So I needed a lightweight exhaust for autox on my s14, but titanium exhausts (11-12lbs) cost $1,000+. SCCA rules for the exhaust simply state the cat must remain within 6in of original placement and that exhaust must terminate behind the driver. An autox buddy told me to simply make a 12in long down-turn pipe that bolts right to the cat, and then put on the down-turn pipe the morning of an event and put the stock exhaust back on if I ever wanted to drive the car anywhere else. Well not only did this sound like too much work for every event, but a just a down-turn pipe is LOUD. So I thought "why not do the same thing with a muffler?"

An autox friend of mine did a similar mod to his S2K and did before and after dyno's on it an gained 11whp from this mod

Here's what I did:

I wanted to find a small muffler to kind of fit up in the drive-shaft compartment, just below the drive-shaft. The only place I could find a muffler with a canister smaller than 5" diameter was on ebay, I found one with a 4" canister, a total of 16" long (cost of $42 shipped):



Next I bough a 2.5" diameter exhaust piping extension from Autozone, they come about 12" long (cost = $6). I then cut this piece down to about 6in with a 10 degree cut. one end of this extension is tapered so it fits right over the inlet of the muffler. You need the 10 degree cut so that the muffler will angle slightly down and slightly to the passenger side so it fits up in the drive-shaft compartment:



Now you need a flange that bolts right to the cat. I decided to make my own from a sheet of 14 gauge sheet steel (don't go any thinner than this, in fact I would use 12 gauge if I did it again) and used the cat/exhaust gasket as a template. Also use regular steel, not stainless, stainless is much harder to drill your holes in. The 2 holes for the bolts are 3/8" and the hole for the exhaust is 2 1/4":





Next I took the whole thing under the car and did a test fit to see exactly where I wanted the angle cut extension welded to the flange and to have the muffler spun just right since I bought a slanted tip one I needed to make sure the the slant was at the top (when you have it exactly where you want it, draw a line across the 2 pieces that way you now where to weld them):



Here it is all welded together. If you don't have a welder a muffler shop quoted me $100 to do his work if I brought in the parts. Now I should mention it is also important to make sure your now whole cat-back exhaust system is no longer than 19.75", that way it mounts just in front of that bracket under the drive-shaft, if you make it any longer the top of the muffler will rub against that bracket:



Here is the exhaust on the the car:



And here is the car back on the ground, as you can see on my lowered car the the muffler is only about 3" off the ground, buts it's still only like 1/4" of an inch lower than my cat. I was going to weld on a hanger to the car frame and use a rubber muffler hanger to hang the muffler from, put being only 19" long it really is pretty stiff and the cat is bolted to a hanger so I decided not to:



Now stats. I weighed the old stock exhaust, it was 35.5 lbs. Weighed the new exhaust it was 5.0 lbs, so a 30lb weight savings . As stated before a down-turn pipe will net you 10-11whp, since I used a muffler instead of just a straight pipe I would guess this nets you a little less (8-10whp gain) but the same as any other performance exhaust you can buy.

I tested it out and love the sound, it gives a very low deep tone, but does pop every once in awhile since it is un-resonated. I'll try to post a video of it later.

Have any questions? Just post 'em here and I'll do my best to answer them. I'm sure a write-up like this has been before but I would to post this up because I think its a great way to loose weight off the car and gain some hp, and save a lot of money too

 

i bet that is super loud, i had a truck with a muffler that was mounted in the middle of the undercarriage like that, it was loud as hell! but you did get the weight savings

 

damn i have a hard time believing that a cat back weights 5lbs lol

 

It's no louder than any other performance exhaust. I have a HKS cat-back exhaust on my DD (98 civic) and I would say they are the same volume.

Believe it man, I weighed it myself

 

this prob wouldnt be good for my set up. My car likes to back fire...

 

nice but i'm not a big fan of canister...

 

and to be that weight im assuming its aluminum. well i dont think that would work for me my exhaust gets pretty hot not sure if aluminum will work.

my buddies rx7 he dosnt have rubber exhaust hangers like normal cars his hangers are welded metal chains cause he melts the rubber ones lol

 

interesting... Maybe you can put a tip on it that points down too

 

Nope, 304 stainless steel. You have to remember that this is a very small canister (the smallest I could find) the canister itself is only 4in max diameter, and 15in long

I thought about that, but decided it was too much work to find a 3.5in diameter light-weight stainless steel 90 degree bend piece (haha, that's a quite a specific piece to find). So instead I just angled it downward a bit and got the slanted tip, also pointing the slant downward.