900 ACE Turbo data!

Dynotech tests the newest Ski-Doo big-HP motor
2019 Ski-Doo 900 ACE Turbo Dyno test
The new turbo just got tested! The power and torque numbers are in, and it is impressive! The first Ski-Doo 4-stroke 900 ACE Turbo tested at DynoTechResearch.com in Batavia, NY was a preproduction demo sled with 625 miles on it, brought in by Billy Howard of Howard’s Inc. Ski-Doo in Coudersport, PA.

I always emphasize “preproduction” because over 29 years of printing and reporting dyno data of preproduction and production sled engines we occasionally see changes upon final calibration. On the preproduction ACE 900 Turbo, we saw 162.8 CHP (corrected horsepower) and 117.1 LB/FT of torque with a lean 13.7/1 A/F ratio (air/fuel or pounds of air consumed for every pound of fuel) and a stingy .43 BSFC (pounds of fuel consumed per horsepower per hour) at full throttle. This was measured by Dynotech on our fully instrumented SuperFlow 902 engine dynamometer. Boost pressure was measured at 11 PSIG (Gauge pressure).

■ Comparing to the 850
But wait, there’s more! The new ETEC 850 motor measured on the same DTR engine dyno, made at peak, 166 CHP and 113 LB/FT of torque. So how come this new boosted 4-stroke is so strong and looks so great on paper?

It’s important that we compare not only the peak HP, but also the overall HP and TQ curves of these two engines in graphic form when comparing data. We did this as tested at the DTR facility at 1000’ altitude. First, let’s compare midrange horsepower and torque. The small but mighty turbocharger on the ACE builds boost instantly with no discernable lag which creates a whopping 143.5 CHP and 116 LB/FT at 6500 RPM where the ETEC 850 makes only 116.7 CHP and 94.3 LB/FT. Granted, some riders don’t spend a lot of time in the midrange wide open, but trail riders who run corner to corner say they enjoy this sort of flat torque and horsepower plateau.

It is also important to note that while the ETEC 850 enjoys a 3.5 peak HP advantage over the Ace 900 Turbo, according to our data, it’s only in a small window from 7600 to 7900 rpm—above and below that, the Ace 900 Turbo’s over-rev and under-rev HP is higher. That equates to great performance from this new 4-stroke without the necessity of spot-on clutch tuning. And if operating revs are perfect in the morning, as the temp rises during the day, both engines’ revs will surely drop some due to the loss of HP in the warmer, less dense air, with lower oxygen content. Loss of revs on the ETEC 850 might cost further HP, but would be less noticeable on the ACE Turbo.

We understand the ACE 900 Turbo’s boost pressure, like the Sidewinder/Thundercat, changes with altitude. The altitude compensating boost control of the Ace 900 Turbo is great, but complicates matters when evaluating and comparing engines with a dynamometer.

Any engine will make torque and horsepower in proportion to the “density” of the air it breathes. Both temperature and barometric pressure affect the number of oxygen molecules in each measured gulp of air an engine takes in—the more O2 molecules, the greater the HP capability.
2019 Ski-Doo 900 ACE Turbo Dyno test Renegade X-RS
■ Tech behind the dyno
Since 1987, DynoTech Research has published snowmobile engine dyno test data based on the most optimal “standard” correction, which is the estimate of torque and horsepower the engine might make at 60° F dry air at sea level 29.92 in. hg (inches of mercury) barometric pressure. Air temperature is straightforward; potentially adding 1% to actual HP for every 10-degree temp reduction (assuming fuel flow is similarly increased). Altitude has a great effect on engine output—some 3% lost for every 1000 feet of altitude increase! Barometric pressure (baro) is affected partially by weather, but altitude has the greatest effect on it. Sea level standard baro is 29.92 in. hg (which equals 14.7 PSIA) where A stands for Absolute or pressure above full vacuum. Here at DTR at 1000 feet in altitude, the standard baro is 28.72 in hg (14.17 PSIA).

What does all of this mean? If the ACE 900 Turbo does, indeed, adjust boost pressure to compensate for reduced baro, then if we dyno tested at sea level the 11 PSIG (G= gauge pressure, or pressure above atmospheric) boost we measured during the DTR dyno session would have been .53 PSIG lower, or 10.5 PSIG boost pressure which would have resulted in about 3% lower corrected horsepower, or 157 CHP.

What if you went up to 5000 feet in altitude? Then the standard baro pressure drops to 24.83 in hg (which equals 12.2 PSIA). So if we’re correct in assuming that the ACE 900 Turbo’s ECU adds boost as atmospheric pressure drops, then the sea level boost pressure of 10.5 PSIG would become 13 PSIG at 5000 feet in altitude and sea level HP would be maintained. So if we were riding at 5000 feet in 60 degree dry air, the ACE 900 Turbo would still make 158 actual observed HP and the ETEC 850 would lose 3% per 1000 feet or 15% and make only 141 actual observed HP! And at 10,000 feet altitude that turbo advantage is magnified— 158 HP for the ACE 900 Turbo vs 116 HP for the ETEC 850! You can see how altitude compensation is a huge advantage for this new Turbo! But if our SuperFlow engine dyno were at 5000 feet in altitude, the correction factor would show the ETEC 850 making the proper 166 CHP. However, the same correction factor would be applied to the over-boosting ACE 900 Turbo giving it 182 CHP. This is about what the engine would make at sea level if that 13 PSIG boost level were maintained.
■ Keeping it simple
The best way to accurately dyno test an altitude compensated turbo engine is to dyno it at sea level. It would be interesting to locate the ACE 900 Turbo’s ECU baro sensor and pressurize it to 29.92 in. hg to set the boost pressure at sea level HP levels. But, then we’d have a bit less actual atmospheric pressure forcing air into the turbo. But with all the tamper-proof sensors on factory turbo sleds it’s unlikely to be that simple. For now, I’ll consult with my dyno-savvy engineers to see if making a 3% deduction in CHP to compensate for DTR facility’s 1000’ altitude might make sense. Will BRP make a 200 HP 850 Turbo now? We hope so!
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