# SD vs. MAF vs. using both



## GM4life (Mar 18, 2007)

Ok some of you that have been tuning for sometime can answer this for me. I know the Aussies use SD/Maf less tuning all the time and that GM has switched back and forth between SD and MAF in the past. What is the pros and cons for SD vs MAF vs using both for tuning or what not? I read about myths, and so on and so on and I'm just confused.


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## 87GN06GTO07IRL (Aug 10, 2009)

I thought it was one or the other? Are you sure you can do both?

I'm not a tuner, but from what i read, s/d on f/i motors and Maf on n/a motors is ideal for ease of tuning.


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## GM4life (Mar 18, 2007)

I'm just getting my feet wet myself. 

I thought stock its using MAF and MAP readings depending. Being moded like with FI I'm not sure. Stock MAP's and ECM's can't/not set-up to read pressure. There is alot of info on HPTuners website but I don't know where to start. I'm thinking maybe I sould learn the basics of tuning NA first before FI. Sad thing is I don't have a NA car to mess with.


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## 6QTS11OZ (Mar 27, 2005)

GM4life said:


> I'm just getting my feet wet myself.
> 
> I thought stock its using MAF and MAP readings depending. Being moded like with FI I'm not sure. Stock MAP's and ECM's can't/not set-up to read pressure. There is alot of info on HPTuners website but I don't know where to start. I'm thinking maybe I sould learn the basics of tuning NA first before FI. *Sad thing is I don't have a NA car to mess with.*


Yes you do! Unless you're afraid of the wife. 

I thought speed density was used solely when the MAF sensor was removed. In FI apps it seems SD would be the best choice since the MAF is limited in the amount of air that it can meter. IDK! I'm just a rookie in this area. I think *svede1212* knows a lot about this stuff than most here.


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## HP11 (Apr 11, 2009)

You beat me to it. I was going to say "What about that G8GT?" I've always heard that SD doesn't work well with 'big' cams. I don't know that for sure, however, so it may also fall under the heading of 'myth'.


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## Poncho Dan (Jun 30, 2009)

The GTO is in SD mode up to 3600, then switches to MAF signal.

I couldn't really tell you the pros and cons, other than MAF is slightly less accurate than SD, which _can_ make quick throttle transitions slightly laggy. SD loses the MAF sensor (if you want), makes for a more stable AFR, but is much more difficult/time consuming to tune than MAF calibration.


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## svede1212 (Nov 1, 2005)

I don't think I'm the end all of tuning but I have gained some knowledge especially with this car. MAF/MAP is what is used stock. Car manufacturers like the MAF as it can deal with changes caused by aging of a car over it's lifetime and ease of tuning. The MAF can not react quickly enough to air flow in transition so the comp uses the MAF for more steady state flows and a blend for transitions. Even people that have MAF tunes can benefit from having a properly tuned VE table for SD as it uses that in those transitions. I went SD because the stock MAF on a LS1 is a bottleneck as is the stock MAF on a LS2. You can go to a bigger MAF such as the LS2 MAF on the LS1 or a 100mm one for the LS2. FWIW the stock LS2 MAF is 85mm feeding your 90mm TB. You need to retune to use a different MAF and at that point you could have just saved the cost of the MAF/tune and just gotten a SD tune. A properly tuned SD tune doesn't really need a MAF at all and the throttle will feel very crisp. From what I've seen big cammed cars work better in SD because of things like the high overlap causing reversion which allows air to backflow and mess with the MAF. It is even more so on intakes like the Vararam intake which places the MAF as close to the TB as possible.


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## jpalamar (Jul 22, 2008)

Here are some interesting read, there is a link to an article in the thread on page 2 that is decent as well.

Why not use MAF for entire RPM range?


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## Poncho Dan (Jun 30, 2009)

jpalamar said:


> Here are some interesting read, there is a link to an article in the thread on page 2 that is decent as well.
> 
> Why not use MAF for entire RPM range?


I just read that, good info for tuning n00bs. A lot of the throttle response stuff I knew about already... but I'd have to disagree about the MAF becoming inaccurate close to the TB. I'm personally running 100%MAF just fine, and my sensor is maybe 3-4" in front of the TB.

I'm going to do a full SD tune this summer, time allowing. I went 100% MAF because it's quick & dirty and it works fine. I got into some real tail chasing trying SD, and I simply didn't have the battery life in my laptop (and therefore patience) to log, then park & tune SD more than once. MAF tuning I could squeeze in 4 calibrations before the battery went out.


