Inliners International Forums General Discussion Ford Should I? 390/np435 to I300/C4/C6

Hey guys, I have recently bought and am rebuilding a '70 Ford CrewCab 4WD shortbed pickup. I currently have a 390/NP435 drivetrain and am looking to see if it would be worth it or possible to trade this monster of a motor out for a good I300 with either a C4 or C6 transmission. It is a 4 wheel drive pickup. I guess this all begs the question, what am I looking for and why am I considering doing this. I have always liked the I6s, have had a couple 240s and never had much trouble with them. With my CrewCab, I don't plan on doing any rock climbing, just using it as my nice driver truck and if I ever needed the 4wd, I would have it, but not to pull anything huge. It is a city slickin truck from now on :p I would like to find a newer 4.9 efi with the automatic tranny to fit in it. What do you all think? From what I have found, I can get more hp/torque out of a reasonably built I6 than I can out of my stofk 390. Anyone have any specs to back that up? Thanks for your opinions!

Dear Bud;

The FRENCHTOWN FLYER is the one to get the answers from on that one.

Good luck.

If you wanna drop a 300 in it to be doing it, go for it.

If your looking to make some serious HP and TQ, keep the 390.

The 300 is what it is but if you warm up the 390, it can generate more TQ from idle to what ever rpm as compared to a warmed up 300 and actually give you respectable hp to boot.

Cheapest and easiest method to get the 300 rollin and generating respectable hp/tq, say 250-300hp and 350-400TQ is to keep it carb. If you go efi, then you'd wanna go with a stand alone efi controller, something you can tune the daylights out of or find a dyno operator and chip company thats willing to work with you. Another option is to use a mustang A9L computer but again, requires someone to reprogram the computer for your needs but relatively easier, as there is support for this eec.

Good luck

I'm about to put an offy/holley 390 on my 81's 300. If I like how it runs and the milage is good enough, I may swap a 300/T18 into my '77. But I don't plan on towing anything bigger than a bike trailer on the highway, and I won't be cruising over 55-60. I do plan on building a slide-in camper with the best aerodynamics I can provide.
A C6 will cost you @1.5mpg. C4 is more efficient but not nearly as strong. If you swap, consider keeping the np435.

Thanks for the info guys! I think I will stick with my 390. I might want to find some different gears than my 4.10 though. I don't plan to pull anything too heavy.

My 77 does great with a 3.54 rear and 30" tires. Dad pulled a 27' Airstream with this truck, 65mph with ease. 2400-2500rpm @60mph.
390s are great, esp with edelbrock equipment, but they have perhaps the worst cast exhaust manifolds ever made. I would want headers.