Hot/cold Boost Pressure Difference

[Vrdesign]

Hi,

Ive been logging some boost pressures at different ambient temps, also I hooked up a second boost gauge on the wastegate line out of the turbo to see the pressure drop accros the whole system.

14 psi Manifold, 18 psi Turbo @ 30 deg C

16 psi Manifold, 20 psi Turbo @ 20 deg C (tune was done at this temp, 340 rwkw)

17 psi Manifold, 21 psi Turbo @ 15 deg C

Are other people seeing these sorts of numbers?

[I JET]

I like data logging.....Maybe someone more knowledgeable could chime in,,,,.....is the variation in boost pressure with the change of temperature the ecu adjusting boost and timing to suit intake air temps when tuned in closed loop???

[FiftyOne]

Epic thread in progress

[discostig]

Good question, I imagine if humidity was constant that 15PSI is the same volume of air regardless of temp...so ECU might be allowing more power in colder conditions.

The number of years I've been reading here you'd think I'd know by now, hahaha.

Also, good to see someone logging it.

Edited 15/12/14 09:32 AM by -Stever-

[Vrdesign]

It defiantly seems like safety built into the tune as the compressor efficiency seems to change predictably with temp, I'm not sure what else could cause this.

Also, Is a 4 psi pressure drop across the system a typical result? 2.5 hot side, plaz1000, 3" cold side into std plenum

[JVK]

Did this quite a few years ago on the stock system and iirc came up with the same results, 4 psi drop across the system.

[Peppy_t92]

There are a few variables when I comes to boost, mainly if it was tuned in closed loop or open loop... Open loop is just like a bleed valve that can be adjusted for a different RPM, this is quite commonly used and you will see variances in boost pressure through the gears, but I didn't really think that IAT came into play... Closed loop is a PI based system where you command a boost level and the pcm will try to target this value all the time

[ratter]

and it can also be tuned to vary with intake temperature

[Vrdesign]

Thanks, it sounds to me like air temp compensation tables that drive solenoid duty cycles? Probably a question for the tuner

[gaz097]

How many logs at each temperature did you do?