This is a reproduction of a portion of the wiring schematic that can be found on the Web in the MegaSquirt installation instructions.
Test Time
We loaded up our trusty small-block Chevy and headed for Westech Performance where we bolted the 355 up to the dyno and, after some mild difficulties, created a carbureted baseline for the engine. That's when the fun stopped. After bolting on the TPI manifold, the engine struggled but never ran correctly despite our efforts. We discovered we really weren't ready to test the system because we hadn't spent enough time reading the MegaTune instructions. Eventually we also realized we had not loaded the base fuel map into the new chip we installed (see the "Installer Errors" sidebar--it's high comedy). Eventually we ran out of time and packed up our small-block and headed back to the barn.
Later, we regrouped and headed to Ken Duttweiler's facility for another shot at the dyno. This time, the engine fired right up and ran pleasantly, responding to tuning changes for a short time before an errant ignition ground caused us some grief. Once that was repaired, the MegaSquirt system responded instantly to tuning changes and within a few minutes we had tuned the entire wide-open-throttle power fuel map, making an impressive 450 lb-ft of torque with the almost-stock TPI manifold and SLP runners. We also quickly tuned the idle air-fuel and a portion of the part-throttle map before calling it a day.
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.
Conclusion
Despite some initial skepticism, it's clear that this MegaSquirt system works extremely well, becoming easy to work with once we learned how to navigate through MegaTune. There's a bunch of detailed material that isn't in this short story due to space constraints, so it's worth going up on MegaSquirt's Web site to dial yourself into all the details involved with this program. The biggest thing we learned from this project was that the system works as advertised, but that the overall project required a little greater investment than we anticipated. If you already have a complete EFI manifold with injectors, this will dramatically reduce the overall cost. We would suggest doing a cost estimate first before diving in if you're planning on spending less than $1,000 to complete a system. It's also important to note that we did not include the cost of building a high-pressure fuel delivery system.
Overall, we feel our MegaSquirt effort was successful, it worked as advertised, it is the least expensive system on the market, and it's a great way to immerse yourself in the world of EFI. The system has its limitations, as you might expect, but it will make power and do the job for a whole bunch less money, especially if you're good at shopping for parts. If you look at the MegaSquirt system as a great entry-level EFI system that will teach you all kinds of things about EFI, then you've got the right idea.
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. | |