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      04-12-2010, 10:48 PM   #23
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You're both right. The argument is stemming from the difference between 5.5psi "absolute" pressure (technically 20.2psi absolute pressure)and 5.5psi "relative" pressure (20.2psi absolute at sea level or 17.7psi absolute at 5000'). Both of you are making correct statements -- you're just not using the same standard...
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      04-12-2010, 10:51 PM   #24
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Quote:
Originally Posted by spdu4ea View Post
He's right assuming he's talking about 5.5psi "absolute" pressure (technically 20.2psi absolute pressure). You're right assuming you're talking about 5.5psi "relative" pressure (20.2psi absolute at sea level or 17.7psi absolute at 5000').
I though SC and altitude would want to know more about relative pressure since that's what influences the power gain? Hopefully my balloons and butt lube example illustrates it in laymen terms
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      04-12-2010, 11:23 PM   #25
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I'm between 0 to 250 max above sea level ( stamford connecticut ) and running the 6.5 psi 600 hp kit , dynoing soon .........
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      04-12-2010, 11:54 PM   #26
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Quote:
Originally Posted by m33 View Post
I'm between 0 to 250 max above sea level ( stamford connecticut ) and running the 6.5 psi 600 hp kit , dynoing soon .........
can't wait to see your results since you're fairly local to me.
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      04-13-2010, 12:51 AM   #27
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BobMG, which weighs more at 5,000 feet 100 pounds of feathers or 100 pounds of butt lube?

Ha, sorry had to ask!
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      04-13-2010, 02:14 AM   #28
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Ok I see I emphasize the word QUANTITY and everyone keeps harping on about the ratio. Of course the ratio is the same. There is still 80/20 Nitrogen vs oxygen. But there's less O2 and less Nitrogen. You may end up climbing up to the top of Everest and you may end up getting 2 02 molecules and 8 Nitrogen molecules in each gasp of air (not actual numbers, I'm just trying to illustrate that the ratio stays the same).

And Eugene, the diving example of taking air at a location and compressing it and then taking it to a different location is invalid. We up here joke about bottling sea level air and taking it up to altitude. Although it's a joke, that's what you are taking about. Bottling oxygen rich air.

The air at the second location is LESS DENSE. IT has less of of everything. Why do you think there's less drag at altitude. See how your car accelerates from 250 to 300km/h at altitude? Try that in the thick muggy coastal air and the car takes longer (with more power) to reach 300. The car is much more slippery at at altitude due to less resistance. So is there less air there for a given volume? No, the volume is the same. Thes is just less "stuff" in the air and everything is spread further apart.

I have practical examples where you crank the presssure a couple psi to compensate (on my turbo cars), and you still make nowhere near the power you dyno at sea-level. And the car spools so much quicker at the coast and peaks so much later (with big turbos that are not outside their efficiency islands).
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      04-13-2010, 03:52 AM   #29
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Quote:
Originally Posted by M&M View Post
Ok I see I emphasize the word QUANTITY and everyone keeps harping on about the ratio. Of course the ratio is the same. There is still 80/20 Nitrogen vs oxygen. But there's less O2 and less Nitrogen. You may end up climbing up to the top of Everest and you may end up getting 2 02 molecules and 8 Nitrogen molecules in each gasp of air (not actual numbers, I'm just trying to illustrate that the ratio stays the same).
we told you that lol. But you kept saying the amount of oxygen 5,5psi volume of air at sea level was more than 5,5psi at 5000 ft. This is WRONG. You can understand that now?

And Eugene, the diving example of taking air at a location and compressing it and then taking it to a different location is invalid. We up here joke about bottling sea level air and taking it up to altitude. Although it's a joke, that's what you are taking about. Bottling oxygen rich air.

It is very valid, as inside the cylinder the air has the same amount of oxygen and nitrogen, but when you release that air at sea level vs 5000ft, the molecules will immediately expand at the higher altitude, leaving less actual oxygen/nitrogen available to breath with each breath. He was explaining the partial pressure theory to you

The air at the second location is LESS DENSE. IT has less of of everything. Why do you think there's less drag at altitude.

