Highlander

Yashar Fakhari.

m29formula

Going back to the speed density vs. mass air argument. Mass air is a way better system for say a 500 and below hp street car as it delivers way better driveability, but on a turbo or supercharged car it offers one big drawback. It compenstate for the compressing of the air in the manifold and speed density can because it relies on a pressure sensor to come up with its calculations rather than a flow sensor. Now they both read the air, but when it is compressed speed density is way more accurate. Plus the mass air meter actually will run out of tables after a certain cfm rating and that depends on the sensor, I know DSM's actually run out at about 400~hp, tuned one before. After that they lose all accuracy. Getting rid of the air restriction is just a plus to me, eventhough it is only a few hp. If you guys don't believe me, ask any guy in the import world, gasp , that is fast, 10's and lower what he uses, it will be speed density, because they are better for a boosted vehicle. Even most domestic guys that are that fast, especially GN's, run speed density. So, suming it up, they know where there market is, fast car's beyond the factory computer limits, and they designed them for that purpose.

Highlander

Well... i disagree... if you remove the maf limitation you will see that you can tune for the greater airflow.. still use the PE tables and the such...

If our LT1s used the VE Tables like the LS1s do... MAF will always be a better system... With the VE tables it will simply compensate accordingly to pressure, etc...

m29formula

Well we still disagree, I've been to many stand-alone tuning clinics taught by the best tuners for accel dfi and aem ems, who say that speed density is a better system for turbo/supercharged cars because of the way they meter the air. That is beside the point though, and I will say for a street car I think the best setup would be a system that uses a maf when out of boost and a map when in boost combining the two systems, and I will also say that for the most part a mass air system is much better for driving, but that is not what I am arguing. I am say that if you have a high horsepower car that is turbo/supercharged, it will make more power and be easier to tune when in boost. If you have played with a stand alone that uses a maf and one that uses a map you would understand. I have used both a UTEC for a WRX mass air (a piggyback but has total control, uses factory ecu for gauges and such), and an AEM EMS speed density on a DSM. The AEM was ten times easier to tune even at idle. The WRX still doesn't idle right it surges like crazy because of the injector difference and TURBOXS is now releasing a speed density program for it, but the DSM runs perfect not a problem. Now you said that you compensate for the air flow on a mass air car, let me ask you this what happens when you go past the air flow rating which is usually rather low? Speed density will do just pressure and will go to a lot higher rating (29.2 psi with a 3 bar sensor on any motor).

m29formula

This is an image of one of the things I am trying to explain. This was done on a simulation software that is really cool check out simcar.com Now the graph is showing what happens when you floor the car. It shows the flow into the intake manifold, the spike is the filling of air into the manifold not all the air is being used by the motor. This is where mass air vehicles are very inaccurate on turbo/supercharged cars. When the vehicle is floored there is a time between when it is not creating boost until full boost there is a time where flow into the manifold does not equal flow out of the manifold and therefore the mass air car is running rich causing poor spool and prone to more studdering on spool up. This is also a factor into how the car drives, how many times do you fluctuate the throttle on your drive? Many, I'm sure, now each time you touch the gas there is a manifold filling time that is not compenstated for in the tuning, its impossible to tune that out. It all comes down to the mass air reads the air at the throttle body and the map calculates air at the valves. Now the manifold filling has less of a spike on na cars compared to boosted cars, which is why on na cars mass air is a great system, but on turbo/supercharged it is not always the best system. This is why if any of my cars are boosted in one way or another they will be speed density it is more accurate of metering air that is going into the cylinders. The only problem with speed density is that is has set VE tables so tuning is required to get the most out of any mods done. While mass air cars can "learn" as people like to put it. Sorry for the long posts.

97WS6SCharged

You guys both make good points, but honestly, I'd rather have a MAF setup on the street (I'll eventually be running an aftermarket SD system though). If you max out the MAF, you can still tune the car based on wide band readings similar to a SD car. At x RPM, the motor needs y fuel which requires z pulse widths. Blown or whatever, you're still only moving so much air. Granted if you decided to increase the boost you would need to retune it, but how often do you increase the boost in a street application? Did I make any sense there? It's 3 am after all... Oh boy, lunch time.

Highlander

In speed density you still have the "learning" option.. there is closed loop in speed density... What are you saying is correct... But im pretty sure that the PCM has software to compensate for the fast filling and i am pretty sure the pcm has an offset for the position of the maf vs the distance traveled by the air before it gets into the cylinders...

I have dealth with speed density and i have dealt with maf.. and for a car that sees street time... maf is 100x better...

Max power will still be attained with the maf, i dont think that changes anything regarding total max power, as that (fuelwise) will be determined to the final AFR you get it to. So if both get the same afr in the same spots then they get the same power...

If you see right now, the mercedes turbo and supercharged vehicles have a mass airflow sensor... So does the ford cobra S/C, and so does the supra that is supposed to be the GOD of the turbo cars (i dont know why though, can someone please explain???). I dont think they are all wrong about it...

Most speed density systems are a bit more convenient, but if you see the maf ones are a lot more expensive... They require more software development to take account all that you have described in order to run as it should.

Remember people recommend what they sell and the majority of electromotive and fast pcms, Accel are all SD.

Speed density has its advantages... so does the MAF.. i guess oppinions are entitled.

m29formula

I will say that on the street most people will prefer the way a mass air car acts driving around, speed density can do some really weird things if not tuned right. I can also understand maybe a supercharged car doing really good on a mass air setup they have a linear boost response, I personally don't know I have never tuned one and hopefully I will soon Now from what I know turbo cars act very strange when you get away from the factory turbo on mass air cars. When ever I have tuned a mass air turbo car with a bigger turbo it was a PITA to get running right and even then they had some driveability issues. Plus I have personally had a dsm which I switched from mass air with an Apex AFC to a HKS VPC (speed density set up) and with the same AFR got 14 more whp on a 420whp car. Now speed density gave a much better powerband and a lot smoother doing it, but gas mileage did decrease and I wouldn't pass cold start emissions. Plus anybody who does a turbo car into the 10's goes speed density look at all the "god complex" supra guys, dsms, RX7's, Grand Nationals and so on. These setups won't have factory driveability because they don't have the years of engineering behind them, but my 93 formula which is speed density drives great not a single issue. The reason you don't see speed density anymore is because of emissions and fuel mileage. The neon srt4 is speed density, ferraris, lambos, and almost any supercar you can think of run off speed density because it does make more power.

I will also say that if my car is all motor I will run mass air it does have it definate advantages, but for a FI I personally would go speed density. To each his own.


But we all forget the real reason to go speed density, because if we are turbocharged we can uncork our blow off valve and make loud woosh noises. j/k

Highlander

The woosh noise is a no point... you can do it on a maf car too you just have to pop the blow of before the maf.. not between the maf and the engine...

Still... you are right to each its own. I will probably go to SD because the maf maxing is an issue and it does bother, but if i can get around it... I will use the maf.

m29formula

Yeah I know that you can uncork with a maf but I was just being a ricer

One thing you may wanna try to keep a maf setup would be the new Z06 mass air unit. If I remember right it has a higher cfm rating, but I don't remember where I saw that.