The Map Limiter works great!! (filetofit is the man)
11-17-2002, 10:58 AM
#1
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The Map Limiter works great!! (filetofit is the man)
I bought one of those map limiters from Filetofit for $21 recently. 
Last night I finally got around to installing it, a resistor box, and DSM 450cc injectors. The car started up as if I had never even touched it. I used the map limiter to adjust idle and it worked perfectly. Anyone considering using their AFC just to knock down the MAP signal is wasting money when there is a good and very inexpensive alternative.
Last night I finally got around to installing it, a resistor box, and DSM 450cc injectors. The car started up as if I had never even touched it. I used the map limiter to adjust idle and it worked perfectly. Anyone considering using their AFC just to knock down the MAP signal is wasting money when there is a good and very inexpensive alternative.
11-17-2002, 12:14 PM
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Re: The Map Limiter works great!! (fsp31)
... got pics?... also, did you get one with 3 potentiometer or 2?... how did you know which one to adjust for idle?... lemme know... (i am still considering this vs the vafc/smc)... thanks...
11-17-2002, 03:44 PM
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Re: The Map Limiter works great!! (turbod16y8)
The AFC hack works on the principle of reducing the MAP sensor voltage that the ECU "sees" in conjunction with larger (usually 450cc) injectors. The SMC and AFC both apply RPM dependent scale factors to the MAP sensor voltage and pass the scaled down voltage to the ECU. Usually people use a scale factor of about -35% across the board to run 450cc injectors.
Reducing a voltage by -35% across the board is not that difficult. You could use a variable resistor to do this ($2 at radioshack). In fact I tried it. Unfortunately, I found that the larger injectors don't deliver as much fuel as you would think at idle because they take longer to open than smaller injectors. SO I needed a smaller percentage scale factor of about -20% at idle to get everything to run right. Now this is a little harder to do, that is, to run a different scale factor at idle than at other points. So the next thing was I made a circuit that applies a linear corection to the MAP sensor voltage of the form: f(x) = mx + b
where f(x) is the corrected MAP sensor voltage that is passed to the ECU.
x is the uncorrected MAP sensor voltage input to the circuit.
m is the rate of change of output with input and b is a constant voltage.
The net result is a scale factor that is applied to the MAP sensor voltage that varies linearly from -20% at idle to -35% at WOT. Those factors are adjustable but I just found -20% to -35% works well.
The difference between this method and the AFC or SMC is that the scale factors are not RPM dependent, rather they are boost or vacuum dependent.
http://www.angelfire.com/ab7/diymaplimiter
Reducing a voltage by -35% across the board is not that difficult. You could use a variable resistor to do this ($2 at radioshack). In fact I tried it. Unfortunately, I found that the larger injectors don't deliver as much fuel as you would think at idle because they take longer to open than smaller injectors. SO I needed a smaller percentage scale factor of about -20% at idle to get everything to run right. Now this is a little harder to do, that is, to run a different scale factor at idle than at other points. So the next thing was I made a circuit that applies a linear corection to the MAP sensor voltage of the form: f(x) = mx + b
where f(x) is the corrected MAP sensor voltage that is passed to the ECU.
x is the uncorrected MAP sensor voltage input to the circuit.
m is the rate of change of output with input and b is a constant voltage.
The net result is a scale factor that is applied to the MAP sensor voltage that varies linearly from -20% at idle to -35% at WOT. Those factors are adjustable but I just found -20% to -35% works well.
The difference between this method and the AFC or SMC is that the scale factors are not RPM dependent, rather they are boost or vacuum dependent.
http://www.angelfire.com/ab7/diymaplimiter
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11-17-2002, 06:56 PM
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Re: The Map Limiter works great!! (maztur)
But wouldn't boost dependent be more accurate and safe than rpm dependent?
I plan on running about 8 psi for a while until i have the money to build my motor and tune it with a standalone.
Would this map limiter + dsm 450s yield a nice a/f ratio throughout the powerband or would i be better off with the safc and 450s?
thanks for the info and it sounds liek a great deal
I plan on running about 8 psi for a while until i have the money to build my motor and tune it with a standalone.
Would this map limiter + dsm 450s yield a nice a/f ratio throughout the powerband or would i be better off with the safc and 450s?
thanks for the info and it sounds liek a great deal
11-17-2002, 07:07 PM
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Re: The Map Limiter works great!! (tegasaurus)
me Too
But wouldn't boost dependent be more accurate and safe than rpm dependent?
I plan on running about 8 psi for a while until i have the money to build my motor and tune it with a standalone.
Would this map limiter + dsm 450s yield a nice a/f ratio throughout the powerband or would i be better off with the safc and 450s?
thanks for the info and it sounds liek a great deal
I plan on running about 8 psi for a while until i have the money to build my motor and tune it with a standalone.
