You have to keep in mind that it is all an interconnected/interdependent system; engine design, intake design, exhaust design. With a short stroke engine like the C-series, the "sweet sport' as far as overall efficiency (mileage) is where the common area is maximized, in graphical form, under both the horsepower and torque curves.
Street engine design is COMPLETELY different than Racing engine design. Your entire intake track, from velocity stacks, through the throttle bodies/injectors, though the valves in the head (controlled by the specific cam lift/duration/overlap/ramp profile) out through the downpipes, through the cat and past the muffler, is all a compromise balanced design.
It's even MORE critical on a CVT design, as you cannot change gears to stay in any particular rpm band; it's preset by the CVT assembly. If you change any major link in that chain (exhaust system, cams, variator, throttle bodies, etc.) it usually impacts another area negatively. One reason that the C-series are doggy off of the line is where the engagement design point was set for the clutch, to attempt to maximize in-city mileage for quoted comparison. The problem is, this engine was NEVER designed with a lower-rpm torque peak; it's all higher rpm, both torque and horsepower.
So, you change -out the entire exhaust system, head-back. Now you've radically increased initial exhaust port scavenging in the downpipes, but may have completely lost the ram-tuning effect of a TUNED exhaust system, where the internal volume is a multiple of the exhaust charge fraction. You are louder, feel cooler, actually go slower, run leaner and hotter, and your mileage decreases.
This is what almost every home-bred Tmax Tuner does in Europe. Oh, it SOUNDS NICE! RACIER! And it now is DEAD off the line, because they lost the major portion of the engine torque at lower rpms. So, on goes the J-Costa Evo4 or screaming Mallossi to get the rpms up to where there actually is some power....and it runs even leaner. So, on with the Power Commander to richen it up. THERE! Much better and actually faster than stock! But wait, now it's running at 7,000 rpm all the time and mileage has dropped by 30%!!!
And you end-up with a Pseudo Race-bike that really isn't, and is now a PAIN to ride on the street...
My brother wanted a cooler exhaust on his Tmax 500, so he got a Yoshimura R-77 out of LA ("Race Use Only") and on it went. Wow, from 80Db to 96? That's a bit loud. Off the line? An absolute PIG. Lost ALL it's lower end, or, as they say in all the Spanish Tmax forums "he perdido todo de bajos!". It was SUCH a larger-bore race system that it lost all the necessary back pressure to flow through the head correctly. We modified the removable Db killer to a smaller diameter, and got back 80% of the losses. $500 and a shitload of work later, and he had an annoyingly loud, slower bike...but SHINEY, SHINEY!!
Ah, but there ARE options to keep an eye out for! After he got his 2012 530, he tried to swap-out the Yoshi onto the new bike. O2 sensor interfered with the new rear suspension design. CRAP! Now what? I'm tired of Tmax stock Water Heater Exhausts!
He found the MIVV "Stronger" system, which just came out for the Tmax. They claimed power/torque increases ACROSS the BOARD. Right.
Got it in, put it on. Paired downpipes a TICK larger than stock, but with a Crossover??? A long system, running through a partially baffled muffler and out through a DB killer assembly the SAME DIAMETER as stock? Looks like a LOT of engineering went into this! but how does it WORK?
The nice, rumblier sound measured-out at 84Db vs the stock measured 81. Close enough! Off the line, where before his stock 530 and my modified 500 were dead even, he now just WALKED AWAY! Whaaat? At speed, punching it side-by-side, where we had been even before, he again WALKED AWAY. Holy CRAP. Ah, but I bet his mileage changed!
Yep, it did. On our Sierras trip, he averaged 8-10% BETTER mileage that he had before with the stock system. So what happened? The MIVV engineers designed the system to maximize every aspect of performance of a STOCK bike. NO ONE ELSE does that; it's all Ricky Racer Mods, which are MUCH cheaper to engineer. Just make the pipes BIGGER and LOUDER.
My advice? HOUND MIVV to add a "Stronger" system for the C-series bikes. Everything else is just opening-up a can of worms...
