[1sickzl1]

Hey guys,

Since e85 requires the injectors and fuel pumps to run 30-35% more fuel through the system many people have added some combination of a cam, low side, high side, injectors or even a full blown PI system to run full e85.

If you are tuned for e85 you'd have the AFR / timing / etc. used for the equivalent octane you're flowing through your system.

My question is: If you're tuned for e85 (and obviously have a flex fuel sensor) but run say 91 and then dump a bottle of Torco in there would the tune recognize the boost in octane and act accordingly? My gut says yes, but I'm not totally sure. Also, and this is the more important question, would the addition of Torco tax the stock fuel system as e85 does?

Lastly, in theory if you're built for it and you're running 100% e85 you'd be at ~110 octane + torco (128 oz. = 14 octane) = 124 octane. Is there diminishing return at this octane level or could you get some serious gains with this set-up.

Mike

[arpad_m]

The flex fuel sensor cannot detect octane levels (nor can any other sensor for that matter), it reads alcohol content only. The one thing you do control via higher octane gas or additives is knock and thus knock retard. With E85, the measured percentage of ethanol selects the applicable stoich set in the tune, and timings are tied to that as well, based on the known properties of ethanol.

That said, octane boosters (or race gas) can still be very useful if you're limited by octane (aka knock resistance), because when the ECM sees no knock sensor activity, it will allow more timing and you'll get higher performance.

[Joshinator99]

Originally Posted by arpad_m

The flex fuel sensor cannot detect octane levels (nor can any other sensor for that matter), it reads alcohol content only. The one thing you do control via higher octane gas or additives is knock and thus knock retard. With E85, the measured percentage of ethanol selects the applicable stoich set in the tune, and timings are tied to that as well, based on the known properties of ethanol.

That said, octane boosters (or race gas) can still be very useful if you're limited by octane (aka knock resistance), because when the ECM sees no knock sensor activity, it will allow more timing and you'll get higher performance.

I would just clarify by saying the lack of knock allows “full” timing up to whatever the max advance is for that particular situation. It will not “add” timing, it simply doesn’t take it away due to knock. You can still lose timing due to other factors, like high IAT/MAT. Arpad is on the right track, just thought that was an important distinction.

Also, there is a limit to octane usefulness. You only want enough to cover the timing you need to run. If you can hit, for example, 24 degrees of timing with 104 octane and that’s where you make max power, you won’t gain more power with 124 octane.

[KingLT1]

As previously mentioned flex fuel sensor only detects alcohol content not octane. torco will make your pump fuel more detonation resistant. The ECU won't know it's there. You won't get anymore timing then what's in the high octane spark table. I wouldn't even waste money on torco if you can run a blend of E. E50-60 provides plenty of octane for these engines.

[radz28]

There are cooling and cleaning properties of E' also. That'll probably be the direction I end up going down the road. I have it around me, so it's kinda' a no-brainer.

[1sickzl1]

Yes you'd need to be tuned to take advantage of extra octane. But these cars in stock form are tuned on 93 octane, correct? So for those like me in CA, we'd see a power benefit from raising the octane level from 91 to 93 and nothing past that, except for reduced knock, stop ECU from pulling timing...

[Joshinator99]

Originally Posted by 1sickzl1

Yes you'd need to be tuned to take advantage of extra octane. But these cars in stock form are tuned on 93 octane, correct? So for those like me in CA, we'd see a power benefit from raising the octane level from 91 to 93 and nothing past that, except for reduced knock, stop ECU from pulling timing...

A bone stock LT4 is still octane limited with 93. So you’ll gain power on an LT4 bumping the octane to 95/96, especially on a hot day with heavy load.

[KingLT1]

Originally Posted by 1sickzl1

Yes you'd need to be tuned to take advantage of extra octane. But these cars in stock form are tuned on 93 octane, correct? So for those like me in CA, we'd see a power benefit from raising the octane level from 91 to 93 and nothing past that, except for reduced knock, stop ECU from pulling timing...

You are still going to get some timing pull due to iat vs spark table being set to pull 3 degrees @ 130 MAT.. Nothing can be done until that is changed in tune. Stock blower cars live in the 130-140 degree MAT range unless it's cold out.

[1sickzl1]

Originally Posted by KingLT1

You are still going to get some timing pull due to iat vs spark table being set to pull 3 degrees @ 130 MAT.. Nothing can be done until that is changed in tune. Stock blower cars live in the 130-140 degree MAT range unless it's cold out.

Ahh I see, so maybe some gains could be made before those MAT temps are reached, but if that's where they are normally then I guess a tune is what is really needed

[radz28]

Originally Posted by KingLT1

You are still going to get some timing pull due to iat vs spark table being set to pull 3 degrees @ 130 MAT.. Nothing can be done until that is changed in tune. Stock blower cars live in the 130-140 degree MAT range unless it's cold out.

I've been cautiously playing with that table. It seems like the car will tolerate a good amount of timing without retarding (based off MAT) until around 160* or so. I have commanded 0* retard until about then, and with mid-90* heat, and MATs near 160*, I don't get any knock. I THINK I have the theory of that table correct, and the car SEEMS to be reacting as I would like, but I'm still weary...

That's all because of fuel additive though. I bet I couldn't do this without a blend around 93 and the 2650 helps, I'm sure. As soon as there's airflow, MATs come down.

[KingLT1]

Nothing to be overly worried about on a LT4. You would have to do some serious dumb shit to blow one up. GM has to be conservative and factor all the nut jobs out there that will put 87 octane in theses cars. Even dealerships do it.