After I get my STS kit installed, I'm going to need to have the car tuned. I was planning on just having the typical MAF dyno/street tune done on the car by a tuner. But now I am also interested in the possibility of a 2bar MAP Speed Density tune done for the car.

Please offer your thoughts on these two types of tune, and how they would apply to a stock Vette running more or less the base STS kit. I will not be using any boost controllers, but I will run .5 bar (7lb) springs in dual wastegates.

What are the benifits and drawbacks to each one. I'm looking for a fast, reliable street car, not a track car. I remember hearing that SD is potentially a better tune, but it is also much more involved and tricky. Would this affect longevity of the engine if it were off a little bit? Also, I really want to have the tune be done once, and then be done with it. I don't want to have to tweak it all the time. And like anyone modding their car, I do want optimal performance, but definetely not at the price of reliability (drivability) or increased potential of damaging the engine.

I would have either tune done professionally.

Thank you,
Chris

 

You are going to have a hard time finding someone who can really do the SD tune 100% correctly. So my initial thought is to stick with a MAF tune for now. SD is really not worth the effort for a low boost setup.

If you were going to be tweaking it on your own, or pushing the car really hard... SD would be the way to go.

I run SD and would never go back to MAF, but it took lots of tweaking to get it right.

 

QuickSilver has got it right.

Also ... MAF is cheaper by 230-300$. GM uses MAF to tune vettes.

SD ... is for the big boys ... like CajunDude and perhaps Amer. HP (someday he might get R finished ).

For 7-8 lbs boost on stock vette .... MAF (done right) will give you 100% satisfaction.

 

I tuned my STS car myself using my MAF. The tune is as dead on as you can get for a MAF setup. I set mine for about 11.3:1 and 14 degrees of timing at WOT.

The drawback with a MAF tune is the car has no way of knowing how much boost is present at any moment, since the stock MAP only reads to 0 vaccuum. So, when tuning with a MAF, you need to figure out when boost comes on related to throttle position, and adjust the PE enable accordingly. Since boost is not instantly on or off (ex. boost does not go from 0 to 7lbs in a 100 rpm range), I set my PE to come on just as boost starts to occur. So you run a little too rich in the lower boost moments, but when you hit full boost, it is right on.

Bottom line. A good MAF tune can give you stock drivability with tons of power. But you cannot change the boost setting without reflashing the computer.

An SD tune is much harder to get right, simply because it is much more time consuming. You need to log and correct a bunch of times. But if you do get it dialed in, your car will recognize boost, throttle response should be quicker (for the reasons mentioned above), and you can change the boost level without reflashing the car's computer.

That said, I have EFI's custom OS and a 2-bar MAP sensor sitting in my living room, but the car runs so well right now, I hate to mess with it....

Tommy

 

In addition to maxing out the MAP sensor (obviously) you will also likely exceed the MAF sensor's limit of 512 g/s. On a centrifugal blower that is not a huge deal because boost is a function of RPM and can be predicted repeatedly. So on a C/F blower tune you will see the P/E start to climb at a linear rate at whatever RPM the MAF gets maxed out when WOT. I guess it would be the same for a turbo setup. The part throttle P/E would be more difficult to tune though as mentioned above. You could be at anything from 20" Hg to 7 PSI at any given RPM with a turbo and the PSM won't recognize anything over atmospheric so you have to assume full boost in your atmospheric cells to be safe with a MAF tune. A S/D tune would account for all the various RPM and pressure/vacuum situations but you need to tune each cell numerous times to get it right. With an on board wide band and EFI or HPT you can make that a lot easier but it's still some work.

The bottom line is a S/D tune is more accurate but takes much more time to dial in.

 

I max out my MAF, but full boost comes on pretty quick with my turbo setup, so it is not too hard to dial in. In other words, the boost leve lis constant for much of the RPM range.

Tommy

 

The main problem with a MAF tune on a boosted car is the limited rage of the MAF. It can only meter so much air and then you have to hard code in additional fuel based on RPM. The point at which it is out of range varies based on the MAF style and where it is positioned on the car and is generally only a concern at higher RPMS (since is this where the really high airflows occur).

