4.0 Exaust port size

[nhmann]

long story short, My 99 4.0 OHV needed two heads. Bought two new heads and not noticeing one head had a small exaust port and one had a large exaust port I installed them. (all other aspects of the heads are the same) my truck ran horrible and would hardly Idle. Took motor apart and had vender ship a new large port head (all that is availible new) Truck runs pretty good but when going up hills ect it feels like it is running lean and has water in the fuel. My issue is my exaust manifolds have a small port and the port on the head is is much larger (BY about a third and shifted off to one side) I feel it is screwing with the scavenging effect and causing some reversion in the out let path. The vendor tells me they sell these heads every day and if there was a problem with putting them up against a small port manifold he would get calls all day long, I do not buy it but maybe trucks other than mine have a larger port exaust mainifold. ( the small ports were only a two year deal 98-2000) they do not know how i got a new small port head from them as the only new ones made are a large port. I do not want to buy one remanufactured thin casting ford head and end up with another cracked head down the road. I guess I am wondering if there is a large port exaust manifold that will bolt up so I can solve this issue once and for all.

 

[heptofite]

if the small port was only for two years, find a manifold from a year that is NOT those two years.

 

[nhmann]

I am not sure what others will bolt up.

 

[heptofite]

the bolt pattern never changed

 

[nhmann]

I ment the outlet and egr tube locations need to be the same

 

[heptofite]

I ment the outlet and egr tube locations need to be the same

that's part of the y-pipe, not the manifolds.

 

[Bird]

98+ 4L OHV engine used a different head than the earlier models. Pre95 heads had a bigger exhaust port and a bigger combustion chamber that , if you install them on a 98+ shortblock, will result in lower compression and restricted exhaust of which both combined result in much less power. The 95-97 heads have the smaller combustion chamber, but the larger exhaust port which will still cause you problems. You should have gotten the smaller port heads that are of the type that originally came on your motor.

Bird