Just curious with all of the standalones, fuel systems, etc, why we aren't converting to MAF instead of using the speed density maps still?
Anyone got any ideas?

 

WTF, M.A.P and in conjunction with TPS is all ya need with a standalone, who the hell wants to run AFM's of any type? NOT ME!!!!!!

 

I think MAFs are ugly

 

The FD designers got rid of the MAF for a reason.

 

Yet somehow you cannot name the reason?

I also wonder why people don't use MAF's. I mean, by DEFAULT they directly MEASURE the MASS of air going into the engine. When you make changes you don't need to spend hours reprogramming the computer... the computer measures the mass of air and supplies the correct amount of fuel.

This is a great thing for people like me who like to tinker. Every time a change is made is an opportunity to get the tuning wrong.

BTW - If you've ever seen Dahlback's 5-cylinder, AWD, "Golf". Take a look at the air filter, now look where it attaches to the turbo inlet duct... a MAF. Well gee Barney, if it's good enough for ~900hp then it should be good enough for us too, right?

edit - Do not confuse MAF's (hotwire style sensor) with AFMs (flapper door / plunger style sensor). AFMs have the right idea but they go about it all wrong, since not only do they necessarily have to be somewhat restrictive, but they only measure air volume, not air mass.

 

my friends have sr20det's with MAF's all they do is crank the boost up and it adds more fuel. well with the stock setup anyway! the bad thing about MAF is you are limited by how big your MAF is. you can max them out you know. MAP's are limited by the boost you plan to run hell they make like 8 bar if you want..... lol

 

The reason why MAP's are more common in a stand alone situation has to do with the general nature of a MAP. You can hook up a MAP to any engine, be it a 50 cc single cylinder, or a V12 Behemoth. MAF's are very application specific. They have a minimum and maximum limit of air flow that they can accurately measure.

So if you were in the buisiness of general standalone EMS, which would you chose? If you were makeing a application specific EMS then MAFs would perhaps allow more flexiblity, otherwise....

 

I was looking for something to add to my post, but didn't find it till now...

-----
I ran into an interesting fellow this weekend at the 5th annual Datsun
Z-car Convention in Knoxville, TN. He had the fastest Zcar I'd ever
driven. acceleration/coast down estimates of road horsepower is around
600 at 20 psi of boost from his homemade turbo system from a 2800 cc
engine on 110 octane racing gas. I'm going to write his work up
for the list and for the Z-car list as soon as I get time and I'm going
to do a very detailed article for the magazine because of his nifty
work. He reminds me of me but without the electronics knowledge.

He used the stock 280 FI manifold, suitably ported, with the injectors
mounted in the stock location right above the valves. The throttle valve
is in the stock position. An intercooler is used.

The interesting thing is he had someone build him a very simple analog
fuel injection controller that works from a custom made hot wire airflow
meter. He used a Bosch hot wire mounted in a 5" diameter pipe. What is
VERY interesting is the system does NO acceleration enrichment (no
manifold surface is wetted), takes no throttle position input and has
no cold start enrichment to speak of. All of this flies in the face
of most conventional wisdom. There are simply idle and WOT mixture
pots that represent the zero and span adjustments of the pulse width
controller.

The throttle response is instantaneous - much faster than I thought
possible with the size turbo used. On the autocross course there was
a straight coming from a >90 degree turn that was about the length of
the width of 10 parking places in the school parking lot. I stood behind
the turn and radar gunned the contestants. Most hotrodded Zs (triple
webers, etc) hit about 45 on the straight. The built-up small block
conversions (I WANT one) ran in the 55 range. This turbo car,
despite the large amount of tire spin, hit 65. This in spite of him
babying the tranny to keep from breaking 1st gear. This same engine
idled quietly at 900 rpm (spec) and slogged around in traffic just
like a stocker.
-----

 

Thanks for all the discussion. My point was exactly as pee jay stated. Just to monitor mass air flow into the motor and set up a standard fuel map for that flow. Looks like then it would ease tuning a bit on the A/F scale especially when you change things on your setup.
As long as you have your timing setup already with a MAF you could add and pull parts without any tuning being needed.
good topic either way though.

