Muffler replacement huge horsepower gains!

[vector1]

here's a template for an exhaust system for a 427 with 10.5 comp and mild cam.

--- Single Primary Pipe Specs --- for 427.650 CID from 4600 to 7100 RPM
Diameter= 1.873 to 1.998 Length= 29.6 to 32.4 inches long
--- 2-Step Primary Pipe Specs ---
1st Dia. inches= 1.873 Length= 14.8 to 16.2
2nd Dia. inches= 1.998 Length= 14.8 to 16.2
--- 3-Step Primary Pipe Specs ---
1st Dia. inches= 1.873 Length= 14.8 to 16.2
2nd Dia. inches= 1.998 Length= 7.4 to 8.1
3rd Dia. inches= 2.123 Length= 7.4 to 8.1

--- Header Collector Specs (Conventional Straight Tube) ---
Diameter= 3.422 to 3.672 Tuned Lengths= 17.1 best and also 8.6 or 34.2

--- Header Collector Specs (Megaphone or Diffuser Cone Shape) ---
Diameter= 2.922 taper to 3.922 Megaphone/Diffuser Length= 17.1 inches

Best HP/TQ Tuned Collector Lengths= 17.1 , 34.2 , 68.4 , 136.9 inches long

Worst HP/TQ Loss Collector Lengths= 25.7 , 51.3 , 102.7 , 205.3 inches long

Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness

---- Primary Pipe's Harmonics ----
1st Harmonic = 130.7 inches long ... typically never used
2nd Harmonic = 49.5 inches long ... longest recommended
3rd Harmonic = 29.6 inches long ... highly recommended , best Torque Curve
4th Harmonic = 20.6 inches long ... shortest recommended
5th Harmonic = 15.5 inches long ... typically never used
6th Harmonic = 12.2 inches long ... typically never used
7th Harmonic = 9.9 inches long ... typically never used
8th Harmonic = 8.2 inches long ... typically never used

---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 136.9 inches long ... longest with Mufflers and TailPipes
2nd Harmonic = 68.4 inches long ... longest recommended with Mufflers
3rd Harmonic = 34.2 inches long ... more bottom-end Torque
4th Harmonic = 17.1 inches long ... highly recommended , best Torque Curve
5th Harmonic = 8.6 inches long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 4.3 inches long ... reduced Torque , not recommended

as you can see it is based on harmonics.

[mickmate]

Wow there's some super feedback and info coming out already. The first car (Doug hold your horsepower) is John's SPF with a pretty rumpy 7 in it. He actually saved Deans post and info for a looong time to source his mufflers. He got them from Stainless Specialties here http://www.stainless-specialties.com/products2a.htm and I believe they were the Perform Master. The pipes we were putting them into were mild steel and they were getting ceramic coated so there's no need for stainless here but the results were unquestionable, read on. The SPF use the flange to flange for a header sidepipe connection. John and others say it's a bear to get at some of the bolts there's a thread on it in the SPF section on CC. With this first set of pipes I lined them up with the edge of the welding table, tacked some washers to the bench that were bolted through the flange so I could accurately relocate the parts relative to each other. Then I measured the length and tip height of the tail pipe or dump tube. Take a minute to know for sure that you can get back to where you were. There's better methods coming so hang tight. At this point we unbolted it from its makeshift fixture and ceremoniously cut the old muffler out with a chop saw. It worked out really well having the new muffler 1" longer. That gave us a nice clean cut and piece of tube to work with instead of cutting right on a weld and trying to clean that up without losing any length. I obviously recommend an extra inch as the actress said to the bishop! Having adjusted the lengths and squaring up the collector tube and tail pipe they were cleaned up for welding. Next the parts are realigned back on the fixture carefully with the mount being relative to the flange end. At this point they are tacked together in at least 3 spots. Check it all again to make sure nothing has moved and weld the parts together. If you're using MIG to weld stainless to mild you'll want a 308 wire and Argon backing gas. We used the TIG to tack and weld. Interesting to note with a job like this most of the time is in the set up and prep. By the time it comes to switching your MIG over and paying for a spool of wire etc it really was quicker and easier to TIG them. The TIG welds are a whole lot nicer than the welds I'm seeing on all these factory pipes done with a MIG. Ceramic coating covers some sins but the MIG welds have got holes and inconsistencies in them that the ceramic coating doesn't hide. A good MIG welder would do a bang up job on these I'm sure and they are really good for filling in dents and disc pad sanding them back before coating. Most of these pipes suffer a little underbelly roadrash. I'll show you guys what we saw side by side on the old and new mufflers. Stay tuned