Header/side pipes questions
 

My side pipes are designed to slip into the headers, which leak and rattle. I am going to weld flanges to both, as many of you recomended. I have looked at flanges sold by a couple companies. Both offer them with 3/8" plate material. Two machine shops and two engineers have looked at this and all said 1/4" should be adaquate.

Question #1: is 1/4" plate heavy enough?

One companies design uses 4 bolts located midway between the pipes. The other uses 8 bolts, same location as the 4 bolt plus all four corners of the plate.

Question #2: go with 4 bolts or 8 bolts?

I have EFI and the O2 is located in a single pipe in the header. I have read many EFI experts saying it is better to go with a single tube and stay within 15" of the head, including my EFI systems instructions. So, if I am welding flanges in anyway, it would be possible to make a small (say 2" long) chamber that was open for all four pipes to combine. Then the O2 could be located in this chamber where it would read all four cylinders. This would allow each cylinder to flow through all four of the side pipe tubes. I know from a tuned header point of view this small expansion chamber would be a bad idea. I think 29" give or take is considered the best length. The headers are not equal length anyway.

Question #3: would this small expansion chamber hurt performance much?

PS
Thought I would clarify: It is best to have O2 after all four pipes combine into one but only if the O2 is with in 15" of the head. Locating 30" at a header collector is often said not to work well. So they say it is better to locate O2 in a single pipe close to the head than too far away at the collector.

Use 3/8" flanges. 1/4" is too thin & will warp, also 4-bolt flanges are much better than using 3-bolt. Headers with 1/4" flanges always have problems with warpage & leaks. "Cheap" headers have 1/4" flanges.

I'll field #2 and 3 for ya...

I have the 4 bolts on mine. 8 bolts would be better. The more bolts (within reason) you have holding a flange together the better your chances of keeping a good seal and not blowing out gaskets or RTV.

Introducing all 4 primaries in an open chamber, aside from and before the collector, can cause undue exhaust turbulence and possible reversion. That can cost you a few ponies. I think I'd try to find a way to weld a bung on the inside of the collector, in a fashion that would hide the O2/wiring from view as much as possible.

on a side note: I agree with Eric,a minimum of 3/8" on the flange. Mine's 1/4" or 5/16" and is prone to deformation after nut/bolt torque.

olddog

I installed flanges on my exhaust and used 1/4 inch with eight holes and have not had any problems in 5 months of operation.

Bonos

BTW, part # for an O2 bung: #88103. To plug this, use part #35299. You can order these through any NAPA, or any place that carries Walker or Dynomax exhaust products. All of NAPA's exhaust is Walker (Tenneco) stuff.

I will go with the 8 bolt pattern, which will put the bolts about 2.5" centers apart.

I'm thinking 1/4" bolts to hold the flanges together. Do you agree?

One person suggested using soft copper for gaskets. Good idea?

I will not go with the small expansion chamber idea. I'll keep the individual tubes seperated as designed.

I will put an extra O2 bung at the collector. I want to be able to get a wide band O2 there for tuning anyway. Good suggestion and thanks for the part numbers.

For you welding experts, how far from the ends of the pipe do I need to strip off the Jet Hot coating? I was thinking a 1/4" and a friend recomended 1". I don't want to remove any more than necessary, but want good welds. What say you?

Old dog when you make your flanges, just make sure your side pipes where they mount to the frame have some kind of a rubber isolater, or bushing to take up the slack, or your gunna have some vibration problems, and cracking, just thought I would throw that at ya.