Superchargers vs turbos vs altitude

[jbz]

It is said that a supercharged engine behaves like a normally aspirated one when operated at altitude. At 1500m above sea level, both these engines will loose about 18% of the power compared to sea level. A turbocharged engine will loose 3%.The pressure at 1500m is about 850mB, 1013mB at sea level. A 2006 MCS that makes 125kW at sea level will make 103kW at 1500m.The 2007 MCS turbo at 128kW will make 124kW.

By reducing pulley size on the supercharger it should be possible to get the supercharged engine to make the same as the turbo.
My questions:
1. When this setup is taken down to sea level, Will the ECU see the high boost and maybe retard the timing to prevent knock?

2. With a turbo, will the maximum power be reached at higher r.p.m. at altitude? (the blow off valve operate at higher r.p.m.)

3. Boosted engines make the same power at altitude with less air to cool them down. Can this cause problems?

I think the new MCs engine will be good, it will be more economical and the variable valve timing spreads the torque. The electric pump that cools down the turbo automatically is a very nice touch - no need to leave the engine idling to cool the turbo down. A standard turbo
MCS will perform better at altitude than the standard supercharged MCS. I do think that the MCS will loose a bit of its character - that whine is soooo good!

[wow]

Hi JBZ,

Wish I could answer your question but i am not too clued up with the MINI's ecu.
I currently have a 125kw MCS which performs extremely well up here in JOZI but based on your points about the turbo at JOZI altitude, I am very excited about the new MINI S.

If you do not get answers to your questions I recommend you call Steves Auto Clinc or Rob green.

Are you going to get the new MINI?

[Peter2002IBMC]

I had no idea there were so many South Africans here!

I am also looking forward to the R56 MCS becuase of the altitude up here in JHB.

[popey]

I thought the the air got thinner at altitude.

Turbos work better with denser air (fact), infact they love cold dense air.

[Peter2002IBMC]

My understanding was that both superchargers and turbochargers loose power at altitude, but that turbos loose less?

[wow]

Well In Sunny SA it will be hot, dry and my AIR CON will be on full blast in December.

[wow]

All cars lose power when there is less oxygen in the air but the degree at which they lose power varies. Does any one have exact stats on how much a:

Naturally Aspirated engine loses?
Super Charged engine loses?
Turbo Engine loses?

[Peter2002IBMC]

jbz in the first post quotes 18% for naturally aspirated and supercharged engines, and 3% for turbos. 18% sounds high, but after having driven various cars here in Johannesburg and then at the coast, I can believe it...

[jbz]

I got these numbers from CAR magazine. By reducing pulley size you can get a supercharged engine to perform just as well at altitude. I think that if you go too far with the mods and go down to sea level, the engine will knock and it will retard the timing. You will then loose perfromance. If the octane of the fuel is high enough it will be better.

The air flow sensor of the ECU may see the massive airflow and do something even before it knocks. I have done a lot of reading on this but I do not have all the anwers yet. Asking Steves Auto clinic is a good idea (thanks Wow).

[Ken Cooper]

Having lived in the vincinity of 6,000 feet over this past 20 years, I've owned 4 normally aspirated cars and 4 turbos (Mostly Saabs & Audis). With the normally aspirated cars, driving to the coast (sea level) meant having my car morph into a hotrod so to speak. Loved it! With the turbos I've owned, I've never noticed any difference at all. They always responded in a spirited way regardless of elevation.