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Old 05-18-2006, 12:28 AM   #1
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Default Advantages/disadvantages of SD?

I know with speed density you dont have a MAF (advantage), what other advantages are there?

What are the disadvantages of SD?
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Old 05-18-2006, 12:34 AM   #2
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would like to know to
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Old 05-18-2006, 04:05 AM   #3
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Why is having the maf an advantage? IMO its a disadvantage. Its there as a crutch for shoddy ve tables and engine wear over time. If you are tuning and can dial your tune in and check every few months then you are better off without it.
Take a look at the maf, does it look like it enhances air flow? If the answer is "no" then why do you want it?
Does it make the car drive better? No, Does it adjust for minor mods?, yes. Does it adjust for engine wear over time?, Yes.
If you tune your engine yourself do you want it? No.
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Old 05-18-2006, 04:27 AM   #4
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is the majority of the PCM code written and designed around having the MAF as the primary source of air measurement? yes.
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Old 05-18-2006, 05:28 PM   #5
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Did the C5-R guys decide to use a MAF when they could have just as easily went SD? yes.
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Old 05-18-2006, 05:50 PM   #6
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Quote:
Originally Posted by Nithros
Did the C5-R guys decide to use a MAF when they could have just as easily went SD? yes.
Do F1 motors have a MAF? No
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Old 05-18-2006, 06:49 PM   #7
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If we aren't being LS1 specific then the argument boils down to, would you rather try to measure something directly or estimate it? There are lots of analogies to real world situations.

eg. would you work out your house electricity usage by looking at the rating of all your appliances, measure how long you had them all on for each day and then add them for your final result? Or would you just read the meter?

the MAF is a means of directly measuring the airflow into the engine. The main errors involved here are:
1. the MAFs accuracy which depends a lot on the flow characteristics (ie. smooth vs. turbulent)
2. an assumption based on airflow distribution to each cylinder (most code i have seen assumes equal distribution). The more symmetric your intake design is the better.

SD is a way of estimating the airflow into the engine using RPM, MAP and IAT. The errors involved in SD are:
1. the VE table assumes your engines efficiency never changes. Obviously any engine modifications change this. Also, the VE is often calibrated by trail and error using other measurement techniques such as WBO2 sensors etc. which also introduce extra error.
2. estimation of the inlet charge temperature, this is not just the measured IAT value (which is usually far from the cylinders) and can have a complex model of manifold and cylinder head heating effects. This can be a significant error depending on where and how the IAT sensor is located and the techniques used to estimate the cylinder air charge temperature.
3. Manifold pressure, assumed uniform and accurate.

By it's nature SD introduces more error into the calculation and hence why it is often used as a backup to the MAF. But, SD also allows a lot of freedom in tuning especially on wild intake setups where having all the air run thru a single point is not desired. eg. 8 throttle body setups, some twin turbo's etc.

SD is also often used when the airflow requirements of the engine are beyond the MAF's measuring capability, typically on a 5.7L LS1 this is around 8psi boost.

You can see that the MAF offers the most "set and forget" value but has some limitations in serious performance applications. SD offers the most tunability and flexibility but you need to keep an eye on it more and understand it is no panacea of exactness.

For most OEM applications that use a torque-based control model, the MAF is a key component to indicating the torque estimation calculation is giving accurate results and often if the MAF fails many other systems resort to a "default" behavior. This is very evident in the later vehicles that have TCM's fitted where basically the whole trans operation depends on a valid torque signal being transmitted from the ECM to the TCM. Unpicking the puzzle of what depends on what to make SD work the way you would expect is sometimes not trivial. In many cases the complexity of SD far outweighs the perceived gain by removing the MAF. IMO, unless the gains are clear and obvious leave the MAF on.

