Muffler replacement huge horsepower gains!

[Rick Parker]

Several years ago there was a company in Phoenix Arizona, Arizona Exhaust Fabricators @4009 Nth 39th Ave (no longer in business). They had the tooling and were making glasspack style mufflers with louvers or slots cut in the interior. At the time many folks on this site were using his products. They were available in any requested length and different diameters. I had some done for my 289 with 3" OD and 2.5" core ID. Without exagerating, they were around $20.00-$25.00 each in mild steel. Does anyone in or around Phoenix remember this person Lucien Donofrio or his business? Is the tooling being used by someone else??

[bigrob]

My motor is rated at 375 HP and dyno'd 306 at the wheels, which is cool for me. But.....more power is ALWAYS a welocome friend. And louder would be cool too....I think FYI I had a 5.0 mustang years back and removed the mufflers and the car definitely felt slower. Had the same issue on a newer Tang GT when mufflers were removed. Not sure if I lost HP or torque, maybe both. I rememeber reading you usually lose one or the other when tweaking your exhaust system.

[mickmate]

OK so here's a good side by side comparo of the SPF stock pipes compared to the specialty stainless bad boys

The stock mufflers were not only very small on the ID they had also been crushed across to restrict them even further. The cross section of the ID at the most restrictive parts measured about 3/4" x 1 3/4".
Having cut, trimmed and squared off the pipes cuts it was simply a matter of reinstalling the components in the jig. As I said tack them in a few places and I try and skip around with my welding. That does a couple of things, most importantly dispersing the heat so you don't finish up with banana pipes and also for ease of weld positioning and a nicer resultant bead. Then it's off to my pal Zac http://www.directcoating.com for the ceramic coating process. He tells me sidepipes are not easy to do. The reason for that is they are long (obviously) and when they have been ceramic coated, which is brittle by nature. They have to be finished with a polishing/burnishing media by tumbling. That can cause chips and dings in all the nice work we've done. The good thing about it is that these guys do top notch work and can rework if necessary always with super results. He has redone "other" peoples work for me as well as some superb systems we have built for Hot Rods. Doug had a good solution to avoiding shipping damage which is also a serious consideration with these things. He took his to the UPS store and said "package and send em". They did a great job for fairly short money compared to the pipes value and wrapped them up really well in a guitar box.

[RedBarchetta]

Originally Posted by mickmate

Mick, consider some sort of transition cone insert to allow the exhaust to overcome the abrupt 90* weld of the new inner muffler. I whipped up this sketch for someone else here as an example:



Without it you will experience some "fluttering" when letting off the gas. Not as pronounced under moderate acceleration between shifts, but you will definitely here it when you approach stop lights. Very annoying. If I had the money I'd rip out my existing pipes and start over.

My $0.02.

-Dean

[cdnus]

Dean,
I was able to get out yesterday for my first run with the replacement s/s mufflers. They did relace the defective mufflers N/C, but my cost for shipping & re & re mufflers was about $540.00 can. + my labour.
I did fab & install the transition cone in the inlet side.
If you look at the posted photo by mickmate (above) you can see the difference in the upgraded version of their muffler.
I went with the 2 1/2" core as previous & I am very pleased with the sound, I can again enjoy driving without blood running from my ears.

NOTE!
I still get that fluttering sound on de-cel below 2000 rpm. & idle, but no tweeting with this set. I did a few mid throttle spurts (roads are still pretty dirty from the last snowfall) & the sound was very nice & I did not have to wince at all.
In fact it was so smooth I found myself surprised several times when I checked the tach & saw the rpm much higher than I thought.

So far so good

Regards Craig

[RedBarchetta]

Originally Posted by cdnus

Dean,
I was able to get out yesterday for my first run with the replacement s/s mufflers...I did fab & install the transition cone in the inlet side...If you look at the posted photo by mickmate (above) you can see the difference in the upgraded version of their muffler....NOTE! I still get that fluttering sound on de-cel below 2000 rpm. & idle, but no tweeting with this set.

Regards Craig

Craig, thanks for the update. The upgraded mufflers don't look all that different to me...maybe a thicker weld bead along that 90* section to "build up" the deflection area, but I don't see much else. The fact that you are still experiencing that fluttering noise at/below 2,000rpm on d-cel, WITH THE REDUCTION CONE, concerns me greatly. Not from a performance standpoint, but just that this fluttering is a frustrating aspect that shouldn't be there.

I would suspect that the 2.5" ID are considerably quieter than the baseball-esque 3".

-Dean