Is true dual exhaust a good idea for a 3800SC? (Page 1/4)
zmcdonal SEP 11, 09:32 PM
I know there are tons of threads on here about 3800 exhaust, and I've read pretty much all of them, but I think mine is a little different and I could use some input from you guys. My trunk is already cut, so I pretty much have a clean slate to work with.

I recently purchased a Ferrari 355 muffler that I am intending to use on my 3800 swap. The Ferrari muffler has 3 inlets, one is designed for a vacuum opperated bypass, which I will probably just cap off. Currently my swap is running stock manifolds into a high flow cat, and down to a dual outlet flowmaster, but the way it was done, it takes up about half the trunk. I am trying to decide if I should upgrade to headers when I change the exhaust, and if so which kind would best suite my setup? The speed daddy style that all tie into one collector, or would the pacesetter style be better with the modular Y pipe, or possibly not even use the Y and run each side independently into the muffler, which is where my question about the true dual exhaust comes in. Also I live in a county that requires emission testing, so I will probably have to plan on having a cat or 2 if it's a dual setup.



Also I could use opinions on what would be the best way to mount the muffler. I am thinking if I put it horizontal and have the inlets towards the motor I would probably only lose the thickness of the muffler, then just clock the outlets accordingly although I have not measured if it will fit this way yet.
doublec4 SEP 11, 09:49 PM
Interesting! Would love to hear how that sounds when you're done!
2.5 SEP 12, 09:33 AM
Me too. Wild muffler.
dobey SEP 12, 11:28 AM
Running dual, you will need to have probably 2 O2 sensors on each side, one pre-cat, and one post-cat, for each cat. I'm not sure if the ECM you're using has support for that, or if any 3800 cars came with that, though. To do it, you'll eat up a lot of space in the trunk area, to have shorter exhaust like the Ferrari has, and run dual cats and with that huge Ferrari muffler. You could run longer exhaust with one cat in the front, and one in the trunk area, but I'm not sure how that would mess up the sound or the flow.

For headers, I would definitely go with custom headers, regardless of what the rest of the exhaust looks like. The problem with all the 3800 headers available on the market, is that they're designed for front engined cars like the Grand Prix, and not a Fiero.

Personally, I would scrap the Ferrari muffler plan. It sounds cool, and "I have a Ferrari muffler" is a good conversation piece, but it's a giant muffler, and using it in a Fiero if you want to retain the trunk, is going to be pretty difficult, especially with a transverse engine. With a longitudinal swap like an Audi V8 with the Audi trans, it would probably be a great option, as you could build an exhaust similar to the actual Ferrari setup, much more easily. But you still might need to lose the trunk in the case, due to the muffler size.

Also, what are your future plans for the swap? Are you planning to go turbo or anything? How big a turbo if so?
phonedawgz SEP 12, 12:18 PM
While some 3800 equipped GM vehicles came with two pre-cat O2 sensors (Camaro) none of the SC S2 3800s did. So no stock S2 SC programmed PCMs will support it. As far as I know, no one has came up with a tune that supports the SC S2 with dual pre cat O2 sensors.
zmcdonal SEP 12, 12:26 PM

quote
Originally posted by dobey:

Also, what are your future plans for the swap? Are you planning to go turbo or anything? How big a turbo if so?



I plan to keep it SC, I actually haven't even driven it yet, and I'm sure that will plenty of power, and if I'm itching for more I can always go intercooled.

Currently my exhaust setup only runs 1 precat o2 sensor. I thought I read a post somewhere in my searches where someone posted about true duals, and darth replied that 1 o2 would be sufficient, you just wouldn't be recieving any data from the one bank, which is fine if your motor is in good running order. I could be wrong.
[URL=http://s100.photobucket.com/user/zdm cdonal/media/32444__zps9ad9wtix.jpg.html][/URL]

I was thinking if I ran headers like in the first picture but without the Y, with small cats and tighter bends like in the second pic. Or if I have to I could do without the cats and figure out a way to plate it in another County.
nosrac SEP 12, 12:39 PM

Just my 2cents
Do the Ferrari exhaust as it may turn out awesome. The ONLY reason to stuff that big azz muffler back there is to make a great sound. The 3800 SC needs all the help it can muster in the sound department. Custom headers would be the best but anything can be MADE to work with enough time and skill.
dobey SEP 12, 12:44 PM

quote
Originally posted by zmcdonal:
I plan to keep it SC, I actually haven't even driven it yet, and I'm sure that will plenty of power, and if I'm itching for more I can always go intercooled.

I was thinking if I ran headers like in the first picture but without the Y, with small cats and tighter bends like in the second pic. Or if I have to I could do without the cats and figure out a way to plate it in another County.



If you really want to stick with the 355 muffler, first thing I would figure out is how you're going to mount it in the Fiero, and get the outlets tweaked to fit how you're going to mount the muffler and fit the Fiero exhaust tip pockets in the bumper. It won't mount into the Fiero at the same angle as in the Ferrari, without cutting the trunk, and you'll still need modification to the outlets on the muffler I think.

Then with the muffler and drive train mounted in the car, figure out a reasonable exhaust routing.

What you can do with the exhaust depends on how much space you have. You'll want to at least use an X-pipe if you do want to run dual exhaust. But you will be very limited on space with a transverse engine, so will take some creative work to use that muffler.
phonedawgz SEP 12, 12:45 PM
+1 on running just a single O2 sensor. Not the optimum way to do it but it will work fine.
infinitewill SEP 12, 12:56 PM
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[This message has been edited by infinitewill (edited 01-01-2016).]