I must be crazy but I'm almost getting 180 miles in the 1st half of tank then less in the 2nd half. I was getting really crapy mileage right after I put a cat back muffler on. I took this for 2 tank fulls, and then seeing how regular was so expensive, I put the highest BP offered surpreme, I think. Now its back to my 330 a tank which I can live with. Rember this Ohio gets the garbage gasoline I've heard, Not enough regs, and oversite of the pumps.

 

why does threads like these pop up like mushrooms? there must be hundreds or thousands of thread pages in total here on FF... WHY???

 

The honda fit is a econ. car, so some talk about why they bought it, so what wrong with that.

 

ayup. that's about right...

 

like I said there's already hundreds of thread pages about this topic...

 

easy solution, unsubscribe and ignore the thread.

 

Our extensive testing indicates 2 to 3% better mpg but at a 10% cost increase so 87 is choice unless you're going on track.

 

I don't think your 10% cost premium is true anymore... And this is something easily calculated (not estimate).
Around here it's 16cents/$4.50=3.5% price premium.

I mentioned it before in another htread, but if regular cost $100/gallon but premium cost $100.16/gallon would that change your thinking

 

$0.30 spread here (north Atlanta). 0.3/3.59= 8.4%

Is that better mpg, HP, or both Mahout? I would have thought HP to be the only concern at the track...

 

ok... sheesh

 

Has anybody put a scangauge or ultragauge on a non high compression engine and switched fuels? I'm curious as to whether the timing changes would happen there too.

 

The 3% is mpg and if memory serves about the same for hp. Yes hp is important for the track but so is the faster ignition, which in part is a result of higher power. Theoretically there should be a 3% increase as well because typical premium has about 3 to 5% more energy per pound of fuel than regular, mostly due to enriching one component, toluene.

 

So if premium doesn't have more energy, then MPG should be the same.

All sources I've been able to find indicate the variation in BTU (energy) content between premium and regular is no more than between two different tanks of regular. The energy content of the fuel is more a function of the crude it was refined from, and the actions of the refiner. The only qualifier for premium fuel is octane rating; not BTU content, not detergents. Some premium fuel may have higher BTU and more detergents, but this is not verifiable. Some will have less depending on who you buy it from.

Some sources point out the additives that increase octane reduce the BTU content. Some even say, as a rule, use the minimum octane necessary to avoid knock to get the most power.

If gasoline retailers could advertise "more power" as a result of using premium fuel, I think they would. Some will advertise better MPG as a result of cleaner injectors through greater amounts of detergent, but without verifiable, comparable values, this is just puffery.

I appreciate your response.

 

Just because it has the same energy, it doesn't follow that mpg would be the same, as the system is not even close to 100% efficient at extracting or using the energy.
This gets back to the underlying basic point of the flexibility of how much the engine will change it's cycle to extract and use more of the energy.

 

There is so much that is continually, and seemingly intentionally misunderstood here.

As ray was kind enough to point out, it doesnt really matter how many kJ/kg you have on hand if you cant use it.

Which goes back to the beginning of my contentions... you cannot make speculations and assertions about fuels when you dont even understand the most basic principles involved.

But this being the internet, ya'll think your experts.

There may be 3-5% in a given mass of premium vs regular dependent on composition, but that doesn't mean you are limited to extracting only 3-5% more energy. Because among other back-assward assumption that would be making, it suggests that you are extracting 100% of the energy out of that given fuel mass.

You most certainly are not. In addition to losses in pumping, heat, friction you are also neglecting what doesnt get burned or is burned where there is very little to no mechanical force provided due to the angle of advance and flame front propagation. As well as what the actual lambda differences are between a comparable scenario directly pitting a control fuel vs the variable.

Nobody has even considered what the actual valve timing/cam phasing changes involved look like either.. or how much the engine nanny is actually letting the TBW system open the butterfly.

This concept is most effectively displayed with alcohol fuels. But again this would all be lost on the majority of posters on this forum.

And Brain, if you are genuinely curious and not looking to make one of your famously fallacious conclusions from the stuff you skimmed off the top I would be happy to discuss the effects with changes in compression.

Though I expect that to be derailed with more appeals by the peanut gallery to the lowest common denominator as well.

