Boost Pressure Theory ?

[newman]

@Inn-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.

I think he’s got a blower though… Does the BPV control boost on those?

[99_civic_si]

This is the smartest, most knowledgable thread ever on NYSpeed. Cheers to good info.

[jetlounge]

@newman

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.

What else is wrong that hasn’t been clarified so far? Still trying to learn here…

@newman

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.

Understood but I’m not clear. My assumption is that since colder air is more dense than warmer air, each cubic inch passing thru the MAF-Blower-TB-Engine chain is packed with more air…so it’s jamming up the chamber with more pressure.
Wouldn’t hotter air result in less post-compression pressure?
Also, isn’t it possible to actually get better efficiency…assuming we don’t really know where we were on a VE curve before the air temp drop?

@Inn-Tune

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.

So if I understand correctly, the MAF + IAT interpolates pressure, MAP is known, but still uses IAT. Does one beat out the other in terms of efficiency, consistency or reliability?

@Carnut

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.
More often than not MAF based systems handle climate (elevation, temperature, barometric pressure, humidity) changes more efficiently than MAP based systems.

First off, your posts and Mike’s answers to my questions always kick ass. I always learn something new. That, and the NWS threads is what keeps me coming back to NYSPEED.

@Carnut

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.

Wouldn’t that really only be a marginal difference though? How much pressure drop is lost to a thin sensor in a MAF? If I assume approx .5psi on a A2W intercooler, the change in MAF elimination should be a mere fraction, no?

@Carnut

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.

I understand and absolutely agree on cheap tuning.
So I guess I am def hearing that from an OEM standpoint, MAF > MAP ? OK.

Now on that same hypothetical system which accounts for changes in tables based upon formula and pressure change…I assume it can only go so far? Meaning, it can account for some differential in boost pressure due to ambient factors, but slapping on a smaller pulley will have a similar effect, right? And my assumption is that you can only go so far with an aftermarket bolt on, before the stock ECU can’t effectively manage it?

Another question, let’s take standalone tuning out of the equation. Instead you have a piggyback on stock MAF system, and the option is to tune based upon MAF sensor input, or by adding a MAP sensor and tuning off of that. Is there one method that is more efficient than another, or is it simply the MAP (high HP goals), vs MAF (drivability goals)?

[Carnut]

High horsepower and great driveability can be had and thats not a problem if you take the time needed to dial important parameters in.

If you are using a piggy back on a system that is already MAF based then the best way to tune is to use compensate the maf values and only add fuel to your base map when necessary ( assuming you are using stock injector sizes). This again depends on the software and hardware you are using but this works well with something like DSMlink etc. Every car is a little different depending on many factors like how the ECU interprets data, what type of sensor you have etc…

[cdvma]

(speaking generally)

Its a weird way of thinking about it but all else equal, more boost pressure measured at the intake could be worse. In essence, the air isn’t making it into the engine as easily so its “stacking up” in the intake. For example if you replace a intercooler with a less efficient one. You suddenly get a few extra lbs of boost but lose HP. Vice-versa getting a good intercooler you often see less boost but things feel better or the same.

But in reality we step on the gas when its cold and the car is faster. The engine still processes the same CFM but the density is greater. Its obvious if you measure MAF volts wide open in Jan vs. August. So the engine is eating denser air and producing more HP but that means the compressor is working harder…

@newman

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.

I’d agree with that explanation. I’m certainly not a thermo expert but it makes sense to me.

[Carbonfiberhooded]

@99_civic_si

This is the smartest, most knowledgable thread ever on NYSpeed. Cheers to good info.

:word:

These boys know their shit!

[Inn-Tune]

@newman

I think he’s got a blower though… Does the BPV control boost on those?

On a 1.8T GTI the T is for turbo. Don’t you own a VW now bud? Or did he remove the turbo setup, install a blower, and it’s time for me to put my foot in my mouth?

I know the OP has a blower…

@jetlounge

So if I understand correctly, the MAF + IAT interpolates pressure, MAP is known, but still uses IAT. Does one beat out the other in terms of efficiency, consistency or reliability?

Actually MAP is not necessarily known. Some cars have MAF and IAT, but not MAP, just baro pressure. Others have MAF, IAT, baro, and MAP. I agree with Don that having all 4 works best for efficiency at low throttle conditions on most stock vehicles, but again once you start modding there are some issues with MAFs. For example they’re affected hugely by placement and the diameter and construction of the housing they’re placed in. On a properly designed stock vehicle with mild cams you can stick the MAP sensor just about anywhere in a plenum of adequate size and you’ll get a good reading just fine. That said, I’ve tuned high HP turbo cars with heavily modded engines that suck so much air per intake event that they pulse the plenum hard and placement of the MAP sensor drastically affected the oscillations from these pulses. The first time this happened I got a big smile on my face because I knew the setup was going to make some serious jam. It took some trial and error to find the best spot to get a MAP reading on that manifold, but once I nailed it the oscillations went from huge ones of 15-20 psi to about 0.5 psi. Yup I’m saying that boost pressure in that first example of this was actually consistent at 20-21 psi, but the MAP sensor was reading 7-27 psi bouncing around and simply moving the MAP sensor made it read 20-21 psi. The gauges weren’t reading it because the pulses happen far too quickly for them to respond. Think of how many cycles an engine completes in a second… Needless to say the car was impossible to tune until this was resolved because it was pulling fuel and timing values from 7-27 psi which are obviously hugely different.

@jetlounge

First off, your posts and Mike’s answers to my questions always kick ass. I always learn something new. That, and the NWS threads is what keeps me coming back to NYSPEED.

Awesome!

@jetlounge

Wouldn’t that really only be a marginal difference though? How much pressure drop is lost to a thin sensor in a MAF? If I assume approx .5psi on a A2W intercooler, the change in MAF elimination should be a mere fraction, no?

Don has dealt with a lot of Mitsus that have karmann vortex MAFs with honeycombs in them. Many of those are a markable restriction to airflow at moderate HP levels.

Hot wire MAFs are generally FAR less intrusive.

@jetlounge

Now on that same hypothetical system which accounts for changes in tables based upon formula and pressure change…I assume it can only go so far? Meaning, it can account for some differential in boost pressure due to ambient factors, but slapping on a smaller pulley will have a similar effect, right? And my assumption is that you can only go so far with an aftermarket bolt on, before the stock ECU can’t effectively manage it?

The smaller pulley will drive the blower faster, making it pull greater vacuum into it, drawing in more air. This extra air that results in extra boost will be metered by the MAF. Whether the ECU is mapped for that or not is another story, but the air is metered so with a good retune you could go back and forth between pulleys without issues.

@jetlounge

Another question, let’s take standalone tuning out of the equation. Instead you have a piggyback on stock MAF system, and the option is to tune based upon MAF sensor input, or by adding a MAP sensor and tuning off of that. Is there one method that is more efficient than another, or is it simply the MAP (high HP goals), vs MAF (drivability goals)?

In a case like that you use both. You tune the MAF scaling for drivability and in boost you use a separate table that adds/subtracts a % duty or pulsewidth value based on MAP readings.

[dftsilvia]

if you have a maf you will be fine. it meters in all the incoming air, plus turbo cars ecu’s have a pretty wide window for this like that.