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How does temperature affect boost?

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Old May 9, 2007 | 02:27 AM
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Default How does temperature affect boost?

For the last few months, under full throttle, my car shows 7-7.5psi at 6,500 rpm in the 70’s. Today it was in the 90’s and I saw 9 psi at 6,500 rpm. Is this the way it goes or is something wrong?


Thanks,

Clayton from Las Vegas
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Old May 9, 2007 | 07:38 AM
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I always see a few lbs more boost in colder weather.
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Old May 9, 2007 | 08:00 AM
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Originally Posted by LV Vette
For the last few months, under full throttle, my car shows 7-7.5psi at 6,500 rpm in the 70’s. Today it was in the 90’s and I saw 9 psi at 6,500 rpm. Is this the way it goes or is something wrong?


Thanks,

Clayton from Las Vegas
According to KB:
10 degrees (F) air charge temperature = 1% HP
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Old May 9, 2007 | 08:08 AM
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You would usually see higher boost in colder weather with a SC. Maybe you have a little belt slip that is more pronounced in the colder weather???
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Old May 9, 2007 | 09:06 AM
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I suspect Belt slip as well....

I see about 7-8lbs in the summer and 9-10 in the winter....
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Old May 9, 2007 | 09:12 AM
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I think it is pretty common you will see less boost during hotter weather.
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Old May 9, 2007 | 10:28 AM
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Originally Posted by Vince99FRC
I think it is pretty common you will see less boost during hotter weather.
In ssome cases heat=preasure, as in our tires while driving, closed containers left in the sun, balloons left in the sun gains pressure and blows, our motors heat up and expands. just my opinion
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Old May 9, 2007 | 10:53 AM
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Originally Posted by tramminc
In ssome cases heat=preasure, as in our tires while driving, closed containers left in the sun, balloons left in the sun gains pressure and blows, our motors heat up and expands. just my opinion

Last edited by FreddyG; May 9, 2007 at 11:27 AM.
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Old May 9, 2007 | 11:00 AM
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Uhmm I would double check your facts… cold air is more dense then hot air and that is why centrifugal superchargers make more boost when its colder outside.



Mike

Last edited by Skunkworks; May 9, 2007 at 11:49 AM.
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Old May 9, 2007 | 11:02 AM
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Originally Posted by LV Vette
For the last few months, under full throttle, my car shows 7-7.5psi at 6,500 rpm in the 70’s. Today it was in the 90’s and I saw 9 psi at 6,500 rpm. Is this the way it goes or is something wrong?


Thanks,

Clayton from Las Vegas
I would double check things because you should loose boost pressure as temps go up.


Mike
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Old May 9, 2007 | 11:26 AM
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Originally Posted by Skunkworks
Uhmm I would double check your facts… cold air is more dense then hot air and that is why centrifugal superchargers make more boost when its colder outside.



Mike
You were the guy I was hoping would jump in and correct me. I'm Sorry for the misinformation, but I got that screwed up in my head. Thanks for the correction Mike!
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Old May 9, 2007 | 12:47 PM
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Originally Posted by longdrive70
You would usually see higher boost in colder weather with a SC. Maybe you have a little belt slip that is more pronounced in the colder weather???
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Old May 9, 2007 | 03:02 PM
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I agree the colder air is more dense and therefore the boost should read higher. This is due to the compressing air inside your intake and heating it up therefore expanding and creating higher pressure. But would also depend on temp of the motor. Boost is only reading the resistance of flow essentially. So as engine temps increase and metal expands the clearances can get tighter and therefore can create more resistance to flow depending on condition of the engine. Not to mention that the tolerances in the actual supercharger will get tighter as temperature rises increasing the efficiency of the supercharger substantially. Just a guess. typically though assuming the supercharger and motor are both completely broke in and in good mechanical condition, you should see less boost as temps increase.
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Old May 9, 2007 | 03:44 PM
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Originally Posted by Skunkworks
Uhmm I would double check your facts… cold air is more dense then hot air and that is why centrifugal superchargers make more boost when its colder outside.



Mike

This is my understanding as well.

VR
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Old May 9, 2007 | 05:02 PM
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All I know is, when it's cold out the car goes like stink. When it's hot, it still goes like stink, just not as good......
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Old May 9, 2007 | 05:07 PM
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Originally Posted by LV Vette
For the last few months, under full throttle, my car shows 7-7.5psi at 6,500 rpm in the 70’s. Today it was in the 90’s and I saw 9 psi at 6,500 rpm. Is this the way it goes or is something wrong?


Thanks,

Clayton from Las Vegas
an eyeball on the boost gauge while driving is not an accurate mesaure, especially @ 6500RPM in a SC vet. Things go by WAY to quickly for the brain to register. Also mechanical boost gauges are none to not be 100% accurate. get your self a map sensor so you can actually log boost, that will tell the whole story.
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Old May 11, 2007 | 08:18 PM
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Originally Posted by LV Vette
For the last few months, under full throttle, my car shows 7-7.5psi at 6,500 rpm in the 70’s. Today it was in the 90’s and I saw 9 psi at 6,500 rpm. Is this the way it goes or is something wrong?


Thanks,

Clayton from Las Vegas
Sounds like your BOV may not be working right all the time. May be time to take it apart and replace the rubber diagram if thats what it has.
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