Anyone on here ever do any testing with different brands of gas? Used to be you had Super Shell and Sunoco 260 I think it was, long time ago, and I was wondering if any thing out there in super unleaded is better. I'll be running a turbo on this build but when I had my Chevelle, 434 SB, 11 to 1, pretty healthy engine, I ran 40 total, big solid roller, and it ran fine on any of them but the cam bled off a lot of cyl pressure. I was just curious if certain brands are better, you don't really know what you are getting anymore and if they would have E85 available around here it would make the choice a lot easier.

 

Its a question about application and compression

Fuel quality varies day to day, hour to hour, pressure to pressure, atmosphere to atmosphere, place to place, you can always get bad gas somehow or contaminate with water or whatever. Fuel density is pressure and temp dependent.It may pump into the tank at once density and then heat up to a new density. Heating causes fuel molecules to jostle, rotate, spin, etc... more movement which affect octane rating, usually reducing it as higher energy input to molecules as they become a gas state means harder collisions with sterically hindered hydrocarbons which increases the number of successful forward reaction coordinate per unit time in some chemical reaction. Higher temps speed chemical reaction of combustion which influences pressure as the piston changes position.

If you are building a forced induction application the lowest compression will tolerate the worst fuel and support the most power. Expectation for a fuel and power consideration for that fuel is based on heat throughput, heat handling capability of the setup (any engine size), power per unit time (how long the engine needs to run for WOT i.e. boat engines sustain WOT for 5 or 20+ minutes must consider sustained heat control), and such things obviously octane rating which varies and compression which varies with boost pressure dynamically over some range of operating variables as RPM and load(rate of change of engine rotating velocity for internal components). Safety factor is originally built as systemwide when OEM engineers decide ultimately how much heat is able to be transferred via some engine parts they include from the factory. From there it is our job to determine whether more is needed and how to achieve that end. For example drilling additional coolant passages or changing the material science of the head and intake manifold to accomodate higher heat throughput will reduce the challenge of volatile fuels as gasoline in situations where high heat throughput is required, like a mile or ten mile race or something without cooldown periods. Most drag racing is done in short bursts allowing cooldown in between which drastically simplifies the heat throughput problem, you can heat the parts up rapidly just under max temps then cool them down at leisure for the next race. So the question you are asking is application dependent; driving a vehicle all day in the heat, uphill, heavy vehicle, towing a boat, on poor gasoline fuels, is quite different than the same fuel being used in a lightweight vehicle on a cool day for example at the same torque or power output. You can't judge the fuel without considering the heat throughput and application its being used in, time based, load based, compression based, etc...

For example 2.0L and 3.0L Nissan/Toyota skyline/silvia/supra engines 92-02 run 8.5:1 factory compression static. This compression as well as 9:1 even 9.5:1 modern engines, are sufficiently used for 250,000 miles on 93 octane fuel from 'any station' approx 400 to 650rwhp (~250bhp/liter) in those applications as daily drivers, will tolerate high ambient temps with proper intercooling (the engine can remove heat acceptably even with sustained output in hot climates and the compression ratio is low enough that the fuel is tolerated throughout changing conditions).

 

It all comes from the same place. The additive packages are what makes the difference in brands. There's always going to be someone claiming their car runs better or gets better mileage with a certain brand. I have yet to see any difference on the dyno while using any brand of 91 octane.

 

Unfortunately octane testing is a very expensive and specialized thing to do. Unless you can find some recent study or report published by a university or testing company, all you're going to get are anecdotes. From there, all you can really do is tune for the worst-case fuel you expect to get, have ways to mitigate damage caused by knock(like knock detection that pulls timing), or be sure to use fuel of a known pedigree...which is expensive.

E85 is no savior here; you would have to take the same precautions because it is even more variable than pump gas. It can vary from 70 to 85% per the DOE spec, but anecdotal reports indicate that it often drifts outside of that range by several percent. It just about requires EFI with a flex fuel sensor or measuring it and mixing it yourself to a known percentage.

 

It's quite a bit more than that. Winter blends are usually around E50. Around here it is E50 year round (makes my life easier). The good news is this can be tested with a reusable $10 test kit.

 

I've seen the E85 test kits, if we had it around here, I'd have one. I'm going to spray straight meth with pump gas, about the only choice I have. It'll be blow thru, at least for awhile and I have a Daytona Sensors Smart Spark. I'll have to purchase the good stuff, $$$, at the track and hope for the best. If it wasn't for taking the chance of running low or out of fuel, I'd just buy E85 by the barrel. I don't want to drive around and constantly watch the fuel gauge.

 

Admittedly I was going off of stale information. At one time it had to be 70-85%, but I see now that E "85" is allowed to be 51-83% ethanol. It does reinforce my point that the consistency is pretty crap.

 

E85 by my house has been 70-85 the last 14 years I have been running it.

E70 to E85 isn't that big of a difference when dialing in a/f. You can tune it for e85 and it will be around 4% richer on e70.

 

I keep checking stations around here hoping they'll get it. A lot of the Kroger's have it I've seen on line. We are suppose to get a bigger one so I can always hope.

 

Not sure how it is in other regions but around here every Kum & go has it. There are a couple aps for finding it as well.

 

I think it was 3 locations in Ky, one is around 38 to 40 miles from me but it is the opposite direction we usually travel. I'll check into the apps.

 

Ethanol percentage VS performance isn't linear. E50 basically performs just as well as E85. Its like a .6 octane difference. SO a station varying from E85 to E70 or any where in between isn't hurting your performance a lick. It can be annoying tune wise if you don't have an ethanol content sensor and and EFI system that can compensate.

FWIW I was blending m own fuel with our ethanol free 91 and E98. Which is sold here at the pump. To around e50-e60. My ms3 and ethanol sensor handled the tune changes with the lower blends. All I had to do was dump it in.

Id wager this fuel is actually better than our pump E85 as it doesn’t use questionable octane base fuel to mix with the ethanol. It also used up MUCH less of my injector and fuel system. Made 560/600 on E85 with my 80lb injectors tapped out on 11-12lbs. I was able to run 19lbs on E50-E60 blend. As to the fuels knock resistance, I’ll add that this was non-intercooled with in IAT’s pegging out the sensor at 255 before the 1/8th mile.

 

Something else to consider is how much going from E51 to E70 or 85 without changing the tune could or will affect knock sensitivity from leaning the mixture even if octane limits aren't otherwise reached. Another question that probably very few people have the answer to or at least not one that applies outside of a very narrow application.

 

There's no mystery... test the ethanol content, use a chart to find stoic, dial that in your tune as stoic afr. The rest of the tune will compensate. Modern widebands will show 1.00 lambda for stoic on E0-E(whatever). Makes it really easy to tell if something is off. Good reason to use lambda for tuning rather than AFR.