Thats correct. But what you were wrong on, was the comparison between the parcels of air, same volume and same pressure, at differing altitudes being made up of more oxygen at the lower altitude. Wrong

See how your car accelerates from 250 to 300km/h at altitude? Try that in the thick muggy coastal air and the car takes longer (with more power) to reach 300. The car is much more slippery at at altitude due to less resistance. So is there less air there for a given volume? No, the volume is the same. Thes is just less "stuff" in the air and everything is spread further apart.

correct. You mean less drag? And the air is less dense than at lower altitude. BUT THIS IS CAUSED BY THE LOWER ATMOSPHERIC PRESSURE, ALLOWING THE MOLECULES TO EXPAND, THEREBY SPREADING THEM OUT AS YOU PUT IT

I have practical examples where you crank the presssure a couple psi to compensate (on my turbo cars), and you still make nowhere near the power you dyno at sea-level. And the car spools so much quicker at the coast and peaks so much later (with big turbos that are not outside their efficiency islands).
anyway, we all now get the idea, so we can stop over analyzing this. I believe a smaller pulley is the point for SC at higher altitudes
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      04-13-2010, 03:55 AM   #30
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Quote:
Originally Posted by biglare View Post
BobMG, which weighs more at 5,000 feet 100 pounds of feathers or 100 pounds of butt lube?

Ha, sorry had to ask!
Are you trying to trick me
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      04-13-2010, 03:57 AM   #31
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I think the butt lube since most likely it is used so the contaminants added will be a little over 100lbs
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      04-13-2010, 04:01 AM   #32
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Quote:
Originally Posted by Green///Hell View Post
I think the butt lube since most likely it is used so the contaminants added will be a little over 100lbs
so you also re use your butt lube.. I thought I was the only one

Only problem is when you get some really big pieces, they jam up the nozzle, so I decant mine into a larger Tupperware for easier ejection without mess
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      04-13-2010, 01:47 PM   #33
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Well, I tried to find my aerodynamics and thermodynamics of jet and rocket engines textbook last night but couldn't find it. So, I couldn't find an answer to questions that I was looking for. (Don't ask me how long ago I had this text. Let's just say it was long enough for me to forget.)

What I was looking for, and still haven't found the answer yet, is exactly how the a centrifugal compressor works. What I mean is, is the boost, say 5 psi all the time, or a relative 5 psi. Let me see if I can explain.

If at sea level you add 5 psi to the ambient pressure, then when the ambient pressure is 20% less at higher altitude do you get 5 psi over the 20% less, or do you get 80% of 5 psi, i.e. 4 psi of boost? I strongly suspect it is the latter. In any case, for a centrifugal compressor, you don't get full boost until it is moving fast, i.e. in the top RPM range of the engine for a supercharger.

Unfortunately, the boost is not a simple linear function of the rpm of the compressor. It is an exponential relationship, probably with the exponent being a ratio of the heat capacities of air (1.4). But, at this point, I just don't know. So, with all of that said ...

Increasing the speed of the compressor with a smaller pulley will get you more boost (up to a point). How much smaller do you need to compensate for the increased altitude I cannot say. It is not a matter of, ok, I lost 20% density from high altitude so I need to spin this sucker 20% faster. I will keep researching this.
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      04-13-2010, 01:51 PM   #34
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Quote:
Originally Posted by Bob MG View Post
so you also re use your butt lube.. I thought I was the only one

Only problem is when you get some really big pieces, they jam up the nozzle, so I decant mine into a larger Tupperware for easier ejection without mess
No, no, no. You're doing it all wrong. You must use a proper vessel to decant into. And please, let it sit for at least a half hour before using it. Do some research man. Hmph, those backward Kazak hillbillies .
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      04-13-2010, 03:09 PM   #35
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Gents I will be finished with my VT2 kit on Friday.
Instead of the 100mm pulley which boosts 5,5psi,
Roman supplied a 95mm pulley good for 6,5-7psi at sea level.

Based on the calculated loss of 0,17 bar or 2,46psi at 5000 ft, I would be safe to assume that my boost pressure will be between 4,0-4,5psi.

If it's closer to 4psi after dyno, we may contemplate a 92mm Which is normally a 7,5psi pulley at sea level.
92mm is the smallest pulley you can use with the VT blowers without changing belts and software.

Practical will be better than this speculation
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      04-13-2010, 03:21 PM   #36
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Quote:
Originally Posted by Bob MG View Post
Gents I will be finished with my VT2 kit on Friday.
Instead of the 100mm pulley which boosts 5,5psi,
Roman supplied a 95mm pulley good for 6,5-7psi at sea level.

