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Discussion Starter #1
so, ya, why does it?? i get how both parts work, but why do you need the chip? if the SAFC can tweak the fuel, thus compensating for the different sized injectors, boost, etc, then why does the VPC need different chips?? is it just for an easier base tune??

i thought it might have shifted the voltage curves to allow for a higher HP levels since higher amounts of air is needed, but it reads PSI, and the highest psi i have heard of used with the VPC couldnt be higher than 35psi, and i couldnt imagine that being out of the range of the normal VPC, so this idea is moot....


:1poke:
 

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King of the NA-T's
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The VPC converts speed density into a karman signal that the stock ECU can use. Without a chip the VPC can't do anything.... sorta like if you removed a chip from your laptop.
 

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Discussion Starter #3
oh yeah, that makes sense. my question is more why is there more than ONE chip available if it doesnt itself do the tuning....
 

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I thought its becaause the safc can only tune so much, and you need a prewired dynamic basic map to start converting with depending on the injector size, then you can fine tune it with safc. My understanding is that it does both convert over and run its own map like a map-ecu in conjunction with the stock ecu maps to conpensate for the larger injectors. I'm sure this is also somehow related to the injectors duty cyle, I'm really not sure, I could use a refresher. Dave please correct me cause I'm probably wrong
 

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The mass of air entering the engine can be measured many ways. One way is with a hotwire sensor, like the TT uses. You can use a flapper door, like older EFI systems, which measure the velocity of the air entering the engine. The computer uses this and the info from a Baro pressure and temp sensor to calculate the mass of air getting into the engine at any moment. A Karmen frequency sensor measure the frequency created by a vortecy generater which is directly related to the mass of air moving past it. Or you can use a "speed-density" system which uses a MAP sensor, air temp sensor, rpm info and a good idea of the engines VE to predict the mass of air filling the cylinders. This last one is especially good for forced induction applications. But each does the same thing, it measures the amount of air getting into the engine.

So, you have a stock computer using a stock Karmen sensor sending it a certain frequency to inform it how much air is entering the engine. The computer uses this to know the exact amount of time to keep the injectors open and keep your engine running correctly. That's great if you're keeping the injectors stock.

Now, you install bigger injectors and keep everything else the same.....not good. Your Karmen sensor is still telling the computer the same amount of air is entering the engine but now each injection squirts a lot more fuel in the cylinder = running rich. OK, tell the computer there is less air getting into the engine and your good. Do this with a SAFC or a VPC.

How the SAFC works: You're still using the Karmen sensor, the frequency is intercepted by the SAFC before it makes it to the ECU and is manipulated. A lower frequency, lower airflow signal, is sent to the ECU and you've got a happy engine.

VPC: With this, the Karmen sensor is removed. It uses the RPM of the engine, a MAP sensor and Temp sensor and info about the VE of your engine to calculate the mass of air entering it at any given moment. It gives your ECU a Karmen frequency so it can do it's job of controlling the injectors.

Your question is, why is there more than one chip available for the VPC. Well, for one thing, some stock ECU's need a certain voltage for the airflow signal. Ours needs a frequency. There are two chips for the MKIII turbo supra. A 550cc chip and a 440cc one. If you can see what the SAFC does then you can see what the difference is between the two chips. One tells the engine there is a lower mass of air getting into the engine than the other.

OK, so you have a VPC with the correct chip that should have the right map programed on it for your engine. With just this, your egine will run well but there will be room for improvement. This is where the SAFC comes in. It intercepts the frequency sent by the VPC and modifys it before it gets to your ECM. This system removes the restrictive airflow meter, compensates for the larger injectors, and gives a way to measure airflow with boosted applications.

Hope this helps to illistrate why there are different chips available.
 

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Discussion Starter #8
i get how both the safc and the vpc work....i am still lost though as to exactly WHY the vpc NEEDS a chip...

see, the vpc can create a resistance (variable voltage drop..), impedance, capacitance, lots of crazy things. it ultimately, though, is used to take one signal (rpms, temp, MAP), and change it into a karmen vortex signal so the ecu thinks it is a normal sensor. then the ecu makes its calculations, blah blah blah, and then the safc modifies the fuel. IF the vpc chip WAS a PSI chip, then i could understand the NEED. but when you put in a bigger turbo, injectors, higher FP at boost, those are FUEL modifications that need to be made, NOT air! if the psi range and rpm ranges are the SAME, then the only real thing that must be changed is fuel input. i understand that the chip COULD be used to do this modification, but WHY????

the injectors read two things, ampre's and sinusoudal waves. the larger the injectors, the less signal of either is needed for the same output of fuel....thus, the SAME signal on the SMALL inj on a LARGE inj would inject MORE fuel. so if you are running a larger turbo and need more fuel, then hypithetycally you should ONLY need to adjust FUEL. just because you may be running large injectors doest mean you will be running a DRASTICALLY different amount of either the sin waves or ampres.... so why would the input to the sensor need to be changed if the ecu would theoretically be in a close-to-stock range of output signals?? (by range i mean the mins and maxs of stock input/outputs of various signals and sensors would be similar to stock, ie you arent going to run 100amps into your injectors if stock you ran 0.5amps...you will probably run like .6amps or so....)
 

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King of the NA-T's
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i get how both the safc and the vpc work....i am still lost though as to exactly WHY the vpc NEEDS a chip...
It was originally made so you can use the stock injectors, and just plug it in... or you could use it with larger injectors if you put in the chip for the larger injectors. When the VPC was made, there was no such thing as the SAFC.
 

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Moo
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The VPC is a generic unit, meaning it can be used on many cars. The vehicle specific information is coded in the chip.
 

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Discussion Starter #11
ah, it now is starting to make sense. thanks guys!

oh yeah, so does this mean that you COULD use the 550 chip and run like 780's?? with safc of course :)
 

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ah, it now is starting to make sense. thanks guys!

oh yeah, so does this mean that you COULD use the 550 chip and run like 780's?? with safc of course :)

Nope, I tried it. Not enough correction in the SAFC to get 780cc to work. 680cc were the largest I could run and tune well.
 

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Discussion Starter #13
good info, thanks again! some of this info might be good to copy and paste into one of the stickies..... (MOD)
 

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Moo
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I attempted to run 720's with both the 440 chip and the 550 chip. I could tweak it far enough combined with fuel pressure but it drifted too much for my tastes, AND ignition timing was too advanced. Standalone is the way to go at that point.
 
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