Yamaha's new SRX engine is an original creature, designed to offer consumers
the power of a three cylinder engine without the weight penalty often associated
with a triple. The 598 and 696cc liquid-cooled mills were seemingly designed
with an additional goal: last a long time.
While light weight often means sacrificing durability, Yamaha engineers have taken careful steps to ensure their designs will withstand the nasty abuse only snowmobilers can dish out. Individually cast cylinders and heads offer reduced weight plus reduced cost for service, since the whole block need not be scrapped if one cylinder hiccups. A special powder metal forging process allows Yamaha to use a thinner-walled piston to save weight without sacrificing performance. To increase durability and reliability, Yamaha uses five sets of roller bearings in the crank shaft.
To make more power throughout the spectrum, Yamaha incorporated an electronically-controlled variable exhaust valve. Like the Rotax' RAVE and Polaris' variable exhaust valve, the Yamaha Power Valve System adjusts the exhaust port timing to create peak power at low, mid and high rpm. Unlike the other two, the YPVS is computer controlled and engaged via a servo motor and cables for the most precise operation available.
Our dyno technicians had a difficult time finding an SRX to use. It seems that sales of the new blue cruisers have been so high, dealers are reluctant to offer us one to use because they're already paid for. With some sweet talking, our crew at Dynotech was able to call in a few favors and run one for us.
The data from the dyno run proved what we were able to figure out just from riding the SRX 700: there's lots of power in this sled, right from the start. Heck, we were at a cool 110 hp at 7000 rpm, and it just got better from there. Our technicians found the peak 140.9 horsepower right around 8250. The power smoothly creeps up at about 2 to 3 horses with every 100 rpm increase. That's why we have referred to the SRX's performance as "sneaky fast," it climbs steadily instead of kicking in like a turbo.
By way of comparison, last month, we found 142 ponies under the hood of the Mach 1 with the new central outlet pipes. How will they compare on the trail and over frozen lakes? We'll let you know next issue when we put the triple cylinder, triple piped sleds to the test at the Annual Shoot Out.
1998 Yamaha SRX 700
| RPM | CBT | CBHP | BSFC | FUEL | A/F |
| 7000 | 82.5 | 110.0 | .636 | 68.64 | 12.09 |
| 7100 | 83.9 | 113.5 | .629 | 70.13 | 11.97 |
| 7200 | 84.3 | 115.5 | .640 | 72.71 | 11.77 |
| 7300 | 83.5 | 116.0 | .646 | 73.70 | 11.73 |
| 7400 | 84.4 | 118.9 | .629 | 73.70 | 11.93 |
| 7500 | 85.5 | 122.1 | .648 | 77.88 | 11.48 |
| 7600 | 85.9 | 124.3 | .630 | 77.22 | 11.59 |
| 7700 | 87.2 | 127.9 | .623 | 78.43 | 11.63 |
| 7800 | 87.3 | 129.7 | .618 | 78.98 | 11.57 |
| 7900 | 89.0 | 133.8 | .606 | 79.86 | 11.66 |
| 8000 | 90.2 | 137.3 | .604 | 81.62 | 11.68 |
| 8100 | 90.0 | 138.8 | .601 | 82.06 | 11.76 |
| 8200 | 90.3 | 140.9 | .596 | 82.72 | 11.77 |
| 8300 | 89.9 | 140.9 | .597 | 82.73 | 11.84 |
| 8400 | 87.7 | 140.3 | .614 | 84.81 | 11.62 |
| 8500 | 85.6 | 138.5 | .604 | 82.28 | 11.95 |
RPM: Engine crankshaft speed.
CBT: Corrected Brake Torque.
CBHP: Corrected Brake Horsepower.
BSFC: Brake Specific Fuel Consumption.
FUEL: Actual fuel flow pounds per hour.
A/F: AirFuel Ratio.