No Resonator on Exhaust

[beauboy]

Here's one for you exhaust experts -

I recently had my muffler and exhaust replaced on my '91 Ex. Each time previously that I had to replace it, the exhaust pipe rusted away from the resonator (juice can-looking thingy). Well, this time, the shop decided to install an exhaust pipe without a resonator, explaining that mufflers are much better than they were 20 years ago, so I shouldn't need a resonator. Made sense to me.

But in driving for the past week, I noticed that I'm going through gasoline a lot faster than before. My mpg looks like it's dropped off a few.

Question - does the presence of a resonator, or the absence of one, effect my gas mileage? Is there a deal here having to do with more or less backpressure?

I just don't know, so I'm looking for input.

Thanks in advance.

[Jason94sport]

With it off it makes the exhaust free flowing. More air out of your engine. It could decrease gas mileage a little. You may be just on the gas more & don't realize it as well.

[beauboy]

Not on the gas more. I'm not a teenager, nor a new explorer owner. This one I bought brand new back in '91 and haven't been in a hurry for more than 10 years.

Could I attach a resonator to the end of the tailpipe to restore mpg?

[johnvosh]

Just out of curiosity, when did you last replace your o2 sensors? From reading on this site it almost sounds like your o2 sensors may be going out and it just happened to coincide with your exhaust replacement.

[beauboy]

That's a bit of a stretch, john. I haven't changed my O2 sensors for quite a while - because I haven't needed to. An engine analysis (which I do at regular intervals) would've showed a faulty sensor. Coincidences don't happen as often as people might think.

[Jason94sport]

Hell no need to be so arrogant. Damn dude we are suggesting things.....

[Anime]

The presence or absence of a resonator shouldn't affect mileage in the slightest, at least usually. Resonators are usually straight-through mini mufflers (like glasspacks or race bullets), though some with internal louvres (instead of holes) do restrict exhaust flow. In this case, going from a restrictive resonator to a good flowing pipe might improve mileage by reducing backpressure.

Indirectly, the lack of a resonator usually allows a bit more of a performance tone, so sometimes it might be the staying on the gas to generate that exhaust note that uses more fuel. If you've been driving the same and haven't noticed any difference other than the mileage drop, something else might be to blame.

Most mufflers and pipes for the '91-92 are pretty decent (usually 2.25" all around) and flow what the 4.0 needs, so MPG shouldn't be affected unless something was changed. The factory systems just used a resonator (and some shop-installed systems add one on) since there is a bit of drone in free-er flowing systems on these. I have a '91-92 Dynomax catback with a Super Turbo and the 2.25" pipe on there and it does drone a good bit at 1700-1900 RPM. A resonator would likely mellow that out.

What sort of exhaust system is on there? If the new pipe is smaller (say 2 inches instead of 2.25"), or has crush-type bends, it might be more restrictive than the previous one. If a new muffler was used, it might flow worse than the old one. I have seen some pretty crazy muffler designs that choke the 4.0 with trying to stick the flow through a 1/2" hole. They are quiet, but torque, power, and mileage all suffer for it. You may want to measure/eyeball the pipe and be sure it's the correct size (2.25") and isn't cheap crushed stuff at the bends, or inquire with your exhaust shop as to what they used previously and what they use now to try and account for the difference.

My suggestion for the pipe for the '91-92 would be the Dynomax one. It's 2.25" with mandrel bends, costs about $40, and has the hangers on it like the OE type pipes. It even works along with Walker's non-Dynomax Quietflow3 muffler instead of the Super Turbo.