351 or 302?

[brandywine_pony]

I'm looking at a '66 convertible (project). It has a 351w and a C4.

My first question is, if I want to make this a daily driver (for the summer at least, as we get a fair bit of snow here 'round wintertime), would it make sense to track down a 302 for the gas mileage, and maybe a 4bbl carb for some extra oomph?

And secondly, how tough would it be to throw in a 5- or 6-speed? Normally I'd just wait til one showed up that already had the 302/5-speed set up, but the price on this is just too good ($8400, runs and drives).

Any input in addition to this would be welcomed. Thanks so much for your help!

 

[Rusty67]

Nothing wrong with a 351. You can provably get the same gas mileage out of it that you can get out of a 289 or a 302 as long as you don't sink your foot into the floor all the time.

 

[Wildbill3]

Thers alot of threads posted on the 5 speed conversion also do a serch,sounds like a nice car any pics?

 

[1968-coupe]

Honestly you wont get enough better fuel mileage to make the swap, unless you trade even and spend nothing on the swap you will lose money. Say you spend $1,000 swapping to a 302, thats 384 gallons of gas at $2.60. Lets say you get 20mpg. 16 with the 351. Thats a 4 mpg difference, and it would take a LONG LONG time to save the money you spent swapping, evern longer to see and savings from it. 351 is a good engine, more torque, if it runs good leave it in the car.

 

[2+2GT]

True. I'd reckon 5-10 years to break even on the cost of the changeover vs. price of gas.

 

[mudbilly]

the 5/6 speed might be worth it, if you do alot of highway miles.........??

 

[Rusty67]

A 351 will eat most basic T5's for lunch. You may need a T5z for it to hold up.

 

[tx65coupe]

Since its an automatic car, you could also do an AOD conversion. Either way I will also vote for an OD transmission swap.

I would keep the 351 since its already there. I doubt you would see much if any mpg difference with normal cruising.

 

[65coupe408w]

my 408w which isnt exactly built for economy still pulls 18mpg on the highway with a T5...thats with a 3.70 gear

 

[68stang351]

I recommend the 351w (obviously). If you use a 302 you will always wonder how it would've run with a 351. I have a 351w and a T5 in my 68 and to be honest, it really isn't bad on gas at all. That engine barely has to work to move a car that light around, and with overdrive it's even better. I barely touch the pedal in normal driving.

 

[brandywine_pony]

thanks, everybody! i appreciate all the responses!

 

[brandywine_pony]

something else just occurred to me - with the additional torque from a 351, would it be in my best interest to beef up the frame if this hasn't already been done?
again, thank you all!

 

[tx65coupe]

I would stiffen up the chassis with either setup. I would go with one piece export brace, a monte carlo bar, and subframe connectors.

 

[68stang351]

I would stiffen up the chassis with either setup. I would go with one piece export brace, a monte carlo bar, and subframe connectors.

+1.

That's what I put on my 68, and it definitely stiffened it up a lot.