Hope that helps,

Chris...
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Old 05-18-2006, 09:29 PM   #8
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Quote:
Originally Posted by gameover
By it's nature SD introduces more error into the calculation and hence why it is often used as a backup to the MAF. But, SD also allows a lot of freedom in tuning especially on wild intake setups where having all the air run thru a single point is not desired. eg. 8 throttle body setups, some twin turbo's etc.

SD is also often used when the airflow requirements of the engine are beyond the MAF's measuring capability, typically on a 5.7L LS1 this is around 8psi boost.

You can see that the MAF offers the most "set and forget" value but has some limitations in serious performance applications. SD offers the most tunability and flexibility but you need to keep an eye on it more and understand it is no panacea of exactness.
So you are saying if the Factory System was able to be used to meter more air than is originally designed from GM. Then using a MAF could deffinetly be considered more in High HP Applications.

Would you Consider it to be Quicker to Tune with a MAF? and or Easier?

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Old 05-18-2006, 09:51 PM   #9
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the issue is the MAF being able to meter more air accurately under conditions associated with high HP applications. I don't know a great deal about the design of MAFs and how they achieve accuracy and how that accuracy degrades at high airflows, apart from knowing its a constant area of research because they aren't all that good. Numbers i have heard from engineers range from +/- 5% to 10% accuracy with stock engine style configurations (nicely designed intakes and sotck cam profiles). The day we can perfectly measure how much air is entering the engine under all conditions will be a happy day for many engineers i think

If the MAF is working as a perfect measuring device then there really isn't much tuning to be done. Set your PE table and away you go!

Personally i like the freedom SD gives you to account for your own engine modifications and also removes the restriction on intake designs such as 8 throttle body setups. On a 5.7L bolt-on engine you could barely notice the difference between SD and an 85mm MAF setup.

There are some code specific limitations on the MAF for the LS1 (like the 512 g/sec airflow limit) that SD nicely works around.

Chris...
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Old 05-18-2006, 10:00 PM   #10
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Quote:
Originally Posted by gameover
If we aren't being LS1 specific then the argument boils down to, would you rather try to measure something directly or estimate it? There are lots of analogies to real world situations.

eg. would you work out your house electricity usage by looking at the rating of all your appliances, measure how long you had them all on for each day and then add them for your final result? Or would you just read the meter?

the MAF is a means of directly measuring the airflow into the engine. The main errors involved here are:
1. the MAFs accuracy which depends a lot on the flow characteristics (ie. smooth vs. turbulent)
2. an assumption based on airflow distribution to each cylinder (most code i have seen assumes equal distribution). The more symmetric your intake design is the better.

SD is a way of estimating the airflow into the engine using RPM, MAP and IAT. The errors involved in SD are:
1. the VE table assumes your engines efficiency never changes. Obviously any engine modifications change this. Also, the VE is often calibrated by trail and error using other measurement techniques such as WBO2 sensors etc. which also introduce extra error.
2. estimation of the inlet charge temperature, this is not just the measured IAT value (which is usually far from the cylinders) and can have a complex model of manifold and cylinder head heating effects. This can be a significant error depending on where and how the IAT sensor is located and the techniques used to estimate the cylinder air charge temperature.
3. Manifold pressure, assumed uniform and accurate.

By it's nature SD introduces more error into the calculation and hence why it is often used as a backup to the MAF. But, SD also allows a lot of freedom in tuning especially on wild intake setups where having all the air run thru a single point is not desired. eg. 8 throttle body setups, some twin turbo's etc.

SD is also often used when the airflow requirements of the engine are beyond the MAF's measuring capability, typically on a 5.7L LS1 this is around 8psi boost.

You can see that the MAF offers the most "set and forget" value but has some limitations in serious performance applications. SD offers the most tunability and flexibility but you need to keep an eye on it more and understand it is no panacea of exactness.

