how much difference will a set of GT40s make with 2.02 valves over stock 302 heads

[BOTCHIE]

Hello Everyone butch boccioletti here from London Ont Canada new guy on the block. I am in the process of a build. I would like to ask an open question to any one.
I am in the process of buying a set of GT40 heads. I have confirmed the valves are 2.02 x 1.60. Standard valves by my investigation are 184 x 154 please correct me if I am incorrect in that assumption. I am wondering if with a mild cam and a set of shorty,s will allow a lot better flow---BTW its being installed into a 48 ford panel with no cats and a duel free flow exhaust.I am a small engine specialist and understand flow but will it make a 30hp difference with the bigger valves.Thanks

 

[Mike Pass]

Check out the David Vizard videos on Youtube. There is some good info on the iron heads.
Cheers
Mike

 

[Kevin Box]

GT40 heads are not the best in the world but they are way better than stock quite simply because the ports are cast better.
2.02 / 1.6 combo works fine on a small block Ford but actual performance will be governed by the how they are setup. If you are enlarging standard heads to accommodate the bigger valves maybe consider 1.94 / 1.6 There will be lots of discussion with this but it is my feeling that 1.94 allows better breathing around the back of the valve while also giving you more metal between the valves.
3 or 5 angle valve job will make the difference Also with the bigger valve set is the transition behind the valve improved to make use of the bigger valve??
Shorties will not improve your low down torque which it would seem you will need with this vehicle - maybe try to get some header that are closer to 34 inch primary length to improve your bottom end torque