The secondary problem with a MAF tune is that the fueling is impacted by any turbulence around the maf (this is why SD tunes are much smoother than MAF). Once above 4k rpms, the airflow calcs are 100% based on MAF frequency.

The one STS vette that I played around with had pretty unsteady readings from the maf under boost. I think this was mainly due to it being positioned right off the intercooler. I would personally move it up near the TB, since this would probably greatly reduce turbulence and provide better laminar airflow.

 

With regard to the MAF, don't start thinking (like I did) that if a 85mm MAF maxes out at 512 g/s, then a bigger MAF will go higher than 512.

The 512 limit is in the PCM code, that particular table can't represent numbers greater than 512 in binary.

 

Does anyone have a "set it and forget it" SD tune? It seems like the people who like SD are the same people who drive around with laptops in their cars making regular tuning tweaks.

Mark

 

I think thats only because "You Can"
Yesterday, I was watching Rick over at Synergy SD tune a car and its definately VERY involved. There is literealy hundreds of individual cells that you have to manually adjust.
I'll tell you what though. I have never been a fan of the DynaPak dyno. But after watching how well he can load the car at different T/P's, RPM, and % of load, I am willing to bet that it is probably one of the best "Tuning" dyno's out there.
And coming from me that means alot, being the fact that I ran the US Dyno division for Dynojet for 4 years, and literally have over 10,000+ dyno runs, It takes a lot to sway me from what I think is the best, Dynojet.

As for my car.. I am definately having a "set it and forget it" SD tune.
Since the pulley change on the KB S/C takes less than 5 minutes, I want to be able to run about 9.5lbs on the street, but turn it up for the track without having to install a new tune. SD allows you to run pretty much any PSI level you want without having to hit the dyno every other day. Like anything though, the tune would not be spot on when you switch, but it would definately work...

 

So, what are the advantages to the SD tune? I've still haven't really seen anyone state exactly what they are. It just seems like if it's more expensive it must be better. If it is good, tell me why? Not trying to start a debate cuz I don't know much about it, that's why I'm asking.

There is nothing wrong with the MAF tune as long as you find a tuner that is willing to spend the necessary amount of time with it. Most are not, not for the $500 anyway.

 

Hey guys,

Just one note about SD tunes. With a wideband hookup you can mathematically auto-tune your car. I know EFILive Flashscan is doing something like that now where the more you drive, the more data you log, and the better it can perform adjustments to your tables.

A while back I started looking into logging data with my EFILive v6 software (not flashscan) and/or Zeitronix wideband (since I had it logging boost vs. RPM) to make programmatic adjustment suggestions to my tune. Only problem was (a) my fuel system was so wacky that nothing was repeatable and (b) I caught wind that EFILive was going to start doing this in a way that was incorporated into their software. Turns out it came true so I never spent the effort.

It may not be "the right time" for SD for most of us yet but I think that time is quickly approaching. Also, with more and more auto-tune functionality coming out from the tuning packages many guys with simple setups just looking for pretty good tunes won't need a tuner anymore. The street is a way better place to tune anyway

 

The advantages are pretty obvious on a boosted car and have been touched on, but I’ll try to state them in more clear terms.

1.The stock MAF can only read so much air (somewhere in the 500RWHP range depending on the car) and the pcm code is also limited on what it will convert that reading into (again somewhere in the 500-600RWHP range ). This requires the tuner to hard code the fuel curve with the PE vs RPM table once the maf is out of range.

This works on a dyno run.. but in the real world, things will change and you might have boost spike or boost lulls in that area where the MAF is out of range. This is obviously a huge problem if you plan to run a boost controller and really use it. The tune has to be set for the max setting and you end up very rich on any other setting.

2.The stock MAF reads the airflow based on a heated wire mechanism (the more current required to keep the temp of the wire stabilized, the more airflow is assumed). The problem with this mechanism (although very good) is that it can be fooled by turbulence. Turbulance become much more pronounced when you start flowing more air (high HP). This results in non optimal inconsistent fueling. Yes, the WB might show a flat AF reading, but that does not mean that each cylinder is really getting what it wants. The situation can be improved by a pull through setup where the maf meters the air on the compressor inlet, but this is much harder to package and can cause other recirculation issues on sudden throtle closures.

