Fuel Octanes and Ethanol Additives

[kiwiginger]

Right so over here in New Zealand, we have two options as a 98RON (93 Octane for you guys Stateside).
Option one:
BP 98RON, Has no ethanol additive whatsoever (So they say)
Option Two:
Mobil 98RON (also another company called Gull but same/same), which is a little bit cheaper but its a 95RON (91 Octane) with a 10% Ethanol Additive which they "claim" increased the octane to 98RON.


Which of the two am I better off using?
Keep in mind that I know that the Ethanol additive isn't good for my catylist but I'm planning on removing that anyway.
Also, I am aware that Ethanol burns a little bit quicker than Petrol, so I know my fuel economy won't be as good with option 2, (price of fuel probably reflects it)

Also if option two is better, should I tune it as an E10?

I'm sorry if it seems a little confusing...

[mituc]

The one with ethanol should be more stable at high boost/high rpm. However, the 98RON gas with no ethanol or (3-5%) is going to be a bit more energy efficient. You can only tune for one and then test with the other to determine which one is truly more stable and less prone to knock though.
Neither will have any effect on your catalytic converter, you can use either no problem.

Don't remove the cats entirely, leave at least one sport cat in the downpipe. A 200cel metallic is fine.

[kiwiginger]

Ok, so basically better off tuning for the E10 and using it.
Whats the advantage of keeping my catylitic converter?

[mituc]

Well, E10 and 98RON/93OCT gasoline are about the same. If the gas you use would be rated higher, such as the BP Ultimate 102 which they sell in some "privileged" west-europe countries you could tune for E10 which doesn't take much more timing advance than a regular 98RON/93OCT or 100RON/95OCT gas. The really cool stuff begins with E20-E25.
So start your tuning from a 98RON/93OCT calibration map and see what you can do from that point on.

As for keeping your cat... apart from not slowly killing yourself and your passengers when all those fumes make their way back into the cabin, a cat will also help controlling boost a bit better, especially on a big turbo application. Of course if you're going for 500whp and more the cats will just stay in the way, but at that point I guess we'll be talking about a dedicated race car and not just a street driven sleeper car.
So my advice is, if after removing the secondary cat, the primary cat will continue to stay in the way of your goals, just replace your downpipe with an aftermarket one which still has a high-flow 200cel metallic cat with 3"/76mm exits.