i have a 66 f250 camper special and am taking them at their word! mounted on it is a 11' s&s fsc with all the bells and whistles that weighs about 3000# and i pull a trailer that is about 2000# the engine is 300 il6 with rv cam and headers. i have converted to small block c6 and power disk breaks, power steering. the catch? no intake or distributor yet! so, the question is this, 1bbl, 4 bbl (cfm???)with offey 6019 dp, or efi? and what would you recommend for ignition?? hoping to get about 10 mpg after its all said and done and still lug the extra 5000# around (410 diff)

 

If it truly only weighs around 5000# all said and done, you should definitely get over 10mpg with most any configuration you decide to go with.

Granted, you'll never get stellar mileage with that C6 transmission and 4.10s, but if 10mpg is your goal, then it shouldn't be very difficult to reach it.

If you have the money, go with a DUI ignition, since they can completely custom tailor it to your specifications. Other than that, the late 70s/early 80s stock DuraSpark II ignition is a great setup, inexpensive, and relatively easy to recurve yourself if you know how to do it.

The Offy DP is a nice setup since it gives a little more low end grunt, but I have both the Offy C and Offy DP on my two Broncos and like both.

For a 4bbl carburetor, most go with either a 500cfm Edelbrock, a Holley 600cfm (they're a dime a dozen), or a Holley 390cfm.

 

um thats 5000# on top of the truck curb weight lol does this change your opinion?
and how do i avoid overasperation with a 600?
thanks so much for the advice, as i can only do this once

 

Oh, oh, I missed that the 3000# was on top of the truck, I thought it was the truck's weight itself. (Was thinking that was pretty light, but hey...) Yeah, that'll make a little difference.

At 5000# extra, I'm guessing you're looking at around 10,000# total with the truck included?

What speeds are you thinking of driving? What size tires are on the vehicle?
With 4.10s and a C6, I can't imagine you plan on going super fast. 60mph (with stock sized tires) is probably already encroaching on 3000 RPMs, which is quite high.


With a 600cfm carb, it'll only use as much of the carb as it needs, so you probably will never fully use the primaries.

 

DUI makes some nice stuff but it's total overkill for what you've got. Go with Duraspark II. It's cheap, plentiful, easy, and very good.

I've got an Offy C and like it a lot. One advantage it's got over the DP is ability to run a 2BBL carb if you want. Autolite 2100/MC2150 2BBLs are cheap, plentiful, simple, and very good. I don't know for sure that a 2BBL would get better mileage than a 4BBL but you at least have the option.

OTOH, any vacuum secondary 4BBL is only letting as much air (and fuel...) into the engine as the engine can pull through. How much are the secondaries ever opening anyway?

 

tires are 235 85 16 e rated, got the duraspark, as for carb, i was thinking a holey 390 square bore with mechanical secondaries, so that should give it the gas it needs, i do know if you put too much carb on an engine, you don't get sufficient venturi flow at low throttle and i am dependant on low end to make it up a hill at 45, what is the cfm on that autolite 2bbl?

 

anyone play with predator carbs?

 

You're right on the insufficient venturi flow at low end. That's generally where I suffer with my 600cfm carb right now.
I never pull anything, and my Bronco's pretty light, so it isn't a huge issue, but I do wish it wasn't there. However, it's definitely something you wouldn't want to deal with when you have a big, heavy load.

I had a 390cfm for quite a while. I don't know if it was just mine, or if it was 390s in general (don't have the money to try more than one), but the gas mileage was horrible. I tinkered with it for 2 years and never got above 13 on the interstate. My average was 10 - 11 in town and 10 - 11 on the interstate. I swapped to the 600 "just to try it" and after a few tweaks, I regularly get 13 - 14 in town, and 17 - 20 on the interstate. So, for that, I'll deal with my lean low end.

235 85 R16s = 32" tires. That'll put you at around 2500 - 2700 @ 60mph. Was just curious what RPM range you'll be driving in. Stock tires with 4.10s would be miserable for any highway speeds.


I've heard of people using Predator carbs and liking them, but I think there's a few drawbacks on them for daily driving. Can't remember what they are though.

 

so.... not as nuts as i sound? lol

 

My 500cfm carter doesn't kill my low end, but thats with the DP manifold I haven't tried it with my C series. I'm geared about the same in a lighter truck but I have as much low end as I did stock if not more.

 

What kind of gas mileage do you get with your setup Joeseph?

 

On average about 14 city 16 freeway but you can do a tad bit better if you drive slower. Loaded down I would imagine slightly less then my average.

 

I have a C with a 390 Holley, 4 barrels are open a lot with big loads. If that old truck ever gets back to the priority list, I'll try an Autolite 2100 or maybe a Quadrajet, throttle body efi sounds like a great idea. One thing I can't preach enough on is my ignition. I have the Duraspark II distributor with a GM module and the EFI coil. Best ignition I've ever had and probably all that any of my Ford projects will ever use if I have to lay hands on the ignition for any reason.
10,000# isn't too much for the engine but the extra rolling resistance of the trailer and all the headwind that camper will push are probably more of a concern. My 300 hates head wind. Even with my small 2 wheeled trailer and a low, light load, a 30 mph head wind will leave me running mostly in 4th and hardly ever get in 5th. And that's not with a big camper.
Now about the C6, too much tranny for a 300 IMO. Nothing about a 300 needs more than a C4 and the parasitic power loss from the C4 is considerable less. I've read dyno tests where they claimed the C6 was robbing over 60 horsepower (granted at a lot higher rpms than you'll ever see) and some builders claim even more.
One thing I didn't do on my offy, but from what I read ,really needs done, is the heater for the bottom of the intake. Make sure to tend to that.

 

I believe Predator carbs are designed for WOT performance and not so good everywhere else. Not that I've ever seen one or anything.

Autolite carbs vary on the cfm rating depending in the venturi size. Anywhere from ~220 to 350 cfm, IIRC.

Heating the intake is a must. It made a huge difference, even here in Texas during summer.

 

Most of the documentation I read say that Predator carbs are amazing for low end throttle. They're a variable venturi design, so they only allow as much air/fuel into the engine as it needs. Most people that use them are amazed by them.

I think the issues are more along the lines of there are NO vacuum ports on them of any kind. No choke. And they're designed to replace 600 - 950 cfm carbs, so they're kinda big.