Hello,
for my recently purchased F100 from 1981 with the 300 engine I am searching for a plug&play fitting and performance+sound increasing complete exhaust system. After a quick search there was nothing matching. I would be grateful for some hints.

Further I want to ask if this exhaust manifold fits on the 4.9 form 1981?
Genuine FORD F-Series Pickup E-Series Van 4.9L 300 6 cyl Rear Exhaust Manifold | eBay

And does this manifold fits?
FOR FORD/MERCURY 144/170/200/250 CID l6 STAINLESS STEEL HEADER EXHAUST MANIFOLD | eBay
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Your first link shows one of the 3 into 1 exhaust manifolds that were standard on the EFI equipped 300 six starting in 1987 or so. I am not sure how many variations there are of those manifolds. They are different front and rear though.

Many people have retrofitted these to eariler carb'd sixes with good results. It does require some fitting due to some tabs on those that must be removed.

Your second link is for the smaller six and will not work on a 300.

There are headers made for the 300 which can be found on line.

As for a "plug and play" there is nothing. You can fit the EFI manifolds or a header, and you can have a muffler shop bend up a system with the muffler of your choice.

As to performance you will enjoy a very modest improvement performance all else being equal.

 

Generally speaking, unless its already got the EFI Manifolds on it, I prefer to go to a proper full length header, like the Hedman 89300's. But they can obviously make for packaging issues, depending on the truck. And sadly, no, there is nobody making a full bolt-on exhaust system. Summit has a "Catback" kit that is pretty good (I've got it on my 87 with the 300) but you'd still have to fab anything between the collectors and what the kit covers.

 

Thank you for the quick reply.
I have bought yesterday two of the efi-Manifold for together 150 bucks and hope I can mount them on my engine. The rest of the exhaust system will be done by a muffler-maker.

Now I have some more questions and dont want to spam this forum with another new thread:
I also want to recondition the whole engine. Is it indicated to bore the cylinders and choose bigger pistons and rings? The truck has now around 90.000 miles, but 41 years old. I would prefer to use the standard size for rings and pistons.
Is at all indicated to change the pistons?
The Truck will later be converted to use Propane/butane as fuel (usual in Europe). So its indicated to use hardened valves and valveseats due to the lack of cooling gasoline. Does this kind of valves and seats exists for this engine?
With this occasion the cylinder head should be machined too. To increase efficiency I want to increase compression ratio. Stock ratio for my engine is 8:1 afaik. Something around 10:1 would be nice. Is this possible? What kind of additional modifications will be needed?
Any other hint to this topic is welcome.

 

The EFI manifolds are they for a pick up or a van?
I do not know if the 2 are different. Guess you could look up manifolds for both and see if the part numbers are the same.
If not the same then I would look for a set from a pick up.

When I rebuild my 81 F100 Flare Side I wanted to be able to get the parts anywhere be it local parts store or (long shot) dealer.
With that said I used pick up EFI manifolds, stock 81 intake manifold & carb (hopping) for better MPG.
I used a 94 Y pipe to hook to the EFI manifolds, no cat, and 94 pipes (middle & tail) and welded Thrush muffler.
The factory mufflers were just a little to quite for me, I like the sound now.

Now to get the EFI & factory manifolds play nice you need to place them on a flat surface (sealing side down) to see if where the thick washers sit to make sure they sit flat between the manifolds. Also check if there are any "tabs" that may keep the manifolds from working together.

Then you have the hot air choke that the metal tubes went to on the log exh manifold the EFI will not have this so what to do?
You could swap on a manual choke but then if you need to swap carbs you need to swap the choke set up too.
My fix was to take copper tubing and make a few loops around a manifold to pick up heat.
It was run the same way as the factory had it. I found I was not getting enough heat so I took header wrap to cover the loops and the seam to work so far.

The other thing and this is also an issue if you use an after market intake, no heating of the intake floor.
Remember the two manifolds were bolted together and exh gases heated the intake to help vaporize the fuel.
I was able to buy a heating plate off Ebay that bolts to the bottom of the intake (after market also) that you run heater hoses to and the water heats the intake floor.

I built my truck to drive and have had it out when 28*f with vary little warm up. Start it in the garage, back it out, run back in to turn lights off and close garage door (auto) and drive off.

I can not tell you how much more power it gave as I did not drive the truck with the factory log manifolds before the 4 year cab off frame rebuild.
Dave ----