Can a muffler make a vehicle run better?

Been resurrecting the Ranger a little bit at time. Friday I had a new stock type muffler put on. It had an occasional hitch just off idle and sometime at midrange. All that's gone now. The OEM muffler had split open at the seam. The truck has California (PZEV) emissions. The only thing I can think of is that maybe the additional backpressure of the new muffler makes it run just a bit richer. Any ideas?

"The only thing I can think of is that maybe the additional backpressure of the new muffler makes it run just a bit richer."

Not having that back pressure can cause a drop in low end torque. With a new muffler you may have gotten that back.

After the cats, nothing significantly affects backpressure or performance.

Also, contrary to popular belief, "backpressure" is not a good thing, scavenging is.

Here is a good read on exhaust:

http://www.dsmtuners.com/forums/frequently-answered-dsm-questions/168578-exhaust-straight-scoop-backpressure.html

A work associate of mine had a '97 K1500 350.  He installed Edlebrock headers, and catback.  He complained about a lack of torque missing after the installation.  My input back to him was to add additional power enhancers that could better match the greater capabilities of the exhaust, intake, chip, cam, rockers, or simply go back to the stock manifolds, and exhaust and chip the OEM setup for a modest gain.

IMHO there are "matched" characteristics that have a relation to performance characteristics of other related components, much more than considering only individual part itself and any max HP/TQ gains.  The intake,cam, heads, exhaust manifolds, y-pipe, and exhaust are all a tuned unit.  Change in one can effect the others.

Freeing up the exhaust will typically otherwise OEM vehicle will likely increase HP, this means there is an increase in torque, but most will find the additional torque is higher and the band of torque is higher in the RPM band.  Thus there is an increase, its just not where it used to be relative to RPM.  Thus the feeling of X% throttle input netted previous Y torque, now after the aftermarket part there's Y -10% at the X% of throttle.  

In your case rustbucket its my belief that the new OEM muffler reclaimed the design flow characteristics that were lost by the compromised leaking old muffler, thus correcting some of the odd behaviors experienced previously.

joemac wrote:

Freeing up the exhaust will typically otherwise OEM vehicle will likely increase HP, this means there is an increase in torque, but most will find the additional torque is higher and the band of torque is higher in the RPM band.  Thus there is an increase, its just not where it used to be relative to RPM.  Thus the feeling of X% throttle input netted previous Y torque, now after the aftermarket part there's Y -10% at the X% of throttle.  

In your case rustbucket its my belief that the new OEM muffler reclaimed the design flow characteristics that were lost by the compromised leaking old muffler, thus correcting some of the odd behaviors experienced previously.

It makes sense, especially with a 4 banger with almost 165,000 miles on that doesn't have an abundance of torque to begin with. The seat of the pants dyno agrees- it pulls better off idle and will pull fifth gear better at a lower rpm.

VMax wrote:

After the cats, nothing significantly affects backpressure or performance.  

Also, contrary to popular belief, "backpressure" is not a good thing, scavenging is.

Here is a good read on exhaust:

http://www.dsmtuners.com/forums/frequently-answered-dsm-questions/168578-exhaust-straight-scoop-backpressure.html

Thanks for the link, V. This part- "So, at low rpm I need a small pipe to maximize scavenging, and at high rpm I need a big pipe to minimize pressure drop" I think ties in with what JoeMac was saying.