[Nezil]

Originally Posted by ZM2

This brings up a question: can we look at E85 as just another form of octane booster?

Meaning, if your HPFP isn’t strong enough for E30 and you can only do E20, is it OK to run the pump gas maps with E20, just to raise octane a bit?

Or, are there other inherent differences bn the pump gas and Exx maps, and this isn’t recommended? Altho, if you can’t run more than E20, it probably makes more sense to just use booster to increase octane.

So, I guess I’m wondering if it’s OK to use the pump gas maps with a tank of E25-30? I’m thinking about if I’m headed to the track with a tank full of E30 on a hot day and need to dial the tune back bc of IATs.

I'm not tracking my car (yet), but I've been doing exactly what you suggested every fill up. I run the 91 OTS Stage 2, and I add 5 litres of E85 to every tank of CA 91 AKI fuel. Last I checked, and it has been a while, this was helping to improve my timing by raising the octane.

The E30 map is intended to be used with 70% 93 AKI and 30% E85 which will result in quite a bit higher octane than you'll achieve with crap base fuel and only a little addition of E85. The E30 map therefore targets higher timing and boost than the pump gas OTS maps.

My resultant mix is close to E20, and is at the limit of the HPFP. Its ocatane, according logs rather than calculations, is about 91...

[ZM2]

Great feedback Nezil

So, is the race gas map just more aggressive and needs even higher octane than the E30 map? Using 93 as a base fuel, the effective octane for E30 in our cars is around 96.

Edit: Yup, I’m seeing in the race gas map notes that needed octane is 100+. Helps to read first.

So, flipping this logic around, can we run the E30 map if we’re using booster to get 96-97 octane in our cars? I know the right answer is “depends on the logs”, but just playing out the theory here a bit.

[Pray for Mojo]

No, you can't use booster instead of ethanol and vice versa, ethanol has a different AFR than dinosaur juice. It's an oxygenated fuel so you will lean the car out by running a lot of ethanol without a tune adjusted for it. Conversely you could run too rich by using a booster on an ethanol map. The reason the E30 tune taxes the fuel pump is the amount needed to make the same power. Adding a bit to a 93 map to fix timing should be ok, but I wouldn't go nuts because the tune was probably meant for E10. I've gone E20 on the 91/93 maps and it helped a bit.

[Nezil]

Pray for Mojo is correct that you need more ethanol than gasoline for a correct combustion, but the DME is more than capable of compensating for this.

Our DME adjusts AFR based on the oxygen sensor in a closed loop system, so the only real problem is that you run out of HPFP, and then LPFP capacity as the DME asks for more fuel.

[pal]

I've used Boostane and Race Gas (the brand of octane booster) interchangeably at the track on hot days in my TT RS (hybrid turbo, FBO). I find both work quite well as an added safety mechanism. I like Race Gas for its packaging in small cans where I can use the entire can and chuck it. Boostane I have to carry around for a couple of events. They both tend to make the tailpipes a touch orange.