All this talk about fuel, but...

[Tamadrummer88]

Seems like every week there's a thread that pops up about 87 vs 91 or so octane.

But what about mid grade?

Would midgrade (89) be similar to 87? Or is it closer to Premium?

Can any of the experienced tuners home in?

Thanks.


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[m4udin]

Another fuel question is why some tuners are tuning for E85 with no issues and others are claiming an E85 tune requires fuel system upgrades. I'm guessing it's the difference between Cobb Accessport and an SCT device?

 

[dausmus]

Well I know Adam is tuning with E30, I don't know anyone tuning straight E85 using the stock system cause the stock fuel system can't handle the extra fuel requirements that straight E85 requires (30% more if I recall correctly.)

 

[Rogues Gambit]

I never use anything less than 93, even if the price difference is significant

 

[Brian V]

I would have to think that the question would have relevance when an individual would like to know how does 87 octane affect the combustion processes while considering what this low octane fuel can and does create considerable knock and timing issues for the turboed engine because of the low compression and less pressures released during combustion . This combustion is low in pressures to gain HP during the warmest seasons especially during continued use of the AC unit with it's added constraints on HP .

The Higher octane an individual can afford for these turboed engines the better . 1 does not really have to afford a tune for the turboes to attain optimal efficiency while running a higher grade and octane fuel .

I guess it is really about choice and ideas plus the amount of money 1 is willing to spend while getting from point A to B and then C ..

I Personally prefer 93 octain and can claim better gas mileage during these summer months while pushing out AC and standing on it to get ahead of the econobox crowd that just seems to wonder down the road perusing the cell phone and stopping every red light along their journey .. me I would rather catch the green lights anfd keep a steady pace thereby increasing my MPG 's ..

Shoot I would like to burn E0 , but chitown has no such offerings and there are very few of those rare stations in this state .. Must be the corn Industry that I am surrounded by .

 

[Glenn G]

Its all about Air fuel ratio. Pure Gasoline the Ideal afr per weight is 14.7 to 1
For Pure ethanol it is 9 to 1, making e85 9.85 to 1. on full boost you need to run much richer to protect the engine from det so lets say 11.5 for Gasoline and about 8 to 1 for E85
MAPerformance has determined the the Stock turbo flows around 36 lbs of air per min maxed out.
on gasoline this would require injectors and fuel pumps capable of flowing 3.13 lbs of fuel per minute. These are direct injected engines that unlike a port injected engine cannot keep spraying fuel at the back of a closed valve to hit 85% or more duty cycle.
a GDI injector can only operate for a MAXIMUM of 25-45% duty cycle if it begins injecting during the intake stroke and all through the compression stroke. Which they don't, so you need injectors 3- 4 times the capacity of port injectors to make the same power. That means a fuel system that can support 9-12 lbs of fuel per minute for the stock turbo which the ecoboost does with a bit of room over head.

E85 running at full boost would require 4.5 lbs per minute on a port injected engine and 12-18lbs per minute on a GDI engine and thats why you would go lean on e85 without additonal injectors, not to mention the stock turbo just can't flow enough to make anymore power on e85 vs e30. The additional 2 injector TBI MAP will add can run 85% or greater duty cycles no problems and can add significant fuel volume to support a much larger turbo safely

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