Hey, I searched around here for a bit, but I couldn't see anything on this topic, so here goes:
I am looking at modifying my exhaust ('91 4runner) to a true dual exhaust setup, with two cat converters, two 40series mufflers, and absolutely no crossovers, y-pipes, x-pipes, or the like (old jeep CJ-style!). My idea is basically having two seperate exhausts for each side of the motor, as short as possible, and turning down and out well before the rear wheels. Any idea on what this would do for my backpressure? I hope that I will still have backpressure, as I will have the cat installed on both pipes. What do you think?
-Shawn

 

You'll probably lose power with the 3.0 if you go bigger than 2" but I don't think the performance gain vs the cost of having a true dual exhaust is worth it. You'd probably get the same result by running a 2nd pipe after the cat so you have the look and it's still a real exhaust and it'll be way cheaper.

 

I like the idea and have thought about it, however the problem i see is getting by the gas tank even if you put it out before the tank it would be right below the door where you would get a fume problem. the other bad thing is all that heat around the gas just doesn't make me feel safe. So we are left with the option of put both out one side. Not a bad idea but why waste the $$ when you could just do one pipe and do the crossover later with one Cat and have the close to the same performance? Just my 2 Cents worth. If you find a way let me know cause i will be replacing my engine in the next week and could possibly do something then.
Brandi

 

To get true dual performance out of the 3.0 wouldn't you want to run smaller pipes to maintain back pressure? My understanding is this - in a normal traditional one pipe system when guys run headers they usually run 2 inches in the crossover section until they connect to 2 1/4" (more torque geared - more back pressure) or 2 1/2" (more hp geared, a little less back pressure but helps you rev the engine) to the cat, then muffler, and then out for a single exhaust. In this case Switching off of two adjoining 2" pipes into a 2 1/4 or 2 1/2" pipe will naturally cause more back pressure up those 2 - 2" pipes to their respective 3 cylinder valves off the headers.

For duals I'd imagine you'd probably have to run smaller pipes, like 1.75" or maybe even 1.5" if you were to keep the same back pressure as the above mentioned system single exhaust system. At least in theory I'd imagine anyways. Any thoughts on this particular issue?

 

Check out my header installation writeup on this site for more info. I've done plenty of experimenting with 3.0 exhaust setups.

 

I don't think the 3.0 flows enough air to warrant a duel exhaust. I think 2 mufflers and 2 cat's will choke the old 3.0.