Wrist: Aaron Frank
MSRP (2011): $11,999
Mods: Yoshimura R-77D exhaust
As sportbike performance continues to advance, simple bolt-on performance upgrades become less effective.With exotic materials becoming commonplace and manufacturing techniques continually improving, the law of diminishing returns takes effect. The gap between stock streetbikes and race-tuned Superbikes is constantly closing, and aftermarket performance upgrades increase actual performance less and less.
This has never been more evident than after I installed a Yoshimura R-77D slip-on exhaust ($599; www.yoshimura-rd.com) on my Suzuki GSX-R750 long-term testbike. Not long ago, a slip-on was the best bang-for-your-buck mod you could make; a cheap and quick way to add 10 horsepower and drop 10 or more pounds. Let’s just say the benefits today are somewhat more modest. How good is the GSX-R’s stock titanium muffler? Installing the carbon-fiber R77D slip-on added just 2.6 bhp—raising peak horsepower from 126 to 128.6, measured on the Moon’s Supercycle dyno—and it actually weighs 5 ounces more than the OE part.
We would have seen more significant gains with a full exhaust system that deleted the pre-muffler and catalytic convertor, but I wanted to keep it street-legal—and the intake roar at 5000 rpm already makes the GSX-R750 loud enough! The dual-outlet R-77D sounds perfect, with a deeper, less-tinny tone but no appreciable increase in overall volume. The R-77D is a gorgeous cosmetic upgrade, too, crafted from glossy, rich-looking carbon-fiber held together with trick, laser-cut stainless-steel reinforcing ribs.
Yoshimura’s R-77D slip-on comes with a stainless-steel mid-pipe and mounting hardware. The
We still have to correct the fuel mixture, which will probably produce a few more horsepower at least at lower revs. The freer-flowing slip-on exacerbated an already lean condition, resulting in an air/fuel ratio anywhere from 15-55 percent leaner than optimum at certain revs, with the worst discrepancies occurring between 3500 and 5500 rpm—right where you feel it on the street. Rather than add a Dynojet Power Commander or other aftermarket tuning module, I want to use ECU Editor software to “hack” the stock black box. Tuner Greg Moon tells me this will deliver significantly better results since the stock ECU lets him adjust air/fuel ratios in much finer increments than comparatively crude aftermarket units, which only allow adjustments at 500-rpm intervals. Hacking the stock ECU is much more labor-intensive, but the result is a more precise fuel map without the expense of a $300-plus aftermarket part.
Adding fuel across the rev range should make a big difference. Moon bets we’ll gain a few more peak horsepower and as much as 8-10 more bhp around 4000 rpm, where the lean condition is most acute. Now we just have to figure out which ECU port we need to jump in order to access the programming channels. It appears we’re the first in the nation to re-flash the 2011 GSX-R750 ECU—even the ECU Editor folks don’t know which port is the right one—so this is taking longer than anticipated. We’ll keep poking around and report back soon. MC