toddk911

It has been discussed in here plenty that cars, specifically turbo models, seem to perform much better in the cold air/season.

However, on a few cold nights here in FL, I have noticed that I see an extra pound or 2 of boost in 3rd,4th gears, WITHOUT making any changes to MBC.

It is set at 15psi and holds 15 rock solid in the warm temps, but the last few times it was cool here at night (high 40's low 50's), I notice about 16psi in 2nd and 16-17 psi in 3rd,4th.

Is this just the tubo/IC being much more efficient with out the heat and with the same boost settings is able to generate more boost????

Sami951

No clue, but it sure as hell feels downright mad to drive the 951 out there now - it was ~25F in here today, what a rush when the boost hit

pk951

I've noticed that to the other day to it was about 30f my boost gauge is set for 15psi in 4th and 5fth i was hitting 17psi. At those tempatures the air is a lot denser. I think these cars were made for this kind of weather.

cpt_koolbeenz

I need to get my car back together... Its going to be ~ 16 on Sunday! Mmmm high air density...

Jfrahm

Check and see if you are over 1 bar with the engine off. If the barometric pressure is high to start with, you should boost more total.

-Joel.

toddk911

Makes me wish I had the snorkle on the car

I guess this is also how a car responds to water injection.

Perry 951

The cold weather advantage has many performance gains on turbo cars-

1. Cold air = dense air
2. Intercooler gets extra help with the colder air flowing through it
3. DME adds a touch more fuel in cold weather
4. DME uses a more aggressive timing profile in cold weather

I say RUN IT until the snow flies, then park it and be sad.

toddk911

Mine was pretty much stock last winter and still was bad ***. Now, with current mods, can't wait for full winter weather here.

So does the boost need to be turned down if you are seeing extra 1-2 psi in cold air???

TurboTommy

There is a reason why our cars make slightly more boost in cold weather. It is a phenomenon with dynamic compressors that they make more boost with denser air at the same turbine speed. This is the only reason. The turbine has to work less. So depending on the wastegate setup, you'll either have slightly less back pressure for the same boost or slightly more boost for the same back pressure. Intercooler eff. or water injection has no effect since this happens after the compressor sees the air.

Perry, ...I thought the topic was very briefly touched on a while back about the DME advancing timing with colder temps. Correct me if I'm wrong but I think the verdict came back that it doesn't advance timing. I always wondered about this myself.

Justin Browning

I am going to have to slightly disagree with Brian on this one. Don't tuck it away for the winter. Do like I do, drive it all year round.

Perry 951

It does not advance it, it retards it, according to the maps I have seen. FR Wilk had some timing maps on his site

14psi @70f = -17degrees timing
14psi @20f = -19degrees timing

That 2 degrees is not going to net much power, but with the little extra fuel and the late timing for a complete burn, it can do a touch at modified boost levels.

I have tried to do a ton of research on timing lately because of my high exhaust temps. I have advanced timing 2.7 degrees VIA the DME and it helped on the hotter days. Now that it is cold, I have much more flame pops and actual FLAMES from my exhaust. Retarding the 2.7 degrees took most of that away, and retarding 2.7 more gave me a touch of knock.

Ignition timing in a boosted car is critical!! I wish I could tap into the Motronics and adjust where I need it.

toddk911

I always thought that advancing the timing improved performance and retarding the timimg pulled back performance.

Therefore, why would retarding your timing create knock?? Also, why would advancing the timing help on hotter days?? On hot days you would retard timing, cool days advance timing.

TurboTommy

Perry, you have it backwards. Even according to your post from FR Wilk, the timing is advanced 2 degrees on the colder day.

toddk911

It seems that it has to be a good drop in temps though to see a 1-2 psi gain. Usually 20-25 degrees, for me to see this psi gain, about 55 degrees out or colder. I wonder if it keeps gaining if temps keep dropping or does this taper off.

Anyone here in super cold climates notice more of a gain, i.e. 2-3 psi, on below freezing days???

I know in Maximum boost Mr. Bell states that for every 15 degree drop in intake temps, you can safely add 1 psi more boost. I would guess ambient temps to intake temps would be about 2:1??? So for every 30-40 degree drop in ambient temps, you could run 1 more pound of boost safely.

Any scientific types have info on this???

H2Opumpr

Today I had to turndown the boost 2 psi, I was hitting 17 psi easily. Temps were mid 50's, car was strong. Before about 85 F I was barely seeing 15psi. Seems as though my car is as consistent like most everyone elses on the board. Also tires are spinning in second at part throttle..... not full throttle. Kind of unnerving... Feels as though there is no progression for power control with the throttle. I am guessing I am running leaner at part throttle hence more power. I would like to change this. any thoughts?