Actually the cats are not a choke point, My parents have a 3.0L with a single high flow converter which has a 25% wider cross section that the original front converter. The overall result was not really better than stock. It has a new y-pipe design as well, which might be a touch better than stock.

The OEM mufflers are highly restrictive on the 4.0L. I can tell the difference with mine. Before I replaced the muffler, I had to take the engine out of overdrive up every hill on my way from Salt Lake to St. George. It just couldn't hold the speed I wanted in overdrive and I didn't want to overheat the tranny. After I had the muffler replaced, It can sustain 75 and actually accelerate slightly in overdrive with an otherwise identical configuration. Since it is able to hold in a higher gear this indicates that it was bottom end power than was enhanced. Actually the entire powerband increased for mean, since downshifting gives a better responce than before. I used to downshift and it could sustain the speed, now I downshift and start passing everyone else. Its a shame these vans can't go faster than 95.

To remind everyone here what my exact setup is on my exhaust setup, I have the factory cats and y-pipe. The original rear flange was removed to keep the pipe going out at 2.25" It has a new 2.25" flex pipe, and goes into a Fullblown 50 series muffler. From there it is a 2.5" tailpipe all the way out to the shiny Stainless Steel tip.

For me the power output was improved noticeably. But the fuel economy did not improve a noticeable amount, so if you are planing to add a performance muffler to improve economy, think again.

 

Performance muffler on my F150 did not add economy. In fact, the power increase was so enjoyable (and the sound) that I was putting my foot into it much more and fuel mileage actually dropped. Haha.

If the cats are more restrictive than the 1.33 square inch total opening in the muffler restrictive point, then they might as well have saved dollars and put 1.5 inch piping. Why did Ford use 2" piping? Also this was an aftermarket replacement muffler.

I would think that the restriction is worse than 1.33 inch because it is broken into 12 little holes rather than one big hole.

964-wdr: Your Walker looks pretty good, but it does appear those perforated tubes are smaller ID than the incoming pipe. You should get about 1/4 to 1/2 inch over sized inlet muffler then use adapters to your pipe. How's it sound?

Also I don't think it's a given that the glass will mat down over time. Maybe, but we'll see.

 

I do often run this baby over 4K rpm, sometimes right up to 5700!

Now it occurs to me that (and I could be totally wrong, but...) if the cats exhert that much back pressure on the engine, then they should also be doing quite a bit of muffling of the sound, but that isn't the case (the muffling anyway), so I surmise that the cats are really not that restrictive.

Oh, I did talk to the tech folks at Dynomax. They said the glass will tend to consolodate and the muffler will get louder, but probably not for 3 to 5 years. Also, to tone it down a tad I can put a glass pack or similar resonator on it either side of the muffler and to keep it at least 8 inches from the muffler. So I am looking for a cheap short (max 16 inches) resonator or glass pack to put near the end of the tailpipe.

 

most of the noise muffling in a well designed muffler is from power pulse smoothing and from active noise band cancellation in the resonator section of the muffler, reason the OEMs are so large
many are designed to the exact body configaration they go into for max. active active noise dissipation. Mercedes and Rolls were world renown for their muffler systems, no resonances with the body interior and exhaust point well away from pass. comp.

i've watched dyno tests done on several rigs before and after testing looking for the best exhaust performance for street racing, grocery getting or towing.
many after market attempts actually cause a loss in either high end HP or low end torque.
measure the pressure before and after the cat at the O2 sensor holes with a pressure gauge, only requires a 25>50 psi max gauge. will find a 15 to 25 psi drop from front to back of most OEM cat systems. most OEM mufflers add less than 5 psi backpressure.

friend runs a full line hi pro exhaust shop, everthing from stainless steel/ceramic coated headers to the diesel PU exhaust bigger is better craze. he has a shop dyno that is busy most weekends with the diesel shootout boytoy rigs

low restriction extra large exhaust, muffler does improve a diesel performance, especially turbo'd, since it is basically an air pump from air filter intake to exhaust tip
reason the diesel boy toy rig guys are complaining so much about the '08 diesels. manufs had to boost displacement and still there is a performance loss with the particulate burnoff filter and the new restrictive diesel cat.

 

Well I finally got to give it a longer run, about 30 miles mostly freeway, tonight. It does seem to run better. Did not downshift on several grades that used to give it some trouble. Also this van was very high strung, downshifting multiple gears at a time, but tonight I could stick my foot into it pretty good and not get it to downshift too much. I think with the extra power freed up by the less restrictive muffler it is behaving more like a proper car, not the overweight van that it is. Now I am aware of the pacebo effect, but really there does seem to be a difference. And this is similar to Bear River's experience.

Again I say, if the cat is that restrictive, then Ford could have gone with much smaller piping behind the cat, say 1.5 inch or less and saved money, but they didn't. Also, the sound is pretty nice, not ricy at all. Wife and kids didn't even complain this time. Haha, they are getting used to it. I pointed out that at freeway speed it has more wind noise than exhaust noise.

