Well, it's kind of an obvious question, but I don't know by how much? It's pretty hot today.. 90F... Mine went from 11psi to 8.5psi.. Or is there something wrong? Thanks

 

Mine is 10psi on COLD 40 or below days, and 9psi in the dead of summer 90+ so yes, but not as much as you....

 

The density difference of air at 90F and 40F is approx. 10% less. Less air results in less compression or boost pressure...2.5psi Boost difference might suggest a leak...???

 

Well it sounds like you are not comparing winter versus summer just today as a hot day comapared to a not so hot day so as mentioned to lose 2.5 psi sounds more like a leak.

 

Springs don't know what the difference in temperature is. They open with force applied to them. A 9 pound spring opens at that same pressure in 50 or 90-degrees. Unless the spring is suffering from heat fatigue then it should always read the same PSI.

 

Amen !

JET

 

BUT, not everybody runs off spring pressure, i for one dont, and my boost drops too on hotter days, and temp does affect air intake temps and density, boost should be a little lower on hot days. thats why you need to pay close attention to your boost gauge if your car is tuned for hotter temps and then it gets real cold, your boost will rise. on cold days turn the boost controller down.

 

Thanks guys..
I'm going to get the electronic boost controller soon. The stock one is just too unstable. Today is pretty hot again and I punched it and got 10.8psi.. Off topic, but is it just me or the APS fuel pumps gets louder as the car gets warmer? Last night I drove around quite of bit all day, and the fuel pump started to buzz pretty loud.. I thought it was going to blow up or something...

 

" density difference of air at 90F and 40F is approx. 10% less"

Density changes 1% per 11F assuming same humidity and barometric pressure.

 

What you're saying is partially true. Air is more dense on cold days, but to reach a certain pound per square inch the same force has to be applied. If you're using a boost controller that opens the wastegates at a certain RPM, then yes you will get most boost, but like most people we run the stock wastegates which use a spring. And if you sit on that spring in the winter or the summer you weight the same. I don't weigh more in the winter that the summer. But think about what you're doing. You're forcing air iinto a set amount of space, and a spring is holding the door closed. Once the set pressure is applied the spring opens. The spring doesn't know it took longer and more air to reach 9psi.

IF you're turning up boost on hot days (I wouldn't recommend that with hot unstable air and 91 oct) you're compensating for the less oxygen per unit volume, not how much pressure.

 

I'm not getting less boost, i'm just getting a lot less power thanks to the goddamn heat and humidity.

 

I see you have the APS ST. I'm surprised you only have that little of a drop in boost, no matter what the temp.

 

haha true,

 

Haha~ Funny~ I read so much stuff about the boost drop, I put a custom dual exhaust with 3" pipes, so I have a very small boost drop. Zeitronix datalogger showed 1psi boost drop from 11.4 to 10.5psi. Only problem is it's freaking loud!!!!!!!!!

 

If you don't mind, what did that custom exhaust cost ya? Did you use a custome reverse Y pipe or buy one made already?

 

Also, did you upgrade to the Forge Actuator? If so what spring did you use?

 

If you don't have closed loop boost control then boost will defintely drop to some degree on high ambient days.

 

$1500. Custom reverse Y pipe. I didn't replace the actuator nor the spring. Everything is stock. I actually have a overboost problem on 6th gear.. My normal boost is 11psi, but I get 13psi when I WOT on 6th gear... Again I need an electronic boost controller...

 

Very nice exhaust!