For most OEM applications that use a torque-based control model, the MAF is a key component to indicating the torque estimation calculation is giving accurate results and often if the MAF fails many other systems resort to a "default" behavior. This is very evident in the later vehicles that have TCM's fitted where basically the whole trans operation depends on a valid torque signal being transmitted from the ECM to the TCM. Unpicking the puzzle of what depends on what to make SD work the way you would expect is sometimes not trivial. In many cases the complexity of SD far outweighs the perceived gain by removing the MAF. IMO, unless the gains are clear and obvious leave the MAF on.

Hope that helps,

Chris...
that could warrent a sticky me thinks.
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Old 05-18-2006, 10:32 PM   #11
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Old 05-18-2006, 10:43 PM   #12
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Correct me if I'm wrong, but I see some people mention about tuning in SD, then putting the MAF back on and then fine tuning? What does this practice do to improve the airflow/temp management for the car, and result of performance?
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Old 05-18-2006, 10:59 PM   #13
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basically gm plops in ve tables & maf tables from year to year to match the stock motor...when you change parts & airflow basically things change...your ve table changes as well as your maf calibration to some extent...what many of us(including myself) do is calibrate the ve table then re-enable the maf & calibrate that...in the end your wot fueling table should be equal to your actual wot fueling verified via wideband o2 sensor. You will hear from people its not necessary & to be honest it probably isnt necessary but it gives me that warm fuzzy feeling inside knowing all of my tables are accurate rather then tricking the pcm in one direction or another.
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Old 05-19-2006, 01:49 AM   #14
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Disavantage: I live in an area where it can be 40 and dry followed by 88 degrees with 100% humidity within a day. Now try daily driving using SD under those conditions, might as well drive a carbed car. Yes, SD is great. However to many people act like SD is required for every ls1, even bone stock daily drivers, which is a false assumption.
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Old 05-19-2006, 06:14 AM   #15
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Quote:
Originally Posted by SmokingWS6
Disavantage: I live in an area where it can be 40 and dry followed by 88 degrees with 100% humidity within a day. Now try daily driving using SD under those conditions, might as well drive a carbed car. Yes, SD is great. However to many people act like SD is required for every ls1, even bone stock daily drivers, which is a false assumption.
it's b/c the term "Speed Density" just sounds like it means big time racer... It gives people a reason to make a "Fast and Furious" scene their real life at the car meets...

On my old car, I hopped back and forth b/w MAF and SD all the time, the only reason I ever liked SD was just the versatility of the tuning methods and also the ease, not that MAF tuning is all that difficult either.

For the next round of newbs:

FOR MOST LS1s YOU WILL NOT NOTICE SD vs MAF IF EITHER IS WELL TUNED!!! SD IS SIMPLY ANOTHER WAY THE PCM DETERMINES AIRFLOW!!! IT IS NOT WORTH ANOTHER 50 HORSES, IT IS NOT ANOTHER "MOD," AND ONE DAY WHEN SOMEONE SAYS "I'M RUNNING SPEED DENSITY" AT A CAR MEET, PEOPLE WON'T COME RUNNING TO THEIR CAR LIKE FLIES ON SHIT..... I HOPE...
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Old 05-19-2006, 06:37 AM   #16
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Quote:
Originally Posted by txhorns281
FOR MOST LS1s YOU WILL NOT NOTICE SD vs MAF IF EITHER IS WELL TUNED!!! SD IS SIMPLY ANOTHER WAY THE PCM DETERMINES AIRFLOW!!! IT IS NOT WORTH ANOTHER 50 HORSES, IT IS NOT ANOTHER "MOD," AND ONE DAY WHEN SOMEONE SAYS "I'M RUNNING SPEED DENSITY" AT A CAR MEET, PEOPLE WON'T COME RUNNING TO THEIR CAR LIKE FLIES ON SHIT..... I HOPE...
I like this. I might add it to my sig if it wasn't already so big. I agree with you on this Tx.

