Do Ambient Temps Effect Boost ?

[Scatt Nasty]

Hey there just had quick question. Last week here in SV,(5000 Ft. elevation) I was able to hold 20 PSI when the temp was in the low 30-40's... But today It was about 70 degrees and I could barely hit 19 PSI in 2nd and no more than 18 in third. I know nothing is loose. So either A) It's the temp or B) My turbo is starting to go (It has been smoking for about 4 months)

[bova]

cold air is more dense, so it is not odd that you will see higher boost levels when it is colder out.

[bykeryder4life]

yes as said cold air is more dense so boost will be higher and you will be running slightly leaner due to more air present. This is PART of the cold weather cut this car gets for some people...it boosts higher and isnt ready for it so it cuts.

[TRU-BOOST]

If i dont tweek my MBC for temp changes i can see huge differences. I keep it set at 20psi. If the temp drops below 50 degrees that turns to 25psi real quick !!

[bnoon]

Originally Posted by TRU-BOOST If i dont tweek my MBC for temp changes i can see huge differences. I keep it set at 20psi. If the temp drops below 50 degrees that turns to 25psi real quick !!

Our weather is up and down so much in winter, I feel like I'm turning the damn knob every other day on my MBC. With my winter tires I'm only set for about 14 psi right now anyway though... and still spin into 3rd. Dang 205's just give it up to easy.

[FantasmoNegro]

Maybe I am wrong but I thought that our wastegate regulates boost to a specific number no matter what the temperature is. You may spool up faster but not nessecarily more. Again maybe I am wrong, maybe our cars even alow more boost in the cold due to the less chance of temperature sourced detonation.

[bykeryder4life]

the WG does regulate boost, but 18psi of hot air is not the same as 18psi of cold air, the cold one is more densely packed with oxygen atoms so even though the turbo is pushing 18psi and thinks it all good the motor is seeing more air due to it being more densely packed with oxygen so it reads higher boost. Thats a basic- not exact -explanation of how I see it.

[phantom6294]

Interesting... there is a thread here where several people, including me have the exact opposite issue -- the colder it gets, the less boost we see.

Theory that made the most sense (to me) is that the car does not target a boost level but rather targets a specific load. Well, since colder air is denser air, less boost is needed to reach a target load, if in fact that is how the ECU is programmed.

[Hectik1]

Originally Posted by phantom6294 Interesting... there is a thread here where several people, including me have the exact opposite issue -- the colder it gets, the less boost we see. Theory that made the most sense (to me) is that the car does not target a boost level but rather targets a specific load. Well, since colder air is denser air, less boost is needed to reach a target load, if in fact that is how the ECU is programmed.

Yeah. I was thinking the same thing. I posted in the other thread too.

I see less boost when cold.

[bykeryder4life]

I spike higher when cold but then it quickly cuts from my fuel pressure dropping and then its lower boost to redline. it is lower boost overall so you guys are right on that....

[phantom6294]

Originally Posted by bykeryder4life the WG does regulate boost, but 18psi of hot air is not the same as 18psi of cold air, the cold one is more densely packed with oxygen atoms so even though the turbo is pushing 18psi and thinks it all good the motor is seeing more air due to it being more densely packed with oxygen so it reads higher boost. Thats a basic- not exact -explanation of how I see it.

Um, 18psi is 18psi.... if the ECU is targeting a boost target and reading boost level from the MAP sensor, 18 psi is 18 psi. Yes, the mass flow will change because colder air is more dense... but 18 psi is 18 psi.

[bykeryder4life]

well thats basically exactly what I meant, I said how whether hot or cold the turbo always pushes the same psi but the motor see's more air. just didnt use correct terms. The mass air flow will be greater due to the increased density while the turbo is doing 18psi.

[TRU-BOOST]

Even on stock boost control my car always sees more boost in the cold. I can tell you this the ecu sure as hell doesnt use the map sensor to determine boost. I had my map clamp set to 2psi and as long as i used stock boost control, i got stock boost levels. I honestly think the map sensor on this car serves only 2 purposes.... 1 to give the ecu an intake air temp reading ti determine proper fueling, because lets face it the temp at the Maf is uselesa on a turbo car. And 2 to trigger overboost cut.

[wassup61]

stock boost controller will hold stock boost until the wastegate is maxed (on catless exhaust only i guess<---my experience) and then it will start to creep like crazy.

[bova]

this car basically has 3 different mappings for the throttle which controls boost. it bases it off of requested load, boast air temps, barometric pressure and rpm's. there will be more info on this soon.