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John Mason · 04-22-2008, 12:08 PM

Ed,
You need to change heads as well as the carb to make it a 1963 250 HP. 1.72 intake valve and smaller chamber in the 520 (250 HP) head. Also, it's 250 HP in S/S but 258 HP in GT.
I run GT/IA (12 lb/HP) @ 3266 minimum with that combo.
The 1965 250 HP uses your 275 HP head but it's factored to 260 HP. Maybe the Q-jet is worth the 15 HP. It's got to be close.

04-22-2008, 12:08 PM	#5
John Mason Member Join Date: Apr 2002 Posts: 147 Likes: 0 Liked 0 Times in 0 Posts	Re: Correct GT class Ed, You need to change heads as well as the carb to make it a 1963 250 HP. 1.72 intake valve and smaller chamber in the 520 (250 HP) head. Also, it's 250 HP in S/S but 258 HP in GT. I run GT/IA (12 lb/HP) @ 3266 minimum with that combo. The 1965 250 HP uses your 275 HP head but it's factored to 260 HP. Maybe the Q-jet is worth the 15 HP. It's got to be close. __________________ John Mason 7743 SS Last edited by John Mason; 04-22-2008 at 12:20 PM. Reason: dropped last paragraph