 

You know, various mechanical fuel injected VWs used a pure AFM system like was mentioned. And again, MAF is a lot better than the air-door AFM.

I actually have to wonder how hard it would be to make a cheap-as-hell EFI system using a MAF and a little circuit board to vary the pulse width of the injectors. It wouldn't do anything as complicated as, say, timing the fuel events with anything that the engine is doing, but...

I mean, hell. All the homebrew EFI stuff that I've found info for online is MAP. Seems like it'd be easier and cheaper to make a simple MAF system, like the post peejay mentioned.

 

MAF isn't the wundersystem it's made out to be. The fact is that AFR requirements change based on revs (lower AFR as VE increases), so you still need a 3D-control system, except that you're basing your load on airflow instead of manifold pressure.

Speed-density is also more flexible, in that MAF meters have upper and lower limits of flow. At the lower limits, fuelling becomes erratic as the meter begins to read no airflow, and at the upper limits it becomes a restriction to flow. You also must deal with vacuum leaks in the more conventional sense, instead of the relatively "nice" S-D leaks, which only raise the idle.

Oh, and speed-density is also much cheaper to manufacture.

Brandon
BR7 Racing

 

Thanks Brandon, this is the kind of information that helps all of us out.
Does anyone have any pro MAF comments.
I do know that S-D on a mustang was one of the worst things in my opinion. The MAF made it easier to adjust and I guess toy/tinker around with stuff without requiring tuning.
thanks for everyone's comments.

 

Oh, sure.

MAF is quite nice in that it only requires minimal retuning after mods. If you do something major (like a cam or new heads), the system will compensate well enough to let you keep beating on your car until you get back to the tuner and squeeze out that last 3 hp.

MAF systems also don't require air temp correction (nay, an air temp sensor at all), making installation and tuning that much easier.

In the end, I feel S-D systems are better because they're more flexible (and I like to drive my car home, even when I've popped an IC hose! ).

Brandon
BR7 Racing

 

LOL.... I can see your point about the IC hose. LOL....

 

So wait a minute here. You're saying that as the VE of the engine is going up (thus the RPM, generally) the engine is going to need to go richer or leaner? You're not being very clear here. I know for damn certain that it's possible to run a fuel injection setup with no more input than airflow though; the mechanical air door system on various VWs does that, to name one.

For limits of flow, this is true, however... let's look at one MAF, the one that appeared stock on GM LT-1s. The lower limit is 5g/sec of air, and the upper is 335g/sec; those correspond to around 7hp, and around 430hp, respectively. Now, I don't believe that a rotary flows *THAT* little air, even at idle. It's a logarithmic curve too, so there's a lot more precision at the lower end of the scale, for idle and whatnot.

Vacuum leaks I have to grant

*shrug* Personally, I'm looking at making a simple-as-**** BASIC stamp based MAF EFI system; I've studied the Megasquirt quite a bit and I've decided I don't like the idea of having to tune even that small of a map by hand. And I can build the MAF system for cheaper, and have yet to see any real reason why it couldn't work just as a completely open system.

 

For a given RPM point, as load increases, fueling needs change. You would generally need more fuel for 15 psi at 3500 RPM than at 9000 RPM, with all other things being equal. A 2D MAF setup will work, but it's not optimal.

Well, 44.3 lb/min isn't too hard for a serious enthusiast to exceed, and I'm pretty sure that if you look at the next-larger MAF, you'll find the lower limit to be quite different. In addition, there's the economics of the situation - MAFs cost much more than an air temp sensor.

In any case, I'm biased. Let everyone know how the custom MAF setup goes.

