We have posted in the past the ill effects of being forced to use E10 gas ( feds require E15 by mid year) for performance as it takes more volume of E10 to produce the same level of energy then straight gas.

Where straight gas at part throttle would require a 14.7:1 AFR due to E10 causing a leaner AFR for best performance the NON WOT engine conditions for EPA would require at the least the PCM tuned for a richer AFR of 14.2:1

We obtained straight 91 octane gas to compare it to other tests where E10 was used to see what the effects are

The PCM had been tuned for E10 so that the fuel trims which were at 8% too lean back to around zero

Leaving that tune in and using straight gas and the engine being 11.3:1 compression we see where the fuel trims were at zero with E10 that now with straight gas the average fuel trims are now -5% rich with a maximum of -11% too rich.

Notice WOT timing was at 29 degrees, zero knock and misfire.

Clearly gives a image that in using E10 your PCM would be running 5 to 10% too lean ( leaner in hot weather) which induces engine knock and lower timing to reduce HP and Tq

Since E15 will be required by EPA around mid year you can expect your engine to be running even leaner and less performance unless you tune the PCM to solve the issues of using ethanol

Further testing of costs to using E10 gas.
Weather was 70 degrees.


WOT at 150 MPH



Mixed speeds

This is the test results of the captured scanner data.

As seen it made no different in the slower cruise part throttle run or the run with more WOT/higher speeds that a stock tune from GM is not adjusted for E10 ethanol and would cause engine to run 10% too lean
( worse with E15 coming out soon) and when PCM is tuned for E10 where the LTFT stay around a perfect zero that when normal gas with no ethanol is used then LTFTs will be about 10% too rich.

This shows the ethanol and the more percentage is used that your engine will run way too lean, have more engine knock, less timing, less fuel mileage and less performance

If finding straight gas and your PCM was tuned for E10 then engine will be about -10% too rich and will need retuning for either cases.

As to our custom NFW exhaust design ( review other thread about design and testing) with weather at 70 degrees at idle with windows up the exhaust sound measured between 78-84 Dba and car in motion measured between 84-90 Dba

Read more about the coming of E15 at

E15 gas mandate