Tuning high octane fuel

[Plumber]

I decided to to try 50/50 mixture of 104 unleaded and our 90 octane pump fuel as I would when I am going to spray the car.

I am a little confused with the results logging auto ve, the log showed the car to be lean wanting additional fuel every where.

I thought more octane would result in a richer mixture. Any one have any input or thoughts on this?

[11sprocket]

Not sure about your mix, but in the UK I believe some of our high octane fuel is blended with alchohol (bio-ethanol) to increase the octane. Trouble is, alcohol needs a richer mixture (11.x for stoich). 10% alc would pull you 2.5% lean. This may be part of the cause, or I could be talking BS.

[joecar]

Using higher octane allows you to run with more ignition timing...
increased timing may cause leaning, so you need to add more fuel;

octane by itself will not affect the afr, but running more timing may;

$0.02...

lets see what others say... :)

[Plumber]

The mix is 104 sunoco with the standard 90 octane not sure if the 104 is using alcohol but I don't believe so. I'll investigate it.

[Maggie]

The mix is 104 sunoco with the standard 90 octane not sure if the 104 is using alcohol but I don't believe so. I'll investigate it.

No Alcohol in the Sunoco 104. It is a highly oxygenated fuel for NA EFI racing engines with compression ratios up to around 12:1
IMO not the best choice of fuel to "spray"

[Plumber]

No Alcohol in the Sunoco 104. It is a highly oxygenated fuel for NA EFI racing engines with compression ratios up to around 12:1
IMO not the best choice of fuel to "spray"

I've been spraying nitrous oxide in conjunction with this fuel for years, it works just fine.

The question was related to a higher octane fuel causing a lean condition.

[Maggie]

I've been spraying nitrous oxide in conjunction with this fuel for years, it works just fine.

The question was related to a higher octane fuel causing a lean condition.

The Sonoco 104 GT plus is aprox. 4.8% oxygen by weight so it carries a higher O2 value (and more than likely a higher nitrogen percentage) than comparable fuels of similar anti-knock rating. The lean condition is more likely a result of the burn characteristics of the fuel.. ie, Blending the fuel changed the specific weight of the base fuel to a lower value. It is not necessarily the Octane rating of the fuel that determines the amount of 'air' to fuel for optimum performance, but how much 'air' is needed to provide the optimum burn with the EGT's within a safe range (A Ratio of the Volume of detonation gases to Heat of Reaction). This is called "oxygen balance" and has a impact on the specific energy of a fuel.
It is conceivable that you could have comparable EGT's with the blended fuel that you had with the base fuel even though you have a leaner AFR...But, I wouldn't chance it.

[Plumber]

Thanks for the reply Maggie, very informative. :cheers: