Acceleronics FAQ

While the electronic circuit theory behind VersaFueler operation can be intimidating, you don't need to understand any of that to see how the VersaFueler can help you make big power with minimal cost.  In fact, my grandson Evan made a poster that shows the VersaFueler's role in engine operation for his 3rd grade class.

Why not just run high impedance 60s or 80s?

If the VersaFueler is patented, why do I see knockoffs on the market?

Will the VersaFueler run my stock injectors?

Is the VersaFueler hard to install?

My car has 4 or 6 (or 5, or 10) cylinders, can I use the Acceleronics VersaFueler?

Can I run big injectors on the street?

How do I tune my engine for low-impedance injectors?

Why can't I run low-impedance injectors with the factory computer?

What is the difference between low-impedance and high-impedance injectors?

 

Why not just run high impedance 60s or 80s?

High impedance injectors are getting bigger, but they are not getting better!  The problem is that big (60 lb/hr and larger) high impedance injector sets that are flow matched under wide-open-throttle conditions in many cases are horribly  mismatched at idle and cruise conditions.  We frequently see this on our flow bench.  Not all sets are this bad, but do you want to take the chance?

The mismatch is because high impedance injectors vary widely in the time it takes them to open.  We have seen variations in opening time as large as 0.4 ms (millisecond, or 0.001 sec) across a set of 8 Siemens-Deka 60s (also known as Mototron).  This variation may not sound like much, but remember that the injector is typically only open for 1.0 ms - 2.0 ms at idle.

Here's an example of the 0.4 ms difference in action.  Suppose your engine works like this:

   - fastest injector opens in 1.0 ms.

   - slowest injector opens in 1.4 ms.

   - injector open time at idle (the pulsewidth) is 2.0 ms.

The fast injector is fully open for (2.0 - 1.0) = 1.0 ms.

The slow injector is fully open for (2.0 - 1.4) = 0.6 ms.

The fast injector is open 20% longer than the average (0.8 ms).

The slow injector is open 20% shorter than the average.

The spread is a whopping 40%!!!  Unless your ECU has individual cylinder fuel control and you have 8 wideband O2 sensors, you are NEVER going to get a decent idle with these injectors.

How do low impedance injectors produce a better idle and crisper throttle response?

An injector that flows 80 lb/hr is going to have a much larger valve inside than the typical 24 lb/hr stocker.  Fuel pressure pushing on the back side of these bigger valves makes them hard to open, which really means slower to open.  The larger valve is also going to be heavier than a stocker, which further slows the opening time.

So how do low impedance injectors get around problem?  The answer requires a bit of science.  The "motor" inside an injector is a coil of wire.  When electricity flows through the coil, it generates a magnetic field that pulls the injector open.  The amount of electricity flowing (the current) determines how hard the coil can pull.  More current means more pull.

 

High impedance injectors flow no more than 1 amp of electric current, usually more like 0.8 amp or so.  Low impedance injectors will flow as much as 7 amps if you let them, but the VersaFueler's built-in brain limits them to 4 amps so that they do not overheat.

Here's the real key:  The force generated by the coil of wire is proportional to the current squared.  Using 1 amp for high impedance and 4 amps for low impedance, this means that the low impedance injector coil generates 4 x 4 = 16 times more force!  Think about comparing two cars, one with 1600 hp and the other with 100 hp.  Which one do you drive at the track?

What this all means is that low impedance injectors are easier to tune, and typically result in a better idle and crisper throttle response compared to large high impedance injectors.

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If the VersaFueler is patented, why do I see knockoffs on the market?

United States patents are like locks, they keep honest people honest.  But just as a lock can be broken if a thief wants to steal your car, a patent can be ignored if a thief wants to steal your design.  And while most people agree that car thieves are bad and should be punished, many people don't think that someone who copies a patented design is a criminal.

Patent infringement court cases are extremely expensive, and in most cases, drag on forever.  We at Acceleronics hope that customers honor our patent by purchasing our product, not a knockoff sold by a patent infringer.  Not only is it patented, but the VersaFueler is also the most reliable and robust design on the market!

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Will the VersaFueler run my stock injectors?

Yes!  The VersaFueler will run any gasoline injector!  Low impedance, high impedance, 19 lb/hr, 220 lb/hr, you name it we run it!

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Is the VersaFueler hard to install?

Not at all, it's easy!  The box simply splices between your ECU and injectors.  Connect one cylinder at a time to our color coded channels.  All the channels work the same, so any channel color can connect to any cylinder.  Click here for the installation instructions.

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My car has 4, 5, 6, or 10 cylinders, can I use the VersaFueler ?

Yes!  VersaFueler channels are all the same, and are completely independent.  You can use 1 channel, or all 8, or any number in between.  V10 and V12 owners can use 2 VersaFuelers. 

