Your build has been an inspiring thing, Walter. I spent part of this holiday weekend trying to fit a new exhaust manifold, which caused quite a few problems for me.
It touches the transmission and puts the catalytic converter at a funky angle that isn't physically possible to use. Unfortunately, most of the stock exhaust fell apart enough during disassembly that I'm not willing to put it back together, and I couldn't get ahold of any new tube because apparently it's a holiday weekend. I ended up having to drive the thing home with just the exhaust manifold on it, and it was
painful, even with ear protection for the whole drive.
Boring Part
This morning, I put together my shopping list and ordered some parts. The manifold terminates with a 2" OD, and terminates in a silly bolted flange that I've found often causes leaks. I'll replace that flange with a 2" vband clamp. All the components I already have are 2.5" stainless, so i decided to continue that trend and step up to 2.5 immediately after the vband clamp. It allows me to easily remove the entire exhaust system, without having to pop the hood. That feeds into a 2.5" braided flex pipe (I can't tell if it's ribbed or smoothish inside, but it's cheap and flexy enough).
The flex pipe is the last rubber-mounted component of the exhaust. From here on in, everything is fixed to the frame. It's not a decision I made lightly, as there are several downsides to solid-mounted exhausts, but that's currently the plan. Up next is a high-flow catalytic converter. I could get away with not running a cat here in NH pretty easily, or just running a test pipe. We have no emissions testing for vehicles this old ... but other than the fact that it costs some money, I don't understand why anyone would forego a cat on a street vehicle. The performance costs are negligible, and the environmental benefits are substantial. I paid $55 for an inexpensive 2.5" stainless model on eBay.
After that, I'll just have a straight run back to the differential, and have a few leftover 409 stainless mandrel bends that I can cut and weld to keep ground clearance without disrupting exhaust flow too much. 409 isn't as pretty as 304, and will eventually rust (where 304 is far less likely) but I'm going to end up with some alu sheeting (or similar) under the car before too long, so it should protect it from corrosive road salt before winter even arrives.
Work Log
I had to look at the bends and the bandsaw for awhile before I really figured out how to position the piece to get a nice clean cut, but everything went according to plan from there.
For the very end, I have a few spare sportbike cans lying around. I tend to like the OEM models, since they're more likely to be stainless (aluminum can soften/fail in some cars' exhaust temps), have really efficient designs, and are generally quite good at muffling. I was given three of these, since sportbike owners have a tendency of upgrading things just to upgrade them.
The f4 is a pretty good fit for this application, with a 2.5" inlet, great baffling, and a relatively subtle 3" outlet. It's slip-fit by default, so I chopped that section off.
The baffling goes all the way to the vey end on these. You can see where I went through some of the insulation here.
It's essentially a glasspack with a chambered muffler on the rear. I certainly flows well enough for the 90-ish whp I'm currently making, and allows me to remove several of the excessive bends in the OEM Mazda exhaust.
Because I don't have all the components I need yet, I'm just cutting and tack welding parts together with my little Miller TIG. These things are just awesome. The duty cycle is limited, and they can't run very long over 80a or so, but that works fine for everything I've come across. I love these little things.
Finally, the current state of my tack welds. No hangers, and the straight center bit is waiting for supplies, but the tough parts are mostly done. I really wish I had a lift for this. It'll be slightly higher in its final form, within 1/2" of the height of the unibody 'frame rails'. Clearance is tight around the differential, even after I switch the horizontal reinforcement bar back into its rear-facing position (I moved it so the exhaust would have something to hang on temporarily).
I still haven't sorted out what I want to use for hangers, but I'm thinking of going with the rally-style bushing-on-each-side. Something like these hangers, in all the usual points on the car.
Nice. When's the Indy T's coming out to play?