Would this map limiter + dsm 450s yield a nice a/f ratio throughout the powerband or would i be better off with the safc and 450s?
thanks for the info and it sounds liek a great deal
11-17-2002, 07:19 PM
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Re: The Map Limiter works great!! (tegasaurus)
If you do some research on the AFC Hack which this is a bastard child of, you'll see it is boost dependent. The Honda ECU is now seeing boost and responding to it....without knowing it.
11-17-2002, 07:39 PM
#14
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Re: The Map Limiter works great!! (1.8T_EG)
>>... got pics?... also, did you get one with 3 potentiometer or 2?... how did you know which one to adjust for idle?... lemme know... (i am still considering this vs the vafc/smc)... thanks...<<
My motivation for getting this is that basically I am on a tight budget and I didn't want to purchase an AFC just for the purpose of fooling the ECU into allowing boost. I am *NO* electronics wiz, but this solution seemed pretty reasonable, and at $21 I didn't have much to lose. I think an AFC may offer a bit more fine tuning, but this works as well as I need for sure. I don't have any pics but filetofit has one on a website I think. It would probably be easy to make, but I've done more soldering in the last 24 hours than in the rest of my entire life so I felt it would be best just to buy the thing pre-made. The toughest part was figuring out which of the map sensor wires was which, but it just took a few minutes with a voltmeter and the key turned "on". Signal, power, and ground...
It's the one with 2 pots. Doesn't sound very scientific, but I just fiddled with them to figure out which pot adjusts idle and which adjusts the "pitch" of the curve. It took about 30 seconds because basically the idle will only be affected by one pot, and you only have to make about a quarter turn of the screw to see a difference.
I did some rough tuning with my A/F meter, but I'll need to visit a dyno to get things worked out precisely. I was extremely happy with how smooth the idle turned out. Talk about easy. Took me about 3 minutes to have a perfect idle. The 450cc injectors can make idle tricky because their duty cycle is so slow by that time that it actually makes the engine run rough. To compensate, I adjusted the idle a little more rich than than it was with the old injectors, then everything smoothed out and idled great.
My motivation for getting this is that basically I am on a tight budget and I didn't want to purchase an AFC just for the purpose of fooling the ECU into allowing boost. I am *NO* electronics wiz, but this solution seemed pretty reasonable, and at $21 I didn't have much to lose. I think an AFC may offer a bit more fine tuning, but this works as well as I need for sure. I don't have any pics but filetofit has one on a website I think. It would probably be easy to make, but I've done more soldering in the last 24 hours than in the rest of my entire life so I felt it would be best just to buy the thing pre-made. The toughest part was figuring out which of the map sensor wires was which, but it just took a few minutes with a voltmeter and the key turned "on". Signal, power, and ground...
It's the one with 2 pots. Doesn't sound very scientific, but I just fiddled with them to figure out which pot adjusts idle and which adjusts the "pitch" of the curve. It took about 30 seconds because basically the idle will only be affected by one pot, and you only have to make about a quarter turn of the screw to see a difference.
I did some rough tuning with my A/F meter, but I'll need to visit a dyno to get things worked out precisely. I was extremely happy with how smooth the idle turned out. Talk about easy. Took me about 3 minutes to have a perfect idle. The 450cc injectors can make idle tricky because their duty cycle is so slow by that time that it actually makes the engine run rough. To compensate, I adjusted the idle a little more rich than than it was with the old injectors, then everything smoothed out and idled great.
11-17-2002, 08:01 PM
#15
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Re: The Map Limiter works great!! (filetofit)
The AFC hack works on the principle of reducing the MAP sensor voltage that the ECU "sees" in conjunction with larger (usually 450cc) injectors. The SMC and AFC both apply RPM dependent scale factors to the MAP sensor voltage and pass the scaled down voltage to the ECU. Usually people use a scale factor of about -35% across the board to run 450cc injectors.
Reducing a voltage by -35% across the board is not that difficult. You could use a variable resistor to do this ($2 at radioshack). In fact I tried it. Unfortunately, I found that the larger injectors don't deliver as much fuel as you would think at idle because they take longer to open than smaller injectors. SO I needed a smaller percentage scale factor of about -20% at idle to get everything to run right. Now this is a little harder to do, that is, to run a different scale factor at idle than at other points. So the next thing was I made a circuit that applies a linear corection to the MAP sensor voltage of the form: f(x) = mx + b
where f(x) is the corrected MAP sensor voltage that is passed to the ECU.
x is the uncorrected MAP sensor voltage input to the circuit.
m is the rate of change of output with input and b is a constant voltage.
