Installing headers on 1990 L98 TPI
 

I want to intstall headers on my 1990 L98. I noticed that the existing exhaust manifolds have small tubes coming off going to a larger tube that runs along the valve cover. I am sure the headers don't come with the same set up. If you install the headers what happens to small tubes coming off the existing exhaust manifold (this must be something for emissions).
Second question
Will the headers get rid of the pre-cats? I was told i wouldn't need the pre-cats but to replace the main cat.

RE: Installing headers on 1990 L98 TPI
 

Precats are deleted. Also I believe the A.I.R. is deleted but you will need a alternator braket to keep your alternator from cracking. You dont HAVE to have a main cat if you convert to true duals as there is no emission checking here in N.C. but it may be different for your case. The tubes, I am not sure what they do but I would think that you would just plug them off. Hopefully someone with more info will be able to help you out. I think the part your looking for is the EGR block off plate.

RE: Installing headers on 1990 L98 TPI
 

pre-cats are delteted, yes, but you really dont need them. hooker and tpis make headers with provisions for EGR, AIR, and anything else you need to pass emissions. so you dont necessarily need to delelete all that stuff, though the AIR delete isnt a bad option.

you dont have to replace the main cat. the pre-cats were only designed to control emissions when the engine is cold, after that, they really have no function. you can get a nice 3-way cat that will do the job of all 3 cats, and still have very little flow restriction. today's cat technology far exceeds that from the 80s and 70s, there's really no reason not to have a cat. save the enviroment.

RE: Installing headers on 1990 L98 TPI
 

The tubes are air injection tubes for emmissions and you can buy long tube headers that have the tubes on them. I was looking at a set for my 86. [8D]

RE: Installing headers on 1990 L98 TPI
 

Thanks for the good info. My plans were to use a good quality set of Hooker headers. Any ideas of which to go with: either use existing set up of Y-pipe to one pipe and split in the back or do individual pipes coming off each header?

The little tubes coming off each exhaust pipe, it think, go to some kind of emission pump in front of the engine located on passenger side next to throttle body (it is black plastic with a couple of hoses coming off).

RE: Installing headers on 1990 L98 TPI
 

What was the brand of long tube headers with the emission tubes?

RE: Installing headers on 1990 L98 TPI
 

Individual pipe. Some back pressure is good as it will keep your horsepower steady. Loose all of it and you loose power. Get to much and you loose power.