[ONEof500]

Put 2 gallons of e85 in with 13 gallons of 91 in my 340 with mppsk? I want to get the experience of 93 octane....

I've read many of the threads and I believe the summary is don't exceed two gallons. Is there any downside?

Appreciate the feedback.

[paimon.soror]

Its an 'old' trick to supplement 91 octane for knock resistance, so yea, effectively it gets you "93 octane".

Just note that you will see a slight increase in your fuel trims, not much, maybe about 3-5% or so to compensate for the lack of energy from the e85 mix.

Much better option than adding "octane booster"

[riskmaker76]

Try boostane... it doesn’t leave the residual ...though not cheap but can get you above 93

[Bullitt1841]

Been doing it for a year and 20k miles. 3 gallons will get you ~E25, which is the most you can run with a JB4 and no meth (for max power). If you run any more ethanol on Map 4 or 0 (or with no piggyback), your DME boost target will lower and your timing, AFR, and everything else will be perfect. But if you run more than E25 on any other map, you will run extremely lean and potentially damage your engine.

[ONEof500]

Thanks no tune for my other than mppsk. Just looking for easy way to do better than California 91 octane.

[eluded]

Originally Posted by 1911and340

Just looking for easy way to do better than California 91 octane.

Move to Texas ?

[bradsm87]

I wouldn't go over 1.5 gallons.

[dereksM3]

Just remember many of the mainstream octane boosters contain MMT and generally leave deposits on your plugs. They can also wreak havoc on your catalysts. Lucas, NOS, Torco, VP, etc. all work well but they can lower your sparkplug lifes span. I generally would only run a tank here and there.

With that said I would go with a couple gallons of E85. You can find online mixing calculators to give you a general rule of thumb. Assuming you don't have a JB4 I would be careful mixing too much as to not throw off your fuel trims too much.

For reference our tank is ~16 gallons IIRC, so if you did roughly 14 gallons 91oct and 2 gallons E85 you get just under 93 octane. You should be able to go up to 3 gallons without issue but I would start small.

[paimon.soror]

...and keep watch on your LTFT ( if going above 2gal)