The net result is a scale factor that is applied to the MAP sensor voltage that varies linearly from -20% at idle to -35% at WOT. Those factors are adjustable but I just found -20% to -35% works well.
The difference between this method and the AFC or SMC is that the scale factors are not RPM dependent, rather they are boost or vacuum dependent.
http://www.angelfire.com/ab7/diymaplimiter
Reducing a voltage by -35% across the board is not that difficult. You could use a variable resistor to do this ($2 at radioshack). In fact I tried it. Unfortunately, I found that the larger injectors don't deliver as much fuel as you would think at idle because they take longer to open than smaller injectors. SO I needed a smaller percentage scale factor of about -20% at idle to get everything to run right. Now this is a little harder to do, that is, to run a different scale factor at idle than at other points. So the next thing was I made a circuit that applies a linear corection to the MAP sensor voltage of the form: f(x) = mx + b
where f(x) is the corrected MAP sensor voltage that is passed to the ECU.
x is the uncorrected MAP sensor voltage input to the circuit.
m is the rate of change of output with input and b is a constant voltage.
The net result is a scale factor that is applied to the MAP sensor voltage that varies linearly from -20% at idle to -35% at WOT. Those factors are adjustable but I just found -20% to -35% works well.
The difference between this method and the AFC or SMC is that the scale factors are not RPM dependent, rather they are boost or vacuum dependent.
http://www.angelfire.com/ab7/diymaplimiter
Tuning for fuel is always based on the MAP signal and rpm on any factory ECU or standalone. Check out the fuel table below.
So, for both the SMC and VAFC you'd have the same columns and rows essentially expanding the fuel delivery scale for boosted conditions. Both the SMC and VAFC can behave similar to filetofit's if you set the correction the same throughout the rpm regions. Why would you want that when tuning involves different settings throughout the rpm region?
The rows add the rpm regions, which is the key factor in tuning. The SMC has more flexibility in terms of being both applicable to turbo and sc applications. Superchargers, especially Jackson Racing, do not need the same amount of fuel across the board. Leaning out the mixture at high rpm is key to getting good power since they aren't intercooled or compressor efficient, compared to a turbo setup w/ a intercooler. The percentage cut maybe the same for similar setups (i.e. 6-8psi, intercooled, and DSM 450cc injectors). With some other setups I've experienced, such as 550cc and 10-12psi; the idle, mid, and high rpm fuel enrichment is not the same. With a one dimensional voltage divider circuit it's impossible to differentiate fuel delivery at various rpm regions especially with volumetric efficient high rpm Honda engines.
The SMC also has added features such as reverse/surge voltage protected circuitry for long-term reliability, internal voltage clamp to prevent CEL for the MAP sensor, logic circuitry to prevent the barometric CEL common in some VAFC setups, one touch EEPROM programming for great dependability, on-the-fly tuneablility, enclosed package, and much more.
Here's what MikePalm wrote about the SMC compared to filetofit's:
I have both the little circuit from filetofit (chris hart) that costs $20 shipped and the SMC....I'll say that the SMC is definitely worth the extra money. The SMC comes with excellent directions and looks very professional. The circuit from filetofit would be great if you know what you're doing, but it just comes in a little pouch with no directions and only has a couple inches of wires. For me, I would be completely lost trying to install it or use it, that is why i'm going to use the SMC. WELL WORTH THE MONEY.
You do get what you pay for.
Go here for more info on the SMC:
http://userwww.sfsu.edu/~ecg/smc.htm
11-18-2002, 08:59 AM
#16
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Re: The Map Limiter works great!! (zip)
>>You do get what you pay for.<<
Ah yes, but since we're talking in graphs and charts, that's only one axis. The other axis is 'you get what you need'.
In my case, to pay in excess of $100 for what I needed would be a waste of about $80.
The reason I don't "need" the added adjustability is that I'm not looking for the extra .02 seconds off my 1/4 time. This is an autocross car where only a certain amount of HP is useable in the first place. I also have rather extreme budget constraints, so for anyone in my situation this option is great.
Ah yes, but since we're talking in graphs and charts, that's only one axis. The other axis is 'you get what you need'.
In my case, to pay in excess of $100 for what I needed would be a waste of about $80. The reason I don't "need" the added adjustability is that I'm not looking for the extra .02 seconds off my 1/4 time. This is an autocross car where only a certain amount of HP is useable in the first place. I also have rather extreme budget constraints, so for anyone in my situation this option is great.
11-18-2002, 09:13 AM
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Re: The Map Limiter works great!! (zip)
Just a word of warning, you may want to be careful where you are linking to. You are hosting a profit making product on a not-for-profit organization's servers.
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