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General Speed density vs MAF

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diesel yj

Supporting Member
8
1
May 28, 2009
onalaska, Wisconsin
I'm at the point in my build and I need to make a decision for my engine wiring harness. Is speed density the way to go now or is MAF. This is a 99 GSX aka with the black box for the engine management system. I was looking to make in the 450-500 HP range possibly with e85 but I have questions concerning E 85 but I'll try the search button first. Right now the car has been on a rotisserie for the past 2 years so it's basically a blank slate
 

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I don't have any experience running speed density on the H8 factory ECU but I don't doubt that it is capable of safely managing a 500+ hp 4g63 with the higher resolution maps Ceddymods offers. However, if you are running a stock MAS, you will be pretty close to the maximum airflow it can safely read at that power level. An Evo MAS might go a little further, but still it would be in your best interest to err on the side of safety and choose speed density.

It seems to me like your question is more about what the differences are. If that's something you want to discuss, let us know.
 
Speed density on all my csrs. Newer cars don't run MAF/MAS they are on SD.
I personally love SD since the car will still get you home in a emergency like a blown coupler or such. All of my DSMs run SD.
Personal opinion after blowing couplers at 40 psi, or worse, killing a turbo.
 
I get the basic principle of the two but you're saying the GM tried-and-true blow through MAF is still good to go? To be honest this car has been apart for more like 4 years (I'm kind of embarrassed about that) and I have seen alot of post concerning speed density. I had heard that speed density didn't like modifications to much. But that was a couple of years ago. And I'm not trying to reinvent the wheel right now I would just like to get the car done at this point and the engine wiring harness is kind of holding me up. Doing and after market harness BTW
 
Its user choice. Just what I like to run and tune and doesn't rely on feedback from an airflow box and sensor. Just MAP and IAT sensors. Frees up the intake area too.
 
I get the basic principle of the two but you're saying the GM tried-and-true blow through MAF is still good to go?
That's not speed density. And even though it works to a fair extent, the GM MAF was never intended to be used in blow-through with positive pressure. The problem is that when pressure in the uicp rises and the airmass flow rises, that airmass tends to not flow evenly through the entire cross-section of the pipe, but to flow faster in the center where the hot wire element is located. This artificially inflates airflow measurements at increasing boost and airspeed, or in other words, a nonlinear response from the sensor which causes a lot of headaches when tuning.
 
I have been tuning GM maf cars and speed density cars for over 5 years now. Personally I prefer speed density. Much more resolution in the tuning. Also is very easy to tune with if you have a wideband logged correctly.
 
Speed density on all my csrs. Newer cars don't run MAF/MAS they are on SD.
I personally love SD since the car will still get you home in a emergency like a blown coupler or such. All of my DSMs run SD.
Personal opinion after blowing couplers at 40 psi, or worse, killing a turbo.

Marty, new cars use a MAF. The will use SD as a fallback if the maf fails.

OP I personally like using a maf. I am running a modified Coyote maf on my car nearing 800hp. A 2g maf will likely do what you want, but they are sort of hard to package. I ran a 3" gm maf and a maft for a long time and liked it a lot. One thing to watch out for is the MAFT doesn't do a good job "locking" the baro and ait signal, which is needed with the way the maft works. If you want to run a maft I'd suggest trying to find a way with the ceddy mods or something to lock the baro and ait in the code. @95GSXracer used to have a long write up about that on his website from back in the day. He was doing this shit back when the ecu's used vacuum tubes LOL.

If you are not super up to date on the state of the art on black box tuning, I'd suggest switch the car to use ecmlink. It will be a lot easier to integrate different maf setups or SD. I've not followed the bbt stuff, but back in the day there were some guys having problems as not everything was all figured out, and they hurt some parts because of it.

