1991 exhaust picture

[Barney Eaton]

In the event you thought the 1991 3800 exhaust header was manufactured better than the earlier headers, here is a photo of one.

Looking into the exhaust port...going to the converter.

Note the ring of excess material extending into the diameter of the pipe.

With a little high school math, I calculated about a 25% restriction on this unit. At first it does not look significant until you realise it circles the entire pipe and cuts the 2.5 inch diameter down to about 2 inches.

Jim Finn sent me this header and I plan on doing some work on it. I originally planned to cut it in half and add about 1/2 inch to the main tube, but after sleeping on it, that is a major task for an unknown improvement.

PS..if any of you want to blow this up so it can be viewed without clicking on the attachment, please do that, I don't know how.

[Guest Reatta1]

Looks like it wouldn't be that hard to grind it out with a die grinder.

[Machiner 55]

Sorry about the size of this photo. Tried to post a smaller one but can't seem to get it right.

[jonlabree]

Do it the easy way. Take a 2 1/8" or 2" (I don't remember which) hole cutter on a 12" drill, remove the center drill and go to town. It takes no time at all and you get a finnished hole. <img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" />

[Machiner 55]

Like this one? (photo courtesy of EDBSO)

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> I'd prefer the die grinder/carbide burr combo due to the interference of the Oxygen Sensor port. With it I was able to remove absolutely all of the obstructing metal without damaging or altering the Oxy. port. The small size of the die grinder made for easy access in the confines being worked in. (engine still in the car - working from underneath.) I really don't know if one could get a drill in there. Maybe a right angled drill. Also, the carbide burr cuts through that steel like it were a piece of pine. Wish I had a photo of the hole after I worked on it but, I don't and won't untill the next time I pull down the exhaust which hopefully won't be for another year or two from now.

P.S. I wouldn't attempt this with something like a Dremel tool. I don't think it has the power.

Edited by 88ReattaJohn (09/08/05 03:57 PM)

</div></div>

[jonlabree]

It's fine to do it with a die grinder, But you still have restriction in the pipe.

Tha oxy sensor fitting. With the hole saw that is trimed also and makes it much cleaner.

I will admit I did mine when the manifold was off because I ported them and had them rewelded on the out side instead of rhe inside as rhe facrory did.

[2seater]

Hole saw is best, die grinder is acceptable. The O2 bung hangs into the opening, same a little bit, some a lot. The O2 sensor seals like a gasket type spark and only needs a few threads for installation. If you do use the grinder, you can smooth and taper the O2 bung for better flow. A canoe sort of shape is best.

[Machiner 55]

I'm in an argumentative mood tonight, I guess.

I stand my ground with the die grinder/ carbide burr method.

1.) I don't think there's adequate room to use a drill/ holesaw combo, especially if the exhaust manifold is still in the car.

2.) I personally don't think that shortening the threads of the O2 sensor port is a good idea. One turn of thread would hold the sensor in but, is that a good idea?

3.) Speaking of obstructions... look at the sensor head hanging down right smack dab in the middle of the exhaust flow. Now how are we gonna get rid of that? (a little tongue in cheek humor here) <img src="http://forums.aaca.org/images/graemlins/tongue.gif" alt="" />

4.) Any and all comments welcome.

[jonlabree]

That's the point, you can't get rid of the sensor head, But you can get rid of all of the other restrictions.

And I have no idea if there is room for a hole saw while the manifold in on the car.

as I said I did it with ot off.

And I stand by my view. You get a much better flow with a hole saw, because you remove all of the restriction.

[Machiner 55]

You gotta love this board. I know I do! <img src="http://forums.aaca.org/images/graemlins/laugh.gif" alt="" />

[2seater]

No problem with standing your ground <img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" /> I have done more than one, and prefer the hole saw, but I never tried it under the car. I can't imagine that would be a lot of fun to do, and my hat is off to any that do it that way. The O2 sensor only has a few threads on it anyway, so the remainder of the bung that isn't used is just in the way. You are right that there is no way to get rid of everything, it's just the way it has to be. Any improvement is good.

[Machiner 55]

The hole saw does make for a really nice and perfectly round hole though.