Boost Reduction with AC on? Options

[Geddes]

It was a fairly hot day today (over 30 degrees celcius) and I was cruising down the highway with the ac on which I don't normally have on.. and noticed that the car was not boosting as per normal..

I know the TSVS setup will reduce boost levels if it thinks its seeing knock, so with the very hot air im assuming it was pulling a bit of boost for that reason, but having the ac system turned on drops the boost even more (I have no actual numbers to give you as I dont have my boost guage hooked up yet), but for comparison, the car with the ac off will peg the boost needle near the top (on a colder day it will hit the plus sign above the top of the guage) but when i turn the ac on, it only makes it to about bar 4 of 6 on the guage..

TLDR version: any one else with a GT-4 with no boost controller installed notice a reduction in boost with the ac on? or is mine just doing something odd..?

for reference, I checked between ac on and off in 3rd gear every time.

[stephen_lee]

both wrong. engine output * rpm = exhaust flow. if you produce 100 HP at the crank, at 2000 RPM, exhaust flow will be the same no matter what accessory load there is on the engine. im betting the lower boost numbers has to do with the added heat in the engine bay from the ac condenser, or some kind of stock boost reduction.

DEATH has a/c on his 3s that doesnt reduce boost. BUT its ran on a switch, bypassing the stock setup...