My car usually makes 10-11 lbs boost on warm days which I have set through a manual boost controller but on cool nights the boost tends to sit around 15 lbs. I know that cool dense air makes more hp but I dont understand how it has anything to do with the amount of boost being generated through the turbo. Anyone have a good answer?

Thanks
Rick

 

you almost answered your question yourself. Cold air is compressed by the turbo and then heated up and pushed into the intake. Now lets say that normaly @ 85f the turbo takes in 10x of air and compresses that to 10psi.
On a colder day like 60f the turbo is taking in 10x of air but it has way more power and then it expanse to lets say 12psi.

basically, cold air has more air in it so when compressed and expanded you get more psi.

hope that helps im not the best at explaining stuff but i know what im talking about

 

you can even see a 1-2 psi spike after washing your car (assuming you got cold water on your intercooler).

 

What xile6 said. It's normal to see an additional 2-3 psi. You seem to be getting a good bit more though.

 

Makes sense. Thanks.

 

It varies more if your boost reference is based off the turbo housing, not the intake manifold. Regardless, a manual controller will always vary with temp, since the spring inside the WG and MBC work differently at different temps, as well as the air interfacing with the springs.