Brandon
BR7 Racing

 

... er. Load is directly shown by airflow; if the engine's under more load (making more power) it flows more air, and the MAF senses that. I'm wondering why exactly you seem to be wanting to lean it out at higher RPM. And BTW, I'm talking a 1D system, not 2 or 3d.

Quote:

Well, 44.3 lb/min isn't too hard for a serious enthusiast to exceed, and I'm pretty sure that if you look at the next-larger MAF, you'll find the lower limit to be quite different. In addition, there's the economics of the situation - MAFs cost much more than an air temp sensor.

Well, 44.3 lb/min is a good starting point for an NA rotary, IMO. Also, even at idle a 13B is going to be flowing around 10-20g/sec of air. So let's have a theoretical idea of running a pair of those LT1 MAFs; now we have a maximum of 88.6 lb/min of air, and can still measure air precisely enough to idle and have low-range power. In reality, a bigger single MAF would be better but even still there's a lot out there.

Also, here's economics for you: junkyard MAF for $25-50, homebrew control hardware for another $20ish... or a Microtech for $700ish (lowball; I think the group buys were going for around that?), followed by however much dyno tuning it'd take to get the map right.

... mind ye, I've got nothing against speed-density systems. I'd love to have a Microtech or Haltech, I just don't have the cash. And while some would say that this would be a sign to save my money, I say that I bet I can do something for cheaper.

Quote:

In any case, I'm biased. Let everyone know how the custom MAF setup goes.

Brandon
BR7 Racing

Will do; might be a while though, because we have to rebuild our race car's motor *AGAIN*. And I'm poor. Or maybe I'll just end up getting a Megasquirt in the end; there's a new heavily upgraded version coming out that'll drive ignition too, and take input from a wideband.

 

Well, 44.3 lb/min isn't too hard for a serious enthusiast to exceed, and I'm pretty sure that if you look at the next-larger MAF, you'll find the lower limit to be quite different. In addition, there's the economics of the situation - MAFs cost much more than an air temp sensor.

In any case, I'm biased. Let everyone know how the custom MAF setup goes.

Brandon
BR7 Racing [/B][/QUOTE]

i think thats what the factory does, at low speeds it seems like they blend the afm and the tps. i looked into mafs its hard to find bigger than 3" and they are $250-275, and its made by ford so you're gonna be replacing it periodically

mike

 

FYI, guys, 44.3 lb/min is roughly 390-410 crank hp on a rotary (depends on a few things). On a boinger, it's closer to 440bhp. 400hp for an N/A rotary is a good starting point indeed.

BTW, an adjustable fuelling curve over a single load range is 2D; consider x to be load, and y to be injector duration. A 3D fuel map combines load, RPM, and injector duration. That should make more clear my load vs RPM fuelling requirement statement.

Brandon
BR7 Racing

 

Yup! Not like I'll likely *quite* get there, even with the ports I have in mind, but I can dream, no?

Quote:

BTW, an adjustable fuelling curve over a single load range is 2D; consider x to be load, and y to be injector duration. A 3D fuel map combines load, RPM, and injector duration. That should make more clear my load vs RPM fuelling requirement statement.

Brandon
BR7 Racing

Mm. For some reason I've seen it called a 1D map a lot. Doesn't mean it's right, upon reflection.

I think I might have to go junkyard hunting again next time I have a bit of cash... this keeps poking at my brain. Well, that and I need to make a few practice intake manifolds, which is an entirely different matter.

 

Airflow meters, in general, are more expensive to build (and buy).&nbsp The airflow meter is always going to give a more accurate picture of the "amount of air" going into an engine (versus a MAP sensor).&nbsp Of course, you can build your own simplified airflow meter, but that's an extreme case.

(OEM) Systems using MAP sensors are designed to run in a very narrow performance range.&nbsp Running outside of this narrow range usually rewards you with a dead engine - i.e. FD's.&nbsp This has to do with mucking with the engine V.E.

A MAP sensor load system is almost always going to be cheaper and easier to implement versus a system using an airflow meter.



-Ted