Dedicated Exhaust Discussion

[Striker01]

Mounted for hopefully the final time!

[Striker01]

Hopefully my last post about these AA look-a-like headers. I'm going to call them sorted and send them out for ceramic coating.

Thanks to digger for talking about gearbox clearance, that's something I wasn't even thinking about and got lucky by just needing a slight modification for them to clear.

In this picture you can see the countersunk holes for the flange nuts. Unfortunately the holes aren't cut very precise and some of the studs weren't centered in all of them. Also the copper flange nuts are too big to fit into the ones that are centered, maybe 1/32" too small. I didn't like how some of the nuts didn't have much material to clamp on so I decided to fill the the countersunk area.



Filled, then lots of grinding and drilling.



I forgot to take a picture after grinding and drilling but here they are mounted, with the proper nuts.



This gap was at least an inch before I decided to shorten the primaries at the flange. It's fairly close now but both headers feel pretty solid and hopefully won't rattle together.



I got lucky here, I hadn't even considered removing the transmission. Just had to cut this little ear off (circled) and it will slide into place with the headers on. I also ran the grinder between the flanges, they were touching after the final welding.

[digger]

I'm don't think I follow what you're saying. I'm not familiar with the post you're talking about. I also don't see any way the exhaust can move an inch, I don't think the stock transmission hanger has the ability to move that much and the 30 some year old M20 mid section I took off is still in great shape.

He’s talking about when disconnecting the exhaust to get it off the stud and that there should already be plenty of play once gearbox mount is removed .Thinking more about it corrosion is probably not your long term friend and a bolt is easier to replace. Each to their own

[Striker01]

If the exhaust wont slide back an inch minimum you don't have enough room for thermal growth.

Kinda like that muffler hanger on the car Garage Welt posted. That'll totally fatigue and break put through some proper paces.

Along with flexy on one side and non flex on a dual exhaust system, to much strain on the non flexy side, till fatigue and crack.. IE a lot of E30 down pipes.

I'm don't think I follow what you're saying. I'm not familiar with the post you're talking about. I also don't see any way the exhaust can move an inch, I don't think the stock transmission hanger has the ability to move that much and the 30 some year old M20 mid section I took off is still in great shape.

[Striker01]

i like the good old flange myself, but IMO you dont want the connection too far downstream from the bell housing otherwise its a headers off job to remove the gearbox.

I would also think about whether adding studs might make it more difficult as you need to the clear the studs to drop it down. it depends on the layout overall

I would love to have the connection closer to the front but that would require significant changes to the rear bank, forward of the collector. That's not something I want to take on. I think I can still get the transmission off, it will be tight though.

[moatilliatta]

If the exhaust wont slide back an inch minimum you don't have enough room for thermal growth.

Kinda like that muffler hanger on the car Garage Welt posted. That'll totally fatigue and break put through some proper paces.

Along with flexy on one side and non flex on a dual exhaust system, to much strain on the non flexy side, till fatigue and crack.. IE a lot of E30 down pipes.

[hoveringuy]

Never really considered them, just figured Flanges will work better and be easier to build.



Great idea welding studs. never thought of that!

I love having the studs. It lets me slide the mid pipe up and it just sits on the studs while I secure the back. Plus, just a single ratchet/extension and M13 socket and done. No wrestling with two separate wrenches. It's Lux!

[digger]

i like the good old flange myself, but IMO you dont want the connection too far downstream from the bell housing otherwise its a headers off job to remove the gearbox.

I would also think about whether adding studs might make it more difficult as you need to the clear the studs to drop it down. it depends on the layout overall

[Striker01]

why no vbands?

Never really considered them, just figured Flanges will work better and be easier to build.

I had V-bands and now I have flanges.

Much, much prefer the flanges because they're so much easier to align and connect, and they fit a tighter space. With the studs welded into the header flanges, just slide the mid pipe on and tighten the nuts.

V-bands were always a wrestling match for me. hated them!

Great idea welding studs. never thought of that!

[hoveringuy]

why no vbands?

I had V-bands and now I have flanges.

Much, much prefer the flanges because they're so much easier to align and connect, and they fit a tighter space. With the studs welded into the header flanges, just slide the mid pipe on and tighten the nuts.

V-bands were always a wrestling match for me. hated them!

[moatilliatta]

why no vbands?

[Striker01]

So I tried to mock up the exhaust with the wrong engine mounts. My engine was about an inch closer to the driver side frame rail, didn't realize until I tried to fit the intake with the bosch ibooster installed. Lesson learned, Revshift 24 mounts will not work. I got the AKG ones and now that the engine is centered one of the flanges is closer to the CAB than I would prefer. I cut the rear header primaries just past the flange and shortened until the rear set just cleared the front set.

It got rid of the weird bend in the rear set and I tucked the front one a little closer to the transmission.



I should even be able to use the stock heatshield with just a minor modification.

[hoveringuy]

As far as the flex, I'm thinking about doing one on each mid pipe, fairly close to that flange. Reasoning is that I'm pretty sure the stainless will move between tacking and fully welding but I'm open to suggestions, figuring this out as I go.

you don't want two flex pipes, because then it will flex. Constantly. And you'll be replacing cracked flex sections in short order.

You just need one, if any, so you can align the second flange.

[Striker01]

Ugh thank you so much for doing this. Great work, great pictures. Welcome to the "it's really hard to get a picture of this and explain to everyone what's going wrong" club. I LOVE the plate to align the flanges. I wish I'd done that. hoveringuy and I did a bunch of "do we need a flex on one side before they come together?" arguing, so we'd love your thoughts on that.

Is there any hope to match up to an existing catalog rear section or rear and mid?

I think you guys went into a single exhaust, if I remember correctly. My plan is 2" dual with an x pipe before the cats. I want it to match up to my M20 stromung catback. I didn't even look at any of the existing mid section stuff, figure any catalog option will need adjusting so probably easier to just start from scratch. I ordered a 2" "build your own" kit, 2 high flow cats, flanges for the front and a donut/flare connection for the rear. I'm hoping the flare donut thing will work for the rear as the stromung pipes are slightly smaller at 1 7/8" OD. Have to play that by ear as I go, I don't really want to modify the stromung in case decide to go a different route. As far as the flex, I'm thinking about doing one on each mid pipe, fairly close to that flange. Reasoning is that I'm pretty sure the stainless will move between tacking and fully welding but I'm open to suggestions, figuring this out as I go.

[hubcapboy]

Ugh thank you so much for doing this. Great work, great pictures. Welcome to the "it's really hard to get a picture of this and explain to everyone what's going wrong" club. I LOVE the plate to align the flanges. I wish I'd done that. hoveringuy and I did a bunch of "do we need a flex on one side before they come together?" arguing, so we'd love your thoughts on that.

Is there any hope to match up to an existing catalog rear section or rear and mid?