Dune-Buggy.com - Tim Systems EFI Controller Basics

Tim, you've been driving buggies for years, what got you started using Fuel Injection and Turbos, and why would someone want to use one?

Years ago, we wanted our buggies to go faster and faster so we started looking for a way to do it. Turbos were just starting to show up out at the dunes, so we visited our local junk yard and scrounged a few. Next we asked everybody for info and found out that the first liar doesn't have a chance. We found a bunch of "Self Appointed Experts" that wouldn't tell us anything, or the info we did get was conflicting. Some of these questions were Should we go "Draw Through" or "Blow Through" configuration? How much boost is safe? What amount of timing should I run? And so the list went on and on.

Definition: In the US, Boost is measured in pounds per square inch. It is the extra pressure that is being pumped into the intake manifold by the Turbo.

Our first attempt was a draw through set up. That is where the carb is mounted on the intake side of the turbo. We found out fast that this is a less than ideal setup. The advantages are that you don't need a high pressure fuel pump or special fuel regulator. The disadvantage is that the throttle response is terrible. The fuel when it hits the spinning turbine wheel, separates the fuel from the air at low speeds, and causes a big lag off of idle. When you do get up to speed, the liquid fuel that is laying in the bottom of the snail shell on the turbo, is picked up and washed through the engine, causing the plugs to get fouled quickly. The fuel management for the engine was terrible at best.

Our second attempt was to go blow through. That is where the output of the turbo blows through the carb. At first we didn't know how to seal up the carbs, so we took an idea off of the 68 GT Ford Mustang, where they put the carb in a box. So, we built boxes around our dual carb setups, and sealed the throttle linkage (using a 10-Speed inner tube), and off for the first run. Problem was we couldn't shut it down at the top of the hill because the inner tubes had grown in size and caused a twisting effect on the throttle linkage! Good thing we thought about hitting the ignition switch fast!

We later solved all these little details and the driveability was much better without the lag. Problem was that while under boost, it went very lean! We would richen up the jets, but then the bottom end was too rich and we lost power at low RPMs. We then rejetted the carbs back to a naturally aspirated condition, and then used a nitrous gas fogger nozzle with a pressure switch that would turn on at a trip point under boost, adding more fuel. This was definitely a step in the right direction, but it was a step. It was not smooth, and the fuel management was still not under control. Better, but not right.

Tech: To make a very long physics lesson short, a carb is an "Air Density" device, it's job is to measure the amount of air going through it, and add fuel to it. So, if you were to put twice as much air through it, you would end up with about twice as much gas, Right? The problem with a turbo is that the carb does nothing for pressure correction. The math is that the air flow through the carb is linear, but the pressure is exponential. PSI is a square function. The bottom line is that it tries to draw a straight line through an exponential curve. You can jet it for the top, but it would be way too rich at the bottom.

Next we came up with the idea of using fuel injectors under the carbs for the boost enrichment. I came up with a simple electronic controller that would activate the fuel injectors under boost. This controller would start the injectors spraying a small amount of fuel at about 1/2 PSI, and this amount would "Grow" until the max boost was reached. At this point the injectors would be turned on maybe 75%. Instantly the boost was incredible!

The fuel management was now working! This success gave the boost enrichment controller it's name as the "Magic Box." It wasn't long after this that we were saying, "What are we doing with carbs when we have these fuel injectors on the engine?" So the search was on for a fuel injection computer. Now there are a lot of real good systems out there, and there are differences between them, but we wanted something very simple that didn't have all the bell's and whistles. After all, this is a sandrail! We looked high and low and could not find what we wanted, so, with the help of a lot of friends and engineers, rocket scientists, (and yes, the village idiot too), we ended up making our own fuel injection computer.

Right off the starting line, this had some great things going for it. To start with, no more linkage problems, because we use only one air valve (just like the new cars do). No more clogged idle jets, no more flooding out when going through the big bumps, sides of hills, etc, it doesn't care! The throttle response is crisp, even off of idle!

Here's why. With a carb, one of the major problems is the fuel wets the insides of the intake runners. With fuel injection, the fuel is put in right behind the valve. You can putt around in 3rd gear at 900 rpm, and floor the gas, and the engine will start pulling without spitting, coughing, etc.. Now it's only going to pull as good as it can for being in the wrong gear, but the "Driveability" is the real gain. The other advantage is with the turbo, the fuel management is adjustable so dialing in doesn't take very long. No more jets to buy!

So you're saying that Fuel Injection is ideally suited for Turbo Chargers because of the fuel delivery problems of a Carburetor. At this point I can hear the Carbureted crowd yelling "but my setup works fine." What do you have to say to them?

I say, "If it isn't broke, don't fix it." The real question I ask them is, "Ok, you make good power under boost, but how is your throttle response off of idle?" or "How is the driveability when putting around at low RPMs?" and "What happens when you go from the dunes, sea level, to up in the mountains, like 8000 feet? Do you still have good driveability?"

