Quote:
Originally posted by SVXRide
Mychailo,
Will this equation really hold, given that the cats (all three of them!!) aren't true circular cross sections? I can see how it would work if we had straight pipe all the way back to the resonator.
-Bill
|
Yeah, I wonder about this too. Any time the diameter changes, this can cause some reflection. I read that for a strong reflection to occur, the exhaust gas wave has to encounter a sharp increase in cross sectional area, and the area increase has to be at least a factor of 8. The primary cats has a maximum ID of about 105 mm. The exhaust tubing before the cat has a diameter of about 43 mm. This is about a factor of 6. Pretty close. Also, the cats have a thick (several mm) screen in the exhaust flow. I would think this would cause some dampening of the sound wave. So, my thought is that the cats reduce the effectiveness of this resonance action.
As Harvey said, Subaru probably put the whole mess on the dyno, and through trial and error, got the most out of it with the limiting conditions.
My one thought at this point is whether or not it would be wise to replace the center cat with a merged collector.
__________________
Mychailo
:: 2006 Silver Mitsubishi Evolution 9, E85, 34 psi peak, 425wtq/505whp DJ ::
1995 Laguna Blue SVX L AWD 5MT (sold)
Visit my locker
SVX Mods: ND iridium spark plugs, Impreza RS fpr, afr tuned to 13.2:1 using a custom MAF bypass, custom exhaust, WRX 5MT w/ STi RA 1st-4th gear & stock WRX 5th gear, Exedy 13 lb flywheel & Sport Clutch, STi Group N tranny & engine mounts, urethane spacers in rear subframe, rear diff mounts, and pitch stopper, SVX Sport Strut Springs (185f/150r), custom 19 mm rear swaybar, urethane swaybar mounts, Rota Torque 17x8", 225/45-17 Proxes 4 tires, Axxis Deluxe Plus organic brake pads.