Just in case anyone might be interested, I just put a 240 head on my 300, and ended up with a compression ratio of 10.25:1, I highly doubt that it would be emissions legal, but, it is good for ~10 hp and 15 lbs/ft, so if you are building a 300 for off highway or emissions exempt use, it is a very cheap way to up your C.R., and may be cheaper than having a normal 300 head milled, I don't know. Well, have fun.
Evan MacDonald
82 F100 FlareSide
84 300-6, 66 240 head
83 NP435(6.69 low)
Blue

 

Alright Evan!
1. What year 240 head did you use? Did it have predrilled (or just the cast-in bosses for) holes for the thermactor system?

2. How did you arrive at the 10.25 number? What pistons did you use?

3. Have you run your combo past the emissions tailpipe sniffer?

4. Does this head have hardened valve seats and valves for unleaded fuel? What fuel grade are you using, and how has the crappy gas we are now blessed with with affected your timing?

5. What cam are using to take advantage of the CR increase?

6. Yeah, I'm interested all right.
Eddie

 

I used a 66 240 head, it has no provisions for a thermactor system, same as the head off of bolth my 82 and 84, the air pump is hooked into the egr spacer on them(where the egr mounts on the intake.) I removed mine, and the mounts for it, I got the parts off of a non catalist truck(carb spacer, alternator mount, emissions decal)so that I don't need it. The 10.25 number is with stock pistons, with flattops it would be ~12.77:1. No, I have not run it by a sniffer, no emissions testing to worry about, they're gonna implement it, but I'll be exempt. The head I have has hardened seats, don't know why though. I can get away with running regular(87 octane) with some pinging, if it don't push it hard(it only turns ~1900 at 60, 2.73 rear end,)usually run 91 octane. I never moved the timing, and it seems to be at 6 degrees(damper was put on wrong, TDC notch is at TDC on #4, and no it's not my doing.) I'm curently running the stock cam, stock intake & 1 bbl, and the exhaust manifold off the 66 240, it's cleaner than a 300's(no egr port.) I am thinking of going with a Crane Cam, PowerMax grind no. H-272-2, it's a dual pattern with 272/284 duration, .487/.515 lift, more radical than what I wanted, but it's good with up to 10.5:1 compression.
Good luck
Evan MacDonald
82 F100 FlareSide
84 300-6, 66 240 head
83 NP435(6.69 low)
Blue

 

Oops, I forgot your question about fuel mileage, my truck got 21 mpg before I started, and as far as I can tell, it hasn't changed any.
Evan MacDonald
82 F100 FlareSide
84 300-6, 66 240 head
83 NP435(6.69 low)
Blue

 

I read the flow and hardware specs on your 240 head on another news group...whose valves are you using, i.e, manufacturer, P/N, modifictions? Whose shop did the deed? Contact: ? Thanks, dude!
Eddie

 

Sounds like you have me confused with someone else, I haven't had my head near a flow bench, and I am running stock valves out of a '82 head, along with the springs and exhaust valve rotators, I have yet to port and polish it, but I am going to pull it off again soon, as I can't affort to pay for hi-test fuel, once I pull it, I'm gonna see about cleaning it up some, then I'm gonna drop it on the engine I pulled out of my truck, which I just finished re-building, and is destined to become a ginuea pig...
Evan MacDonald
82 F100 FlareSide
HD 300-6, 240 head
NP435(6.69 low)
2.73 Geared 9"
Blue & Silver

 

What years was the 240 available that sounds like a great idea and I am going to the junk yard tommarow anyway, Maybe I can find one for my 300

 

I have a '68 240 F100 and am going to install the 300crank, rods, and pistons and was wondering what the compression ratio would be if I used my 240 head and if it is too high can I use a thicker gasket to bring it down? I want to run pump gas and want to keep it down to 9.0:1.

 

Vlad, Chilton's lists '66-'70 240 C.R. at 9.2:1. I beleive these heads have 68cc H.V.

I would ensure things by cc'ing your head, and be careful which piston you pick for your build.

Don't use 2 head gaskets.

There's a good compression ratio calculator here:
http://falconperformance.sundog.net/compcalculator.asp