91 header on 90 4.0???

[hellabad]

can I use the 91 header on a 90 cherokee 4.0 if I change the downpipe? The 90 downpipe is a piece of crap anyway?

Obvoiusly I need to change the exhaust manifold, so I'm thinking while I'm a at it, the 91 looks a LOT nicer.

Thanks, Jay

 

[4xBob]

I believe it will fit, but the '91 header will not have a fitting for the EGR tube. On non-HO 4.0 engines, Chrysler changed the cam to allow a bit of exhaust into the fresh charge. This is what the EGR does on the Renix engines. The benefit is in keeping emissions down and in keeping temperatures a bit lower in the cylinders, especially when under load. This has to benefit engine life and help out the cooling system, but I have no hard data to support it. Switching a 1990 or earlier 4.0 to a 1991 or later OEM cam is a lousy idea- our (1990) torque comes on earlier, with 220 ft lbs at 2500 rpms. The later engines the peak torque is up quite a bit higher.

 

[hellabad]

Thanks, I am a pretty good welder, so I may just do that. What I can see is that the 90 seems to go straight down, but the 91 slants back a bit. The first section of the downpipe is so bad, that I figure I can just make a new one.

jay