Yamaha definitely caught us off guard last spring at our test session. We absolutely did not expect to see a new 600 baby triple clad in Factory Racing blue. With conventional snowmobiling wisdom leaning toward lightweight, potent twins, here comes another new triple.
The '99 SX only added four pounds with the addition of the extra cylinder. In 1998, the SX tipped the scales at 481 pounds. This year's model is brochure-listed at 485 pounds dry. With the extra weight comes an extra 2.2 horses under
the hood, based on our 1997 Shoot-Out test sled. You may be wondering why
Yamaha planners even bothered with re-outfitting the SX if the sled is only
marginally stronger with the new motor. We did, too.
"We went with a triple cylinder motor for a number of reasons," commented Yamaha's Assistant Product Planning Manager, Greg Marier. "For one, it is a much smoother running engine than a two-cylinder. Second, we felt that we got better throttle response with our lightweight triple package. Plus we have seen improved fuel economy with the new sled."
We can verify the smoother operation and crisper throttle response on the new sleds, based on our experience at our spring test session. As for the fuel economy of the new mill, we will withhold judgment until this season, when we have a chance to put it to the 1,000-mile test.
The 593cc motor is based on the lightweight 700 triple which marked the beginning of Yamaha's recent climb in market share. The nicasil-plated cylinders have been sleeved down from 70.5mm on the 700 to 65mm on the 600- both motors' stroke measures 59.6mm. Both case-reed engines use liquid-heated, racked, flat slide Mikunis to keep the fuel flowing. The 700 utilizes 33mm units, while the 600 sports slightly more miserly 31mm carbs.
Our dyno testers were satisfied with what they found, once they got the sled hooked up to the Super Flow dyno.
"This should be a good motor for consumers," commented Dynoman Rich Daly. "It's set up very well out of the crate. We didn't really have to do much adjusting to make the power. We did find that it responded better once we got the pipes warmed up, though."
While the torque and horsepower numbers are low by comparison with the
rest of its class, the Yamaha baby triple does offer tuners a very wide power band.
"There's a 600 rpm range where the SX is making the most power," noted Daly. "That, to me, says that it will be easy for tuners to clutch, and it will also probably be very responsive to triple pipes, if a guy was so inclined. Plus, the fact that the motor responded so well to heating up indicates that pipes might wake this baby up."
The new motor will not only be found in the SX this season, but it will also be in the Vmax 600 Deluxe and the Venture 600. If all goes well with its first year on the snow, we'd expect to see it in the rest of the lineup for the new century.
1999 YAMAHA VMAX 600 SXAir Density: 93.9
Fuel: 94 Octane Pump Gas
| RPM | CBT | CBHP | BSFC | FUEL | H2O |
| 7249 | 57.5 | 79.3 | .660 | 50.2 | 91.5 |
| 7300 | 57.5 | 80.0 | .652 | 50.2 | 91.5 |
| 7400 | 58.2 | 82.0 | .634 | 50.1 | 91.5 |
| 7500 | 58.6 | 83.7 | .634 | 51.1 | 92.5 |
| 7600 | 59.0 | 85.4 | .632 | 52.0 | 93.0 |
| 7700 | 60.2 | 88.3 | .614 | 52.3 | 94.0 |
| 7800 | 60.8 | 90.3 | .600 | 52.6 | 94.5 |
| 7900 | 62.0 | 93.3 | .590 | 53.0 | 95.0 |
| 8000 | 62.5 | 95.2 | .580 | 53.2 | 95.5 |
| 8100 | 63.0 | 97.1 | .570 | 53.4 | 96.5 |
| 8200 | 62.7 | 97.9 | .571 | 53.9 | 97.0 |
| 8300 | 62.1 | 98.1 | .580 | 55.0 | 98.0 |
| 8400 | 61.5 | 98.4 | .590 | 55.9 | 98.5 |
| 8500 | 60.3 | 97.4 | .598 | 56.2 | 100.0 |
| 8600 | 59.5 | 97.4 | .602 | 56.5 | 101.5 |
| 8700 | 58.4 | 96.7 | .611 | 56.9 | 102.5 |
| 8800 | 57.2 | 95.9 | .614 | 56.7 | 103.5 |
| 8900 | 56.3 | 95.4 | .617 | 56.7 | 104.5 |
| 8958 | 55.4 | 94.5 | .620 | 56.7 | 105.0 |
RPM: Engine crankshaft speed.
CBT: Corrected Brake Torque.
CBHP: Corrected Brake Horsepower.
BSFC: Brake Specific Fuel Consumption.
FUEL: Actual fuel flow pounds per hour.
H20: Water temperature in degrees F.