I'm not 100% but I think if you were interested in running a maf, ecmlink would allow you to use one of the newer "slot mafs" like the coyote maf that I use. They are pretty small and don't affect the "look" in the bay as much as a mitsu or gm maf. You'd need to use one of the ECMLink GMMAF cable, and possibly add another pull-up resistor in it. But it would be a cool experiment.

One thing to remember is that you'll likely change your mind about 800 times on what to do, so it's hard to get the harness right and pretty right of the bat. I'd suggest try and think in advance and make the maf wiring so that you can easily change it later. Maybe put some sort of a common 8 pin plug near the strut tower on a pigtail so you can have an easiliy changeable maf/sd subharness if you want.

That's not speed density. And even though it works to a fair extent, the GM MAF was never intended to be used in blow-through with positive pressure. The problem is that when pressure in the uicp rises and the airmass flow rises, that airmass tends to not flow evenly through the entire cross-section of the pipe, but to flow faster in the center where the hot wire element is located. This artificially inflates airflow measurements at increasing boost and airspeed, or in other words, a nonlinear response from the sensor which causes a lot of headaches when tuning.
I'm not sure that's a real thing that happens. I think there were a lot of worry-worts back in the day that perpetuated that theory. I did not see any issues like that when I used one. It was mostly trouble free. If I changed it's position it would cause issues needing tuning, and it didn't like if the box got full of water.
 
I don't know much about speed density, other than I've had constant issues with my omnipower 4 bar and ecmlink harness from day one. Could never get the breakout wiring to work, bypassed it and still won't read map correctly.

As for the gm MAF on blowthrough, it's been amazing since I put it on. Never hickups, runs great and is easy to place. All my piping is 3" due to the w2a intercooler, and I believe that's where the problems come from for some, necking down and back up so far with the gm MAF. But that's just an observatory opinion.

ECMlink is the much easier option in my opinion for tuning, though there is speed density options for the black boxes.

Speed density kinda intimidates me, but once I get the car back together I may switch over fully, if I can get the map to work correctly...
 
Marty, new cars use a MAF. The will use SD as a fallback if the maf fails.
Shows I don't have anything new, LOL. ROFL
My bad on the comment, but I do like running SD,IDK why. I guess I am just familiar with it. Thanks for the correction Kurt! :thumb:
 
I don't know much about speed density, other than I've had constant issues with my omnipower 4 bar and ecmlink harness from day one. Could never get the breakout wiring to work, bypassed it and still won't read map correctly.

As for the gm MAF on blowthrough, it's been amazing since I put it on. Never hickups, runs great and is easy to place. All my piping is 3" due to the w2a intercooler, and I believe that's where the problems come from for some, necking down and back up so far with the gm MAF. But that's just an observatory opinion.

ECMlink is the much easier option in my opinion for tuning, though there is speed density options for the black boxes.

Speed density kinda intimidates me, but once I get the car back together I may switch over fully, if I can get the map to work correctly...
Did you tune your car to speed density?
 
I'm a fan of the process. I wanted to learn the difference, so I put off Speed Density until I had gone as far with MAF as I could.

Once I got the tuning under control, where AFR estimated and actual AFR from Wideband were aligned using the MAF comp sliders, I then started increasing the boost level and re-tuning. I eventually got to a point where I was at max boost, max timing, mixed fuel (E25) with a Big16G.

Finally, the internet convinced me to take the Speed Density plunge, and then I started tuning SD. I can say with confidence, Speed Density tuning is very straight forward, and I feel like I can actually reach a stopping point that holds, where MAF tuning I was always tweaking.

Justin
 
I've tuned & worked with both. My opinion is overall mass air systems are very stable & work well with daily driving & many different throttle angles. SD is not as forgiving with changing climate conditions or throttle angles but work well closed or WOT. SD can deal with vacuum leaks better. Also mass air systems take a little more time tuning to get dialed in than SD, but not much more.
 
