTrader: (33)

Joined: Apr 2006

Posts: 1,008

Likes: 0

From: Chicago Area

PRC LS6 heads milled .030 with 2.02 valves. The dcr only changes by .15 but I was just trying to tighten up the quench a bit.

Think I'll wait for the forged internals, (next winters project), before I get too crazy with it...

Apr 3, 2007 | 11:00 AM

PREDATOR-Z

TECH Senior Member

Joined: Mar 2004

Posts: 14,620

Likes: 17

From: BFE

It all depends on you piston to deck clearance.

I have my slugs .010 out and with .050 gaskets = .040 quench, and at 12:1 no issues with misfires or detonnation.

Good range is on average .040 for street.