I'd like to upgrade the exhaust on my 1981 911SC. My heat exchangers/headers are still in good shape, so I'll only be replacing the muffler and possibly the Cat with a bypass. I don't have inspection or emission testing where I live, so this is not an immediate factor. How much HP can I gain with just the cat by-pass and different muffler? I am looking for "real" results, not claims made by manufacturers. The engine is stock.

Todd
1981 911SC

 

Popular opinion is you would get 15-25 hp if you replace the entire exhaust with an earlier pre-
1974 complete exhaust. If you replace just the cat back you'll have around a 5-10 hp gain according to some. A few folks say doing that is a wash or even a slight loss in power.

 

I put the B&B muffler with the cat bypass. I don't know how much more HP, but I do know that it's a lot more fun. Zoom, Zoom.

Ken ~~~~~~~~~~~
'82SC

 

I'd go with the Fabiani Euro pre-muffler instead of the straight cat bypass. By most accounts, it offers better performance and sound than just a straight pipe. I bought one recently, and it is a beautiful piece of polished S/S. A second benefit is that is has a "bulge" to it that looks like it is a cat converter. At $235, it is probably $100 more than a straight pipe (Bursch for example which is just painted), but well worth the extra $.

 

If you have no emission testing (visual or tail-pipe) go for the pre-74 or SSI exhaust. Even if you go with a lesser quality muffler at first (because of $ constraints).

You'll be money ahead in the long run. It's a greater gain in HP than just a muffler and a cat replacement pipe.

 

Matt is right on. SSI's are tuned pipes which extract exhaust gases more effectively than the stock SC system, while maintaining your ability to get heat, which you might use for the demister, I mean you might Otherwise, you could just go with tuned headers. Adding a cat bypass and muffler just isn't going to get you the same benefit. When I added SSI's to my 81SC, I went with a cheapo muffler, to balance the economics, intending to put a better muffler on when it wore out - but sold it before then.

 

I went with a Bursch By-pass and the Bursch muffler for just under $400.00 and my dyno numbers on my 83SC are 183HP at the rear wheels, so it was 180 at the flywheel with cat pipe and factory muffler to 183 at the wheels, roughly 200HP at the flywheel,so about 20HP gain, I also have a K&N filter and I just went over 245,000 miles on an origional engine.I say that if money is the deciding factor, the Bursch gives the best bang for the buck. HOWEVER...what Matt and Bill said is the best way to go for an 3.0 SC exhaust.

 

Thanks, guys. Your answers were helpful. I'd love to replace the entire system with SSIs, cat bypass, muffler, and dual outlet. Unfortunately, this is currently beyond my budget. I'm really looking for the "best bang for the buck."

Todd
1981 911SC

 

Todd,

i've got an extra fabiani 'fabspeed euro premuffler' made of stainless with a one wire oxy/sensor included, yours for the price of my winning bid on ebay, $167.79 + shipping of ~$10.
A new one was $259. incl s/h w/o oxy sensor.
let me know if you're interested. here's a link..
<a href="http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=1869406347" target="_blank">http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=1869406347</a>

 

Todd, keep in mind if you upgrade to SSIs, you can cut out the cost of a catalytic converter bypass -or- "test pipe" as you cannot have a converter with SSI type heat exchangers.

Just trying to add a little "hope" for your idea.

FWIW, when I had my SC, I had a bypass and a B&B muffler for a couple years, loved it...dunno if it really increased power, but the butt-dyno thought so...and oh that sound improvement...oh!

Later I upgraded to the full B&B header setup with B&B muffler due to a 320+HP supercharged 3.0L I built - the sound was TOO much, but the power - OH MY!

I will NEVER purchase another header/muffler system for a street driven 911 again. <img src="graemlins/nono.gif" border="0" alt="[nono]" />

SSIs MAY land you in the same boat, depending on the muffler you use...keep that in mind.