So yesterday it was 28 degrees and I’m seeing 10.3psi on my 9.5psi pulley. In the mid thirties I saw 10.0 , so when we hit the teens I am thinking, jackpot!
Sure, I know the colder it gets, the denser and more boost…but that got me thinking.
1 - Upstate, Canada and Alaska…do they boost like crazy??
2 - A little more serious. My ECU is flashed by TRD, and its based on the MAF, as there is no MAP sensor. Assuming it accounts for air flow, but not pressure, do I assume that this system is NOT as efficient for a/f management as a MAP system? If the systems tables are based on load, airflow and RPM, then the colder it gets (and more boostier I get)…if that’s not accounted for by the reflash ( I assume it can only guess, or at best take intake temp into account and use a formula to figure estimated pressure), then I am running leaner, no?
Would a MAP based system be more advantageous where you have high fluctuation in temperature and land elevation?
If you were to go with a more efficent intercooler i think its not unusual to see a # or 2 of more boost.So the outside air in effect is acting like an inproved intercooler.That is my guess.I have never driven my GN when its cold out to compare boost #s…The only way to know for sure if its leaning out would be to use a wideband.
Colder air is more dense so of course it’s going to make more boost. If you’re tuned for summer conditions, you need a winter tune so you don’t lean out.
Factory boosted cars are usually okay in the winter but they are pig rich in the summer.
ok, i get it. but is there a difference between MAF and MAP based tune? My assumption is that a MAP based tune would be more efficient/advantageous to account for the seasonal fluctuations.
if the maf is before the SC then its reading the extra airflow and your fine. if the maf is after the SC then its seeing little or non of the extra airflow
but a pound of boost is nothing to worry about unless your tune is already on the ragged edge. plus its cooler air to begin with so its less likely to detonate anyways
^
i don’t know if I understand that.
Wouldn’t the amount of air before and after the SC be the same? It will be more dense after the blower, but since you can’t create more air molecules, only the pressure and temperature changes, not the airflow?
also just because you have a lower ambient temp, doesn’t mean you have “extra airflow”, right? or can a MAF determine the density of the air as well?
All things being equal, won’t the measured air flow in the MAF be the same regardless of temp, whereas the MAP would sense the pressure increase due to the density of the air?
wait a second, I see half truths. Winter tune is “different” due to denser air. If you are seeing higher boost pressure that shouldn’t necessarily cause your tune to be lean as most tuning programs are pressure vs rpm dependent. So if the boost goes up, your tune should jump into the next “cell” on your tuning map and give the correct amount of fuel. There are also many options in these programs that could fix this problem (such as an IAT correction factor to name just one) which most people won’t tune for as it would be difficult to do properly seeing as you can’t make the weather swing 50 degrees in a single tuning session. Typically, you’ll just tune all your extra “options” to safeguard an overly hot situation to retard timing or dump extra fuel so you decrease the chances of frying your motor rather than using them to correct the tune for changing weather.
but on a system that is MAF based, how does that work exactly? Without a pressure sensor, is it estimating based upon ambient temperature from the IAT and MAF airflow?
Is my assumption that a MAP based fuel management system beats a MAF or is that not correct?
the air before the turbo / super is atmospheric pressure @ a higher velocity
the air after a turbo / super is a higher pressure at a lower velocity
take 2 maf sensors that are exactly the same, and put one before the turbo / super and one after the turbo / super, and they will give VERY different readings during boost
and if your IAT sensor is working properly and your car is tuned properly, you AFR should NOT drasticly change just because of cooler air, the IAT is there to tell your computer how much correction to give the AFR.
any car that runs lean in cold weather and rich in warm weather has a shitty tune on it
Colder weather climates might tend to produce denser air but you also have to account for the elevation changes as well per location.
MAF systems are always more accurate when it comes to fuel metering. There are a few different MAF sensor types that measure a rushing column of intake air in different ways but in the end provide the same kind of data. Rather than explaining how each type of sensor works and how the data it provides is interpreted I think based on your question it is more important for you to know that MAF based systems have a much larger range of fuel control over the wide operating and climate conditions an engine is to see on day to day service.
