I know, it's an exhaust subject. But really it's about a particular engine. Specifically, the 300 six.

I'm in the planning stage of building a short tube header. Why? When a header is available?
The short answer is, because I can! Besides, I can make it the way I want. Along with that, I can build it, AND get it ceramic coated for way less money than buying one. Besides, those long janky tubes look like hell, and from I understand, are too close to the starter.

To the question...
Even though it's a low rpm stump puller, but it's also 50 inches per hole. So, 1.5" or 1.625" primary tube size?

 

Just gut reaction, no science behind it, but go 1-5/8"

 

Use the 1 5/8" primary tubes.
I'm assuming that is an OD dimension?
Will it also be two 3 into one like the long header?

 

Yep, 3 into one. Two of 'em. And yes, that is the OD of the tube. So the actual inside diamter is pretty close to 1.5" anyway with 16ga tube.
I have the head flanges already. Nice 1/2" thick. I think the primary tubes will only be a foot or so long. Doesn't look like it'll take a whole buncha bends.

There's a pretty big space above the starter where the two pipes can go to give the starter plenty of space. But I will probably built a heat shield anyway.

So yeah, I was leaning toward 1.625"

​​​​​​​Thanks guys!

 

Because the exhaust system is for a low rpm "stump puller" consider joining the two pipes with a "Y" about 24" after the primaries.

 

Thanks. I thought of that. I'm going duals all the way because I like the way a straight six sounds. I might put an X crossover in though

 

An "X" would help also.

Would you mind describing your engine build?

 

It'll be bone stock, as it will be a driver. Probably never see anything north of 4000 rpm. Maybe a little cam. If an EFI head happens to fall into my lap soon, that would be icing on the cake.
Fuel mileage is the name of my game. I've done the hot rod street car thing, and I'm long over it. It's about efficiency now.
Most likely go with the AussieSpeed intake since they are actually available, and the cost, although kinda steep, is on par with the clifford since it is necessary to buy the adapter too. That puts it in line with the Aussie manifold with shipping.
I'm on the fence between a small four barrel carb and EFI. I want the simplicity of the four barrel, yet want the efficiency of the EFI, particularly since both Clifford and the Aussie manifold have injector bosses cast in. In my mind, if you're gonna do EFI, put the injector at the port, or don't bother. The downside is having an EFI problem on the road. Aftermarket EFI systems are not nearly as reliable as factory units, and this is what makes a carb desirable. With a few spare parts and basic tools, they can typically be fixed quickly, even on the side of the road....IF one know what they are doing. And I do know my way around a Holley. I used to modify them and set 'em up for hot rod guys "Back in the day"
Anyway, it'll be with a T5 manual trans. I've just begun. Only had the truck a couple weeks. This will be my third header build over the last few years.

 

Are you going to rebuild the engine?

 

Yep. I have it out. I just couldn't put it back together without rebuilding it. It's an unknown, and I want to be able to depend on it. So, probably an overbore, grind the crank if needed, resize the rods...the whole nine yards

 

The 1965 to 1968 300s have a .912" piston pin and use the Ford 351W pistons.
If you are going to use the EFI head in order to maximize fuel economy you have to decide now in order to figure out what piston you need to get the correct compression ratio.
The 1965 head has a 76cc combustion chamber while the EFI head has a 68cc chamber.

For best fuel economy you want to push the static compression ratio.
The highest Dynamic Compression Ratio for the 300 six using 87 octane pump gas is 7.00
The stock cam has a 268 degree .006" duration and closes the intake valve at 68 degrees ABDC.
With only one exception, All of the small to medium performance catalog aftermarket cams have less .006" duration than the stock cam and close the intake valve earlier than 68 degrees ABDC meaning the stock cam allows a higher static compression ratio at 8.8 to 9.0 to meet the 7.0 DCR limit.
Instead of going to a small aftermarket cam you can increase the stock cams valve lift by using the Chevy six 1.75 ratio rocker arms or if going to the EFI head using the 1.73 ratio Scorpion roller rockers.

The majority of the wrecking yard EFI heads have cracks so it is advised to get an autoparts store rebuild or better yet get a new and improved casting with hard intake and exhaust valve seat inserts from Promaxx.

 

Good info.
I'm no stranger to calculating static CR. I've been drag racing for about 45 years. The current ride, an air cooled VW which I've recently handed off to my son, was just a fuzz over 15-1 CR when I ran in in normally aspirated form. It was difficult to get. Chamber size was right about 30cc, but any smaller than that, the valve notches got deeper, (.680 lift at the valve and 282° dur @ .050 valve lift) so it was diminishing returns. Once I went turbo, it got easier. 50cc chambers and flat tops with about .040 deck got me a bit over 9-1.
At any rate, I have the tools to measure actual chamber volume, and don't rely on "advertised" volume. It can vary several CCs depending on several factors. I also like to run a fairly tight deck. I also have a milling machine in my garage, so if I need to machine a dish that mirrors the chamber, I can do that if needed.
It'll be fun!

 

The best 300 head gasket is the Fel-Pro 1024 which has a compressed thickness of .039"
That gives you a good quench distance with a piston at zero deck.

I would like to see you use the EFI head for this project.

 

I'll post as I get into it. The motor came out today. I'll probably get into in a week or so. Won't know what I got till I get in knocked down

Thanks for the tips!