Editor's Note: For the past several issues you have read a number of articles on Circle Track's latest project. It's a project where we intend to break away from conventional thinking about what makes a great oval-track race car. As promised in the March issue, we headed to Texas for an engine dyno session at Mast Motorsports. The volume of data gathered was beyond expectations both in content and in volume. Given that situation we thought it appropriate to set the stage and tone for the coming analysis of that data by asking the two men critical to that analysis (Jim McFarland and Forrest Jehlik) to share some perspectives. So without further ado we give you Circle Track's latest endeavor, Project G.R.E.E.N. (Green Racing Experimental Engine Narrative).
At the outset of this project, there were an assortment of questions pertaining to how the engine would perform once subjected to the array of configurations planned. Among them were such issues as what might be the difference in brake horsepower when switching from carburetion to electronic fuel injection and could we identify the underlying causes? Would there be any material changes in torque characteristics comparing these two methods of fuel induction? Was there a chance that combustion efficiency might be affected and where in the engine speed range could this occur, and could we link it to the differences between carburetion and EFI? How much power would be sacrificed when catalytic converters were installed? Was the use of such converters going to make any significant difference in emissions levels from a bona fide racing engine? How would the engine respond to a switch from conventional racing gasoline to E85? Was it possible that the torque curve generated by an EFI system would become reshaped to show increases in the lower and mid-range engine speeds? In fact, would less fuel be required to produce the same or more power when swapping EFI for carburetion? And the list of curiosities didn't stop with these questions. After all, as racers or former racers, we're all headed in the same direction. It's just a matter of how, perhaps in a more "green" sense, we should be trying reach to our collective goals. The purpose of this little "introduction" is to lay out some fundamental considerations that need to be aired before you digest the dyno results in the next issue. We feel this is both important and critical to understanding and getting the most value from the data. For example, winning race engines aren't just about how much power is being made. There are instances where an engine of lesser peak power than another performs better at the track. In these cases, shape of the torque curves can play a major role in why the engine of lesser peak power was quicker on the track. Comparing the torque curves between a carbureted and EFI version of the CT525 engine clearly notes the low- and mid-rpm benefits from the use of EFI. There are other notable comparisons you'll discover when we share specific data next month.
At this point, it's helpful to review some of the fundamental design considerations of the basic LS engine, looking back to when it first came to life. I recall fuel injector aiming being a key element when information was shared with me in the early '90s during the engine's conceptual period. In fact, layout of the inlet path was largely dictated by the direction in which air/fuel charges would enter the combustion space. Both swirl and tumble were incorporated by combining inlet path targeting and how air and fuel were treated prior to and during the burn.