View Full Version : Exhaust questions for a 22R-E DD

05-30-2008, 09:27 AM
Red truck tech: I have a hole in my muffler, and was curious if that would affect my gas mileage? Or, I'm suspecting that if there's a hole in the muffler there may be other problems that I don't know about that might affect my gas mileage.

Also, I have no idea how old my catalytic converter is, and I'm going to assume it's good but for laughs I was wondering if there was an easy way to tell if it was bad.

Going to get a new muffler today hopefully.

05-30-2008, 09:35 AM
While you are at it, get a 2 1/4" cat-back system made, with a Flowmaster, Magnaflow or equivalent free breathing muffler. It will improve power and presumably mileage just a bit. Make sure it is mandrel bent (non-mandrel reduces the diameter such that you get little gain).

The best way to tell about the cat is to sniff test it.

No, not your nose, silly... :rolleyes:

05-30-2008, 10:26 AM
It passes emissions fine, so presumably the cat is good.

Not trying to make this a racecar either :rolleyes:

05-30-2008, 10:27 AM
Just to clarify, assuming the cat is still mechanically good, by sniff test Bill means that the catalyst in there does deplete over time. If you have high HC, IOW unburned fuel, in the exhaust stream the catalytic converter might be done. There isn't really a fixed time frame here, depends on how well your engine is tuned as to how long it lasts. If you can't remember or don't know how old it is, if you don't pass the emissions test but the truck seems to run well otherwise, it's certainly possible that cat needs to be replaced.

I don't know anyone personally that compared a pinch bent exhaust against a mandrel bent system of the same size. Anecdotal accounts I think usually say a system that is mandrel bent can be about 1/4" smaller in diameter than a regular pinch bent one on a 22R. At least the volume is close between the two. The pinch bent pipes will flow more irregularly, so that's the main problem, turbulent flow. Now how much difference that makes, I dunno. My guess is on a low RPM 4WD, probably not nearly as much as a track car. But for highway and commuting, I'd take the time and effort to have a mandrel bent system made.

The rule of thumb on a 22R is that using about 1.5" or 1.625" header primaries into a 2.25" collector and 2.25" exhaust that exits in the stock location is pretty much fine. If you run the exhaust exit out someplace else, like in front of the axle or before the rear tires, then a 2.5" exhaust might be OK. I have a LC Engineering system from exhaust port to tailpipe and at idle there is hardly any pressure at the tailpipe tip. No reason to mess with what's proved to work, 2.25" system from flange to tailpipe.

05-30-2008, 11:55 AM
Actually ORS did some comparisons AFAIK and there was some difference between a 2.25 mandrel and non-mandrel. There is a noticeable difference between either option and the stock system. Worth it.

Ted Stanwood recommends a 2" pipe pre-cat, not 2.25, based on testing. Bigger pre-cat will rob power.

05-30-2008, 12:17 PM
I dissagree.

I put on an intake, ceramic, tri Y headers, and an exhaust with a high flow muffler.

I saw zero mileage increase, and zero power increase.

I consider both mods to be the biggest wastes of money I've ever done.

If its cheaper than replaceing the stock stuff, cool, but if it costs more, I personally wouldn't spend money on it.

05-30-2008, 12:21 PM
The header is why. It is very difficult to improve on the stock iron header, which flows very well. In fact, installing a header can cause a power DECREASE and loss of mileage, due to over scavenging. The cam design needs to be changed to avoid this if you really need a header. That's why I mentioned the 2" pre-cat pipe over the 2.25": bigger is not better.

I have proven in my own experience that a cat-back 2.25", high flow muffler system results in improved power and some additional mileage. Worlds different from your setup. It can be done for very little over using the stock muffler/cat back section.

05-30-2008, 12:43 PM
What's the rational behind a 2" intermediate pipe? Seems to me you need to match the first pipe to both the collector outlet and cat inlet diameter, otherwise you are creating a pocket of higher pressure. Then where do you jump up to 2.25"? I would think tapering the pipe between the cat and muffler would be the best spot to do that. Maybe a 2" inlet and 2.25" outlet cat? That would be alright, too, since the cat is already a liability and mismatched inlet/outlets wouldn't really be any worse. In any case, you don't want an abrupt size change with a corner.

Just thinking about this some more, my question about the 2" pipe I think revolves around the header or manifold. A stock manifold is really a header, not sure if Matt knows that or not. If your stock manifold is not cracked, it's as good a part as any. Anyway, in the case of a header, the collector is supposed to have whatever pressure such that each of the exhaust pulses creates a particular pressure drop when it goes from a smaller diameter to a larger, which creates a vacuum at the other ports and increases the scavaging effect. Matching the between pipe to the collector diameter seems like the only way for the header to work correctly, otherwise you create more pressure or more vacuum than what the header is designed to work with. This was my reasoning behind going with the LCE end-to-end, since they developed the header to work with the exhaust (or vice versa). It's essentially just a 2.25" mandrel-bent system end-to-end, so knowing now what I wish I did then, I would have just had one bent up locally. But my point is only that things need to match to their design criteria to work right. My guess is that a stock manifold might be great with a 2" pipe (stock is 1-7/8"), but I'm not sure that can be a universal statement for all engines. It seems like it would depend on the intake flow, flow through the head, etc.

05-30-2008, 01:40 PM
What's the rational behind a 2" intermediate pipe?
It works and is proven.

I think you are overthinking it. ;)

No, it is not universal for all engines, just 22REs with the stock exhaust manifold. The pipe diameter change (2-2.25") occurs at the aft of the cat, and 2" before the cat.

FWIW, just doing the cat-back works and is easy to do, though.

05-30-2008, 01:45 PM
My mistake. I didn't know that it made a difference. I've learned my 12th new thing today. :D

05-30-2008, 02:14 PM
I think you are overthinking it. ;)
Nah, what's wrong with studying it and trying to understand? It's weird how cracking open all those fancy books from classes I dozed through in school have neat stuff about fluid mechanics and thermodynamics. Who knew those stuffy old dudes with leather patches on their elbows and unkempt beards actually taught useful stuff?

05-30-2008, 02:24 PM
Nuttin' wrong with that. But if something is observed to work, it is the burden of the theory to explain it, not explain how it could not be so...

05-30-2008, 03:13 PM
Differing expansion rates as the exhaust gases cool. Bigger than 2" scavenged too much, smaller than 2" kinda choked things off. And 2.25 was the optimal diameter cat-back based on much trial and error.

You'll have to call Ted and ask him about dyno testing. I'm sure he will be happy to explain how he and others came to this conclusion based on experimentation.

Not knowing any of this, I put a 2.5" non-mandrel bent cat back on the Chili. I lost some low end. Sounded good. Wrapped out pretty well. Of course it worked out pretty well for the 5VZ swap eventually.

05-31-2008, 09:13 AM
Doug Thorley Header, 2.25 Exhaust, MagnaFlow Muffler, K&N Air Filter works great for my 88!