Due to the EU’s Global Data Protection Regulation, our website is currently unavailable to visitors from most European countries. We apologize for this inconvenience and encourage you to visit www.motortrend.com for the latest on new cars, car reviews and news, concept cars and auto show coverage, awards and much more.MOTORTREND.COM
Subscribe to the Free

Road Testing the QFi Black Diamond Throttle Body EFI

Diamonds Are Forever - Road-testing Quick Fuel’s QFi Black Diamond Throttle Body EFI

Jeff Smith Nov 17, 2014
View Full Gallery

There are black diamond ski routes that we know enough to stay away from and KISS wrote a song called “Black Diamonds.” We tried to get Neil Diamond to help us with this story, but he was too busy. But the Black Diamond we want to talk about is built by Quick Fuel Technology and is the latest entry in self-learning, high-performance throttle body fuel-injection systems. By now, you probably know all about these self-learning TBI systems. In fact, we’re now seeing second-generation systems where the early hiccups are being massaged. That’s one of QFi’s advantages. In exchange for its later arrival, it offers a bit more sophisticated electronics and ignition control for those who like to be immersed in the total EFI experience.

We decided to take Quick Fuel’s system for a test drive on our 350ci, four-speed El Camino cruiser. The QFi system is rated to feed upwards of 525 hp with its 950-cfm throttle body. This fit our needs perfectly because our small-block is basically a stock 350 H.O. Chevrolet Performance crate engine with a COMP Mutha’ Thumpr cam installed. The rest of the car is also fairly tame with a Muncie wide-ratio four-speed and a 3.08:1 rear gear. We felt this would be a more challenging test for the QFi system because this is a combination we would tell most everyone to avoid. This is a heavy car with a tall gear, a manual trans, and a camshaft with too much overlap for a light-duty cruising. The car had previously been equipped with a slew of different carburetors and one other TBI system, all of which had been challenged to overcome the big-cam/low compression’s inherent off-idle lean stumble. We could overcome it, but that required the engine to run at a ridiculously rich part-throttle air/fuel (A/F) ratio. We were looking for a solution where we could eliminate the stumble and still have a reasonable A/F ratio at cruise and we hoped the QFi system would be up to the challenge.

Diamonds up close

Let’s take a moment to look at what the QFi system offers and then we’ll get into the installation and our test drive. The heart of the QFi is its standard throttle body outfitted with four, 66 lb/hr injectors that Quick Fuel says will feed up to 525 horsepower. Quick Fuel also says this system is compatible with E85 (assuming that your fuel pump is as well) but this limits the package to around 370 hp because E85 demands about 30 percent more fuel than gasoline. Quick Fuel also says this system will work in conjunction with a wet nitrous system, which is intriguing because that would allow you to use a 150hp nitrous kit, for example, and use the QFi’s feedback capability to fine-tune the QFi’s commanded A/F ratio under nitrous. Ignition control is another option with this system. QFi recommends that initially you work only with the fuel side. Once the fuel portion is tuned and the engine is running well, then you can convert over to full ignition control. For our test because we were under a quick deadline, we tested only the fuel portion.

The throttle body constitutes the central portion of the system. Besides the injectors, the throttle body also incorporates the idle air control (IAC) motor, the inlet air temperature (IAT) sensor, and the throttle position sensor (TPS). The MAP, or manifold absolute pressure, sensor is located in the ECU so a simple vacuum line must be connected between the throttle body and the ECU. In fact, the only external sensors you have to be concerned with are the coolant temperature sensor that mounts in the normal place in the intake manifold and the wide-band oxygen sensor that mounts in the exhaust. The QFi kit comes with an adapter flange that is clamped to the exhaust pipe so you don’t have to weld, but we’d recommend using a dedicated screw-in mount that is welded in place. This will prevent air leaks that could affect the sensor’s accuracy. This is important because all oxygen sensors actually extrapolate the A/F based on the percentage of oxygen in the exhaust. While it’s more complicated than this, an exhaust with very low free oxygen means the air/fuel ratio is rich. More free oxygen means a leaner mixture.

The oxygen sensor is the key to any self-calibrating EFI system. Once the basic operating parameters (displacement, number of injectors, injector size, cam type, and target A/F ratios for idle, cruise, and WOT) are input into the ECU with the handheld device, this creates a basic fuel delivery map. Then the ECU uses the feedback from the oxygen sensor to measure the existing A/F and compares this to the commanded A/F and modifies the delivery until this is achieved. Added features that the QFi system brings to the party are inputs like “Cam Spec.” The QFi offers three choices of Stock (1), Performance (2), Race (3). We initially chose the middle version but changed to 3 because of the Mutha’ Thumpr cam’s large overlap. Later discussions with QFi confirmed that they designed the style 3 with the Thumpr series of cams in mind. These cam configurations are what dictate which one of three different fuel maps the engine will operate under. All the other tuning parameters modify off one of these maps.

