differences between the 4.0s

[jones808]

What is the difference between a 1987 4.0l 242ci(xj) and the 1991+ 4.0l 242ci
Can i make the 1987 242ci carbureted?

[5-90]

The primary difference, mechanically, is that the later engine had the intake ports in the cylinder head raised slightly (I need to reverify just how far...) to allow for greater intake airflow. This required modifications to the intake manifold to accommodate the ports.

I'm sure you /could/ make a carburetted 242ci, but I'm in the dark as to why you'd want to. After all, there are a few advantages to a fuelie (and this is coming from a diehard carb/points guy...) and it would be a fair amount of work - starting with the fact that the 258ci (carburetted through 1990) manifolds won't work properly, since the #3 and #4 ports on the 258 were siamesed (and are separated on the 242ci.)

Easiest way to go would be to make an adapter plate to stick a 2V carb onto the 62m/m hole in the intake manifold. However, with the earlier "log plenum" manifolds, you run the risk of fuel puddling in the corners near #1 and #6, which is going to waste fuel (the primary advantage to port fuel injection is the ability to use a "dry" manifold - fuel is injected into the cylinder around the intake valve. Fuel cannot puddle where it is not...) Were I to try to make a carburetted 242ci, I'd start with a 1991-up cylinder head, which will accommodate the 1999-up "ram's horn" intake (which doesn't really have corners, and therefore significantly lessened risk of fuel puddling,) then adapt a carburettor to that. Depending on the carburettor, you could maybe - /maybe/ - get one that has enough volume for the 242ci, but will still fit overtop of the 62m/m intake more fully - and therefore you won't have to put as much work into making the adapter plate (with smooth radii to encourage the fuel to stay in suspension and the like.)

And don't forget that, unless you fab up an intake of your own, you're going to have to at least block off the injector ports (I'm thinking drill/tap for pipe plugs, probably 1/2" NPT.)

But first - why for do you want to do a carburetted version of an engine that was never carburetted? Any particular reason? Or just "because I can?" It would be a fair amount of work to prove a point...