Entill I have the money to get the parts and time to put together an exhaust for my 3800 series II s/c can I run the stock dual out single in exhaust I got from the Fiero store ? Anyone see any problems with it? Will it cause to much back pressure since its ment for such a smaller engine?

quote Originally posted by lowtrickry: Entill I have the money to get the parts and time to put together an exhaust for my 3800 series II s/c can I run the stock dual out single in exhaust I got from the Fiero store ? Anyone see any problems with it? Will it cause to much back pressure since its ment for such a smaller engine?

I would not run any exhaust system designed for a 2.8L on a 3800 SC engine. These systems are just too small and too restrictive for any supercharged 3800. Using too restrictive of an exhaust system on a 3800 SC engine can result in KR (detonation) problems among other things.

I would recommend nothing smaller than 2.5" diameter pipe using mandrel bends (single pipe systems) and low restriction mufflers and catalytic converters (if those are used). 3.0" mandrel bent tubing is the way to go if you want the best performance.

-ryan

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OVERKILL IS UNDERRATED

Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com

Something like the picture below is usually what people go for if they are not modifying the trunk. Finding a shop to do this with a 3" downpipe would be pretty difficult. The shop that did mine with 2.5" mandrel almost turned me down and they didn't see how a 3" downpipe in my configuration would work.



Here's how much I ended up paying to have it done (~$520 + tax):

Muffler - ~$160
Labor - $120
Flex joint and tubing - $230
Flange - ~$10

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I already have my exhaust designed and im building/welding it my self....just out of project money at the moment and wondering if that stock muffler was to restrictive

Mine cost $65 ($95 if you count the resonated tip)


I don't see how you could make the bend from the stock 3800 manifold around to the stock Fiero muffler. that cramped set of bends would probably be more restrictive than the fiero cat back.

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1986 SE 3800SC/4t65eHD (12.871@104.96) I'll Sell it if you like
1985 GT 3800SC (swap in progress)

You can buy 3" diameter, 3" radius mandrel 90 deg elbows from Walker/Dynomax (p/n: 41221) directly or plug that part number into Summit or Jegs.

These tight bends work great for exiting the stock 3800 rear exhaust manifold and getting the exhaust system to hook up to a muffler in the stock Fiero muffler location WITHOUT cutting the trunk. I've built many systems like this.

In regards to restrictions, even using these tight mandrel bends, the backpressure tests I did on my custom exhaust systems showed my setups had less backpressure than most of the performance systems people put on Grand Prixs and Regals.

Having said that, the picture of the system JamesCurtis showed should work very well. Just make sure that the flex section you use has NO INTERNAL BRAID in it. The higher exhaust temps the SC (and Turbo) engines run will melt, distort, and collapse the internal braiding some manufacturers put inside of their exhaust flex joints and this will cause a huge restriction if it happens.

I just made mine out of three of those 3" bends (over the last weekend), the walker 41221's Darth had mentioned, and I added an inch of pipe to push it to one side, and I'm not a very good welder, in fact this was my first actual project. I ordered a 3 inch flange from jegs, but I got the 41221's from advance just because it would have been easier to return them if I decided to have a shop do it. Mine is very similar to the first one pictured above. I also ended up using the flowtech muffler mentioned on another thread. I'll be figuring out my exhaust tips in the next week or two.