Another great tuning option is QFi lists four target A/F ratios while other systems only look at three. The three typical inputs are Idle A/F, Cruise A/F, and WOT A/F. QFi offers a fourth: Off Idle A/F, which gives the tuner an opportunity to tune this specific load separately from the Cruise A/F. This was helpful in allowing us to add fuel at this specific point to help overcome our off-idle stumble.


01. The Quick Fuel Black Diamond QFi system is about as simple to install and tune as you could expect. It’s possible that the hardest part of the entire installation will be deciding whether you want the polished or Black Diamond finish.


02. The QFi system comes in several different kit configurations. This is the Black Diamond complete system with the fuel pump, regulator, hoses, and fittings. There’s also a basic kit available in either finish.


03. The throttle body is rated at 950 cfm and integrates all but two of the required sensors. The base plate is drilled so you could even bolt this body directly on a 4500 series manifold, with the optional adapter plate.


04. The ECU is separate from the throttle body and the harness is intended to mount most easily under the dash. It also requires routing a small vacuum line to the ECU for the MAP sensor.


05. From underneath, you can see the idle airspeed motor (top) that helps control idle speed. The QFi system introduces fuel below the throttle blades, just like a carburetor.


06. The fuel delivery system might be the most difficult part of the entire installation. The best bet is a dedicated, in-tank high-pressure system. This is a tank for a Chevelle that has been modified with a rear sump.

Advanced Tuning Settings

The following lists the different settings the QFi system allows you to change. Earlier throttle body systems prevented the tuner from accessing these items. This is a double-edged sword because while the user now has access, that also means he can just as easily screw things up making changes. So be forewarned, it’s best not to mess with these settings if you don’t completely understand what they do and how each affects engine performance. All of these settings can be accessed with the handheld tuner. Most are self-explanatory but Decel fuel is an engine speed fuel cutoff rev limiter. This can also be used like a valet key.

Fan 1 Temp Crank Fuel Cold
Fan 2 Temp Crank Fuel Warm
Fuel Prime Cold Crank Fuel Hot
Fuel Prime Warm Accel Enrich Slow
Fuel Prime Hot Accel Enrich Fast
Enrich Fuel Cold Decel RPM
Enrich Fuel Warm Enrich Fuel Hot

Parts list
Description PN Source Price
QFi Black Diamond master kit QFI-500BDM Summit Racing $2,149.00
QFi polished 950-cfm master kit QFI-500SM Summit Racing 2,099.00
QFi polished 950-cfm basic kit QFI-500S Summit Racing 1,949.00
QFi Black Diamond basic kit QFI-500BD Summit Racing 1,999.00
Aeromotive Phantom 200-lph kit 18689 Summit Racing 439.97
Aeromotive Phantom 340-lph kit 18688 Summit Racing 537.9

Bolt-on and go

It’s not quite that simple—but almost! The biggest hurdle to installing this or any throttle body EFI system is the fuel delivery system. The path to a trouble-free EFI system starts with a quality fuel delivery system. Like most TBI systems, the QFi can be purchased complete with a fuel pump, lines, fittings, and filter or as a base kit with just the throttle body pieces. Our recommendation is to purchase the base kit and invest in a quality in-tank fuel pump system. There are several tank options from companies like Tanks Inc. or an excellent universal pump kit from Aeromotive called the Phantom system. The quick and easy way is to mount an inline electric pump outside the tank and use the stock tank pickup. There are several major issues with this approach. The biggest problem is that non-EFI fuel tanks are not baffled around the pickup. So when the fuel level drops below half, fuel slosh under acceleration will uncover the fuel pickup. This causes an immediate drop in fuel pressure and the engine will bog. Then the fuel will rush forward, the fuel pressure will again rise, the car will accelerate, and then the fuel pressure will immediately drop again, running the car through an embarrassing acceleration/sag cycle as long as you keep your foot in the throttle. We’ve been through all that and it’s very annoying. Sure, you can just keep the tank full, but you will quickly discover that’s a hassle.

The smart move is to invest in a good in-tank fuel pump system. We would also suggest investing in quality fuel line with at least half of the high pressure feed line in rubber or PTFE plastic hose that will not deteriorate. Rubber hose, despite its stainless cover will still degrade over time. We’ve seen cheap rubber hose fail in as little as 9 months. The reason that a portion of the high pressure side should be in a flexible hose is because some EFI systems run into hydraulic hammer situations caused by full hard line systems. If nothing else, at least be aware of this.

