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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Weight and drag seem to be the two most significant parts of fuel economy.

CIS and EFI can both be tuned to run near peak efficiency but it is much easier to achieve a near ideal AFR and ignition settings with EFI.

After that it seems to be about increasing the VE of our motors at off WOT settings.

Off boost compression (up to +10%) and exhaust efficiency seem to be the next variables in line. Twin plugging probably being close behind (up to +4%).

One is going to make more power out of the same amount of fuel with more compression and get more from each gallon.

Reduced back pressure reduces drag on a motor during the exhaust stroke for more power from each gallon.

Twin plugging allows for later ignition during the compression cycle for less resistance being created before TDC and more power from each gallon.

Of course, a motor that puts out 500hp is going to use +/- 100% more fuel at WOT than one making 250hp.

With a CIS 930 the biggest challenge is achieving significantly more timing advance at part load cruse to get the most out of every gallon of fuel. Most run about 25 deg advance on curse. Most modern cars run well into the 30's of advance on curse.

Thus, I suspect our most significant limitations are frontal area, compression ratio, and the stock 930's timing system.

Last edited by 911st; 03-22-2010 at 10:45 PM..
Old 03-22-2010, 10:42 PM
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