The Pantera Place
"Your de Tomaso Connection"
ANSA Muffler Modification
By Mike Dailey
Note: This page documents an ongoing process to improve the ANSA muffler flow and includes all the steps I went through. If you plan on doing the changes you can simply jump to the hole saw cutting step and move on from there.
When I found my Pantera in 1998 it was equipped with Hall headers and a stock ANSA exhaust system. The mufflers had gutted themselves from years of corrosion working away on the internal baffles and the internal perforated pipes. Some of the corrosion had worked its way through the outer shell and had been patched with some type of filler. The mufflers looked ratty but had a pretty nice sound.
As part of my early repair and replacement project I decided to buy a brand new ANSA system from Pantera Performance for $775 in late 1998. The new system looked great, but after I installed it I immediately noticed that it was very quiet compared to the old system. I missed the original sound, but I thought over time they would eventually get louder, but that never happened.
Being a typical Pantera owner that can’t leave well enough alone, I recently started thinking about how I could help nature along a little bit and make the mufflers more free flowing and louder. Dave Bell has a web page that shows how he cut his GTS ANSA mufflers open and gutted them. I thought Dave’s idea was good but I didn’t want to cut open my mufflers. The standard ANSA mufflers have a smaller inlet pipe than the GTS mufflers and adding to their flow restriction are discs that are spot welded into the front of the exit pipes. These discs close off the front end of the exit pipes and force the exhaust through small holes drilled in the pipes.
View of Dave Bell’s GTS ANSA muffler cut open showing the internal perforated pipes, baffles and location of the discs on the standard mufflers. The discs can be seen by looking down the fluted exit pipes with a small flash light. The standard ANSA mufflers have the area between the two baffles packed with a sound deading material that looks like steelwool.
View of the exhaust flow route through the stock ANSA muffler. The flow is in through the inlet pipe to the back of the pipe that is capped, then through the holes in the inlet pipe, out the exit pipes and out the fluted tail pipes. Not a very free flowing system!
I wanted to find a way to increase the flow without cutting open the mufflers so decided to focus on how I could increase the flow to the exit pipes. Some people have knocked out the exit pipe discs by ramming a pipe down the tail pipe or sometimes the spot welds rust apart and they fall inside the muffler. But that solution causes the loose disc to rattle around inside the muffler or you must cut open the muffler to remove the disc.
My solution was to buy a 3/8” drill bit that is 12” long to drill holes in the disc from the back of the fluted pipes. The drill bit was purchased from Lowe's.
I was a little concerned that the 3/8” holes could cause a whistling or chirping sound but that was not the case. I started by drilling one hole in each disc to find out how it sounded. As I drilled more holes I could tell that the sound level was louder. I ended up drilling five holes in each disc being careful not to drill through the side of the exit pipe or the spot welds holding the discs. That's ten holes per muffler. Unfortunately it is too dark inside the muffler to take a picture of the holes I drilled.
The idea is to drill holes in a pattern like this but it is hard to control the hole positions with the long drill bit.
From my calculations the ten 3/8” holes in each muffler increases the open area by 1.044 or about 46% of the inlet pipe area . That area along with the existing perforations in the exit pipes opens it up quite a bit. The exhaust tone is louder, but not too much and I expect the holes help reduce some exhaust back pressure.
March 18, 2007 - Update
Being a typical Pantera owner I can never stop tinkering. After I drilled the holes in the disc, I could see that the muffler had a couple of small vent holes in the back baffle and I could see the deading material behind the baffle. I got a longer 3/8 drill and drilled five holes in the back baffle. The deadening material turned out to be steelwool and I was able to remove it by drilling holes in it and pulling it out with piece of coat hanger with a hook on it.
After removing the deading material I was then able to drill a few holes in the front baffle so that the exhaust flow now works like this:
When drilling the holes in the front baffle, make sure that the angle of the drill will place the hole in the baffle and not in the bottom of the muffler. It worked fine for me but I can see that depending how the holes are drilled it would be possible to miss the baffle. The inside of my muffler now looks like Swiss cheese and is a lot louder.
Removing the steel wool and adding the extra holes in the baffles made the exhaust a lot louder outside the car and also inside. The famous Pantera 1900 to 2300 RPM harmonic resonance is way louder so do not make this mod if you do not like the sound. I've always thought that the harmonic resonance could only be heard inside the car but after extensive testing in our local underground Wal-Mart parking area I discovered that it is loud outside the car too. My car has always been good at setting off car alarms but now it does an excellent job!
March 6, 2010 - Update
After giving more thought to my muffler modification, I decided to take it a step further by cutting 1 3/8" holes in the muffler tip cap and the front and back baffles. A total of six cutouts per muffler. The 1 3/8" cutter fits inside the tip with just enough clearance to make the turn into the perforated part of the pipe.
