I have a friend that says 'speed density is a ghetto inaccurate way of measuring a motors fuel requirements', and spent a long time trying to explain that MAF is the way to go, and aftermarket speed density systems would suck if someone would make an aftermarket MAF..

If Speed Density sucks, why do all the aftermarket ECM's use it?

 

Tell him he's stupid, MAF is an excuse to not have to tune the engine perfectly for the mods/requirnments & the maf does the rest, when you go big horsepower you want to tell the computer what to do & have it done properly & not altered in any ways, when you go BOOST the MAF goes crazy because of its inability to measure that much flow/pressure, & if they were to make a maf that could it would become less accurate down low, & every bit of mistake a maf makes is a world of a difference. Speed desnsity is the way to go with big horsepower cars & when you knwo what you're doing, maf is not only a restriction but plain sucks for big power cars, especially boost! but for small HP cars go maf cuz its easier to tune since its fixes those mistakes you made

MAF is basicly like VNR on your televistion, that option thats blends the image in when your watching cable & the quality sucks

 

It doesnt, your 'friend' needs to get a clue.

If its so "ghetto" and "inaccurate" then perhaps he should go to FAST, eMotive, Motec, etc and show them how its done

 

 

well... the actual conversation we were having was about the LT1 SD vs LT1 MAF computers. i haven't done any research on this... so these ramblings are just what i have "common sensed" together. feel free to join in on the conversation.

it's my understanding that SD uses VE & RPM to determine airflow. it uses the AIT & Barometric pressure to determine that airflows density. i think MAP & TPS might play a role in this, but i think those are mostly used to figure engine load to control timing.

when you modify you car, you change (improve hopefully) the VE. this is a set table in the computer, right? ... so how does the computer know about this extra airflow? unless i am mistaken... it doesnt... which is why an AFPR works on an 93.

with a mass air car you have an actual sensor reading the actual airflow. if you improve the engines VE... the MAF will see this. why would you want to guesstimate at your airflow when you could know it's actual flow?

thanks

incorrect... you still need to tune a mass air car.


go ahead and call yourself stupid since you're busting out the name calling.

MAF doesnt go crazy under boost. infact... my car performed perfectly without an FMU, using the MAF to add my extra fuel for the extra AIRFLOW it registered. the only problem i had was when the MAF reached it's upper limit & couldnt read any higher. is this the fault of the "mass air" theory behind engine managment? no... the "fault" is GM's. they never intended an LT1 to flow anywhere near that much air. the same reason we don't have 3 bar MAP sensors on our cars. from GM's standpoint... there is no reason for it. anyway... like i said... MAF cars have no problem with reading boost.


i suspect you're you're guessing that...

 

MAF is a good way to accurately meter the incoming airflow, especially at low throttle positions. This is why GM (and many others, like Bosch) uses it on their larger motors - it's very helpful in allowing them to hit emissions targets, as the margin for error shrinks considerable as the engine displacement and power level increases. SD may not be accurate enough to hit the latest emissions targets, especially as the vehicle ages. GM's implimentation of MAF doesn't provide for very accurate measurements as the airflow reaches WOT levels, but that's of little concern to the factory as emission testing and fuel economy is not measure in this region of operation.

I wouldn't say that the use of a MAF system allows the OEM to get lazy in their calibration efforts; anyone who's played around with a MAF-equipped LT1 should know better than to say that it's a trivial task.

SD isn't quite as accurate, but obviously it's not a terrible system, either - most foreign manufacturers have been successful using it on their LEV and ULEV engines (which are typically smaller than American engines in the same class). I wouldn't call it a "ghetto" system by any means.

The bottom line for OEMs is that MAF is a bit more accurate but costs more, which is why it's only used when necessary. In the aftermarket, SD reigns supreme because of its lower cost, the additional flexibility in routing intake systems, and the lack of high-airflow MAFs. Like anything else in life, there's tradeoffs between the two systems - we've just got different goals than the OEMs do.

 

We have a winner IMHO this is the main reason GM switched back to the MAF system in 94.

