Thinking about swapping 1998 magnum engine into my 1985 D-150. Headers are not an option at this time, and my current 318 has manifolds designed for the air injection system My question is, since the manifolds designed for the air pump have a much larger cut-out and/or hole on the lower side, will they seal with magnum heads which were never designed for the air pump smog system? Smog pump is long gone, I just don't want to swap this engine in and have a massive exhaust leak, nor do I want to try and find different manifolds if I don't have to. Am I screwed, or will this work?

I don't know if that will work or not, but the Magnum manifolds flow much better. They are what we used when we put the 5.2Mag in the '84 Ramcharger.

That's what I was going to ask, why not use the magnum manifolds? Might have to modify the headpipes on your exhaust a bit? I just used the magnum manifolds when I put a 5.2 mag into my jeep.

Sounds like he doesn't have the Mag manifolds.

If that is the case, I think there is a good chance that the AIR manifolds have only the AIR plumbed into those lower ports and there is no connection to the exhaust side in the exhaust manifold itself.

I have a set at home and will try to look tonight.

R.

LA engine air injection would have the tube across the rear of engine to each manifold. and a tube down the drive side VC with a check valve for the air pump.

2 small bolts bolt the flanged tube into the 1/2" hole in the ends of the manifold.

my 93 DAK the magnum engines have a egr tube that bolts to pass side rear manifold and barrel keg intake.

I like to find 2early/late 70s SB 360 LA truck manifolds, I nab 2 from the driver sides of JY trucks to ditch the heat flapper and emission plumbing.

190 bux for a set of hedman headers for the 85 2x are a good price and well worth the $$ spent. IMHO.

this is one of the biggest bolt on improvment that can be done to a 4-v 318 in a truck.

I build all mine the same, small 4-v/headers/duels/stock high stall TC/2.76 thru 3.55 gears for street duty.

cam is optional. results vary.

Already have new pipes bent for these manifolds that never found their way unto my last project truck, so I'd like to use these if I could. I have a set of unknown brand headers, but was never thrilled with the fit of them on small blocks as far as the starter and kickdown linkage went, if this was a performance street truck, then I'd deal with those issues, but this is a driver and I don't want the headaches and would like to use what I have if possible.

The smog plumb in the manifolds are not connected to the exhaust internal to the manifold.

You may, more than likely, need to pay very close attention to how the ports line up between the manifold and the heads, but the air injection stuff is a non-issue. I would test fit the manifolds on the heads and see how they seal up.