Based on the calculated loss of 0,17 bar or 2,46psi at 5000 ft, I would be safe to assume that my boost pressure will be between 4,0-4,5psi.

If it's closer to 4psi after dyno, we may contemplate a 92mm Which is normally a 7,5psi pulley at sea level.
92mm is the smallest pulley you can use with the VT blowers without changing belts and software.

Practical will be better than this speculation
That's very good. But, the real question is how does Suzy feel about this?

Cheers.
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      04-13-2010, 07:43 PM   #37
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Quote:
Originally Posted by Bob MG View Post
Gents I will be finished with my VT2 kit on Friday.
Instead of the 100mm pulley which boosts 5,5psi,
Roman supplied a 95mm pulley good for 6,5-7psi at sea level.

Based on the calculated loss of 0,17 bar or 2,46psi at 5000 ft, I would be safe to assume that my boost pressure will be between 4,0-4,5psi.

If it's closer to 4psi after dyno, we may contemplate a 92mm Which is normally a 7,5psi pulley at sea level.
92mm is the smallest pulley you can use with the VT blowers without changing belts and software.

Practical will be better than this speculation
Your drop will be the difference between barometric pressures. At 5000ft you should only loose .15 bar or approx 2psi. I know this from trial and error.
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      04-15-2010, 01:05 AM   #38
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Originally Posted by ersin View Post
That's very good. But, the real question is how does Suzy feel about this?

Cheers.
Well Suzy is bleating like the goat she is!
She just loves me if I OEM slow or blazingly SC fast!
Can't beat real love now can you??
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      04-15-2010, 01:07 AM   #39
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Quote:
Originally Posted by GeorgeSmooth View Post
Your drop will be the difference between barometric pressures. At 5000ft you should only loose .15 bar or approx 2psi. I know this from trial and error.
thanks George. I hear you guys in SA are really high up?
Doesn't the F1 teams still do their high alt testing at Kyalami?
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      04-17-2010, 07:08 PM   #40
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thanks George. I hear you guys in SA are really high up?
Doesn't the F1 teams still do their high alt testing at Kyalami?
Its been years they haven't done any testing here, I think the track is substandard at this stage. I am not sure if any F1 tracks are at altitude in this day and age. Altitude sucks though, my V10 M5 only makes 370whp up here
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      04-20-2010, 03:08 PM   #41
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lol bob! whats the status on the blower man?
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      04-20-2010, 09:56 PM   #42
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Quote:
Originally Posted by e.n335 View Post
We are all getting older
Turbocharging:

The ECU calls for 5.5 psi. Thus spinning of the turbos is not directly related to the engine revs the turbos will provide absolute 5.5 psi at sea-level or absolute 5.5 psi at 5000 feet. In the latter the turbos will have to produce relative 8.0 psi due to less dense air. To be able to provide the same absolute boost pressure at different altitudes the wastegate is used. So 5.5 psi absolute boost pressure at sea-level and 5.5 psi absolute boost pressure at 5000 feet.

Supercharging:

The Supercharger is driven by the crankshaft and has no wastegate. So it provides always the same relative boost at a specific rpm. Using a 8.0 psi pulley will provide 8.0 psi absolute boost at sea-level or 5.5 psi absolute boost at 5000 feet. That's the difference compared to turbocharging when we look at boost only.

BOV's / DV's:

Blow off valves or diverter valves are used both on turbo- and supercharged systems. They don't control boost pressure, they just blow off the boost spike in the air intake manifold when you close the throttle ( 8 throttle bodies in case of the S65 ). The difference between BOV's and DV's is where they vent to.

Anything missing ?

Cheers,
Eugen
Longtime Troller, 1st time poster...

Spot on. To reflect on my own experiences, I have a 2005 GMC Sierra that has been both Supercharged and Turbocharged through its lifetime. Both systems were built for 10lbs of boost at sea level of a 6.0l V8. When driving to Tahoe, CA (6k' above Sea level) from the SF Bay Area, the Procharger would drop down to about 7 lbs max of boost. When I replaced the Procharger with twin Garrett GT3071r's with no other changes to the motor, I still pull the same 10lbs of boost at Tahoe that I would see at Sea level.

Rick
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      04-20-2010, 10:25 PM   #43
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lol bob! whats the status on the blower man?
Two words.....volcanic ash

no actually three...Fuck Volcanic Ash
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      04-21-2010, 09:31 AM   #44
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^ Shit unlucky man

The wait must be killing you
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