"True" Dual Exhaust--A question

[vrmlbasic]

In reading the massive post on problems with the 3.8l '86, I saw him mention wanting to set up dual exhaust pipes with a crossover for the O2 sensor, the so-hyped "true" dual exhaust.

I've always wondered about the O2 sensor and this setup, especially as I have thought of it for rebuilding my totaled '92.

When you put 2 identical paths in parallel, the resistance from start to finish is halved...the crossover pipe connects each exhaust duct to the other, with the idea that exhaust will hit it on either pipe.

However, not all the exhaust will flow through the crossover.

Wouldn't that mean that the sensor readings would only be for ~50% of the total exhaust gas, making the computer think that you're running lean all the time?

[Blue Bowtie]

Don't over-analyze. The O² gets an exhaust gas oxygen content indication from whatever gasses pass it. If only three cylinders are exhausting past the O², the O² will report the EGO for those cylinders to the ECM, The ECM will adjust injector PW to maintain a target EGO and "satisfy" the O². That design system is intended to closely monitor and control fuel on those three cylinders, and presumes that the other three cylinders are operating under the same conditions, and will therefore react similarly to injector pulse width changes. It had been done like that for years, until SFI became prevalent.

Although a balance pipe (crossover) in a dual system can alleviate uneven pulse backpressure, I'm thinking that the even firing order of the Buick V-6 doesn't require it, unlike SBC engines which have adjacent cylinders firing sequntially.