MAP based systems are much easier to tune from scratch than calibrating MAF tables and thus require much less user input to get the car running. Tens of thousands of man hours by factory engineers and engineer techs are put into making a single calibration that a PCM/ECM/ECU is to use to run a car well at -32 F all the way to 120+ F.
MAP based systems are more efficient in power production on turbocharged/supercharged cars because by eliminating the MAF in front of a turbo you lower the inlet pressure drop which increases the efficiency of the turbo/supercharger.
Almost all modern fuel injection systems whether MAP or MAF based use an Intake Air Temperature sensor to sense the temperature of the incoming air. Some MAF based systems incorporate an IAT sensor into the construction of the MAF sensor others have a seperate sensor. Either way it is there to help the computer calculate the speed and density of the incoming column of air. Most MAF based systems that do not have an external MAP sensor in addition to the MAF sensor have one built into the ECM so that it can get a basic barometric pressure reading of the outside world. Again all data to help calculate external climate conditions and adjust the fuel trims accordingly.
Many ECUs can extrapolate data in their tables to allow the engine to operate beyond the programmed parameters. This is by no means a permanent solution for your concern, it is temporary at best. Most times it results in an overly rich condition or one with timing pulled, something deemed safe by the manufacturer.
More often than not MAF based systems handle climate (elevation, temperature, barometric pressure, humidity) changes more efficiently than MAP based systems. That is not to say that properly programmed MAP based system cannot preform just as well. It’s just been shown that MAF based systems time and time again provide better driveability and overall performance than a MAP based system and is the basis of why most OEM manufacturers use MAF based systems. After all what good is 400 hp and 5 miles to the gallon when you can have 400 hp and 25+ mpg. A good example of this is the highway mileage a decent LS1 can achieve.
When it comes to performance, MAP based systems are used for maximum power production and ease of tuning. When HP and drag times are your goals MPG are a second thought. Good driveability can be achieved with an individual tuned MAP based system it just takes a serious amount of time to dial it in correctly (based on what type of software you are using). Most aftermarket systems that are reputable have a good amount of fuel and spark trims you can adjust to tailor to your individual setup. You pay for 4 hours of tuning you get a 4 hour tune. You pay for 30 hours of tuning you get a 30 hour tune. In the end you get what you pay for.
When comparing what the OEM does for tuning of an ECU and the thousands of man hours it always amazes me when someone tunes a standalone from scratch and expects it to be perfect in 4 hours. It’s just not possible to replicate the type of driveability (that everyone expects) in that amount of time.
Unless you have a leak after the MAF this is incorrect. The blower does not generate air…it only compresses it…so the air still all has to go by the MAF to get there unless you have a post MAF air leak.
Also cooler air isn’t less likely to detonate in all conditions.
Correct on the first issue.
Don already posted a lot of good info. I just want to clarify that MAFs cannot provide the ECU with adequate info without an intake air temp reading, so one is always used, AND the same goes for a MAP based system. Temperature and a baro sensor readings are used to determine air density on MAF AND MAP based systems if the car is going to operate properly in changing atmospheric conditions.
I also want to add that drivability and gas mileage can be very good on MAP based systems, but I agree that OEM apps generally benefit from running a MAF sensor. Also drivability on modded turbo/supercharged setups is often better on a MAP based tune because people love to ruin the closed loop intake system the OEM application had with VTA BOVs etc.
There is a whole lot of wrong in this thread, but i’d like to point out that initial density in adiabatic compression is unrelated to any pressure differential.
But as for the reason you see more BOOST in the cold, it’s probably because at a lower temperature, you’re moving more air mass, which is pushing you further out of the blower’s efficiency. More heat = more enthalpy = more post compression pressure.
You are both correct. The sensor will read differently there even though the amount of air has not changed. The turbulence has a huge effect on the readings. Some MAFs read more accurately in a blow through application than others.
So how does loosing boost in cold conditions as of late fit into all of this?
Car is a 1.8t GTI with Revo Tune. When the temps are below 30ish boost seems to drop off 2-4 PSI. Any relation or crappy tune?
That could be due to a ton of things since you have a turbo setup. The ECU controls the boost control solenoid so it could be set to lower boost when it’s this cold, you could have a leak, etc. etc. Too many possibilities.