I'm getting parts for replacing the old 460 and C6 in my 1977 F250 highboy. I've kind of settled on a straight 6 300 for now (I'd love to do a modern turbodiesel swap, but that's just a tad more expensive...

Going for better mileage than the 460 (double digits would be great, 15 would be awesome....), and still occasionally (like once every two or three months) pulling a trailer -- I do it now with a 4.0 ford ranger, which it doesn't really like. The ranger gets around 17 average, 19 to 20 highway, and 10 to 14 pulling the trailer. 190k on it, so it's getting a little worn. The F250 has a utility box and ladder rack and all on it, loaded with tools, but not that much cargo usually.

The plan is a 300 out of a 1968 truck, with a Ranger III overdrive unit and a NP435 4 speed. 4.10 gears, but the overdrive should help with that. Plus it'll help with the wide gear spacing of the 435.

I was planning on putting on an Offenhauser 6019-DP intake, with a 4 barrel Holly 390CFM and a K&N air filter, and a set of basic Hedman street headers. And switching it to some sort of electronic ignition (I've got a petronix ignition conversion coming for my Ford Courier this weekend, we'll see how that does compared to stock).

I see a lot of talk about intake manifold heating... but I'm not sure I get it. Just about every vehicle I've owned likes cold air better, especially the non turbo ones... I put headers and a cold air ram intake on an old 1.6 liter VW diesel rabbit, and it could keep up 70+ on the highway all of a sudden. What am I missing about the 300 here? Is it throttle body icing we're concerned about or?

Oh.. I do have to get this to pass emissions too... has to be '75 or older to be exempt. Only idle and 2500rpm unloaded tests for a 77 though, not the full dyno test. What do you think that chances of that will be? What happens if you put aftermarket cats on an old engine with a non-feedback carb? Do they help, or just glow red hot?

And one more question... does this engine need lead substitute? I do run it in my 1956 Chevy 2 ton with a 348 big block, but that's a bit higher compression engine as well... not sure if the lower compression of the 300 makes it less important, or not.

Thanks

Z

 

I have the same basic engine, and Holley 390, in a 2wd with a ZF and 4.10s. No manifold heat though and 12mpg is the best it's ever done. 6-7 mpg towing if there is any head wind at all.
BTW, we just spanked this very same subject to death in a thread a couple weeks ago over in the 67-72 section. You shouldn't have to look very far to find it.
What are the standards it has to meet. Usually not too tough. Is it just CO or HC too?

 

CO, HC, and NOx.... but no, not very tough compared to CA. I'll have the help of an experienced mechanic (he was racing stuff back in the 60's, before I was even born) in town, who can make his '79 Chevy pass it.

I'll look for the other thread.

 

"Going for better mileage..." Heat the intake...it's not difficult. EFIs (even mechanical pump injected applications) don't need heated intakes since the intake only delivers air and not an air/fuel mixture. It's not just a 300 thing or even just an I6 thing. Before the days of FI, many carbed engines including V8s had some sort of intake manifold heating right from the factory. Without it there were drive-ability problems due to fuel falling out of suspension with the air and puddling in the bottom of the intake. Carbs also like a stable temperature environment to operate in and the heated intake provides that stability.

 

Ah... thanks. Most of the older non fuel injected engines that I've done to more than just drive around stock have been diesels, which of course are also just air... I never realized what went into making a carbed engine happy. But it makes sense.

Z

 

I used to do emissions test in Anchorage with a program taken right from CARB (California air research board). The 4 gas analyzer was one of the best tools I ever had. I was driving a bone stock 72 F250 with 90,000 miles on the clock. I fiddled with it until I got .17% CO and 117 ppm HC. At that time it was allowed 6% CO and 1000 ppm HC. Which is about the same as raw fuel running out the tailpipe, lol. Anyway, that old truck was running cleaner than most new cars with ecm and cats.

 

If you look at that 300, the factory intake and exhaust manifolds are bolted together. This provides the heat needed to make the engine run better.
Carb icing can be a problem even at temps well above freezing, particularly in humid climates. This is the reason most EFI systems have a coolant line supplying heated water to the throttle body.
Diesel engines don't need this, as they don't have a throttle body, however, many do have some form of heat supplied to the intake.
Warmer air can accept a bit more fuel volume, and is easier to ignite, plus gives a more complete burn. The cleaner burn is becoming more important every year......

 

My old carbed subaru's all had a coolant line run to the base of the carburetor, now that I think about it.

Is it possible to get a coolant heated carb spacer for the 4 barrel carb. Most of the ones I'm looking at seem designed to keep heat away from the carb, not keep it warm. Though it looks like the FE engines had a heated one?

 

Yes, the old FE coolant plate is a popular item to use, but it needs modding to work. I believe the coolant passage is wider than the intake can seal, which calls for something to seal it. Some fill part of the passage with a steel putty, others make a custom plate to go under the spacer and use the original type gasket.
FWIW, most FE's used an exhaust passage under the intake to do this, not sure why some of them also used the heated spacer.

 

hauled home a few parts today...

300 engine, a NP435 transmission with the Ranger III splitter/overdrive input on it, a manual transmission pedal cluster, and replacement front grill/headlights to make it look like a '77 again instead of a '78. About 117k on the engine and 15k on the tranny/splitter since a rebuild.

 

here is a great article on intake heating, to help you out!

Intake Manifold Heat

good luck!

 

I am running the heated spacer on my 300. I was lucky enough to get the steel spacer that goes under it to cure the vacuum leak issue. I'm not real sure how much good it does but is doesn't hurt.