Ski-Doo is gunning to be the "top banana" in snowmobiling. To that end, it has steadily garnered high-end components and made some pretty darned good sleds.
By weight and by volume, there are few that can touch the Austrian-made rotary valve Rotax engine, especially in turbocharging. Although normally reserved for mountain men and their high-altitude needs, the turbo mavens at DYNOTECH thought it might be interesting to put some turbo boost into Ski-Doo's MXZ 670 and see what would happen.
Installing the turbo kit was not a problem, considering the 670 has a side-outlet single pipe similar to the 583. But it was plagued by full-throttle detonation once the turbo was engaged, even at a moderate boost level and plenty of fuel flow. The solution came in the form of a thicker-than-normal rear outlet Fat Boy pipe from FAST.
DYNOTECH had to make a few more modifications to get everything working
okey-dokey. They installed a thicker Crank Shop gasket, which raised the
cylinders and head about .020 inches to reduce compression for operating
at low boost and on lower-octane gas. They also slowed the timing by two
degrees for the same reason.
DYNOTECH managed to pull some pretty good numbers out of this giant banana's 669cc twin. Stock rated horsepower is 122, and its quoted powerband is 7800 to 7900 rpm. At a moderate 7 psi boost, the 670 Turbo hit a mighty impressive 151.1 hp at 7750 rpm. At a still moderate 9 psi boost, the powerband hit at 8000 rpm and cranked out 183.9 hp.
On the down side, while the turbo mod beefs up the MXZ in a major way, it also increases its appetite something fierce. But that was known going into it, and frankly, that's a pretty small price to pay for what you get-a lightweight, low-flying, bright yellow cross-country wonder. Make sure that you don't get hot fudge on you as this banana splits.
1996 MXZ 670 TURBO 7 PSI BOOST
480-470 MJ
Data for 29.92 inches Hg, 60 deg. F dry air
Test: 200 RPM/ Sec. Acceleration
Fuel Specific Gravity: .748
Vapor Pressure: .13 Barometer: 29.52
| RPM | CBT | CBHP | FUEL | AIR | A/F | BSFC | CAT |
| 6500 | 85.8 | 106.2 | 103.2 | 209.6 | 9.3 | .95 | 71 |
| 87.7 | 87.7 | 112.7 | 109.3 | 212.9 | 8.9 | .95 | 34 |
| 7000 | 90.5 | 120.5 | 93.4 | 219.3 | 10.8 | .76 | 31 |
| 7250 | 96.9 | 133.8 | 88.7 | 229.2 | 11.9 | .65 | 30 |
| 7500 | 100.7 | 143.9 | 99.1 | 235.3 | 10.9 | .68 | 30 |
| 7750 | 102.4 | 151.1 | 105.1 | 245.7 | 10.7 | .68 | 39 |
| 8000 | 99.1 | 105.9 | 105.8 | 250.5 | 10.9 | .96 | 32 |
| 8250 | 87.1 | 136.8 | 109.1 | 252.0 | 10.6 | .78 | 30 |
1996 MXZ 670 TURBO 9 PSI BOOST
480-470 MJ
Data for 29.92 inches Hg, 60 deg. F dry air
Test: 200 RPM/ Sec. Acceleration
Fuel Specific Gravity: .748
Vapor Pressure: .13 Barometer: 29.50
| RPM | CBT | CBHP | FUEL | AIR | A/F | BSFC | CAT |
| 6500 | 100.9 | 124.9 | 137.8 | 235.2 | 7.8 | 1.10 | 35 |
| 6750 | 103.7 | 133.3 | 141.1 | 240.6 | 7.8 | 1.06 | 37 |
| 7000 | 107.2 | 142.9 | 140.9 | 247.5 | 8.1 | .99 | 37 |
| 7250 | 114.0 | 157.4 | 140.4 | 257.1 | 8.4 | .89 | 37 |
| 7500 | 116.9 | 166.9 | 140.8 | 263.5 | 8.6 | .84 | 37 |
| 7750 | 120.4 | 177.7 | 141.2 | 275.3 | 9.0 | .79 | 37 |
| 8000 | 120.7 | 183.9 | 139.6 | 283.5 | 9.3 | .76 | 36 |
| 8250 | 111.9 | 175.7 | 136.5 | 285.7 | 9.6 | .78 | 36 |
RPM: Engine crankshaft speed.
CBT: Corrected Brake Torque.
CBHP: Corrected Brake Horsepower.
AIR: Airflow cubic feet per minute.
A/F: Air/Fuel Ratio.
FUEL: Actual fuel flow pounds per hour.
AIR: Airflow cubic feet per minute.
A/F: Air/Fuel Ratio.
CAT: Carb Air Temperature