i have a set of downey headers for a 3.0 that are going to be installed on a rebuilt 3.0(i would love to swap the 3.4 but not enough robert DINER0 right now)has anybody run dual exhaust on a 3.0?i just got the idea in my head that the design of the crossover tube is not all that great in the original design.would it be a waste of money?how much if any power gain + or -?current set up is a 2 1/4 exhaust stock manifolds,free flow cat and a flowmaster

 

You need to go to a stock style (2 into 1)set up to the cat for the 02's then split out with a h cross over to the rear so you can't do a REAL TRUE DUAL set up but you can still run a dual set up out the rear.

 

i have a 1990 runner not an 02 but i see your point

 

02 is short for oxygen sensor not a year

 

Most factory exhaust set-ups not very efficient, and are mainly set-up to conform to noise levels. Usually they are also set-up to deliver the gases to the cat, then out to an area that doesn't recirculate the gases back into the vehicle.
Differing types of exhaust set-ups will deliver different results....2 into 1, crossover(h-pipe sometimes argued these are not the same) and no crossover.
A crossover or even a 2 into 1 will help scavenge high rpm HQ, while a straight dual set-up will not. However, if your crossover is not placed in the ideal location you won't get any advantage. The proper placement of a crossover has to do with distance from the exhaust valve from each cylinder and valve lift duration. This is critical because each exhaust pulse creates low pressure behind itself as it runs thru the exhaust pipe. this is back pressure. Sized and measured correctly(header and exhaust) you will get and exhaust pulse that will actually help pull the next blast out of the chamber and into the pipe.
I had Burns Stainless work up a crossover for my bike by filling out this form.
http://www.burnsstainless.com/RESF.pdf
They gave me the information so i could build my own efficient exhaust.
If you are running stock manifolds(which you aren't) the crossover placement would make little difference. Running headers you may not gain any advantage either, but i doubt it will hurt either.
I could be completely wrong about this and hopefully someone will correct me.

good luck

 

O2 or o2 is short for oxygen sensor, 02 is not.

 

either way its still an oxygen sensor