I have pump gas datalogs I can grab screen shots from that go from 7.8:1-14.5:1 on a wide range of fuels, including boosted and NA applications.

And before you tell me FI is a whole different animal.. it really isnt. It is analogous to simply running very high comp slugs in the same motor with a different cam.. so basically just changing the dynamic compression ratio.. which is what VTEC changing the EVO/C and IVO/C events is equivalent too.

Its why on a particular 7.8:1 comp pump gas 93oct motor I can run 37-38psi with 13* peak timing @ 10.5:1 in the summer, and 18* peak at the same boost while leaning out as much as 5-8 points in the winter.

And on that same setup, introducing water/meth to provide an equivalency of 116 octane I can get away with 21* and 11.8:1. in the summer, and 21* @ 12.2:1 in the winter. Yes this is accounting for IAT and chargecooler efficiency that changes with ambient temp and flow over the core.

Which further demonstrates how much more involved these retardedly oversimplified premium v. regular discussions are.

 

I run 89. Now everybody should love me!

Actually I run 87, but don't tell anyone. I likes all my peoples on FF.

 

At low throttle, I'm gonna go with (ceteris paribus) changes in octane rating over 87 have no impact on mpg.

The question is at medium and WOT what happens?

We have sworn statements (well statements with swearing anyway) that timing is pulled with lower octane. The impact on MPG and HP has not been documented outside of "a feeling."

Mahout's statement that 2-3% gains might be seen due to higher energy content is intriguing, but irrelevant as energy content of retail gasoline is not standardized or documented.

My conclusion is less advanced timing due to 87 octane at wide open throttle when the advent of knock is detected, has a small impact on peak HP (maybe 3%). But this effect is short lived. At less throttle a few revolutions later it returns to ideal advance and fuel mixture (or else it wouldn't be very efficient).

Popular and scientific literature backs this up. If the high octane crew could point to something published to support their feelings of greater performance using higher octane ratings in a car whose manufacturer neither recommends or requires higher octane, my conclusion would alter.

After years of enjoyable discussion, they have not been able to provide a single thing. Except for SB. He put me on to an article supporting my conclusion...

 

TPS doesnt mean shit when you aren't accounting for load, chief. And has been explained to you multiple times, there doesn't need to be actual instances of knock for timing to be pulled or have the mixture enriched.

You have been given evidence, I have given actual datalogs and numbers, you just cling to what you want to see.

There is no point in providing you further documentation because you dont know enough to evaluate what you are looking for and you are hardly impartial enough to pull away anything other than what you want to see anyways.

Let me make this clear..I am not trying to convince you in particular, because you are blind and don't have the basics down to begin with.

I am here for the sake of others actually looking to learn. I could care less what it is you BELIEVE.

You can link to a qwiktrip ad blurb with no actual data involved that pretends to debunk a "myth" as many times as you want, but it doesnt make it true.

Speaking of which, if there is no difference between regular and premium.. why would you accept that certain high performance applications require premium but when we mention an "econo car" the full cognitive dissonance comes back into play?

You readily admit that a 12.5:1 motor or a turbocharged car would require the octane bump, but in the next breath youll tell us it does nothing and there is no difference?

It really makes your "argument" into a bit of a farce.

You keep claiming the Fit was designed for regular, which is absolutely, utterly unfounded. You realize that cars going back to the 80s have adaptable timing and fueling schemes, right?

Hate to break it to you, but for pump gas.. especiallyn 87AKI, 10.4:1 IS high compression. Look how much work was involved in trying to get the motor to survive that on pump gas. Variable valve timing, coated pistons and oil squirters (both of which are typically only found in factory boosted motors)

This is not representative of something made with 87AKI in mind. In fact that arbitrary Octane number parameter scale found in ECUs lists 87AKI towards the bottom of the range. Look at what this motor runs in the country it was designed in..

Hint: its not 87AKI.

Maybe its time to admit that you have no clue what is involved, but have some personal beliefs you want reinforced?

You want something universal, black and white and cut in stone. And will accept nothing less. This is what simple minds do.

 

Sorry, Bubba, I meant at low load. At high loads my foot goes down more.

 

Also not true, you can have high load at low rpm and relatively low tps.. its all about context. Which I know you are not big on.