First thing I would do is fine out what you have now. With the diff cover removed, you will be able to rotate the crown (large) gear until you find some numbers on it. Post on here what the numbers are and we will be able to decode/calculate what you have. It's likely 2.56 or 2.73.
I will go against the flow and say 3.55 may be a bit too much gear (rather a 3.23) if you want to be happy driving this car on the highway every day, at least if you drive 70 mph on a regular basis.
Next would be a cam change, headers, stuff like that as mentioned. Also, I think an aftermarket intake manifold is supposed to be quite superior to the original 400 intake in those years.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars
I will go against the flow and say 3.55 may be a bit too much gear (rather a 3.23) if you want to be happy driving this car on the highway every day, at least if you drive 70 mph on a regular basis.
Next would be a cam change, headers, stuff like that as mentioned. Also, I think an aftermarket intake manifold is supposed to be quite superior to the original 400 intake in those years.
I actually agree!
I have 2.73 in Chief and "had" 3.73 in Ventura..
I love the fuel mileage and smoothness of the Big Block with 2.73 and hated the constant roar of the 327 with the 3:73's
personal preference, but we often gear the car for the 5-10% we actually use the gear, and suffer for the 90% of the time we din't need it.....
I am actually going to send my 3 series carrier to Peter (N.B.)and put guts in a 2 series and run 2:73 Posi in Chief I don't race it and can't speed anymore I can still lay 800 feet of rubber with the 2:73 Posi and get fuel mileage (my 2 cents)
Welcome aboard! Is the the car from Kijiji that was posted last summer? Nice ride. I'd go with the 3.55 or 3.73 personally. I am prejudiced as both my cars have OD. My El Camino with the 3.31 the car is extremely quiet and I'd prefer a bit nosier.
Whereas my Mustang has a 3.70 and at idle it does slightly over the speed limit. Wished for 4.10s in that. Going with 4.30's in my Zephyr.
Welcome to the site. My other GTO is running a 400, headers, Comp cam, Edelbrock performer intake and carb. A posi with 3.73. This car does great burnouts, but on the highway it sucks fuel and the tac was running 3500rpm to keep up to Hwy speed. If you want the best of both worlds....change the transmission to a 6speed or the 700R4 if you want to run a burnout gear and get good fuel economy.
took th 73 to the mechanics Hes gonna take a look at everything do a compression, vacuum test check out the exhaust and Carburetor, and see what i have and go from there, Thanks for your help
