how do i make a legal true duel exhaust?

[junk yard dog]

Im wondering how to make a true duel exhaust legal and pass emissions too? two cats and two mufflers?

Also what kind of gas milage do you guys get with duels or single?

[Orbital]

There's no emissions testing where I'm from, so I couldn't answer you with specifics. I would assume that you need two of everything. My 1990 Nissan 300ZX (miss that car...) was true dual from the factory and had 2 of EVERYTHING from the intakes to the exhaust. Two air intakes, two throttle bodies, Four O2 sensors, two cats, two resonators, two mufflers... It was passing emissions in California where they're supposed to be super strict, so I suppose if you needed to pass emissions, do the 2 of everything thing. For the exhaust that is.

Another option is to ask around and find a inspection station that is a little lax with their requirements. Your choice.

Gas mileage with my setup -- no cats, two Thrush glasspacks, true duals -- is around 16-18 city. Thats on a 1991 RCSB with a 305. I think the biggest improvement for HP and gas mileage was replacing all the old worn out stuff with new parts, (cap and rotor, plugs, wires, air filter, fuel filter, etc...), so if you need better mileage, try going that replacing things first. Plus, the I have the Hypertech Powercharger which helps out too at the higher RPM's.

[Darkside919]

Truck specs might help a little as well. I am in the same boat as Orbital no emissions testing here.

[5.3power]

it is hard but is possible

[nick613]

I think as long as you have two cats you should be gold? I have a single 3" exhaust that I did totally custom from the headers back and I pass emissions.

[Low97tahoE]

I think as long as you have two cats you should be gold? I have a single 3" exhaust that I did totally custom from the headers back and I pass emissions.

tuning does wonders, on my hoe, i had longtube headers, single 3" pipe, no cat, electric cutout and an 18" magnaflow, it had an amazing rumble and sounded great and passed emissions with a little deleting o2 sensors and such, i had no rear o2 sensors and no egr valve or egr hose and it was fine

[sunburnedaz]

What year is your truck? My 98 had true duals from the factory from the manifolds to the single muffler. Installing a cat back system made it a true dual. So from the factory it already had 2 cats, and 4 O2 sensors. All that someone did to mine was cut out the old muffler and install a pair of them.

[Maestro]

Yep. If you're dual cat already, you don't need any fab work; the right cat-back system will render you a dual exhaust, and if you were emissions-legal before, you should be after. If you have a single cat, then you have more work to do, and it depends on your current setup. But bottom line, if you keep all the O2 sensors you have and add either one converter or no converters you shouldn't hurt your emissions status. If your tune is good, you may not even need all of the stock emissions equipment, depending on your local requirements (some will check for things like O2 sensor deletes).

If you post up what truck you actually have, people would be able to give you specifics

[Botan]

if you have a factor 3 o2 sensor y pipe, you can grab an exhaust off a truck with factory dual exhaust, but you will have to use the ecu and chassis wiring harness from "donor truck" to convert to 4 o2 sensors and run correctly with them. I'm actually in the process of going from true dual to a dual cat, 3 o2 sensor 4" y pipe like the diesels have so i can use a 4" stack setup.