Test time

With the QFi system installed in our El Camino, we configured it as recommended in the instructions and the engine fired almost immediately. After allowing a short warm-up period, our first few jaunts down the street brought a serious hesitation right off idle – just like our carburetor. We reconfigured for Cam 3 and made the off-idle A/F richer and the stumble was noticeably reduced. We drove around for about two or three miles and then made some further changes to fine-tune some of the “Accel Enrich Fast” settings in the Advanced Tuning section. Throttle response improved again and we also noticed that it seemed to respond to the throttle very quickly. We also had to add some fuel prime for cold start, which is a really great benefit since some of the other systems we’ve tested do not allow you to modify the cold start. The engine now starts immediately when cold and does not load up because of a too-rich A/F. Once the engine is fully warmed up, if we try, we can still make the engine stumble right off idle by pulling the rpm way down below 900 rpm and crowding the throttle. It’s possible that a little more fuel in off-idle will cure that.

Our kit came with a serial port connector that was supposed to allow us to connect to our laptop, but since all newer laptops only come with USB port connectors, Quick Fuel says that all subsequent kits will come with a serial port to USB adapter, which they sent to us. This allowed us to access the entire system, including the timing portion. The first thing we discovered is that while you can access the main fuel maps for Cam styles 1, 2, or 3 and it appears that you can modify them, QFi will not allow you to modify them. That’s because there is a Number 4 map that you can modify. This is where we ended up making most of our changes to the fuel map to trim it to our liking. What’s nice about this is that if you know a little about EFI tuning, this allows you to go in and make finite changes to the fuel map that most other systems do not. Plus, you have access to an ignition curve as well. We just ran out of time to get around to that portion, but we anticipate it will work just as smoothly as the fuel side. Of course, you don’t have to use the laptop at all if you would prefer to avoid this part. The beauty of the QFi is—you can do either or both.

Overall, we like the QFi system for its great throttle response and because it offers more tuning options. This allows you to fine-tune the system over a broad range of engine operating conditions and you end up with an engine that is really fun to drive and gets surprisingly good gas mileage. That is, if you can keep your foot out of it.


07. Another excellent in-tank system is Aeromotive’s Phantom system. This is the system we’re using in our El Camino. We installed this entire kit in around 4 hours and it works like a champ. We are able to run the tank down to near empty with no fuel delivery hiccups.


08. If you purchase the base kit, you will need to supply the pump, fittings, and a high-pressure fuel regulator like this Quick Fuel unit. Fuel can enter from either side and exit from the opposite side while the return is out the bottom. This regulator uses ORB fittings.


09. This Quick Fuel diagram illustrates the preferred way to plumb the filter after the pump (in the tank), then to the throttle body followed by the regulator and the return.


10. We chose to mount the QFi ECU next to the battery underneath the inner fender. We will probably change this later because we don’t want subject the ECU to battery fumes. This placed it farther forward in the car and we had barely enough room to connect to the oxygen sensor in the exhaust. It appears that Quick Fuel intends the ECU to be mounted in the interior. It would be helpful if Quick Fuel added length to its harness to allow more installation options.


11. All adaptive learning TBI systems demand the main power and ground connections made directly to the battery. This solves electrical noise issues that can cause all kinds of weird problems.


12. The handheld unit allows you to do everything you need to do to make this system operate and to tune it. Here, we’re accessing the off-idle target A/F and we’ve set it about a half-point richer than the cruise A/F to help transition past our nemesis off-idle stumble. We’ve since richened it to 12.7.


13. Here is the final QFi throttle body installed on the car. We installed this system on the car pretty quickly in order to meet our deadline so when we have some time, we’ll reroute the wires to make the final install look cleaner.


14. If you are considering also controlling the spark, you can create a basic curve with the handheld unit, but using the supplied software you can get more creative with the curve using a laptop. Ignition control will also require a locked-out distributor. You can manually lock out a distributor by welding up a GM distributor or you can purchase a new one from MSD.


15. We drove the El Camino to our local cruise night just to put some miles on it to learn. All adaptive learning EFI designs require operating time so the system can produce the desired results. You can expect to make a few changes along the way, but that’s the fun part.


Quick Fuel Technology
Bowling Green, KY 42101
Lenexa, KS 66214
Rick's Hot Rod Shop
El Paso, TX
Tanks Inc.



Connect With Us

Get Latest News and Articles. Newsletter Sign Up

sponsored links

subscribe to the magazine

get digital get print