Then there is the issue of how the single-plane, carburetor manifold used in the Project compares to the "folded hands" EFI version against which it was tested. A recent Enginology column discussed certain specifics about the composite EFI manifold being offered by Comp Cams, as a racing counter-design to the OEM version used in GM production cars and trucks. Of the features shared in that particular column, one focused on the effects of manifold runner length, as it pertains to torque production. Repeatedly we have suggested that changes in intake manifold runner length, regardless of manifold type (all else being equal), tend to shift torque from one engine speed range to another, depending upon whether length is increased or decreased.
So, if we were to review the engine dynamometer-generated torque curves from the Mast Motorsports exercise, it's evident that a torque improvement was produced in the lower engine speed range, compared to the conventional GM single-plane for carburetor use. The principle culprit? Runner length was greater in the EFI manifold, contributing to the lower rpm torque boost...right where the engine was running during corner exit acceleration and resulting in net quicker lap times.
Specifically, the range of engine speed in which the boost occurred was 3,000-6,000 rpm where an average 5-to 7-percent increase in torque was measured. In reality, peak power played a lesser role in shaving off lap times, which happened to be the forecasted outcome from the Mast dyno data.
In order to quantify one of the more obvious benefits to the EFI/E85 combination, we need to take another look at the New Smyrna track data. Recall, this is a banked, 1/2-mile, paved oval. Comparing the carburetor and racing gasoline package to the EFI/E85 system, average lap time for five consecutive laps (each combination) improved by an approximate 0.5 second/lap, and combined with a higher lap speed of about 2 mph. And by the way, fuel was pump E85 at less than $3 per gallon. Over time, that savings would buy a few more tires, right?
The previously-referenced improve-ment in corner exit acceleration was the result of an increase of 0.2 gs. Of particular note was that at 92 mph, exiting the corners, the carburetor/racing gasoline combination was delivering an acceleration rate of 0.14 gs. The acceleration rate for the EFI/E85 package was a significantly higher 0.55 gs, roughly four times the acceleration rate of the other package. Peak horsepower is often believed of greater significance than torque, an obvious misunderstanding of concept for applications like this type racing.
For now, we will not upstage future plans for this project by discussing them here, but it's safe to predict there is much to come as this activity unfolds that's clearly worth considering.