Actually it uses manifold pressure (measured by the MAP sensor) in combination with RPM to determine what it thinks the VE is. I'm sure the IAT sensor has some role in there as well but its not obvious by looking at the programing tables. TPS isnt used for much, just to decide when the car should go into PE mode and when the car is at idle.

 

Since temperature affects density, the IAT is used in an attempt to determine how much air is entering the motor (it's also used to change the spark timing).

TPS is also used in limp-home mode for alpha-N operation, if I'm not mistaken.

If someone wants to check out a "ghetto" setup, play around with a Suzuki TL1000 bike. As it has some pretty large cams, the vacuum signal at idle is fairly rough. So, instead of physically or electronically filtering it, they simply decided to run it in the alpha-N mode of operation at idle, and then switch over to SD at some point in the rev range.

 

exactly... it's more accurate. which is what the entire conversation is about.

Quote:

Actually it uses manifold pressure (measured by the MAP sensor) in combination with RPM to determine what it thinks the VE is. I'm sure the IAT sensor has some role in there as well but its not obvious by looking at the programing tables. TPS isnt used for much, just to decide when the car should go into PE mode and when the car is at idle.

it uses MAP to determine load. the MAP sensor is basically a barometric pressure within the intake manifold. however, once it's under vaccum (engine running) it cannot accurately measure density... because ... well... its under vaccum.

i'm pretty sure the computer gets it's barometric reading from the MAP sensor when you turn the key to "on" but before you crank the car. i think it uses this reading for the duration of that drive. (untill you turn the engine off)

i'm also pretty sure the VE tables are set in the computer... and cannot be changed with out programming... and like said above tempature does effect density.

 

iniviate, what I meant by MAF going crazy is just that, it tops out at 471, sorry you misunderstood.

 

Eric: Forgot about the limp home stuff. I bet it probably used in the tranny tables on A4 cars as well.


Possibly but a MAF system is not without its flaws either. SD is "close enough" for all practical purposes. Besides getting the A/F ratio 100% correct the first try isnt critical, thats what the O2 sensors are there for.

The MAP sensor is not there to measure density, its there to measure pressure. By comparing the manifold pressure when the motor is running vs atmospheric pressure it can calculate the volume of air entering the motor. Since the same volume of air may have different densities if their temperature are different this is where the IAT sensor comes into play. By using both sensors the ECM can come up with an accurate calculation of how much oxygen is actually in the cylinder.

More info here if anyone is interested.


This is correct.

Again correct, but if you make a change drastic change to the motor (say a cam swap) you need to have the programing changed regardless as to whether its a SD or MAF system. And since we know aproperly tuned SD system works just as well as a MAF setup we're splitting hairs.

 

Real world: a MAF system is easier to tune. If your idea of "tuning" is to buy a custom burned chip from TPIS or FastChips or whoever from just a listing of engine specs you'll get better results from a MAF-equipped setup. If you're going to have someone put your actual car on a dyno and map everything out perfectly then SD is probably going to come out on top.

Yes, the MAF is a "crutch" in my opinion, but a very useful one for those who don't have access to all the correct and expensive resources necessary to perfectly dial in a combo.

 

my point exactly !

 

SD has an advantage in that it allows more freedom in intake routing - this really isn't an issue on street drive LTx's for the most part.

It also allows removal of a "restriction". Now if the pumping losses through the maf are significant or even really detectable I would be suprised.

A MAF system *is* more precise and accurate with respect to metering airflow. And it is airflow that you want in the end to determine fueling. A MAF vehicle is also less sensitive to environmental changes, etc. than a SD car is/would be. It is also 1000x easier to get dialed in properly - and when dialed in properly will maintain that tune better than a SD car.

(By MAF I am referring to modern type maf's, not the older 3rd gen style).

Only reason to switch to a SD system would be if you switch to an aftermarket DFI setup - since a MAF option isn't offered. You would be running one of these anyway in a setup wild enough to require freedom from MAF restrictions/intake routing requirements anyway.

I can not think of any reason to NOT run a modern maf setup in any situation where it is possible.


Chris

 

I tried tunning SD and it sucked at low speed.. the car wasn't continuous on its power and I almost hitted 126 on all my blms.. That is why I used again the MAF and the car got the smoothness part throttle offers...

The only problem is the 471 limit... any way above that??