3. The maf is reading air outside/upstream from the actual intake manifold. So there is a slight delay of accurate readings in non steady state conditions. The PCM makes up for this by blending the SD calcs with the MAF calcs during throttle transitions below 4k rpms. The problem on a boosted car is that the SD calcs can be way off, since the MAP sensor can only read 1bar 0psi.

An SD tune replaces the maf airflow calculation with a different set of sensors. The SD calc is based on MAP, IAT, RPM, and the misnamed VE table. It is a very simple calc and works like this.

charge_temp is actually a blend of IAT and ECT, but for practical purposes you can think of it as IAT.

The things that throws a lot of people off here is that they think the VE table is really a Volumentic Efficiency table, Guess what, That is not what it is at all. It is a massflow table that actually stores a number in a rather odd set of units that makes it very easy to perform the above equation. The default units of the VE table are g*K/Kpa. The tuning tools that show the value as a % are a bit confusing and misleading, but most people figure it out by just making slight adjustments and don’t really realize that it is not exactly VE. Everyone thought it was a VE table way back when and this is why it continues to have the wrong name. If it was a ve table you would have something like 80% at 1 bar and 160% at 2bar. You end up with nothing like that in this table since the actual manifold pressure is already part of the base calculation.

Anyway, this SD mechanism of determining the airflow into the motor does not have any of the above mentioned MAF limitations. If the proper MAP sensor and custom OS are used, you can read up to 3bar of MAP (~30psi of boost).

Turbulence are no longer an issue, since you are reading MAP inside the manifold. The thing that makes it hard is that the tuner is now 100% in control of the fueling. You no longer have a sensor that is actually reading airflow to do the work for you. The little secret about tuning a car with a MAF that is in range is that there is really nothing to do besides tweak a few values. SD tuning is a whole new ballgame, and it takes a lot of time to get things just right. This is where a tuner really earns his money and I don’t see how anyone could make a profit doing it. It is very time consuming and requires very expensive equipment (an old dynojet just won't cut it). I guess you could do it pretty quickly if you were doing cars that were all very similar.

Anyway, the biggest difference you will notice in an SD car is smoothness. It is hard to explain, but it feels much more refined. The other thing you will feel is much better throttle response. It’s not that it is horrible with a MAF, just better with SD.

There is an argument that MAF will adjust better to weather changes… but this is really a mute point on a boosted car that is out of the MAF range in the first place since it has no adaptability at all.

I have been living with my SD tune for a few months now and have had no problems with it at all. I took some time to figure out a few things, but now it seems to be quite happy all the time. The problem is that I have to keep tweaking it as things change with my car. This is mainly related to changes I have been making and problems I have been having with my fuel system. Once I get my fuel system stabilized I should no longer need to mess with the tune (but most of us car guys can never leave well enough alone).

I hope that helps explain it.

 

You da man.. I would love to spend a day with you to learn how to SD tune my car... Teach me O master...

 

Very well said. At least someone was able to name the units utilized in the VE tables. The question has been asked on other boards, and I haven't seen a straight answer yet.

 

Thanks for the explanation! It'll take me a little while to go through and digest it as most of that chit is over my head at this time but I'll take a crack a learning just what the hell your talking about. Need to learn tuning sooner or later.

 

Thanks for the detailed explanation, Quick!

 

Thanks, American HP and QuickSilver2002 for you qualified expert input.
I read your stuff three times. If Rick had the time, I would like to see his comments as he has been doing Speed Density tunes for some time.

I would say a good SD needs to be done on dynopak as well.

SD is the only good way to go in my opinion to high PSI well.

MAF relocation has/is being used by Synergy, LPE, Calloway and I would absolutely guess that others are as well.

It also my opinion, many LS motors have blown up here

because of improper MAF tunes at high rpm

and

PVC, oil in the intake, maf, plugs

all leading to bad detonation.

 

Awesome write up thanks

 

Are there any average fuel consumptions differences between MAF and SD?

Mark