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View Full Version : How to tell if gt40 or not?


c43amg
08-27-2009, 04:30 PM
I have a 85 comp, how do u tell if the motor is a gt40? Both speedos say almost 45mph. what should the top speed of a 85 comp be?
chautauquasun
08-27-2009, 05:15 PM
Check with Irish Jack or Knoble on this site...both are experts on the markings to identify GT40 heads. Not sure but there maybe a thread on here that describles how to tell what you have.
DKJBama92Mariah
08-27-2009, 05:17 PM
On the aft end of the heads there will be a number of bars cast into the head. 2 bars is std heads with hardened exhaust seats, and three bars are the cast iron GT40 heads.

http://www.skidim.com/images/351HOhead.jpg
c43amg
08-28-2009, 05:47 PM
On the aft end of the heads there will be a number of bars cast into the head. 2 bars is std heads with hardened exhaust seats, and three bars are the cast iron GT40 heads.

http://www.skidim.com/images/351HOhead.jpg

thanks for the help. I checked it today and saw there were no bars. Ill take a pic of the heads where you are talking about and post them. I would like to have more power but dont know if i want to tear apart a motor that runs so well.
DKJBama92Mariah
08-29-2009, 07:52 PM
Since yours has no ribs, it does not have hardened exhaust valve seats. See http://www.skidim.com/marinization.asp

You should use a lead substitute from an auto parts store in your fuel.
c43amg
08-30-2009, 04:06 PM
Since yours has no ribs, it does not have hardened exhaust valve seats. See http://www.skidim.com/marinization.asp

You should use a lead substitute from an auto parts store in your fuel.

ok, thanks for your help.