I have a 1977 ford F700 dump truck. Can I swap a set of 390 heads and intake onto my 391 engine? I am looking for more performance.What other mods can I perform?

 

Welcome to FTE!

Yes, you can swap 390 heads onto your 391. That's not what I would do though. I would find some heads from a later 360, look for the casting code D2TE (the number in the code is the year, the letter is the decade, example: C6AE would be 1966, and D3TE would be 1973) or newer. They will have smaller combustion chambers to accomodate the dished pistons in the 391 and raise the compression ratio, and also will have hardened exhaust valve seats to work with unleaded gas. They'll also flow a LOT better than the FT heads that are on it. Look on '72 - '76 trucks in the junkyard. I would also get a 4 barrel intake for it. You might find this on a 390 in the junkyard, but you could also find it at DSC for $50.

For more performance, get a Holley 600cfm vacuum secondary carburetor. You'll probably want a fairly stiff secondary diaphram spring, since it's such a heavy vehicle. After that, get a Crane 343971 cam, which will have lots of low end torque and better power than the cam that's in it. After that, get a set of headers. I dont know which ones will work in an F700, but I'd be surprised if a set for a F100 or F250 didn't work.

Good luck!

 

The biggest problem you have with an ft is very low compression. Like 7.5:1. It's gonna be hard to get any fe parts to work with that low a cr. If you do decide to swap parts anyway, you may have problems with an ft distributor fitting correctly in the fe intake and headers likely won't work since the f700 uses mounts off the bellhousing. good luck though.

 

Most of the reason the FT's have low compression is in their heads. FT cylinder heads have 78.5 to 81.5 cc combustion chambers, whereas the heads I recommended above have 68.1 to 71.1 cc combustion chambers. These should get the compression up to around 9.2:1, depending on the cc of the dish in the dished pistons used in the FT, the head gasket bore, and head gasket thickness. I figured a 10cc dish, 4.375 gasket (not cylinder) bore, and .040" thick head gaskets.

 

rusty70f100, thank you so much for your help. I am relatively new at this, I appreciate your advice. I read something about the distributor shaft being a larger diameter on the truck 391. what do you suggest that i do for modifications, or what distributor could i use? I have access to a 390 motor ? from an old ford pickup. the motor was a transplant, so i dont know for sure if it is a 390. it does have a 4 barrel on it. how can i tell if it is a 390 or 360 or what? thank you again. sincerely fred ling. my email is freddyling@aol.com.

 

about the only way you can tell is do a stroke test, but you say it has a 4 barrell on it if its all original it would be a 390 because i dont think 360's came with a 4 barrell, look on the passenger side front of the block just below the head and tell us what it says it should be something like D3TE, C6AE, etc.., i think the 360 came out in 68, i may be wrong someone correct me if i am. so if the block casting # is before 68 then you could have a 390 or 352. the best way to tell is just do a stroke test through the spark plug hole, 360=3.5, 390=3.78, 428=3.98

 

The distributor shaft is larger in the 391. It also has a larger oil pump drive shaft. Since it wont fit the smaller FE intake, you'll need to use the oil pump, oil pump drive shaft, and distributor off the 390. The 390 heads should work good, they'll give slightly less compression than the 360 heads. See if you can get the casting number of the 390 heads, that will tell us if they've got hardened exhaust valve seats and the approximate combustion chamber volume.

 

thanks for the reply guys. i could change the oil pump i guess, besides the oil pan, what has to be removed?

 

I'm not sure if you'll have to raise the engine up or not on an F700. Other than the oil pan, it's just unbolt the old one and bolt the new one on. The pump bolts should be tightened to 12-15 ft-lbs, and the pickup tube bolts should be tightened to 12-15 ft-lbs. You'll have to swap the pickup tube over to the other pump. The oil pan bolts should be tightened to 9-11 ft-lbs.

Make sure you go get new gaskets before you start.

 

rusty70f100. thanks for your help, it is greatly appreciated.