I used the following Ace Hardware tools to cut the holes:
1. 1 3/8" wood and metal hole saw - part number 20223 - $10.49.
2. Vermont American mandrel that matches the hole saw - part number 25536 - $16.99.
3. Starrett 12" mandrel extension - part number 206103 - $23.49.
To make sure that the cutter did not get disconnected from the extension I cut a notch in the mandrel shaft and replaced the straight slot set screw with a hardened hex head set screw so I could really torque the set screw down very tight. Having the cuter get disconnected from the extension inside the muffler would be a major problem so be very careful. I retightened everything after each cut and used oil on the cutter teeth. Most of the cutout parts stuck to the cutter teeth when I pulled it out of the muffler. A couple are still in the muffler but they don't seem to be rattling.
The following are my area calculations for the openings in the muffler:
1. Main 1 3/4" OD tailpipe that connects from the header to the front of the muffler has a ID area of about 2.074"..
2. Perforated main pipe inside the muffler has about 210 3/16" holes for a total area of 5.88". I don't believe a perforated pipe would actually flow like it had an area of 5.88".
3. The two 1 3/8" holes that go from the exhaust tips through tip plug and both baffles. The total area of both holes is about 2.97".
After cutting the large holes I found that there was some steel wool left in one of the mufflers and I was able to pull it out in pieces.
The larger holes made the exhaust somewhat louder and the exhaust has a bit of a bark to it now at RPM. The system has lost a lot of the characteristic ANSA airy sound. At this point the muffler should not be creating much or any restriction when you consider the small size of the inlet.
Images of the tools.
I expect that I'm getting the best flow possible now, without cutting the muffler apart and removing the perforated pipe and baffles.
It is kind of hard to see with the flashlight in the way and the poor camera focus, but in this image you can see with the 1 3/8" cutouts there is a clear view all the way to the front surface of the muffler from inside the exhaust tip.
May 8, 2011 - Update
The muffler modification continues! After running the muffler modification for a year I decided that there had to be a way to cut relief notches into the back part of the main inlet pipe. After some thought I came up with the following:
I used this 1 1/2" grinding wheel and cut-off wheel. The cut-off wheel worked best for the cutout process. I had to grind the exhaust tip inner pipe a bit for it to slide through and also enlarge the 1 3/8" hole in front part of the pipe. I also cut open the 1 3/8" hole so the grinding wheel and cut-off wheel had maxim reach to the center pipe.
View of the cut out areas. Each side is slightly larger than 1.25 square inches of area for a total of 2.5 square inches. It was difficult to measure the openings so it might be larger.
I used a mandrel extension and an old bearing as a pivot point. A small piece of rubber tubing was used to adjust the bearing position so it would pivot at the back inside part of the exhaust tip.
I used a shop vacuum in the second exit pipe to reduce the amount of grinding residue falling in the muffler. Much caution should be used to make sure the vacuum is only attached when the other pipe is not blocked by the grinding stone. It is extremely important not to pull any fuel/air mixture from the engine down into the muffler or the vacuum cleaner that could cause an explosion.
Be carful that the grinding stone or cut-off wheel does not fall off the mandrel. It took a number of grinding stones to cut the slot. The cuts made the exhaust quite a bit louder but still has a muffled sound at idle. Gets much louder at RPM.
I used this modified CVS drugstore dental mirror to check the progress of the cut.
This would be a very easy modification for the factory ANSA GTS mufflers because the GTS muffler does not have the caps on the back two exit pipes like the standard ANSA mufflers.
Summary of area calculations:
1. Inlet pipe 2.074 sq. in.
2. Perforated main pipe 5.88 sq. in, plus 2.5 sq. in. cut out, for a total area of 8.38 sq. in.
3. Exit pipes 3.53 sq. in. total
1. Five feet behind the car at 850 RPM 86 dbA. Twice at loud as GTS item 3 below and 1/2 the loudness of Hall item 4 below.
2. Inside car at 850 RPM 86 dbA and in the 2000 RPM range. 75 dbA to 86 dbA underway.
3. Five feet behind a 71 car with a stock cam and GTS headers and stock GTS ANSA mufflers (at idle) 83 dbA.
4. Five feet behind a 71 car with a stock cam and Hall headers and mufflers (at idle) 90 dbA.
November 20, 2011
Not sure why I didn't think about cutting part of the exit pipe away earlier so more of the main pipe could be easily cut.
View of one exit pipe cut back on the side about 1 1/2" and the main pipe cut away 1 1/2 more inches. The hole is now about 2 1/2" X 1 1/4" or 3.2 sq. in. At his point, I don't think there can be any main pipe restriction other than the air flow direction changes.
The DBa is now about 89 and here is a You Tube video clip of the car at idle. The DV video cam captured the sound really well but a sub-woofer will be needed on your sound system to achieve a play back that duplicates the actual sound frequency recorded.