I've seen some pretty good setups, but one look at the exhaust pipe on some of these, it looks like fur growing in there, it's so black!

Note: Many carbureted turbo setups can benefit from fuel enrichment while on boost. The low budget method is to use a pressure switch that will inject extra fuel while on boost. A more advanced method is to use a controller such as the 'Magic Box" that is capable of regulating the fuel flow depending on the needs of the engine.

Coming Soon: Boost Enrichment Page for Carburetors

What you have to do is ask yourself if you are really happy with how your buggy runs. One test that I like to do is have someone with a carb - turbo setup is this. Put the car in 3rd gear and let it idle. Now while you are rolling along, instantly floor the gas pedal. What happens? 99.9% of the time, it acts just like someone reached up and shut the key off!

Also, you have to ask yourself if you are happy with how it responds to the whoop-tee-do's and big bumps. Does it load-up? How about being sideways on a very steep hill, does it still run Ok?

All I'm saying is if your happy with past performance, etc. then don't change. But, if your building a new buggy, or re-doing a project and want to try something else, think hard, and ask lots of questions. Do your homework first before spending any money.

Your system is designed for strictly off-road use and you stated that you left out the bells and whistles. How is it designed for off-road use and what did you leave off and why?

NOTE: As of late 2003, this controller is no longer in production.

The main reason is to avoid emissions regulations. This was designed to be for Sandrails, and not the street. The "Bells and Whistles" include an oxygen sensor as well. You get into what is called a "Closed Loop" with a lot of these systems. The problem is they are designed to run at 14.67 Air Fuel Ratio. We have found that you cannot run an air cooled VW this lean. You WILL destroy the engine. One of the biggest factors overlooked by the after market computers is that "They" are designed to run closed loop because "Their" engines are water cooled. VW's use some of the incoming fuel as part of the cooling system so they have to run rich.

Because there's no O2 sensor, you're free to use leaded fuels such as AV gas.

Some say that you can set what ever air fuel ratio you want with theirs. Fact is, if you don't spend at least $600 just for a "Wide Band" O2 sensor, it CANNOT read anything but around 14.67. The standard O2 sensors are designed to basically be a switch. You are either above or below that point. Temperature, humidity, etc affect these sensors. To read between 10 to 20 AFR, you need what is called a "Heated Wide Band Oxygen Sensor." Very expensive because it takes special electronics to run these as well. This is getting off the point, but does need to be addressed.

Some of the other options that were left out were air temp, engine temp, cam position, and crank angle position sensors. The reason was we wanted a basic system that "We" dial in, so we can see the effects. One of the reasons that the engine temp was left off was because in the mornings, when the engines were cold, they will make over 100 PSI of oil pressure at idle! We found that if we drove a crisp running engine we would explode the dog-house oil coolers! So after that and a few blown-apart oil filters as well, now we just let them idle until warmed up and use nothing but Fram HP-1's for filters as well.

The design for "Off Road" came about because there are two different types of designs for fuel injection. Air Density and Speed Density. Air Density systems use some sort of device that can measure the amount of air entering the engine. Usually it is a thermal type, or hot wire configuration and usually very fragile. The other type of air measuring device is a spring loaded trap door. The pro's to this type of system is that it can measure small amounts of air change, as well as the temperature. So, if you are cruising down the hi-way and start to go up a little incline, it can detect this and correct. The con's to this system is that it reports after the fact. If your trying to do a drag race and floor it, it cannot compensate immediately, so you get sluggish performance.

Note: The Tim Systems Fuel Injection Controller has the basic sensors necessary to detect how much air is entering the motor; a Throttle Position Sensor, A Manifold Air pressure Sensor, and a Tach Sensor. At idle, the Throttle and Tach sensor is mainly used. As you get on the gas and the Turbo starts doing it's job; the Manifold Air Pressure sensor starts detecting the boost and helps adjust the fuel curve.

The other system uses either a MAP (Manifold Absolute Pressure) or a TPS (Throttle Position Sensor) and a tach input. The pro's to this is that TPS sensor on the throttle shaft reports immediately when you floor it BEFORE the air actually starts to move, and there are no intake restrictions. The con's are that it cannot detect small cruise changes (using TPS only). If you use MAP, then cruise changes can be detected, but, the con's to this are if you have a bumpy cam, your idle vacuum changes all the time. Of course there are systems out there that use all or part of the sensors to compensate, and yes you will pay for this. But remember, WE wanted a basic system that WE could dial as we drove. Because of this, the computer has knobs on it to adjust for each range, idle, mid, top end, boost, etc. Again, it's all what you want, an automatic system that has to use all the sensors, or basic and keep the costs down but you will have to tweak from time to time.

Definition: Tweaking the Fuel Curve: The Fuel Injected version of a jet change. A change in temperature or elevation may require that you readjust the fuel delivery curve to the motor. It's as simple as turning a knob.

Turbo and Fuel Injection Basics

Further Reading: