Conclusive Theory on Design: Dual Outlet Flange, Dual Cat, C.A.R.B. California

I will be purchasing a 2000 Tacoma 2.7L soon.

My question is; why do stock exhaust manifolds on the Tacoma feature a "dual outlet flange" design?

From what I have gathered; there are two designs and one may exist solely for C.A.R.B. compliance in California.

Also; why would some Tacomas have a dual-cat setup? I suppose for the California market and may or may not be inclusive to a dual outlet flange. As the upper catalytic converter may require the exhaust gas pressure from a dual outlet flange to operate at its most efficient temperature.

The dual outlet flange may also induce adequate scavenging from the cylinder so as to force exhaust gases out, instead of remain stagnant in oversized or low-pressure collectors (which this may be what causes low end torque loss via long tube headers).

As I search more on headers, I figure the greater benefit for engines with long tube headers may come from larger, high output V6/V8+ engines that have the power to effectively use that added area for exhaust gases to collect and thus be forced outward.

For racing applications however, I suppose would benefit from long tube headers as engines are built for high-torque, high-RPM strain, no matter the engine size. So a long tube header would effectively replace the front cat on dual cat setups and as a racing build, the rear cat would be eliminated by a full exhaust system anyway.

When searching for an aftermarket header (especially in the California market), albeit long tubes are more appealing in some ways such as "high end torque", but the shorties are the way to go in a 2.7, for city driving and low-speed trail/offroading. With the addition that if indeed I have a dual cat setup, I will need to preserve my ability to smog and thus register the vehicle.

Any thoughts?

 

I believe you answered youre own question as to which is better. The Long tubes are great, but usually are not legal because they replace alot of factory pipe length and usually are made for single cat systems, great gains can be had with long or short tubes from personal experience and will always produce gains over factory manifolds. Anytime airflow is smooth it moves faster if it can so you get gains with n/a but more with boost. For any engine, restrictions in flow are standard, so really, you are doing better with most any quality header/headers. You also have lower engine temps as the heat moves out easier. Carb legal is a must even in other states as restrictions are getting tighter every day. People dont know tampering with an exhuast system on a factory vehicle is violating federal law. The feds dont bother you really but the law is there, I know Carb employees that push it with legality on their vehicles, but who's gonna bother them..