The previous owner of my '81 installed a set of cast EFI exhaust manifolds. I purchased the truck from him last August. My milage is now declining in cooler weather. I've expected this since the swap left no provision for manifold heat or heated intake air.
I found an additional shortcoming yesterday: the swap left no effective warm air provision for the automatic choke. As a result, it hasn't been opening all the way in cooler weather. If you are considering this manifold swap you should plan to convert to a manual choke, as I've just done. I ordered the kit through a REAL auto parts store; it cost more, but this particular kit (HELP! #55104) is packaged specifically for trucks and comes with 9' of choke cable. The long cable is necessary because it must go all the way across the firewall, from driver- to passenger-side, before looping back to the carb. This routing is necessary because there is no place to mount the (carb end) cable bracket except at the right carb mount nut. The necessary bracket comes with the kit, I only had to straighten its right angle a bit and twist it some to provide decent cable-choke lever alignment.
The kit is complete, the instructions more than adequate, the conversion simple The hardest and most time-consuming part was the cable bracket. Total time for me was 2.25 hours, and I'm the sort who can take a 30-minute job and knock it out in 5 or 6 hours, just like that.
Now, if I can acquire manifold heat and heated intake air before carburetor icing strikes - any suggestions

 

I take it that you're using the stock intake (or an off will work as well)? If so, you can can make a heater plate that will bolt right up to the old exhaust heat location. I belive that you may be able to buy them (Stovebolt?), but they are easy to make. I just used a chunk of 1/2" aluminum about 4" square. Drill the bolt holes & then 2 more for some pipe fittings. Tap the other 2 holes for regular pipe thread & install a couple of fittings. You can now run your heater water through the plate. I actually haven't used mine yet as I'm making a valve system so that I don't need to run the heat through in the summer.

 

Good suggestions. I've often wondered what the 300 owners are going to do when all the exhaust manifolds are gone from the Wrecking yards.

How about making one out of Steam pipe, or 3/8ths inch Bronze?

 

Yeah, I'm running the stock manifold/carb. I like the idea of the heater plate, I'll have to look into it. It sounds nice and simple. My only concern would be existing rust in the "heater" area of the manifold - wouldn't want to expose my coolant to it. I think I could sandblast it from underneath without removing anything.

 

We needed all that stock stuff in Alaska.
First of all, the emissions guy wouldn't pass the engine if he looked in there and saw anything unusual or odd.
But most important was the starting and warming up in the winter.
I dont think any of that emissions stuff, even that Cobbled up crap in the 79-80's vintage emissions stuff, ever for one second caused me a loss of power or fuel milage.

The emissions stuff greatly enhanced the fuel milage in the winter. Those 300's are about as rough to keep going in cold weather as my uncle's old Dodge flathead, without having the heated air to help it regulate the choke and mixture.

When my Neighbors exhaust manifold cracked, we brazed it back togather and he sprayed some kind of heat resistant paint on the Braze so the Emissions guy wouldn't see the repair. It passed, but by the following spring, that manifold had cracked and broken to the point of uslessness. In fact the hot gasses was cutting the block. We didn't see that till we pulled the manifold off to replace it.

The manifold he got from a wrecking yard was for a 76, without the emissions stuff on it.
So I swapped the Manifold off my 78, which was a used manifold out of a wrecking yard and had all those ports he needed, to his 80.
I'm such a good guy, so compliant......and he painted my house for me!

I had to get a special wave from the Emissions referee. My Vin showed the truck to be a 79???
So I had to get both my manuals and show him the truck was a 78. Made just as the model year was changing, and never had the emissions stuff on it.

 

I made myself the heating plate using aluminum, it works fine but since I live in a tropical country (Venezuela) I had to install a temperature switch to intake manifold and a solenoid valve to stop coolant flow to heating plate if intake air reach 120ºF

For climatic control I used a piece of cooper pipe 1/4" I.D. and roled it 4 times around exhaust port #5 so the air passing is heated and then it reach climatic control, I'm using also electric climatic control it works better than standar air heated climated control.

 

Got pics ??

Show the folks your truck Javi! The truck is awesome looking!