Speed density on all my csrs. Newer cars don't run MAF/MAS they are on SD.
I personally love SD since the car will still get you home in a emergency like a blown coupler or such. All of my DSMs run SD.
Personal opinion after blowing couplers at 40 psi, or worse, killing a turbo.
Except if your wiring to your MAP sensor is buggered then the car will likely not run or start at all. Last year, I forgot to wrap my wires so my signal was grounding out intermittently. It ran fine in the garage but died on the street at the end of my sloped driveway.
If I had it in mass air mode, even without a working MAS, it would have at least prevented me from having to push the car back up the drive with my wife. In SD, it wouldn't even fire.

When I blew a hole in a coupler while running mass air years ago, I could still drive across the city and get home. It ran stupid rich all the way, but it got me there. SD would have given me the same result in this case.

So in my first hand experience I think mass air, at least with our ECUs, is more forgiving than SD.

But SD is more tinker-able, and I run it anyway.
 
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I bet the wife was super happy Curt............:ohdamn:
I obliterated a turbo shaft and SD got me home 5 miles. I was a mosquito fogger the whole way and a motorcycle had to pull over and just plain stop. I hated driving it like that and now (since I have busted a turbo or 2) I keep a plug for the oil line to the turbo in the car. Embarrassing as all hell I must say. I do drive the cars like I stole them tho.
 
Even tho I run SD, I do have the 2G MAF installed. I have the MAF wiring harness setup with inline blade connectors so I can switch sensors from IAT to MAF and back as needed - no tools. This makes it easy to switch for SMOG testing. I do enable the MAF comp slider bypass checkbox in SD mode, but the MAF calibration is still in place.
 
Is it safe running 20 psi on MAFT? 3 inch GM maf?
Too broad of a question. For example, 20psi on a 16g and 20psi on a 35r are 2 very different things. If you’re talking using JUST the maf translator for fuel control with something like some 560cc or 680cc injectors partying like it’s 1999 with a 16g on 20psi, sure. If you’re talking trying to run a big turbo to 20psi using just the maf translator for fuel control on its limit of 680ish injectors, then no won’t have enough fuel to get there. If you’re talking using the maf translator just to run the GM maf and letting another engine management system handle fuel control, then sure it’ll handle 20psi and much more.
 
I no longer have a MAF car as all six of my gas cars were either speed density from the factory or have been converted via standalone ECUs. Not sure that I have a preference, to be honest. I might even prefer MAF. Maybe.

The van is SD from the factory and it is completely stock. I had some large boost leaks that I didn't even know about, and they ended up throwing things off enough that it blew the catalytic converter down the downpipe and clogged the exhaust, which I am not happy about.

My GSX went from H8 to Megasquirt and I had ~18 months of SEVERE drivability problems that would have been more easily detectable with a MAF than my stumbling upon the problem during an oil change with SD.

Inversely, my first Spyder kept the stock MAF and decided to drop that stupid MAF connector in the middle of a drive and the car became undriveable. Fortunately it was an easy fix, but doing away with that awful connector would have been really nice.

My Talon blew the intercooler pipe twice. The second time was no big deal because I was 30 feet from my tools, but the first time I was driving down a still-being-constructed interstate and thought for sure that uneven concrete had sheared off the oil pan or something. A 20 minute joyride had turned into spending the entire night waiting for my other roommate to get out of class and bring me some tools. I've had couplers blow on SD cars and it's startlingly loud, but the car doesn't really care beyond not being able to build boost. Which may be a good or a bad thing depending on how quickly you diagnose it from the driver's seat.
 
SD for me, Marty touched on the reason why as I feel you can limp it home a lot easier. Blew a coupler on a maf and was barely able to limp it home.

I also like the fact it cleans the engine bay up quite a bit. Also I think it changed the way my car sounds as well. Anytime I’m close to switching from vacuum to boost she’s whistling. Also you can safely vent your BOV to atmosphere. I wanted to for about 8 years. My tuner and I also had a conversation about it and I finally pulled the trigger. It’s also pretty affordable to switch as well.

-Daniel
 
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