TedG

I am buying a supercharged bike, and I live at altitude 4500 feet and ride at even higher alts. My question for you is how badly does altitude effect the performance of your vehicle?
The bike has monster power, and after an ECU flash it will have approx 260 rear wheel horsepower. But I am hoping up here is is still a monster and I don't need to re-gear the SC.
Any experience? Does altitude have a reduced effect on SC vehicles. Turbos have a waste gate and it just opens with enough boost. But SCs are gear driven and are fixed.
A cool detail, the SC spins up to 130,000 rpm.

Racer1735

SC engines are able to make power at high altitude when normally-aspirated engines are struggling. Altitude will come in to play but is a lesser factor than otherwise. Regarding turbos, the waste gate doesn't boost power. It comes into play to regulate boost pressure and not blow your engine.

Eritosthenes

Last year I took I-70 across Colorado. At the Vail Summit exit (8,700 ft) I paddled Red back to 4th at 80mph and stomped on it. The E-Force Roots-type supercharger was still making HUGE horsepower at that altitude.

Vet Interested

Red? You name your car?

Garry in AZ

Aircraft as far back as before WW2 have used supercharging to compensate for lower air density at altitude.

TedG

Very true,
BUT those supercharges were designed and geared for altitude. Whereas this SC was designed for sea level.
So my question remains. Is the power loss at altitude with a SC as noticeable as with NA?

csf

I have a (factory installed) supercharged Audi and nothing seems to change its power delivery . . . . very smooth and even in hot and cold, sea level and mountains ( East Coast ).

That said, you are getting a motorcycle with 260 hp . . . thats one hell of a ride. Is it really a major problem if it runs " only" at 250 instead ?

Good luck.

TedG

True, but the thing at sea level will loft the front wheel in fourth at 80-130 just by rolling on the throttle. I still want to be able to do that up here. The good part is after a bit of research I can get gears for $280 in different stages to bring most of the power back. But Stage 1 gives 15 hp at sea level, stage 2 gives 30 hp at sea level and there is a stage 3. Before I buy I just want to get a good idea of the effect that altitude has on SCs.

TxLefty

I'm sure that there are some tables out there somewhere that can help you tune for different density altitudes.

dmk0210

WWII aircraft were able to change the gear ratio for the blower. They would run the blower at slow speed at low altitudes, then engage a different gear ratio to run it faster at high altitude.

You can change your pulley size to to the same thing. The only difference is you can't do it on the fly.

This is where turbos have a bit of advantage. You can use a boost controller to tune more or less boost under different conditions.

TedG

I agree. We will see how the thing runs up here and then make a decision. I just got a call from the dealer and the factory excepted my order and can expect delivery in March. How many years is it till March?

dmk0210

The conversion table says 1 month = 100 years when waiting for cool performance parts.

Good luck with your project!

IansInGarage

I don't know why it's thought that supercharger or turbo or NA make any difference in altitude. You loose power because the air is "thinner". This affects the "air pump" that is our engines the same no matter how it's getting this air. There are formulas online to see the estimated HP drop; you'll notice they have no variables for turbo/supercharger.

All this being said, 260hp at sea level will dyno around 35 less HP at 4500ft. This is assuming that the bike can compensate for elevation without a whole new tune. Also assuming same gas, although it's 93 octane by sea for me; and a lot of mountains only see 91. Either way that's crazy HP in something under 700lb.

Ben101er

My wife named ours, Scarlett. To me, it's a car, but to her, it has a personality.

dmk0210

Maybe I'm misunderstanding this comment, but Forced Induction (turbo or super charging) pumps more air into the engine than it would be able to pump through itself at atmospheric pressure.

If I'm able to pump something like 3 liters of air per revolution in an NA engine, then using Forced Induction, I might be able to pump 6 liters of air through the engine. This doubles the amount of fuel and oxygen the engine is consuming no matter what the altitude is. If I spin the turbo or supercharger faster, it is pumping even more air per revolution of the engine. Very basically, you are pushing more air into your air pump (the engine) with another air pump (the turbo or supercharger).

Also keep in mind that the air is not only thinner (oxygen molecules more widely spaced) at high altitudes but also has less pressure due to a lower weight of less atmosphere above you. (just like why the weight of ocean water will crush a sub like a beer can at the bottom of the Marianas trench, yet you can swim comfortably at 10 or 12 feet deep)





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TxLefty

You can push the same volume of air thru at a higher altitude, but you will have to spin your pump faster. So for a supercharger you will normally need a smaller driven pulley and with a turbo you usually end up with more lag. Both limited by the maximum rpm.

dmk0210

Absolutely. In the strive for better performance there are almost always compromises.

Obviously the best thing the OP can do for performance is move to sea level, but that's also a big compromise.

ByRiver

I rode motorcycles when I lived in the San Francisco Bay Area. We did rides to higher altitudes, including the Sierras which is at 10,000 feet to get over the passes. If your bike had carbs, you lost a lot of performance at the higher altitudes. Some would actually rejet the carbs to compensate. There was no performance difference with fuel injected bikes. The ECU compensated for the lower air density. I never saw any decrease in performance when riding my fuel injected bikes over the mountain passes.

And as others have said, a turbo or supercharger purpose is to push more air under boost into the engine, so higher altitude's aren't going to affect it. That's why they are used on aircraft, which is to increase HP at higher altitudes where there is lower air density. It is very difficult to get a prop plane over 14,000 feet unless you have a turbo.

Garry in AZ

Let us know how you like the H2R.