I have the opportunity to buy a 390 from a 66 Fairline XL. The seller says it is an S Code motor. What I know is according to my Big Block Ford Engine book,
this should be a 390-4V and is a GT motor.

Three Questions:

1. What is a GT motor?

2. How do I know what to look for when I see the motor. How do I tell if it is it infact a 390 S Code.

3. I am planning on putting it into my 65 F100. It has a 352 that I want to take out, rebuild and store. The 390 is just for fun. The truck has an automatic transmission. Everything I have read tells me that a 390 is a direct bolt-in. Is this the same for a 390 car motor.....

Thanks for any help.......

 

it's a direct bolt in minus the exhaust system. The GT has staggered bolts on the exhaust manifolts/heads. Vs. the standard vertical 8 pattern found on trucks. Not the end of the world. Just not a plop and go scenario.

 

The 390 GT had higher compression, hotter cam, and "better intake", though by todays standards the "S" intake is not worth using. I have used this intake in the past, and it does not produce anywhere near the torque/hp at any engine speed of an Edelbrock performer RPM intake. I suggest going to web site: Woody's WebSite Main Intro., and look for his "390 build up the old way". His site lists all the details that went into the 390GT and offers several engine builds. Todays parts are far superior to building an engine the "old way". Camshafts, valve springs, cylinder heads, intake manifolds, electronic ignition, etc are today light years ahead of 1970.
BUT.... the 390GT engine would be a GREAT starting point for further improvments.
YOU could drill the vertical exhaust manifold pattern in the GT cylinder heads YOURSELF. Then your exhaust would bolt right up the GT heads. Hope this helps.

 

Thanks for the great info.

In my case, I have decided to temporarily replace the 352 with a 390, and would like to use a similar era engine rebuilt to the factory spec. Call me sentimental...

This seems like an engine that will give me more HP than the other 390's I have found. The big question is? How do I know if it is a 390GT?

 

The GT did not have higher compression. They were the standard 10 to 1. They used the same cam that the 428CJ would use. The "S" code intake is an exellent street truck intake and makes a decent tow manifold too. I ran 390GT motor with a piston change for a 9 to 1 compression in my 1968 F250, C-6 with 3.73 rearend and even with my 9' camper and my race boat in tow she ran away from my buddy's 460 F250 going over the mountains. Plus the combo got 13 mpg a couple of times with just a canopy on the bed. Since the cam was the big difference between the standard 390 and the GT you can't. However the GT had different exhaust manifolds than the standard log type. They are real obvious. They look like this.

 

Bear, What kind of carb setup were you using to get 13 mpg through 3.73 gears?

I have gotten 13.6 through 3.00 gears and my motor is turning much slower at hiway speed.


John

 

I was using a Holley List 1850, 600 CFM vacuum secondary carb, worked over by me. Dual stage power valve, heavier spring (just one step heavier) in the vacuum secondary, rejetted (primary and secondary) and keeping the speed down to under 58 mph so the revs stayed down below 2800, as the secondaries opened under load at 3000 rpm.

I'm sorry I let that truck go as the 1984 F250 460, C-6 and 4.10 rearend (ouch) does 10 mpg on a good day but it never slows down regardless of what you are towing.

 

Great link for anyone doin' a 390 build-up! Thanks!

 

I seen a set of them manifolds in the classifieds last week or so. Ya think I shoulda jumped on em?

 

That's why I asked, usually the slower a FE is turning the better it is on gas. I'm turning 2050 at 55 mph and that is still slower that what you were turning. When I get up to 2800, I aint being passed by quite as many cars as I was at 2100. LOL

I might look into your setup.


John