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The MPG Page


(5/21/09) Soon I will include on this page the tips and tricks on how to make your Mopar pretty darn fuel efficient.  How about 20+ MPG with a 426 style Hemi, or 25+ MPG with your small block.  And doing this without giving up even 1 horsepower from the top end.
Yes - it can be done it you use technology and keep your foot out of it.
E85
E85 is an alcohol fuel mixture that’s basically a mix of 85% ethanol and gasoline by volume. It’s widely used in Sweden and is becoming increasingly common in the United States where, lets face it, we grow a lot of corn.  E85 has an octane rating of 100 - 105. It runs much cooler and it can be used in higher compression engines. Ideally the engine should be designed with a higher compression ratio to take maximum advantage.

The fuel energy for E85 is less than gasoline so you use more of it per mile. Therefore, E85 normally gets less MPG in engines that have lower compression ratios and if the engine isn't retuned for it. But it also costs less!  As I write this, Gasoline is over $4 a gallon and E85 is $3.10.  

Retuning a carbureted engine to run efficiently on E85 is hard to do and fairly expensive.  The carburetor must be replaced with one that's been rejetted for E85.  Not doing this will result in a lean condition which could damage your engine.  The distributor should also be recurved.

The procedure for running E85 with EFI is easy, as long as the EFI system has the ability to adjust for the different FEC (Fuel Energy Constant) and the fuel injectors are large enough to handle the extra flow where the A/F ratios are different.  Notice that E85 has an energy constant of .68 and likes A/F ratios in the 10:1 area.  To handle the extra fuel that 10:1 requires, the injectors would have to be 30% larger than for gasoline. So you install the larger injectors to start with, and tune the engine on gasoline, then save that program as program #1.  Then to tune for E85, check the box for Fuel Flex Mode, and you change the FEC value to .680.  Assuming this engine was already tuned on gasoline, that’s all you have to do. Store this as a second program that is selected by a switch under the dash, and you can switch between gasoline and E85 while on the road.

You should also advance the timing under full power and cruise conditions.  I start by bumping the timing by about 5 degrees.  This takes advantage of that 105 octane!  Each engine is a little different but that’s a good starting point.  

Mileage Gains:

Example #1:

We did this level of tuning on a customer’s street/strip car. We were was able to increase the car’s performance with E85 without increasing the engine’s compression ratio. Around the town mileage went down about 20%.  It's hard to tell if the lower cost of the fuel would offset the decreased mileage.

Switching to EFI by itself should increase fuel mileage by 2 to 4 mpg, but in order to take advantage of the extra E85 octane you really need to build the engine with a higher compression ratio to take advantage of that and get aggressive with the timing.

 

Example #2:

We just ran a series of tests on two EFI engines on the dyno. One was a normal 10:1 street 440 and the other was a high compression (11.5:1) 440. Other than the compression ratios they were very similar engines.  (As a baseline, with both on gas, the higher compression ratio engine yielded a base HP that was about 40 HP higher than the 10:1 engine)

I monitored BSFC (with is the brake specific fuel consumption), at various RPM steady state conditions and converted the results to MPG.

* The 10:1 engine had 18% WORSE fuel consumption, even after leaning it out with EFI.
* The high compression engine had 14% worse fuel consumption.

So whether or not E85 is a better solution, boils down to whether it's lower cost offsets the increased fuel consumption.  I will say the E85 cars are more fun to drive and the exhaust smells better.