making a test pipe

jvandyke

jvandyke

True Classic
Looking into making a test pipe for an '81 FI exhaust. Replacing the cat with it. Found lots of discussions on it. I've been soaking the flange connections in PB Blaster for a few days but now I wonder if you can't just cut the cat off leaving it all connected, put a pipe in-between and clamp it. I was planning on taking it all apart and having a pipe welded to the cat's flanges but those bolt/nuts/studs look like they won't come off without a huge fight. Apparently, (see link above) one can clamp and get a good fit?
 
you can do anything

depends on what you want for look, sound and flexibility. as we are in Michigan, putting the cat back on isnt important. (doesnt have to have the flexibility to put it back on) I did exactly what you are talking about. Cut the flanges off and clamped in a pipe. Because of how close the bend is, it was tricky to get a good seal, but I did it. I eventually dropped the X exhaust and put a 14" supertrapp on instead. loud. VERY loud, but I am a deaf drummer anyway ;)


Odie
 
Where did you cut? Outside the flanges? I was thinking inside but either way I guess.
catcut_zps09090125.png
 
Welding is a better solution, if you can get the old CAT out. Then you can measure and cut on the bench, and have it welded, or weld it yourself.

This is the route I went for my Scorpion. I removed the CAT, measured for overall length, found a suitable pipe, cut it to fit and welded the flanges on. On the Scorpion 3-hole gaskets are used at each end.
 
Got a spare, as in, bad cat now? It takes about ten minutes to roto-rooter one out. Visually, it still looks like you have a cat on, if that's a concern...
 
where I cut

and I agree welding it up is much easier. remember with mine, I never intended to put the cat back

catcut.jpg


odie
 
I'm thinking cat removal to eliminate it as one less potential issue for my engine trouble, plugged cat implicated by two experienced engine builders AND I'd like a little bit more sound out of it. I have a complete spare exhaust so if I destroy one, no big deal. Cutting and clamping appeals just because I don't weld and won't have to disturb those flange connections as I suspect they will all break and I'll have to fix it all anyway.
 
Yes, I saw that. Would rather not spend $95ish if I don't have to.:cool:
I think I will try to cut the cat as in red above, leave the flanges all bolted up, put a pipe in and clamp it, if it won't stay together nice, then I'll get it welded, by then I should know if performance and sound are acceptable, or I will just bolt up the other complete exhaust with the cat still on it. Another possible benefit is tweak-ability. Right now, in order to get my lower exhaust mount (the arm that reaches out to the gearbox) to line up i have to really pull back on the exhaust which I think induces a ton of stress on the manifold and helps it leak. This last time around I didn't even bolt that lower arm up and I still have a leaky manifold, if I clamp it, I can loosen it, let the whole exhaust "find it's happy place" then crank the clamps down. Just a theory.
 
What about something like this? Allow the flex I think I need to bolt things up without the manifold getting pushed out of wack?
Would you slot the ends of the pipe to clamp down or not? I could stop by an exhaust shop and ask I guess.
Am I over engineering this thing in my head again?
[ame="http://www.amazon.com/Stainless-Steel-Flexible-Exhaust-Coupling/dp/B0031TQDQM"]Link to coupling[/ame]
maybecatdelete_zpsb5dad41f.jpg
 
A couple more points...

The CAT on my Scorpion was about 20" long, so you may want to find a flex pipe that will fit the entire length, and only use 2 clamps. I wish I could find the measurement.

Usually, if the fit is correct, a U-clamp will seal well. But a U-clamp will create a dimple all around that probably will not come apart without a fight.

For joints designed with future dis-assembly in mind, a slit and a strap clamp would be better.

Another thing to consider. The pipe inside the end flanges on my CAT were smaller inner diameter than the rest of the system. This seems to be a standard thing, so a true high-performance substitute would use flanges with the full I.D. of the rest of the system. In my case the CAT was almost entirely empty of pellets, so the recycler didn't even want it for the precious metals.
 
Great stuff, thanks, so far I've only found a 10" flex coupling with 1 3/4" ends but I couldn't find my caliper last night so I'm not even sure what the OD of pipe is right before it enters/exits the cat. I doubt my engine will notice the slight difference in pipe ID! I'm just pretty convinced I won't get the flanges apart without mass destruction otherwise I'd just unbolt it all, both my systems look like total rust fusion at all those bolts/stud/nut points.
I hope the cat isn't needed for structural rigidity; will the springs on the muffler take the weight if the "flex" part is too flexible? hmmmm
 
JimD said:
Summit has a lot of those style pipes Jeff. Here is one that is close to the Autozone pipe:

http://www.summitracing.com/parts/wlk-42215/overview/

It appears to be half the price, but I don't know what shipping would add to that.
Click to expand...

Good call. Ordered. Total $19.90. Thanks
I don't know how often I order from Summit but it's been a while. Ordered 9 pm last night, already half way here and scheduled for tomorrow delivery. Wow.
 
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Hopefully that one has no inner liner - any that do have the non-rigid liners will reduce in ID very rapidly.

Seems like you are covering all the bases to prevent a recurrence of the HG failure :)
 
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