Figure 4 - LS3 CT 525 engine,...
Figure 4 - LS3 CT 525 engine, full-load power pull results and comparison of E85 to 100-octane, with and without catalysts (100/300 CPI).
What is significant and absent any specific section area data comparing the two manifolds but focusing on the material differences in runner lengths, you can visualize how this influences torque output by again viewing the data plots. Specifically, if you will focus on the overall curve shape above and below peak torque rpm, you can see how the EFI manifold's curve was rotated slightly clockwise, compared to that of the carbureted combination. The result was improved torque below its torque peak and a slight loss above this point, while the opposite held the carburetor package. However, you will also observe that the quantitative improvement in torque from the EFI manifold below its torque peak clearly offset losses above the peak, given where an engine of these torque characteristics would like be geared to run.
OK, that's the first reason. The second deals with the fuel quality issue mentioned in May, particularly inherent differences in the conditioning of fuel delivered by fuel injectors versus carburetors. Of course, there are multiple factors involved in how carburetors and FI affect air/fuel charge quality.
It's the very nature of their design and functional differences. We'll just summarize a core difference by mentioning again that if you view how carburetors produce atomization efficiency over a broad range of engine speed versus that of fuel injectors, carburetors are comparatively lacking. This deficiency is particularly evident within the combustion space, cylinder to cylinder, during real-time combustion pressure and temperature histories.
As pointed out elsewhere in this story, the CT team is scheduling a round of engine dyno testing focused on engine cycle analysis (ECA) techniques that's intended to characterize the burn properties of carburetion versus EFI. These tests will be conducted in an academic, scientific environment void of any bias or presumptions about what the data will show. We encourage CT readers to continue following this project for those combustion-related results.
Are there any material differences in torque characteristics when comparing carburetion to EFI systems?
We included this question to emphasize the importance of considering functional differences between the two manifolds used (as previously discussed) while sharing some comments about optimizing companion parts. For example, an honest appraisal of the two induction systems should include exploring what configurations of other parts would enhance either system, particularly the camshaft and headers.
In other words, it's likely that using a cam and header set intended to operate in the engine speed range for which either the carburetor or EFI manifold was designed to operate should help both. As pointed out at the outset of this project, a principle CT goal was to explore viable possibilities for a greener approach to circle track racing. We intend to create a level of awareness whereby racers who are in the sport or business of racing can pick up where we leave off.
Prior to conducting engine tests, we realized that the critical step in any engineering evaluation is to ensure "apples-to-apples" comparisons of the data at hand. Circle Track's green racing team ensured a baseline comparison that could withstand scrutiny through honest and realistic testing procedures by using the resources available at every stage of the project. There was an internal agreement that, regardless of the results, data would be openly shared and published for the reader to review, discuss, and comment on.
In this environment, the first step in the dynamometer portion of the testing required the team to determine appropriate engine speed/load points for the tests. One method of doing this is to select a weighted series of steady-state points under which the engine operates during a given drive cycle, focus on optimization, and development of those points, and use them as an approximation of what the engine would experience in the real world.