Why does my friends truck have more power now when he put the catalytic converter back on?
He has cherrybombs and hooker headers in a 92 Chevy pickup with a 350 V8
Is there such a thing as "not enough" backpressure?
I'm going to cut and paste this to your other post as well. Not that people will pay attention, but here goes.
First off, I better clarify for all to know: How exactly do you know it has more power? Was it dynoed under controlled conditions in exactly the same environment both before and after? No one wants to hear the butt dyno answer.
Do boats or race cars run cat converters, or tiny exhaust pipes?
Pick an engine size. Pick an RPM you want it to produce the most power at. Build the exhaust around that. It's that simple, and that complex all at the same time.
You do not want, or need backpressure. That is one of the dumbest, most ignorant myths that still exists. Backpressure will ALWAYS cost power. To make it simple, if the exhaust is efficient, it actually travels down the exhaust tube (which is why long tube headers make MUCH more power over manifolds) with velocity. That velocity will create suction BEHIND it, which will serve to pull the incoming air/fuel charge into the cylinder while both valves are still open (two valve cylinder). Since volume DECREASES as the exhaust gas cools, the exhaust ideally will taper down as it gets further from the motor (as the exhaust gasses cool), to keep velocity up.
If you go TOO large on exhaust (like stock manifolds) the exhaust pulses combine, and the exhaust gasses collide and create turbulence in the exhaust, LOSING efficiency. This is no different than the concept of using a single plane intake manifold on an engine designed for low RPM power. The air/fuel mix has no velocity, which reduces power. No one will argue that. Not anyone that knows what they are talking about. GM's own super long runner TPI is an extreme example.
In no way, shape, or form did the catalytic converter re-addition CREATE power in your case. Restriction will NEVER increase power. You can't equate it to fluid flow in a hose, as exhaust is a pulse, not a constant flow. Somewhat the same physics, in that tapering the pipe creates velocity, but if the tapering creates pressure, it creates restriction.
If you need further proof, do you know what *GM's* own test (out of their service manuals for multiple V8 equipped vehicles, truck or car) for a plugged catalytic converter/exhaust is? You drill a hole forward of the catalytic converter, and install a pressure tap. If the exhaust *pressure* exceeds 3PSI under high RPM conditions, the exhaust is plugged and needs investigated. The 3PSI isn't because that is needed to "make power", it's there because that is what GM considers normal restriction caused by the pipes, converter, and muffler.
Finally, as some still don't quite get it I'm sure, anyone that thinks that keeping exhaust gasses in the exhaust pipe (thats what backpressure IS) and thus in the combustion chamber HAS to also believe that EGR is beneficial in creating power, as that too puts exhaust gasses into the combustion chamber. Really? You think that HELPS power? I'd love to hear that one explained.
Oh there's a good one, "need it for the O2 to read right". Really? What does the *O2* sensor measure? That's right, oxygen. How does keeping inert gas around the O2 sensor help it function? Thats a rich one
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