Speed density vs. MAF with EMS on both

[Bob_H]

Ok, still in the "research mode" for the RB26dett EMS.

A large majority of the units on the market today are a Speed Density system. With the 6 individual throttle bodies of the RB26dett, it is harder to put a map sensor in an appropriate location to sense load. You can stick one in the main manifold log, but then it won't see vacuum behind the throttle plates. You could tap into each runner behind the throttle plates and run a log to the map sensor, but with its close proximity to the valve, you start to get funny reversion and pressure changes.

I really don't want to switch to a single throttle body,(personal preference).

The way I see it, using a MAF should be more precise than a speed density setup since you know the exact amount of air coming into the motor at a given time. To me that would make part throttle tuning that much eaiser.

I am interested in hearing opinions either way, and not "I run speed density and it works great". That is not what I am looking for. I want to know why I should choose one or the other, besides simplicity or cost,(and that it works great for you). What makes one better than the other? Also, if someone can point me to links with more info that would help as well.

Also, any info on EMS's that support MAF's vice speed density only is appreciated.

-Bob

[BLKMGK]

AEM's system supports MAF and MAP based systems. If you're unable to program the system MAF is better since it isn't as reliant on a table. MAP based systems rely on a lookup table for fueling whereas MAF actually measures the airflow. Measuring vs infering is better when you cannot reprogram the lookup tables. Just look at how easy the MAF Mustangs can be modified vs th eMAP based ones.

 

However, if you're getting a system you CAN program the MAP is better IMO. It has less issues with intake piping - MAF sensors can have reversion problems and turbulance problems. I think a MAP with a small common plenum hooked to each TB would be the way to go. Just need something small enough to damp the pulses is all - I don't think it would have to be too big...

 

'Zat help at all?

[Bob_H]

That's about what I figured, but not your last comment about the MAP system being better.

As I understand it, you can change what fuel the EMS puts in based on the signal from the MAF. I.E., xx fuel/lb air for a stock setup, modified to xxx fuel/lb air. I know the speed density system can be programed to deal with more, but MAF is much more "accurate" if you will for a given load/airflow intake. To me, x amount of air means x amount of fuel, with a factor for boost pressure and throttle position,(I realize that is all the speed density system is doing, just you have to manually input the points, vice it doing it for you).

But the real question is which systems can deal with a MAF and still be programable? AEM is clearly not an option unless they get off their butt and get the Race system out in a month or two,(which by their posts earlier this month, that is clearly not the case).

So which other systems would offer the ability to support the MAF, data logging, and still have decent selection of options to play with,(tune). Really, most of the systems on the market are the same, just a different name and different interface. Some might have a few more inputs, etc.. But all the ones I looked at aren't designed for a MAF sensor, but a MAP/speed density setup.

Any thoughts?

-Bob

[Brad-ManQ45]

Electromotive is probably the least expensive...

[TimZ]

Originally posted by Brad-ManQ45:

Electromotive is probably the least expensive...

Electromotive quit supporting MAF sensors on the TEC2 for some reason at their "PAFZ" PROM level. As far as I can tell, they have not added it back in for the TEC3. I don't know why, but if I had to guess, I'd say people were having too many problems getting the MAF systems to work right, and E-motive got tired of supporting it. But that's just conjecture on my part.

 

Blkmgk pretty much summed up what I was going to say about the MAF vs. speed density. Really, I've not heard too many good things about using MAF setups on turbo motors - too many complexities in getting the MAF to read reliably, and also possible latency issues, depending on where the sensor is plumbed. Not to mention the well-known problems of vacuum leaks and improperly routed BOVs wreaking havok with your mixture.

 

The market didn't go the other way because it was harder.

 

Also, the MAF setup that the TEC2 used still had a lookup table, and it worked exactly like the speed density - you still had to calibrate it. Assuming you had the hardware working properly, I'd have to guess that the MAF setup was less sensitive to smallish changes, though (like cam timing, for instance).

[Lockjaw]

I know that the MAF on my set-up has to be positioned 18 inches from the turbo in order to eliminate turbulence interfering with the readings. The BOV has to be recirculated or the lag when you shift gears is very noticable. The turbulence issue can be tuned out according to clark at JWT. As for vacuum leaks, I personally don't want unfiltered air getting into my intake system.

 

If you have the engine and harness APEXi has the powerFC which plugs in and is programable. I don't know which method it uses, but I would assume it uses the factory MAF(s).

 

The nice thing about a MAF equipped setup is it compensates for changes, so you do not have to make programming adjustments when you put on a larger exhaust, change cams, turbo's etc.