Head gasket bore vs compression

my69396 · 10-07-2015, 11:13 AM

How important is the bore size of the cylinder vs the bore size of the gasket? Say you have a 4.200 bore and a 4.400 gasket what would be the difference in compression if I went to a 4.250 gasket?

FireSale · 10-07-2015, 11:19 AM

There are a lot of variables in CR. Try putting the info you are playing with into a calculator like the one in the link below to see the differences.

http://www.csgnetwork.com/compcalc.html

Dale

Chipper Chapman · 10-07-2015, 12:48 PM

Gasket bore size doesn't change compression as much as you think, thickness does.

FireSale · 10-07-2015, 09:49 PM

Considering an 0.040 gasket, the 4.4 would create a cylinder with a volume of 9.963cc while the 4.250 bore would give a cylinder of 9.291cc.

That's a 0.672cc difference. I don't think it matters a gnats eyelash.

Dale

camaroagogo · 10-07-2015, 11:15 PM

Would a 3.5cc decrease by using a thinner/smaller bore gasket make much difference? .012" thinner, about .030 smaller bore if i remember correctly. Worth changing?

Mark Yacavone · 10-07-2015, 11:42 PM

Quote:

Originally Posted by camaroagogo

Would a 3.5cc decrease by using a thinner/smaller bore gasket make much difference? .012" thinner, about .030 smaller bore if i remember correctly. Worth changing?

Very generally speaking..Yes , you should see a difference.
Worth changing?
That depends on whether you consider this work...or fun.

camaroagogo · 10-08-2015, 12:14 AM

It's certainly a lot of both....but sometimes i wonder . Thanks

BillK · 10-08-2015, 08:06 PM

Quote:

Originally Posted by my69396

Say you have a 4.200 bore and............. if I went to a 4.250 gasket?

Chris,
You have to be careful with this. Depending on how much chamfer your machinist put on the tops of the bores you could start hanging the gasket into the chamfer area. I put very little chamfer on performance builds but some guys might put more. All it takes is 030" all the way around and you will be into the fire ring on a 4.250 gasket and that's assuming that all of the bore centers, dowel pin holes etc. are perfectly aligned with the gasket.

4.250 should be safe but its just something else you need to look at.

GTX JOHN · 10-09-2015, 03:30 AM

I agree with Dale........Tiny change in compression for bore size variation.

10-07-2015, 11:13 AM	#1
my69396 Member Join Date: Feb 2008 Posts: 266 Likes: 0 Liked 35 Times in 13 Posts	Head gasket bore vs compression How important is the bore size of the cylinder vs the bore size of the gasket? Say you have a 4.200 bore and a 4.400 gasket what would be the difference in compression if I went to a 4.250 gasket?

10-07-2015, 11:19 AM	#2
FireSale VIP Member Join Date: Feb 2014 Location: Lakewood Washington Posts: 1,407 Likes: 29 Liked 236 Times in 127 Posts	Re: Head gasket bore vs compression There are a lot of variables in CR. Try putting the info you are playing with into a calculator like the one in the link below to see the differences. http://www.csgnetwork.com/compcalc.html Dale __________________ Dale Shearon 68 Mustang 6394

10-07-2015, 12:48 PM	#3
Chipper Chapman Member Join Date: Jan 2004 Location: Belmont N.S. Canada Posts: 451 Likes: 210 Liked 141 Times in 63 Posts	Re: Head gasket bore vs compression Gasket bore size doesn't change compression as much as you think, thickness does. __________________ Chris Chapman 1969 Chevelle NHRA F-G/SA 1090

10-07-2015, 09:49 PM	#4
FireSale VIP Member Join Date: Feb 2014 Location: Lakewood Washington Posts: 1,407 Likes: 29 Liked 236 Times in 127 Posts	Re: Head gasket bore vs compression Considering an 0.040 gasket, the 4.4 would create a cylinder with a volume of 9.963cc while the 4.250 bore would give a cylinder of 9.291cc. That's a 0.672cc difference. I don't think it matters a gnats eyelash. Dale __________________ Dale Shearon 68 Mustang 6394

10-07-2015, 11:15 PM	#5
camaroagogo Junior Member Join Date: Nov 2005 Posts: 5 Likes: 0 Liked 0 Times in 0 Posts	Re: Head gasket bore vs compression Would a 3.5cc decrease by using a thinner/smaller bore gasket make much difference? .012" thinner, about .030 smaller bore if i remember correctly. Worth changing?

10-08-2015, 12:14 AM	#7
camaroagogo Junior Member Join Date: Nov 2005 Posts: 5 Likes: 0 Liked 0 Times in 0 Posts	Re: Head gasket bore vs compression It's certainly a lot of both....but sometimes i wonder . Thanks

10-09-2015, 03:30 AM	#9
GTX JOHN VIP Member Join Date: Jun 2009 Location: Boulder City, Nevada 89005 Posts: 2,528 Likes: 2,220 Liked 1,792 Times in 571 Posts	Re: Head gasket bore vs compression I agree with Dale........Tiny change in compression for bore size variation. __________________ John Irving 741 Stock 741 Super Stock