Well, this seems to prove the old saying, "it's easier to get forgiveness, than permission."

 

My 2 Pennies...

Years ago, I bought a lifetime walker muffler, and it came with the free replacement warranty forever... which I have used about 5 times now in the 18 years I've had the van...

I'm a pro at doing the cat back on that van! :-) that and front brakes :-)

I found the walker to be as quiet as OEM, and it lasts about as long as anything else... in bad winters here, I get about 2-3 years out of everything...

I don't know if they changed the set up over the years, but on my 89, I found the weakest part of the entire system to be right in front of the inlet on the muffler - I don't know why it fails there more often than anywhere else, since the main hanger is only like a foot from there, but I have had them fall off at that point...

one other thing I learned - be sure when you hook up the rear tail pipe to it's hanger, that it has plenty of clearance for the axle - once, I tried to turn it a little, so the pipe would be father down, and away from the trim on the side, but then it would vibrate on the axle, and it drove me nuts!

so, if you plan on keeping the van for a while, and want the cheapest and best route, that is my vote - it only costs me like $25 everytime I replace from the cat back in that van, since I get the $100 muffler for free, under their warranty.

All you need, is the receipt too... just go to any dealer that sells walker, and you are set.

also, 96 is most likely right, but I never replaced the heat shield as there was lots of clearance there, and it's not by any gas lines, or the tank...

I wouldn't mind a cheap/easy solution for a strap though... I never want that inner pipe to fail again, and worry about dragging the front of the muffler on the ground...

as long as the carpet back there doesn't catch fire, I think it's ok... but I've had it that way for years, and hasn't seemed to cause a problem...

 

actually...

this leads me to another question...

Can you run exhaust cat free? or does the engine need that back pressure from the cat? - they are changing the emission laws here, and they will not be checking cars older than 96 anymore for emmisions... but if a cat is needed for some reason, of course, that would be needed.

I would think anything that restricts exhaust flow would hamper performance - I want to get the 3.0L in this thing as free flowing as I can :-)

 

Regardless of whether they check emissions, the law requires the cats to be in place. May be allowed to install high flow cats, not sure the regulations. Off road only then anything goes and you can lose the cats.

You do not need any backpressure, but engine is tuned to run with certain amount of back pressure and may require mods to run right without any backpressure. These could be simple tuning mods or may require more drastic, like bigger injectors, camshaft, etc. I really am a novice on that though. Bottom line, least backpressure, tuned to run that way, and exhaust that at least creates a vacuum or pull on the cylinder during the exhaust phase (helps clean out old gasses so new not diluted) will run better.

 

to go a little further...........

i don't see why you should have a problem... ACCEPT muffler shops can't legaly install test pipes (pipe replacements for cats) BUT performance mufflers (fart cans) for import cars (honda's, scions, mitsubishis's, etc.) usulay come with a test pipe vs. a cat cuz its cheaper, and as long as you replace the test pipe with a cat for DEQ purposes and tune it right, you should be fine. just don't brag to the wrong croud would be my guess.

 

Chances are, I will never do this, but I was just wondering if it was even possible... and to what gain? would the little 3.0L Vulcan fly then? or would it barely be any difference?

speaking of cats - my wife's car just had it replaced, she said it runs like a new car... I guess the old one was plugged up so bad, that it was pushing exhaust through the EGR valve! - no wonder it didn't have a lot of pep :-)

I don't care about top speed, I'm looking for lower end toque - and I would love to climb a hill in OD just once :-)

 

I think you can test back pressure at the oxygen sensor port. Not sure if that is before both cats though.

My dream for the Vulcan 3.0 is to build on in a T-bucket. That is the perfect setup. T-buckets are insane with V8s, but the 3.0 V6 would be perfect. For the Aerostar, you could gain some pep with a chip or just adv the timing a tad and run higher octane to prevent ping/knock. Mine was a lot peppier at spec timing, but pinged so much I retarded it 4 degrees so I could run regular fuel instead of premium. That retard really slowed it down, but the muffler seems to have improved it.

 

mediaman,
use plumbers pipe hanging strap aka tape, galvenized steel perf'ed strap in rolls and differnent widths
or for really low cost, coat hanger wire, the tough hvy duty enameled steel type
high carbon steel that is rust proofed with baked on enamel

 

I saw a newer (not the latest gen) Mustang today with sidepipes. It looked sweet but how could they do that and keep the cat(s)?

 

I once used the multi strand copper cable from household electric service for muffler hanger.

 

Well if they don't check emissions, and you think you want to run without cats........ Take them off, gut them out, and put them back on. The visual inspection is all that's required here, no sniffers, so it would pass.

On an OBD II vehicle, you might have a problem with the ECM, since this one has an O2 sensor before and after the cats.

Personally, I think mine runs just fine the way they engineered it with 2 cats. I don't feel a need to do anything else with my exhaust.


VanGo, it might be a 2 into 1 cat, back into 2 setup.