It all started when a guy had a question and I raised my car to find the answer. I figured since it was already up, I'd take a gander at the exhaust system and see what I could pull off with what I had. Just looking, I promise. My welder is out of wire after all.
As it turns out, I had the bends and clamps kicking around the garage to basically make a new exhaust system without touching the gaskets on either side of the manifolds. It appears that the downpipes are about 1 3/4" each and merge to a 2 1/2" connection to the catalytic converter. Oddly enough, it returns to 2" when it exits the cat. I decided that running a single 2 1/2" pipe would be sufficient for Gina's power level and needs, which just so happens to be what I have the most of. I saw no reason to mess with the Y-pipe at all, so I'd be starting right where the cat clamped on. (Even though it had to be cut off)
I've done a couple exhaust systems before so I have an El Camino bed full of bends as well as extra mufflers and other items, and I definitely wanted dual exits if possible but at this point nothing was certain because I was making it up as I went. I started by picking through it all and choosing pieces that I thought I could make work together without too much effort, and laid them out on the ground. I considered running duals out the back since I've got some pipes already bent up for that, but sadly they won't work on this car. I had my choice of Raptor Turbo mufflers, Flowmasters, or a Jones Full Boar bullet muffler if I stole it from Roxanne.
I grabbed a coupler and clamp from my old '86 C10 exhaust, a straight leg and 2 stainless band clamps from my El Camino, 2 90° bends from the bed, 3 clamps from the shelf, and a single Flowmaster (offset in, center out) from under the table. I didn't purchase anything, and more importantly
I didn't cut a thing after removing what was on the car
. I literally pieced together a mockup exhaust with stuff I had just sitting around. And it fit. The first 90 crossed over right by the bolt-in floor support, the other hugged the driveshaft tunnel on the driver's side.
With very minor tweaking I managed to get it to tuck up nice and tight (yes, I left at least 3/4" clearance). Still didn't cut a thing.
Now normally I try to avoid using 90° bends, U bends, or any other restrictive item and I certainly wouldn't use two 90s back to back. But for a smog-era 305 with a pitiful cam I didn't see it hurting anything, especially considering the 2" pipe and old converter it was replacing. I added a turndown after the muffler for now, but mocked up a "Y" with 45° bends & legs that exit near the rear wheels and like it much better. The current setup acts as an echo chamber, and dual exits always sound better to me anyway. I couldn't run it that way for now because I'm out of exhaust clamps and that "Y" has already been modified for Roxanne.
As for the sound, well, outside the car is great. Inside is.... not so bad really. I'm intimately familiar with about a dozen Flowmaster systems and this has the least amount of cabin presence of them all. That's probably due to the fact that it's only a 305 with a single pipe and muffler, whereas true duals would be much worse. My only problem is a bit of the ol' "Flow Drone", but again its not bad at all, really. I think that once I can split it and funnel the noise out the sides the back seat will quiet down- I wasn't able to drive it with that setup.
Edit: I added a single 45° bend between the muffler and turndown after finding another clamp, and interior noise from the exhaust is now virtually eliminated.
