Speed Density or MAF?

[Batmanntexas]

What are yall's thoughts on Speed Density and/or MAF tunes? I was under the impression that most newer cars (specifically my 2012 Camaro SS LS3) combined the two from the factory. From idle to a certain RPM, say 3000RPM, the computer relied on SD, but then after 3000RPM, the computer went to MAF only, or anytime you went into PE then the computer would utilize MAF only also.

So, questions are:

1. Is my impression above correct, or am I out in left field?
2. If you had to choose between the two for a forced induction, mild cam (227/243/.629/.629 @115LSA) setup, and mild boost (10#), which would you choose?
3. Why one over the other?

Thanks in advance for any opinions, knowledge drops, etc.

-Scott

[dreksnot]

GM put a lot of work into the hybrid SD/MAF setup on the car for driveability, economy and power. For our stock Camaros, the changeover RPMs is 4,000rpm. It's not an absolute and drastic SD to MAF change, it's a smooth transition. For PE, it doesn't go to MAF only - it uses whatever mode you're tuned for: SD, MAF or hybrid SD/MAF.

MAF uses a sensor that measures the air velocity flowing past it (in Hertz), and the tune calculates the amount of air going into the throttle body by volume. Changing the values in the MAF table changes the air:fuel ratio. SD uses a “set” value for air:fuel ratio from the matrix. So, there's one big difference. Actual airflow versus a predicted calculated value from a set table. However, the MAF doesn't like low airflow conditions whereas SD is a great predictor. And, MAF works great at high airflow, and so does SD. Hence, why GM uses the hybrid model.

Each SD and MAF has its advantage, or disadvantage, but nothing major. Most tuners will go for the quick MAF tune, as it saves a lot of time dialing the tune in. The MAF table is 1x100 boxes, but really only needs about half of the boxes modified when doing things like power adders. The SD table is a 33x33 matrix, and needs more than 70% of it modified, so you can see the amount of work required to tune. Which is best? It's the usual, it depends answer. SD can provide smoother transitions with throttling the pedal (as you can predict).

I wanted the best of both worlds, and tuned both tables to run in hybrid mode. MAF uses the SD table, and SD relies on the MAF table even in the separate modes of operation – it’s not 100% either. What I benefit from is smoother and more reactive throttle transients for daily driving, and at the strip a rock AFR rowing through the gears. Can you get that with either MAF only? – yes, pretty close. Will SD-only work fine for you? – yes, it would.

The amount of work to tune does vary (see the MAF table on the left and the SD table on the right).

[Batmanntexas]

Thanks for the education! Where do I go in HPT to view the SD table that you showed?

-Scott

[dreksnot]

Originally Posted by Batmanntexas

Thanks for the education! Where do I go in HPT to view the SD table that you showed?

-Scott

The factory OS doesn't have the neat SD table (that I showed up above), but you could tune using the virtual VVE tables in the Edit drop down up top. I prefer applying the SD Air Mode patch and you can edit the SD tables directly. After applying the patch, they're located: Engine > Airflow > General > Maine VE > Normal IMRC Closed. SD tuning is not for the faint of heart.

[JMI]

For a reason or another with my TT setup. The drivability is way better with SD than Maf at low speed.Idle would be in the 2600-2800 Hertz area,but when I was coasting or slowing down,it was going in the 2000-2600 Hertz area (below idle) because of the vacuum effect of the turbo's Crazy lean, So if I would add fuel to that section. It had a bad dip in the Maf table that I didn't like and I was always fighting a slight lean or rich at coasting or at idle,so I decided to go SD with the optional operating system. No turning back.

[Batmanntexas]

Thanks all for the info. So, here's the deal: I recently swapped cams, injectors, and upgraded the fuel system. For the camshaft, I switched from the LS9 cam (211/230/.558/.562 @122.5 LSA) to a custom grind (227/243/.629/.629 @115LSA), the injectors are Bosch 95lb @ 3 bar, and the fuel system is a Fore twin pump setup with flex fuel setup. The car has a 2.9L Whipple as well with a 3.75" pulley. Other than the cam, springs, pushrods, and trunnion bushing upgrades, the rest of the motor is untouched.

Prior to the swap, the car idled and drove just like it did the day I drove it off the showroom floor, and got about 24mpg on the highway. The guy who tuned it with the LS9 cam, spent a lot of time dialing in the tune, and as a result the car was awesome. No hot start issues, bucking/surging, etc.

After the swap of the new parts and cam, I had it tuned by another individual. This individual deleted the VVE and went the SD route. His explanation for doing this was due to the Baro resetting every time the MAP would go over 105kPa. Does this make sense to you guys?

I have posted the LS9 tune below (LS9 tune) and the current SD tune (227 Cam). Can you guys look them over and give me your thoughts?

[Batmanntexas]

I didn't choose a radical cam, right? Is there any reason that I shouldn't be able to run a hybrid tune, both VVE and SD? I'm pretty sure that was how my LS9 tune was done. Thanks for any and all feedback.

-Scott

[dreksnot]

Can't load up your tune files - what version of HPTuners have they been save with?

No issue running any of the tune models: MAF only, SD only, hybrid. It just takes a different route to get good results with each/any of them.

[Batmanntexas]

Originally Posted by dreksnot

Can't load up your tune files - what version of HPTuners have they been save with?

No issue running any of the tune models: MAF only, SD only, hybrid. It just takes a different route to get good results with each/any of them.

I'm using the latest beta from HPT, 3.7.706

-Scott

[dreksnot]

Originally Posted by Batmanntexas

I'm using the latest beta from HPT, 3.7.706

-Scott

Well, gosh, that may just be the reason. I'm trying to open it with the latest released 3.6 version.