Does denser air give up more #Boost?
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From: Granbury Texas
Does denser air give up more #Boost? I am just wandering if say at 5000' you have 12.5# at 800' Would you see more # of Boost? I am thinking with a DISC supercharger you would have more boost vrs. a turbo charger that has a bleed off valve at a certain #.
So would a dynometer be able to factor the added horsepower with the added boost if thats the case. I know the dynometer can facter in the air density to make a correction but it cant know you could be picking up denser air giving you more boost if thats the case, right?
So would a dynometer be able to factor the added horsepower with the added boost if thats the case. I know the dynometer can facter in the air density to make a correction but it cant know you could be picking up denser air giving you more boost if thats the case, right?
I think it does create more boost because if the air is more dense it will change the A/F ratio and lean it up a bit in turn making more power.... not sure how it works exactly though.
I am just wandering if say at 5000' you have 12.5# at 800' Would you see more # of Boost? I am thinking with a DISC supercharger you would have more boost vrs. a turbo charger that has a bleed off valve at a certain #.
So would a dynometer be able to factor the added horsepower with the added boost if thats the case. I know the dynometer can facter in the air density to make a correction but it cant know you could be picking up denser air giving you more boost if thats the case, right?
So would a dynometer be able to factor the added horsepower with the added boost if thats the case. I know the dynometer can facter in the air density to make a correction but it cant know you could be picking up denser air giving you more boost if thats the case, right?
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From: Granbury Texas
A supercharger that makes 12.5 PSI is only making that amount because of the air density. I think a turbo makes 12.5 PS! because of the way it set-up a blower builds and builds unless it has a blow-off valve set at that PS1-- Right??
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This was my thinking as well. I would like to hear from someone who is certain on how it works so i could know for sure. I was under the impression that if either your wastegate or boost controller was set to lets say 8psi. Then it wouldn't matter if you were at sea level or 5000' the car may build boost a little slower due to the thinner air but i would think you should still see the same 8psi peak boost and therefore still make the same peak power. However I could see on a max effort turbo setup that the turbos may run out of steam a little faster due to having to work harder to create the same boost in a higher DA, where as if your not near pushing the limits of your turbo i would think you'd see comparable boost and power #'s at different altitudes. Again this is just my opinion and i would like to here what the facts are on this.
A turbo/wastegate setup will compensate for the lack of atmospheric pressure, since you have feedback control of the manifold pressure/turbine speed.
On a supercharger, or anything else that is simply RPM controlled you will maintain the same pressure ratio/RPM at any altitude. But, since you're stuck with that pressure ratio, you are at the mercy of the ambient air pressure as the starting point.
Sea level you've got about 100 kpa baro (~14.7 psi), head up to say Eisenhower tunnel in CO, and you're down to low 70's high 60's kpa baro (~10 psi). You loose that 4 psi in the manifold with a blower. Been there done that at my last job. 12 psi in a cobalt SS in MI, 8 psi in CO at altitude
On a supercharger, or anything else that is simply RPM controlled you will maintain the same pressure ratio/RPM at any altitude. But, since you're stuck with that pressure ratio, you are at the mercy of the ambient air pressure as the starting point.
Sea level you've got about 100 kpa baro (~14.7 psi), head up to say Eisenhower tunnel in CO, and you're down to low 70's high 60's kpa baro (~10 psi). You loose that 4 psi in the manifold with a blower. Been there done that at my last job. 12 psi in a cobalt SS in MI, 8 psi in CO at altitude
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To the OP, I would say "yes" more dense (lower altitude) will show for a raise in both boost and power. Humidity has to do a lot with it as well. In the summer on a hot humid day my car will only put out 12#'s of boost at 6500 RPM. On a colder day for the same RPM I can see 15#'s of boost.
Air density has a direct relation on performance of your motor, and I don't see how it wouldn't also have a direct corelation to boost.
The runways in Denver are thousands of feet longer than say in NYC. Air density and altitude are why, as they need more runway to take off.
Air density has a direct relation on performance of your motor, and I don't see how it wouldn't also have a direct corelation to boost.
The runways in Denver are thousands of feet longer than say in NYC. Air density and altitude are why, as they need more runway to take off.
Last edited by CALL911; Feb 9, 2008 at 05:17 PM.
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From: Colorado Springs, Co/ Central, Ca
I have driven, and dynoed both supercharged, and turbocharged engines both hear in Colorado springs 62-7000', and at sealevel in Ca. As elevation increases the supercharged engine will loose boost. I had a Whipple charged 383 that ran 10LBS in ca @400' and hear in colorado it would only make 5~ 6psi I had to swap the pulley to get it back up to 8PSI. It wouldn't even make 10 PSI. Power was down BIG. With a turbocharger the waste gate will maintain the same level of boost as altitude increases, as long as the turbo can keep up. But 10PSI hear in colorado (6600') runs about like 5PSI at sea level. Lag also increases. I ran 10PSI on my 6.0l truck out in ca, Im at 14~15 PSI hear in Co and it runs about the same. 16 PSI is all my T76 will put out hear-vs- in Ca it would make past 20PSI if I let it.