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## GM4life (Mar 18, 2007)

6QTS11OZ said:


> Yes you do! Unless you're afraid of the wife.
> 
> I thought speed density was used solely when the MAF sensor was removed. In FI apps it seems SD would be the best choice since the MAF is limited in the amount of air that it can meter. IDK! I'm just a rookie in this area. I think *svede1212* knows a lot about this stuff than most here.





HP11 said:


> You beat me to it. I was going to say "What about that G8GT?" I've always heard that SD doesn't work well with 'big' cams. I don't know that for sure, however, so it may also fall under the heading of 'myth'.


Unfortunatly the wifes car is the V6 thats what she wanted and HPTuners don't work with that ECM. They rather go were the money is.


Poncho Dan said:


> The GTO is in SD mode up to 3600, then switches to MAF signal.
> 
> I couldn't really tell you the pros and cons, other than MAF is slightly less accurate than SD, which _can_ make quick throttle transitions slightly laggy. SD loses the MAF sensor (if you want), makes for a more stable AFR, but is much more difficult/time consuming to tune than MAF calibration.


Humm. 


svede1212 said:


> I don't think I'm the end all of tuning but I have gained some knowledge especially with this car. MAF/MAP is what is used stock. Car manufacturers like the MAF as it can deal with changes caused by aging of a car over it's lifetime and ease of tuning. The MAF can not react quickly enough to air flow in transition so the comp uses the MAF for more steady state flows and a blend for transitions. Even people that have MAF tunes can benefit from having a properly tuned VE table for SD as it uses that in those transitions. I went SD because the stock MAF on a LS1 is a bottleneck as is the stock MAF on a LS2. You can go to a bigger MAF such as the LS2 MAF on the LS1 or a 100mm one for the LS2. FWIW the stock LS2 MAF is 85mm feeding your 90mm TB. You need to retune to use a different MAF and at that point you could have just saved the cost of the MAF/tune and just gotten a SD tune. A properly tuned SD tune doesn't really need a MAF at all and the throttle will feel very crisp. From what I've seen big cammed cars work better in SD because of things like the high overlap causing reversion which allows air to backflow and mess with the MAF. It is even more so on intakes like the Vararam intake which places the MAF as close to the TB as possible.


Thanks for the reply Svede, that helps. I was thinking about going with the LS2 MAF and tuning around that. I also was thinking about should I invest the time and money in just switching to a 2 bar setup instead. 


jpalamar said:


> Here are some interesting read, there is a link to an article in the thread on page 2 that is decent as well.
> 
> Why not use MAF for entire RPM range?


That is a good read.


Poncho Dan said:


> I just read that, good info for tuning n00bs. A lot of the throttle response stuff I knew about already... but I'd have to disagree about the MAF becoming inaccurate close to the TB. I'm personally running 100%MAF just fine, and my sensor is maybe 3-4" in front of the TB.
> 
> I'm going to do a full SD tune this summer, time allowing. I went 100% MAF because it's quick & dirty and it works fine. I got into some real tail chasing trying SD, and I simply didn't have the battery life in my laptop (and therefore patience) to log, then park & tune SD more than once. MAF tuning I could squeeze in 4 calibrations before the battery went out.


The comment about the MAF being close to the TB I've heard that sharp turns intake pipes and filters mounted on the MAF is bad too. Seems like some people have not problems with that too.:confused


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## svede1212 (Nov 1, 2005)

Poncho Dan said:


> I just read that, good info for tuning n00bs. A lot of the throttle response stuff I knew about already... but I'd have to disagree about the MAF becoming inaccurate close to the TB. I'm personally running 100%MAF just fine, and my sensor is maybe 3-4" in front of the TB.


It isn't that it necessarily going to cause a problem but that it can. First the VR is right on top of the TB (some have had to trim the MAF to keep the TB blade from hitting it) and it depends on the amount of reversion that the cam has. That back washing of air can give inaccurate readings. You'll see some people that have no tuning problems at all and some that can't get it tuned right.


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## Poncho Dan (Jun 30, 2009)

Reversion being dependent upon lobe overlap? I have a very vague understanding of what cam lobe/lift/profile/overlap affects.


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## GM4life (Mar 18, 2007)

We talked about cams in the past. Large duration and tight LSA cams run choppy because the intake and exhuast valves are hung open at low speeds. Reversion is like backwash it can occur on the intake and exhuast side of the valves. Low vacume in the intake can make a car run rough, the piston is pushing some of the compression out the intake side. Any restriction or valve being open on the exhaust side can have reversion deluting the intake charge with exhaust within the cylinder.


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