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Exhaust
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Well, here's a few pics of my latest exhaust system. I've been working on it for well over a year now, just doing temporary fixes until I was sure it was routed around everything else I've done underneath. The new muffler I'm using is a Dynomax Race Magnum series. It's one of the large 4½" x 10" x 14" ovals with 2½" inlet and outlets. It is a strait through design with a smoothly perforated core (as apposed to punched which leaves edges) and a ceramic packing. I was a bit leery of a strait through design, but this one came highly recommended from some of the turbo Dodge guys. The new system is mostly 2½" tubing now, made from welding up mandrel bent U- and J- bends. I also used some 3-bolt flanges to bolt everything together instead of using slip fittings and exhaust clamps. I've found those a pain to work with if you ever have to take the system apart (which I have often). The ends deform and don't want to come apart, and you need to slide them apart which you can't always do unless you first drop the entire system. The flanges bolt together easily and when undone, the part in question will drop strait down without having to slide forward or back first. I still have a 2¼" tail pipe that goes up over the axle, between the frame and body and down and out in front of the rear bumper. I'll likely leave that in place for now as it's a fairly intricately bent piece that took quite a while to make. I'm also not sure that a larger 2½" piece would fit. Here's some .wav's of how the new system sounds. And just to jog your memory, this is the Isuzu 2.6l 4 cyl engine. The turbo helps to keep it a little quieter, but the cat rattled it's guts out a few months ago so it's hollow. A standard, non-turbo engine with a good cat should sound about the same. These ones were taken with my laptop sitting on the ground near the
back of the truck a few feet from the tail pipe: At idle (107k) and zipped
(29k) These were taken from the passenger seat during a full-throttle 0 - 75 or so mph run. The first was a slight rolling start. The second was from a stop and you can hear the rpm drop in the first second or two. This is from the slipping clutch finally hooking up actually. You can really hear the turbo sing on these ones :) Run 1 (603k) and zipped
(194k) (chirps the tires on the 1 - 2 shift) And finally, just for grins, I was playing around a little bit with my audio software. Here's the second full throttle run time-compressed so that it's twice as fast. Sounds kinda like my old CBR did. :) Run 2 time-compressed (445k) and zipped (162k) The exhaust note is still a little rattly or resonating on heavy *deceleration* like when at 4 - 5k rpm and I pull my foot off the gas completely, but most small engines are. It's not bad and it's only when I rev it to redline and come completely off the throttle that it happens. It's nothing I really notice while driving. I believe the resonator that some (most?) cars have is used to cacel out this resonance. Overall, the muffler is very quiet, much more so than I had expected. I have read that these do work very well for smaller motors and especially turbocharged 4 cyl ones and so far I'd have to agree. I've not noticed any annoyingly loud droning at cruise either. Now on to the pictures:
This one I coated with hi-temp (~2500 ºF) ceramic coating I had left
over from the turbo and exhaust manifold. This stuff works excellent
and will not burn off. It also serves to keep the heat in the
exhaust quite well. The rest I sprayed with the hi-temp stuff you can find in the parts store. The brand I used was Dupli-Color. It's the silver one and rated at 1200 ºF. It too works pretty well, but it will flake off some of the hotter sections of your exhaust eventually. The cat is a small 4" diameter one. I tried a small oval one first, but there just wasn't enough room between the torsion bar and the transmission. It would fit, but it was very tight and both the torsion bar and the tranny got hot enough to burn you if you touched them.
The cat is bolted to the muffler and the first hanger is right between them. I made a bracket that bolts to the torsion bar bracket and welded another one to the muffler itself. The muffler is suspended from the frame side bracket using two of the rubber doughnut type hangars. The muffler is a DynoMax Race Magnum. It's a strait through design with a perforated core and ceramic packing. It has a 2½" inlet and outlet, and the core going through it is 3". It's fully welded construction and made from rather thick gauge material so it's easy to weld to, especially if you do it at one of the seams. It's surprisingly quiet for this type of design. I was expecting it to be a a lot louder than it is. Before this, I had one of the DynoMax Super Turbo mufflers. This is the standard 3 tube type that routes the exhaust through two 180º turns. I ran that one very briefly without a cat and couldn't stand it. It was way too loud and had a very annoying drone at cruise. This new one is much quieter.
The second hangar is at the back of the muffler and bolts to a tab welded to the underside of the body. This tab was originally used to hold the e-brake cables, but I removed it when I did the lift as it stretched the cables too tight. It's in just the right spot for a rear hangar for the muffler. The tail pipe is still a 2¼" piece that wraps up over the axle, runs between the frame rail and body and then down over the rear cross member just in front of the rear bumper. I'm leaving it as-is for now. I'm not sure that a similar piece made from 2½" pipe would fit or not. It could be routed down in front of the rear cross member like the stock tail pipe was, but come out the back instead of under the quarter panel for more ground clearance. I banged up the stock tail pipe several times with it under the rocker. I'll likely wait until I get a new rear bumper made and trim my rear quarter panels before I do a new tail pipe.
There's still a couple other things I need to do as well. First is to replace the cat since it puked it's guts out. Actually, it rattled loose and plugged up my exhaust. I took it out and knocked the remaining chunks out, but left it in place so that when I get a new one, I can just bolt it in. I also want to get a flex pipe put in between the down pipe and the cat. With the new system bolted together with flanges, it doesn't give as much as before. I'm afraid this might over-stress the exhaust manifold when the engine rocks in it's mounts. It's already got a crack in it and I don't want it getting any worse. One of the high quality, braided stainless steel mesh type flex joints would be good to prevent this. Unfortunately, I priced one at a local muffler shop at over $100 so I haven't gotten one as of yet.
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