This thread is being presented as a factual, technical discussion. This is not the place for snide comments please. It's OK to disagree but it doesn't have to get nasty. If it does I will ask that the thread be deleted immediately.
Many do not know the finer points of the B heads, many think they are just older but just as good as the C heads. This is not the case at all and I will show you why.
One of the biggest problems with the B heads, besides having intake ports that are too large to create the proper intake velocity for performance in an engine that is only 271 cubic inches, is fuel injector placement.
The B heads have 2 intake ports per cylinder. The fuel injectors are placed above the primary intake valves. The secondary intake valves are blocked off from airflow by a butterfly until ~3500rpm when they are opened, either by a vacuum solenoid (early) or an electric motor/cables(later). Both methods are controlled by the ECM.
Because the secondary intake valve doesn't get sprayed with air/fuel mixture, it gets really gunked up. How gunked up?
Check this out:
All of these valves were removed by me from a running and driving Mark VIII. I have more pics but they all look exactly like this. In each picture, the primary intake valve (that gets sprayed with fuel) is on the right, and the secondary intake valve (that does not get sprayed with fuel) is on the left.
We can agree that that much carbon and crap on the secondary valves certainly is hurting performance and can eventually clog completely, creating bigger problems.
Let's look at the fuel injector placement on a B head intake:
With B heads, the injectors don't mount in the intake, they mount in the IMRC plates. Notice that the primary intake ports (square) have the fuel injector placed next to it, while the secondary ports (round) have nothing.
Now let's look at the C head fuel injector placement:
Notice the single, oval ports with injector placed right in the center, allowing both intake valves to receive fuel spray. And those of us who have dismantled these heads know, there are no known issues with 1 valve looking new and 1 valve looking like crap in these engines. Both intake valves will look the same.
There have been people who tried to actually move the B head injector placement to make it more desirable but IIRC it ended up getting really technical and really expensive and was abandoned. I just spent an hour looking for the website that the guy had started but could not find it.
There have also been crazy intake designs, pretty cool designs but no one would raise the money to build it. Again, tried to find the website but was unable to.
So basically these are a few design flaws that make the B head more trouble than it is worth IMHO, seems like all the people who pursued solutions ran out of money and gave up.
Also keep in mind that deleting the IMRC butterflies does not change the injector placement. To be honest I think the solution from Ford should have been 16 fuel injectors, 1 in each intake port, it's hard to spray 2 intake ports with only 1 injector.
Thanks for reading, I will post more as i have time.