The new Polaris 500 twin has been anticipated by the faithful for sometime. The reliable Indy 500 motor has probably powered more snowmobilersaround the trails than any ever made. But a change was definitely in order.While it was a classic trail engine, the 488cc Fuji was certainly no high-performancemill by current standards. We wondered whether the new 500 would be domesticor Fuji-built. If it was domestic, would it be a scaled down version ofthe 600 twin, a bored-out version of the 440, or a completely new creatureunto itself. Here's the answer: the new Polaris 500 is a domestic powerplantbased on the 440 race motor platform.
The new mill uses the cylinder casts from the 440, bored out to 70.5mmwith the same 64mm stroke. Yes, the castings are in place for a variableexhaust valve system, but it is not used on this motor. Polaris opted touse iron liners in its cylinders on the 500cc powerplant. It is cost effective,easier to work with and it leaves room for future upgrades as necessary.
This engine package is fed by a pair of 38mm flat slide Mikunis. Thisensures that plenty of fuel/air mixture is sent through the reed valve,and into the combustion chamber. Direct oil injection keeps a miserly gripon consumption without sacrificing dependability or performance.
When our dyno guys called to say they got their hands on an early release500 XC SP, of course we were interested. Polaris claims a full 18 percentincrease in top end power over the trusty old 488cc mill. What we foundon the new 500 came close to that, with some pretty impressive torque figuresto boot!
The power curve on the motor is rather unique for a stock sled. It risessmoothly from 52 horsepower at 6000 rpm up to 92 horse at 7700. But onceit hits its peak, the power shuts off like a switch. At 7800, the mill isproducing 84 hp and by 7900 the power drops to 60.5 ponies. "This isindicative of a highly tuned pipe," explained chief dynoman Rich Daly."We tried running it cold and warming it up, and it always showed usthat quick drop off after peak."
Clutch tuners will want to have their sled set to rev up to peak torqueat 7500 rpm and then creep up to 7700 for maximum horsepower. "You'lldefinitely know it if you've clutched the 500 XC too high," said Daly.
By way of comparison, we plotted the 500 XC motor against an older 488Fuji motor to actually see the difference. Bear in mind that the dyno testswere performed in two different shops. It is interesting to note how theperformance mill climbs quickly and drops off once it has hit its peak,while the cruising Indy 500 motor makes steady increases and lingers attop output up through 8000 rpm.
"Another interesting thing we found with the XC motor is that itmade the same power one jet size rich or lean. It's quite unusual, but itwill probably end up helping the consumers make top power without gettingdangerously lean," Daly noted.
1999 POLARIS 500 XC SP
Air Density: 97.0
Fuel: 94 Octane Pump Gas
| RPM | CBT | CBHP | BSFC | FUEL | H2O |
| 6000 | 45.7 | 52.2 | .663 | 34.0 | 95.0 |
| 6100 | 47.6 | 55.2 | .633 | 34.3 | 95.0 |
| 6200 | 49.5 | 58.4 | .626 | 35.9 | 96.0 |
| 6300 | 51.5 | 61.8 | .610 | 37.0 | 96.0 |
| 6400 | 53.0 | 64.6 | .606 | 38.5 | 96.5 |
| 6500 | 54.2 | 67.7 | .604 | 39.8 | 97.0 |
| 6600 | 54.8 | 68.9 | .612 | 41.4 | 97.0 |
| 6700 | 55.5 | 70.8 | .611 | 42.4 | 97.5 |
| 6800 | 57.2 | 74.1 | .600 | 43.7 | 98.0 |
| 6900 | 58.4 | 76.8 | .594 | 44.8 | 99.0 |
| 7000 | 59.7 | 79.5 | .595 | 46.5 | 99.5 |
| 7100 | 60.5 | 81.8 | .597 | 48.0 | 99.0 |
7200 | 61.7 | 84.6 | .595 | 49.4 | 99.0 |
| 7300 | 62.7 | 87.2 | .591 | 50.7 | 99.5 |
| 7400 | 63.3 | 89.2 | .590 | 51.7 | 99.5 |
| 7500 | 63.5 | 90.7 | .585 | 52.2 | 100.0 |
| 7600 | 63.2 | 91.5 | .593 | 53.3 | 100.5 |
| 7700 | 62.8 | 92.0 | .606 | 54.8 | 100.5 |
| 7800 | 56.6 | 84.0 | .661 | 54.6 | 101.0 |
| 7900 | 40.2 | 60.5 | .898 | 52.5 | 101.5 |
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.