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Assuming the engine isn't knock limited, the torque should be pretty similar between e10 and 98? perhaps a touch lower with the ethanol but more or less the same?

I had a few people comment in a FB post that I should be tuning for 98 over 91 or e10 as there's a whole lot more power available even just by swapping fuel - even in a low compression (8.8:1) engine without knock sensor.

So I tried it. Dyno runs on e10 and 98 showed absolutely no difference in torque or HP.

Then I started adding timing. Ended up with around 15% more torque in most of the rev range and room possibly for more. This wasn't the case with e10, any more timing rolled the torque off. No detonation was heard through a knock sensor & headphones.

So what's going on? Where is this extra torque coming from? Maybe I'm not hearing detonation in the e10 tune? Does 98 burn more effeciently? AFR's were about 0.1 to 0.2 richer with the 98. Any theories?

Does 98 burn more effeciently?

I believe it burns slower and more thorough

A slower burn would explain the gains with the advance, but then you'd expect a loss compared to e10 with no change to timing?

alcohol requires more flow of fuel for the same energy. so e10 being 10% ethanol, I'd think requires half of 10% eg 5% more fuel for equivalent energy. Noticeable? Relevant? I dont know. I think you'd need to tune fuel and spark for both fuels and then compare the results.

That's why this is confusing - I did tune WOT with e10, about 10 pulls increasing timing in different areas that responded until there were very little gains per degree, then backed it off 2 degrees. I thought that was all there was to be had from the e10.

You'll need to add a little fuel for E10. Stoichiometric ratio for petrol is 14.7:1 for E10 I believe it's about 14.2:1