Budget EFI - Megasquirt

There are several ways to go about creating a budget electronic fuel injection (EFI) system. The problem always comes down to how much you're willing to spend. Generally, the least expensive aftermarket ECM and wiring harness combinations start at around $1,000 and go up from there. Recently, we ran across what has to be the least expensive way to get into a truly programmable EFI system. Called the MegaSquirt, it's available through two East Coast hot rodders, Bruce Bowling and Al Grippo, who decided to offer an inexpensive EFI package that anyone could build.

Condensed to its essence, the MegaSquirt system is a truly build-it-yourself EFI computer. Bowling and Grippo will sell you the entire electronics package for roughly $225, and you solder it all together. Once you've assembled it, you can also build a bench-tester to ensure your box works, then you can install it on virtually any engine from a single-cylinder weed-wacker to a 12-cylinder Formula 1 engine. The MegaSquirt system we experimented with commands only the fuel system, leaving the ignition to be controlled however you wish. That's a very simplified overview. Because the whole MegaSquirt story is more complex, we've had to edit this story down to the major bullet points in order to make it fit. That means we're only going to show you the highlights of this kit. But we will get into how it worked for us, our dyno-testing, and how you can get started on a similar system.

The Kit

This is how the computer comes in the mail when you order the MegaSquirt kit. Tim Moore assembled the kit, and he reports it required between six and eight hours to complete, including the separate relay box system.

If you're old enough to remember the Heathkit build-'em-yourself radios that came in the mail as a pile of electronic parts, that's exactly how the MegaSquirt system arrives at your door. There are a couple of aluminum boxes along with a stack of circuit boards, relays, drivers, diodes, capacitors, and all other sorts of tiny electronic pieces. We're not that good with electronics, so we convinced our pal Tim Moore to sit down and solder in all those tiny connections, which he accomplished in roughly eight hours by following the instructions!

The computer is designed to operate in either an alpha-N or speed density mode. The alpha-N mode is intended for engines with very large camshafts that make using a manifold absolute pressure (MAP) sensor difficult. The speed density mode is far more popular, and it uses the MAP sensor to help establish engine load along with a throttle position sensor (TPS). The MegaSquirt system also employs the popular and inexpensive GM-based sensors such as the TPS and manifold air temperature (MAT) sensors, except for the MAP sensor, which is a dedicated sensor built into the MegaSquirt box.

MegaSquirt claims the relay board can be located under the hood but that the computer should reside in the cockpit where it can be protected from moisture and dirt.

Assembling the computer will also expose you to all the nuances of EFI and is an outstanding opportunity to learn how these systems function. The MegaSquirt system requires a separate computer like a laptop to tune the system once it is operational. This may seem like a much larger added expense, but the laptop is only necessary when first configuring the system. Once your tuning is complete, the laptop is not necessary for daily operation. We all know someone who owns a laptop that can be borrowed for the tuning process to reduce expenses.

Once Tim completed the assembly of the MegaSquirt, he opted to build the stimulator box that allowed him to bench-test the MegaSquirt to ensure that it worked. Tim also then downloaded the free software from the MegaSquirt Web site that would allow us to configure the computer for the engine we would be testing. In keeping with the budget approach of this system, we decided to test the MegaSquirt on a basic small-block Chevy. Rather than invest in an expensive aftermarket fuel injection manifold, we dug up a used TPI manifold from an '87 Camaro that Tim purchased for $200 at a local swap meet.

Since a couple of the TPI tubes had been mangled, we also decided to spice up the intake with a set of SLP runners and a new set of fuel injectors. Since we were purchasing new injectors, we decided to go with larger 38-pound-per-hour (lb/hr) injectors that would allow us to make more horsepower with this same MegaSquirt system. The new injectors were the most expensive single component of our swap at $420, but there are less expensive alternatives. For example, Olds Quad 4 injectors are capable of significant fuel flow and are boneyard cheap. Spend $10 apiece to clean them and you have a performance injector for a ton less cash. The MSD 38-lb/hr injectors will easily support 540 hp at an 85-percent duty cycle with a brake specific fuel consumption (BSFC) of 0.48. Factory 305 TPI manifolds came with 19-lb/hr injectors (the 350 engines used 22-lb/hr units) that are only good for around 270 hp at the same efficiency level.

The best thing we did was order the separate stimulator kit that allowed Tim to check his work and also to diagnose the system to ensure it was working properly. We highly recommend that you purchase this option when ordering a MegaSquirt. There are six variables you can test with this system.

This is the manifold absolute pressure (MAP) sensor that is built into the MegaSquirt board rather than using a separate GM-style sensor. This is our greatest concern with the system because if the MAP sensor fails, the whole system goes down and is not easily replaced. All Version 2 MegaSquirt systems come with a 250-kPa sensor that can handle positive intake pressure of up to roughly 20 psi.

Here is the completed MegaSquirt computer. Note the three small light emitting diodes (LEDs) on the end of the box. These serve as diagnostic aids. When these lights flash, they indicate injector pulse, enrichment circuit operation, and power to the fuel pump.