I have 2 trucks with 300s in them, and a 300 and 240 in the garage craigslist specials. The 240 heads are smaller combustion chambers and raise compression a bit from the later 300 heads.

The Offenhauser manifolds have been delayed for a while, not sure why except they don't sell like they used to and they don't make them except when enough orders, or that's what the scuttlebutt is. I picked up an Offy C used off CL and missed another, but haven't seen any for some time now locally.

For your 240 doing external mods only, get an aftermarket manifold - Offy C or DP, or Clifford. If it were me, find a Motorcraft 2100 or 2150 in any size (I have a 1.14) and put it on your intake.

For exhaust, find used efi exhaust manifolds and try and get the headpipes too. Many use 2 into 1 by Walker, but they used to offer just the pipe, but now have to buy the cat with it which doubles the price. Stock from the factory many had 2 separate headpipes that ran down quite a ways; get those if you can find them. If not, then either buy the Walker setup, use or throw away or try to resell the cat, and tie in the rest yourself or muffler shop.

Those 2 improvements make a great upgrade in power. Of course you can tweak them some more by porting the efi exhaust manifolds, and gasket/port matching all of it.

Many opinions on cams, so read up. Even a small one will help, but at some point you get into the "slippery slope" of improvements that keeps going and going.

 

i just did the clifford dual carb w/hedman headers and im happy w/ it - in stead of stomping the pedal to break the law ive got to lay off the throttle not to -highway mileage is fantastic the hedman headers are a tight fit i think may have to go to an electric fuel pump to feed the carbs as it runs a bit flat off idle up to about 15/1700 rpm then really takes off -never thought it would run this well - good luck w/ yours

 

That's nice, I like the dual carb Clifford. They have a Facebook page; I asked about just buying the dual carb manifold - not the entire setup. They said yes could do it, but I'm not sure price & haven't called to find out. The duals would definitely help with fuel distribution.

 

Im trying to decide to keep the 6 and do a Clifford Upgrade like you have done, what gears are you running? I currently have 4.11 and top out at 55 MPH. I am swapping them out for 3.4 gears and looking to do about 70/80 highway speed if possible, just was not sure if the Clifford upgrade on a 240 would accomplish this goal?

 

 

Just the change of going from an under powered 240 to a 300 was a vast improvement in my '69 F100 Ranger. During the changeover, I got rid of the points distributor and installed a Duraspark II setup from an '83 F150 inline 300 and EFI exhaust manifolds from a '94 F150 4.9L (fuel injected 300), with true dual exhaust run out in front of the rear wheels. I'm running the stock intake and the stock Carter YF 1-bbl. carburetor.

I had the head from my old 240 rebuilt/machined and installed it on the 300.

 

There is no replacement for displacement!

I also have a 300 / T18 / 9" 2.75 gear running the stock v1 carb & EFI manifolds into the stock 1 pipe exh. system.

That air filter was only used to keep stuff from going down the carb wile doing other work, it has the stock factory egg shape filter.
Now my truck came with the 300, I can not tell you how it does on the road because as soon as I got it home I started a cab off frame rebuild.
I am not looking to do 100 MPH but I am sure it can do the 70 MPH speed limit we have around here.
At some point I may want to go with 3.55 gears for pulling my car trailer when I have to.
Dave ----

 

Nice looking truck Having had a few I6's, and being a huge fan of them, my input, for what it cost ya, nuttin
Gearing is a big consideration also, my 66 F250 had the NP435/4.10's and 31" tires, I rebuilt the 300, punched it .030 over, wish I could find the cam grind, Offy 4bbl, Holley 390, Heddman dual outlet headers, it would get 16+mpg running 55-65, and scream when you stomped it.
My 79 F250/4x4/NP435/4.10/33's had same setup, stock cam, (it was an 89 300 I6) got 18mpg driving to MO when I sold it to my BIL, not quite the same punch when you floored it, I think due to the FI cam, it would do anything I asked of it +some.
My current 66 F100 has a 240, 1bbl T18/3.70's, it will get 16mpg+ running to Fresno and back, and it is tired (I have a 76 300 waiting for it) when I first got it, it had 3.00's in the dif, was a pig, luckily the rear-end started making noise and I pulled the 9", found the 3.00's, sold it and put in 3.70's, TOTALLY different truck!! I had actually bought a 302 to rplc the 240 with, thinking it was just worn out, that was 4+ yrs ago.
A stock 240/300 with correct gearing will get the job done all day long, adding 2bbl/4bbl headers and the like will get you grin factor, but all in all, just like any engine, when you're geared right, it's good.
Again, sweet rig!!

 

maybe early enough to have a 2speed transfer case as an overdrive, lotta weird things in the ford garage, in the '60's