MegaSquirt

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.

This is a reproduction of a portion of the wiring schematic that can be found on the Web in the MegaSquirt installation instructions.

Before bolting the MegaSquirt on our test small-block, we decided to baseline the engine with a Barry Grant 750-cfm carb and an Edelbrock Victor Jr. single-plane intake. On the carburetor, the engine made a satisfactory 414 hp on the first pull along with 419 lb-ft of torque. Unfortunately, we ran out of time before we got the MegaSquirt to work on Westech's dyno.

Our next attempt took us to Ken Duttweiler's dyno where we already had the factory TPI manifold in place and hooked to the MegaSquirt. Note that we also added a set of SLP larger-tube runners to the manifold to give it a chance to make decent power.

The MegaSquirt is intended to run just like this, so we placed the open box on the tray behind the engine on Duttweiler's dyno. It sat right next to a functioning MSD-6A box and had no trouble with electro-magnetic interference despite the fact that these MSD boxes are noted for being "noisy."

We also employed a set of MSD 38-lb/hr fuel injectors on this package. This was the largest single purchase for the system. The engine made 350 hp, which required only about a 60-percent duty cycle on the large injectors. This engine could have made the same power with as small as 26-lb/hr injectors if necessary.

We employed the Innovate Motorsports wide-band air-fuel ratio meter to help us quickly dial in the air-fuel ratio on the engine. This took only a matter of minutes and we ended up with a best power air-fuel ratio of around 12.9:1. The MegaSquirt is also set up to run in closed loop with a three-wire heated oxygen sensor that works very well for part-throttle tuning.