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Originally Posted by Max777
IF you happen to read grassroots motorsports, you would know that that is not quite true.
if you run a spun cat on a miata for example, then it gives you a better power band than a test pipe! Also, if you run that wierd stack exhaust that dumps right after the header, it doesnt give any more gain than a good rear exit system, just more noise, so on an NA, a high flow cat does not decrease the flow so much that it robs the car of horsepower.
You know your shit, but aftermarket catalytic converters have advanced a lot further than most people think.
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That is the reason why I said "MOST"...
If anything, the examples you have cited got lucky due to exhaust tuning.
It's just luck.
The combination of parts just so happen to hit a "sweet spot" for power, and that's why the results came out like that...
I'm talking about turbos, and almost always any cat is a restriction which is going to hurt power over a straight pipe.
Normally aspirated exhaust tuning can get tricky, and it's not something I think about myself.
I realize that the OP could've been talking about a non-turbo application...
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So if it isnt the removal of the cats and air pump, then what causes the fumes in the passenger bay? I want to eliminate this problem if possible.
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It's just the nature of the 13B engine.
It comes down to intake and exhaust port timing (well, mostly exhaust) and the dynamics of combustion in the 13B rotary engine...and RPM.
I mention RPM's cause after a certain RPM, the EGT's got hot enough to burn almost everything in the exhaust.
This is why you don't smell the exhaust cruising on the high at around 3kRPM...well, that and your car should be in closed-loop at around 14.7 AFR.
At lower RPM's - i.e. idle - the EGT's are just not hot enough to burn everything up.
-Ted