E85Forum.com

Socal Pat · Joined: 21 Feb 2011 Posts: 6 Location: Socal

OK so My Miata is running great on E85 BUT Both Myself and another Miata owner are seeing somewhat poorer mileage than we hoped for. We are seeing a reduction of +- 30%. Our widebands are both showing stoich so the AFR's are right. My friend is thinking that a base timing increase is in order.

So does E85 require (or allow) a timing bump for optimim tuning? I realize every car is different so I guess this is kind of a generic modern, fuel injected, OBD2, 4 cyl. question.

Thanks a bunch!

hotrod · Joined: 19 Apr 2005 Posts: 872 Location: Colorado

You should probably add a little ignition advance during light throttle cruise conditions. At lean mixtures E85 burns somewhat slower than it does at max power rich mixtures, so in effect at lean part throttle cruise you have slightly retarded ignition timing.

Start off with the ignition timing you would use for a 110 octane gasoline tune for a starting point then refine it slightly as you gain experience.

What I did, was spend a couple days noticing what rpms I tended to settle into most often for highway cruise and city street cruise at light throttle. For my car (Subaru WRX) it turned out to be a very narrow rpm range. I bumped the timing a bit when I was in the low load cells of the engine map.

My normal gear shift selections tended to place me at 3000-3200 rpm when at light throttle cruise regardless of whether I was going 45 mph on a city boulevard or 75 mph on the highway.

You can also make a difference in your fuel mileage by changing driving styles a bit. Up shift a bit earlier than you are used to on gasoline, and skip shift up to higher gears when on level ground.

In my car I could stay in low just long enough to get moving, shift to second up to about 35-40 then skip shift to 4th gear or sometimes even direct to 5th if I was on a slight down grade. E85 pulls under load better at low rpm which is what makes this possible.

Larry

440Jim · Joined: 01 Jan 2008 Posts: 188

Well the Stoichiometric ratio is 34% different than gasoline, so if the engine is the same, that is what I would expect.

Gas: 14.7
E85: 9.76

(14.7-9.76)/14.7 x 100 = 34%

To get improvement, one way is to build the engine with a high compression ratio for E85.