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Old 05-19-2006, 08:40 AM   #17
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Quote:
Originally Posted by foff667
.... it gives me that warm fuzzy feeling inside knowing all of my tables are accurate rather then tricking the pcm in one direction or another.
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Old 05-19-2006, 09:17 AM   #18
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Quote:
Originally Posted by SmokingWS6
Disavantage: I live in an area where it can be 40 and dry followed by 88 degrees with 100% humidity within a day. Now try daily driving using SD under those conditions, might as well drive a carbed car. Yes, SD is great. However to many people act like SD is required for every ls1, even bone stock daily drivers, which is a false assumption.
I agree with that. I can tell you from personal experience with my car in SD. When the weather changes ie..temp. In SD mode it doesn't compensate for the new conditions.

Now yes I know some of you will say that the IAT should see the temp and compensate, but it doesn't. Follow with me here

In SD my car will run the same times (same 60') in say 45* as it does in 75* and we all know that the DA has changed and should effect the engine. If you take the times you run in 75* and correct them to the the 45* weather conditions it will show that the car should run faster, but it doesnt. Good for a bracket car I guess

Now when I had a MAF whatever corrected times for lower DA said it would run it did. The problem that I have found with SD is that you have to retune it to the weather conditions of that particular day to get the most out of it and to be frank I have no time and patients to do that. I race all year long so the weather conditions go from 90's in the Summer to 40's in the Winter at the track so I would have to retune.

Now to mention a little about daily driving. My car was SD tuned in 75* and this past Winter was fun driving when the temps dropped. It got in the low teens to single digits around here and the car ran like total ***. I could barely keep it running even after long trips when comming to a stop sign. And cold starts were even more fun I never had that problem with the MAF. So right now I'm in the process of switching back to MAF after I change a few things and check the VE table to make sure it's good.
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Old 05-19-2006, 10:25 AM   #19
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Quote:
Originally Posted by txhorns281
FOR MOST LS1s YOU WILL NOT NOTICE SD vs MAF IF EITHER IS WELL TUNED!!! SD IS SIMPLY ANOTHER WAY THE PCM DETERMINES AIRFLOW!!! IT IS NOT WORTH ANOTHER 50 HORSES, IT IS NOT ANOTHER "MOD," AND ONE DAY WHEN SOMEONE SAYS "I'M RUNNING SPEED DENSITY" AT A CAR MEET, PEOPLE WON'T COME RUNNING TO THEIR CAR LIKE FLIES ON SHIT..... I HOPE...
Classic!

I am so tired of hearing about the whole speed density thing and how it's worth more so much horsepower. Use the MAF unless you have a good reason to go speed density is my old saying.
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Old 05-19-2006, 10:31 AM   #20
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me thinks those that haven't seen very positive results from switching to SD just have a half-assed tune that was just lacking some serious thought and planning. Of course there will be those who claim the opposite is true.
Switching to SD is definately a modification away from "stock" operation and it isn't for everybody... that is true.

Obviously some people do not prefer or appreciate the simplicity and consistency of running OLSD mode, and I'd say for them to not even consider switching to SD.

Personally I want the most out of a vehicle as far as power and transitional response. I also don't want to worry about what fuel trims that my code and a collection of hopefully accurate sensors has come up with for me on a particular day. I also do not want to be limited to unleaded fuel. If the fueling and spark need a significant change then I definately want to be the one to do it. That's just me.

Here's something I posted in a recent and similar thread about MAF vs SD"

"A good tuner (with added work) can adjust the MAF table until equal power (to a SD tune) is achieved on a dyno,
but the SD tune will run faster on the track still.

The biggest difference between MAF and SD operation is the difference between transitional and steady-state fueling.

You can imagine a difference like this: With the same TPS, the intake density will sometimes increase, decrease, or stay the same as the engine speed increases. With the MAF, the MAF output allways goes up as engine speed increases.
Fuel-trims or not, this is a source of inconsistancy in the MAF tune, and it has its biggest downside during transitions."
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