While exhaust is a personal preference, I thought I would share my experience with my Borla catback. This is installed on my 86 which is completely stock, including the main cat and pre cats.
I did a lot of reading on different exhausts and a lot of watching and listening of exhaust videos when looking for a catback. I liked the sound of the Borla and that is what I went with. I will say that my intention was to buy an exhaust the was not too loud and didnt drone too bad.
After installation I was quite surprised by how loud it really was inside the cabin and how much it droned.
I drove it for a few weeks and decided enough was enough. Having read about the construction of the corsa mufflers, in particular how one outlet is restricted by a smaller opening, I decided to modify my borla mufflers to mimick this. I fabricated my own silencers so to speak and after welding, grinding, experimenting with different outlet diameters and finally powdercoating them I am quite pleased with my results. Obviously I have lost some of the sound of the borlas but surprisingly not a lot. However this modification has drastically cut down cabin noise and drone by quite a lot! Its really a night and day difference so I thought I would share this.
Here are the before and after videos;

 

Awesome, fix!...Thanks!...

Yeah,...If the Corsa's were more affordable, I think a lot more Vette owners would buy it.

 

I have my lap top connected to my set of Bose 601. I cranked it up, and Its very obvious, the before video has more rumble to it.

 

had a borla on my silverado. The drone was terrible. Much more then the magnaflow system on my vette.

 

Dave, this is better than the spoiler idea. Anyway glad yo got it to sound better.

 

Haha thanks Frank. When are we going for a cruise? The leaves are starting to fall!

 

Thanks and I definitely agree with that statement.

 

Yup definitely had a deeper rumble before but it was just too loud inside the car. And it wasn't the deep rumble you heard while driving. That I could deal with. It was more of just a loud exhaust sound. If I were still in my 20's I probably wouldn't care, lol.

 

Ok. Now on to how I did it. Total parts cost was around $18. Two 2 1/4 id X 2 1/8 od exhaust adapters $3 each and two steel wheel bearing caps $6 each. Tools used were welder, grinder, dremmel with cut off, drill and drill bits, sharpie and I sandblasted and powder coated them so that stuff too.



I took the wheel bearing caps and welded them onto the adapter on the inside with the curve facing out(Yes my welds suck). With a grinder I ground the caps flush with the outside diameter of the adapter.




Then placed the adapters in the outer exhaust outlet and using a sharpie traced the shape of the borla tip. After that using the dremmel and cut off wheel I carefully cut the adapter to shape. I took a stone bit for the dremmel and smoothed out the rough edges.


There is a drain hole in the bottom of the borla tip and this is a great place to secure the adapter. I just drilled a hole and used a self tapping screw to hold it in place.



After making sure they looked and fit right I experimented with sound by drilling different diameter holes through the cap. Starting small and working up to a final 3/8 drill bit. 3/8 is a tad louder than stock so if you wanted a little louder you could go bigger on the drill bit. After I was happy with everything I sandblasted them and powder coated them in satin black so they are not so noticeable. Hope this helps out.

 

had borla's on my 90 with lingenfelter headers. no drone and they sounded great. but I had a 3:90 gear with my zf 6 spd. flowmasters were unbearable,so I got the borlas.

 

I'm assuming you put one insert into each muffler and left the other outlet untouched - is that correct? The other question is will this hold moisture in the muffler if not heated up well enough (short runs)?

Very creative, thanks for your effort.

 

Yes one insert goes into the outer outlet of each muffler. Most of my driving is around the town and I haven't observed any water issues.

 

All your efforts on this project show just how far some of us will go to lower the interior cabin noise/drone on our daily driver Vettes. The one who discovers the exact issue in the C4's stock structural design that amplifies most changes made to the stock exhaust (and finds an easy way to cancel it out) will make a lot of $$$.

 

Noticeable, good job
Always wanted to construct a pair from scratch, convinced you can have your cake and eat it too.
Most those truck mufflers are stupid loud (in reference to the poster wiht the silverado)no reason to with a system that loud.
May try a long case dynomax super turbo.

 

 

Thanks for posting, this is awesome. I am going to do this for my borla exhaust as well. It doesn't bother me at all on short trips, but I just did a 2 hour highway trip and wanted to jump out of the car it was so irritating. Do you have a link to the bearing caps you purchased? I'm having trouble finding the right size. This is certainly a great option for long trips and reversible so you can have it really loud if you want!