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Can I run big injectors on the street?

Absolutely!  Big injectors are streetable - the Acceleronics test car idled just fine at 900 rpm in gear with 95 lb/hr injectors running with 1.0 millisecond pulsewidths.  Throttle response on the street would just about snap the passenger's head off!

The 95 lb/hr injectors are as responsive as stockers.  We now stock 120 lb/hr flow matched injectors for you huge blower or turbo guys who like to push the envelope.  The 120s work great for E85, and we have many sets on gasoline street cars making way over 1000 rwhp.

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How do I tune my engine for low-impedance injectors?

Your ECU doesn't care whether the injectors are low-impedance, or high-impedance.  It only cares about how big they are, and how quickly they open.  You will need to change the number that tells your computer how big the new injectors are.  For example, when the Acceleronics Camaro changed from 50 lb/hr high-impedance injectors to 75 lb/hr low impedance injectors, we used LT1-Edit to change the "injector size" from 50 to 75.  Nothing to it!

If you removed larger-than-stock high-impedance injectors, your new injectors will probably open more quickly, so you may need another adjustment.  Again using the LT1-Edit example, we changed the values in the "injector offset versus voltage" table.  Your ECU may call it something else, but there is probably a similar offset number that tells the computer how snappy, or how sluggish, the injectors are.  Once the injector size and injector offset numbers are fixed, continue tuning as usual.

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Why can't I run low-impedance injectors with the factory ECU?

Virtually all cars come with high-impedance injectors. The ECU turns high impedance injectors on and off with a simple switch, much like an ordinary light switch. Turn the switch on when you want fuel, turn it off when you don't.

But you can't run low-impedance injectors that way or you will burn them out!  These injectors need to be carefully controlled, so a simple on/off switch will not work.  They need something more like a dimmer switch.  Turn them on all the way to get them to open, then after they open, turn down the dimmer so they don't get too hot.

The second problem is that the ECU's injector drivers can't handle the large electric current needed for low-impedance injectors.  Low impedance injectors need about 4 times as much current as high-impedance injectors.  This much current will burn out the transistors in the ECU that run the injectors, unless the injectors burn out first!

The VersaFueler is built to handle the needs of low impedance injectors, and to protect your ECU!

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What is the difference between low-impedance and high-impedance injectors?

The important difference between low- and high-impedance injectors is the amount of electric current they require.  The high-impedance injectors used by carmakers do not use much current.  In fact, even if you connect one directly to your car's battery, it will not draw much juice.  This is good for the car maker because the circuit in the ECU that runs the injectors can be a simple switch made from cheap, light-duty components.

A low-impedance injector needs a bunch more electric current to open, about 4 times as much as the high-impedance injector.  This is so much current that the injector will burn itself out unless the juice is somehow turned down right after the injector opens.  Now, instead of a simple, cheap on/off switch, the ECU must use heavy-duty components that can handle 4 times as much current.  The switch must also turn down the flow of electricity after the injector opens so the injector doesn't burn up.  This is a much more expensive circuit, and one that generates a bunch more heat inside the computer.   Getting rid of that heat raises the computer cost even more.

This business of the ECU yanking the injector open with full current, then turning down the juice to keep it open, is why you hear low impedance injectors called "peak and hold".  It takes a big current (the peak) to yank them open, but a much smaller current (the hold) to keep them open.

So why bother with low-impedance injectors if they're harder to run?  Because bigger electric currents can yank harder than smaller ones.  As the flow rating of an injector increases, so does the weight of whatever the injector uses to turn the fuel on and off (for example, a pintle, or a disk).  This is no big deal for stock injectors in the 18 lb/hr to the 30 lb/hr range.  Even though they are high-impedance, they're light enough that the small current can yank them open quickly.

But big (like 42 lb/hr and up) high impedance injectors are slow to open.  This makes it hard to get a good idle, and kills throttle response.  What if you need an injector larger than 42 lb/hr?  Simple!   You buy low-impedance injectors, which are available up to 160 lb/hr.  The large peak current can quickly snap these monster injectors open.

So a low-impedance 50 lb/hr injector will almost certainly be "snappier" than a high-impedance 50 lb/hr injector.  When the 50 lb/hr high-impedance injectors on the Acceleronics test car were replaced with 75 lb/hr low-impedance injectors, the ECU setting that adjusts for "sluggishness" had to be set back to stock.  The high-impedance 50 lb/hr injectors required much more time to open than stockers, but the low-impedance 75 lb/hr injectors are just as snappy as stockers.

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Written by Jeff Stevens.  Copyright © 2002-2012  Acceleronics.com   All rights reserved.  Revised: December 02, 2012.

The Bottom Line

At $269, the Acceleronics VersaFueler is the best way to run low-impedance injectors on your factory EFI engine.  Click here to order yours.