What are the internal differences between a carbed 300 and a FI 300?
Will the carbed manifolds bolt up to a FI head?
Would the FI motor run with the carbed manifolds & carb.?

 

Main difference is the combustion chamber design of the head...

carbed has more open chamber as compared to the efi head, which means the efi head/engine in theory, should need less total timing and be low end torque biased.

The camshafts are the same.

Yes the carbed manifold will bolt up to the EFI head.

Yes the efi long block would run with a carbed manifold/carb...you'll also wanna change the ignition. You can pick up HEI distributors for the 4.9 one wire hook up blah blah blah or theres the OE duraspark II system, cheap and seems to get the job done. You'll also need an adjustable fuel pressure regulator...carbs like 6+/-psi and the stock efi regulator runs at 59psi. Obviously, there are no mechanical fuel pump bosses on the efi block.

Good luck

 

Yes, the chambers are designed as a fast burn cylinder head, swirling the intake charge as it enters the combustion chamber. However, if you want all out performance, go with the carbed head as they flow a bit better, and allow the use of larger valves. Installing larger valves on an EFI head would only negate what you trying to do as the valves will become heavily shrouded. Not good. You could unshroud the valves at this point, but then you lose the effect of the fast burn design.

 

You know, I read where FTF mentioned that once, my first thought, if you do decide you need more flow and unshroud the valves (free), what difference would it make which head you use, thinking, the person has the efi head anyhow and there is no port advantage? Know what I mean?

I read once where a dirt track racer prepped an efi head and he said it pulled real strong in the upper rpms.

Something to think about I suppose.

 

Thats the problem with 300's I suppose, Motorhead. The aftermarket hasn't put the time and money into R&D the 300 for performance to the extent of other engines.
That leaves it up to us to figure out what will work best for the intended application.
I doubt there are enough people out there with enough money to try out different
combinations / modifications to see what works best. If one had enough money, then one could try out different head modifications on both carbed and FI heads. Of course this would also require extensive use of a dyno to see what results are actually produced.

The 300 is great engine plagued with a poor cylinder head. So it will only be as good as the cylinder head will support, and at this point and time, we only have that head to work with.

The fast burn technology is good for power and efficiency, however, the flow of the head is yet to be desired. If we could get the flow numbers increased and keep the fast burn feature, IMO, that would be a huge step forward. The fast burn would allow us to run less timing, thus increasing power, because the piston on the power stroke won't be acting against the rapidly expanding mixture burn.

 

My thinking, with the smaller efi combustion chamber, you have room to manipulate the combustion chamber for optimal burn, with the carb head, not easy to put back material...

luckily for the 300 owners looking for optimal low end, you really don't need a much larger intake valve.

Only reason I could see, to NOT use the efi head, is the fact they are prone to cracking.

I see what your saying though...