CALL911

iTrader: (17)

So, I have been a fan of MAF tuning over SD. I have always seen it as a MAF will constantly sense the differences in temperature, altitude, barometric pressure, ect. and your computer will adjust for it. While if your car is tuned as SD, it is tuned under a specific temp, altitude, ect. and when you drive it under different conditions other than exactly how it was when it was tuned won't be as accurate as there is nothing to sense to make adjustments anymore.

Many people go the SD way because MAF's do max out eventually. I have found this to be a small bump in the road, as a good tuner can continue to fill in the tables from experience.

What I would like to know is; How do guys with SD tunes still have good tunes when there is no adjustment anymore? Talking with more people who do the SD route, it seems even with great differences (like the car was tuned at altitude in the heat, and still drives great closer to sea level in the cold), that their SD tuned cars still perform very well. I just would like to know how it all works.

I am by no means a tuner here, so you may have to keep it somewhat simple.

redtan

iTrader: (5)

What you forget is that an SD tune still has sensors to adjust for altitude and heat. The calculations for SD are based on MAP and IAT readings. If you tune it in all aspects, the computer will be able to adjust for the varying conditions.

I myself have not yet encountered big altitude change, but I've had the same tune in 90* hot and humid summers and in 0* bone dry winters and everywhere in between. Never had a problem with AFR or timing as the tune is setup to adjust those parameters given the temperature and pressure seen.

buddhaz06

iTrader: (8)

Don't mean to steal thread but is there an advantage to going SD? I need a tune and I need new intake piping. Wondering if I should go maf or SD. Cam & bolt-on ls6

1slowbusa

iTrader: (8)

I have always been told that you will get a better throttle response with an SD tune than with the MAF.

Ed Wright

iTrader: (1)

Not if the tuner has a clue. I've had many bring them to me to change them back. Never a loss in response or anything else.

CALL911

iTrader: (17)

Ed is an expert here, so I definitely trust what he has to say (he has tuned mine before a long time ago).

So, redtan, when you say you can tune in all aspects, what do you mean? How can you set a tune for multiple different temps?


Buddyhaz, there are advantages and disadvantages to doing either SD or MAF. The biggest advantage of the SD that I can see is that at a certain point (especially in high HP boosted cars) that your MAF will be maxed out, and you'll need a tuner who really knows their stuff to tune after its maxed, where as there is no maxing an SD tune. That being said, for a bolt on car with a cam, you are not going to max your MAF, so I would recommend a MAF tune for your setup.

Krom

The D in sd is for density, as in air density.

The computer calculates air density by using air temp (iat sensor) and atmospheric pressure, so it can adjust for changes in either (atmospheric pressure will show changes in elevation, and weather like a barometer)

buddhaz06

iTrader: (8)

Thanks call911

redtan

iTrader: (5)

Well you have bias and IAT tables where you can set fueling and timing based on what the temperature of the intake air is. So if you're seeing IATs in the single digits you set a different fuel and timing curve than if you're seeing IATs in the triple digits.

CALL911

iTrader: (17)

That makes sense. Thank you for the info.

This thread is all about learning for me and any others looking to further educate themselves on the topic, so if anyone else has any input, feel free to add.

Ed Wright

iTrader: (1)

Ever wonder why GM's multi-million dollar factory race cars (like 24 hrs at Daytona) have had MAF sensors?
An old friend of mine is a retired GM calibrator (or tuner) tells some very interesting stories about how long they spend on calibrations, and where they hauls a group of cars to so they can actually tune for extreme conditions. He finds it very strange a guy can have a car for one day and think a speed density "tune" is going to be correct. He says "I guess if the car owner can't tell the difference, it's close enough." Thing is, the MAF doesn't simply measure air flow, it measures the air mass, or density. Speed density uses very different correction tables than a MAF calibration. No way to develop those correction tables in one day, in one location. Don't care how smart you are. No way to do it with a spread sheet. Ever notice those tables don't make a pretty graph?

Btw, why the hell are some guys shutting off DFCO?? What could possibly be the point? It improves fuel economy and emissions, with no down side.

mm_n_p

I agree, because I started out tuning SD before I understood how to tune the MAF correctly.... and now that I have been tuning for a few years and somewhat know what I'm doing, by comparison it's much easier to tune the MAF over SD, with no negative effects that I have encountered. This is from mostly NA and a some Low Boost tuning experience.

RonSSNova

iTrader: (3)

I found this post interesting from HP tuners.

http://www.hptuners.com/forum/showth...ll=1#post14397

I'm still in MAF only and the car runs well. I've been tuning it with help from CTD here and it does take time to get it nailed so that Commanded matches measured on the wideband. I have been doing it at the dragstrip and the stalled auto does mak it interesting.

I still need to do the VE. We will do that on the dyno when we get the chance.

Ron

CALL911

iTrader: (17)

So this may be a dumb question, but what is the difference between the PE table and the VE table?

MontecarloDrag

iTrader: (3)

VE table is the fueling source for SD calculations. If the MAF is working it has little effect, however if the car is in speed density VE is the main fueling table.

PE table is Power enrich, it adds fuel on top of the MAF/VE tables. If fueling is accurate, the PCM will command stoich at WOT, the job of PE is to add the proper enrichment.

Ed Wright

iTrader: (1)

The VE table has more to do with a MAF tune than some seem to think. Very little to do with fuel trims or WOT air/fuel, but does with throttle transitions and tip-in.

Also, if you do enough modified engine, you will find cars that just will not have a PE air/fuel ratio that agrees with the "commanded" (my GM calibrator friend says it is a CALCULATION, not a "command") air/fuel number. Some guys obsess over that and call it "PE table raping"If the numbers aren't what they think they should be. Sometimes in the real world you just won't see the air/fuel ratio you "commanded". Just doesn't always work that way. Especially if COT mode is on. I have had guys tell me they have never seen that. I have seen several. The GM calibrator (That is his job description) did some of the factory tunes you guys see.
He has been a great source of information to me since about 1997.

joecar

When running with MAF, the VE table is used during throttle/airflow transients upto to the dynamic air threshold, and also to sanity check the MAF.

VE is not a fueling table... VE is a cylinder airmass table, it provides cylinder airmass at the operating point (RPMxMAP)... fueling is then calculated on top of this (same with MAF, cylinder airmass is calculated from it)... separating this out allows for a better understanding of how fueling functions...

PE is a fueling table... PE does not add fuel on top of VE or MAF... if active, PE specifies the desired/commanded fueling (if its operating point/cell is the richest of the currently active fueling tables) indendently of VE or MAF... (and, if CL was present, the last/learnt positive LTFT is added on top of PE fueling).

Ed Wright

iTrader: (1)

Read that last paragraph on the Internet? :-)

MontecarloDrag

iTrader: (3)

I know, but I wanted to write it in a way it can be understood by someone who doesn't even know what VE and PE means

decipha

If your commanded AFR isn't what's in the PE table then you have a fuel multiplier in affect, there's no two ways about it

keep in mind there's a bunch of variables in the ECU that the tuning software doesn't give you access to, like more than half