A thought on Fuel, mileage, and cost

[tiki240]

To keep it short and simple, I just serviced the fuel system including adding octane booster of a to remain un-named brand. I noticed a significant jump in throttle response and fuel economy.

As often as possible I run shell or hess 93 octane fuel, however, all stations have 10% ethanol and I HAVE gotten into badly contaminated gas before.

At the fillup immediately following the fuel system service, I added nothing to the tank, and noticed an 8 mpg decrease in MPG, lost crispness in the throttle, and lack-luster performance. I drove out that tank, and changed stations for the next one, again, 93 octane, no additives. Same result. (Approx 18-20 mpg averaged between city and highway with no flogging on it)

The next fillup, I returned to the same station, and used the same fuel again, but this time added the booster. I saw a notable increase in mileage of about 2-3 mpg but no throttle response or power gains. I made sure car was loaded weight wise the same, in similar driving conditions. I was going to dismiss this as i just had a dirty fuel system prior to the initial service but I happened upon a vendor of some CAM 2 (110 octane) fuel.

I did some research here on prime, and purchased 5 gallons of this pricey funny colored stuff, and mixed it with 10 gallons of 93 from the previous gas station. I took great care to drive the car again as near to perfectly the same as I could muster and I was absolutely floored with the results. The car was -alive-. I've never felt the throttle that responsive. I monitored each and every single mile, and patiently awaited the soft amber glow of the low fuel light.

Here are the results:
Year: 1992
Mileage: 111,265
Gearbox: Manual
Average daily commute: 53 miles
Air filter: New oem
Oil: Royal purple 10-30
Exhaust: cat-back taitec GTLW

Max combined MPG average with 93 octane (10% ethanol) unleaded and no additives: 20mpg
Cost average to fill up with 15 gallons: $56.75

Max combined MPG average with 93 octane (10% ethanol) unleaded + unnamed additive: 22mpg
Cost average to fill up with 15 gallons + additive: $76.75

Max combined MPG average with 10 gallons 93 (10% ethanol) unleaded + 5 gallons 110 race fuel: 28-30 mpg I wish I could say it with more certainty, but its almost impossible to drive the car the way I do with the first two tests for the entire tank while it feels so much more responsive (and ive tried THREE TIMES)
Cost Average to fill tank: $81.83

My rough math works out to ~2-3$ more to run the race gas mixture on the low end of the spectrum assuming 300 miles to 15 gallons on pure 93 (10% ethanol) and 420 miles on 10 + 5 (~.19 /mile x 120 more miles). If I could drive the car the exact same, I reckon I could probably eek out that magic 30 mpg.


Now heres where you come in... I would've chosen the race gas mix based purely on the intoxicating effects, the mpg bump is just a bonus to me.

What my curious mind is begging to know, is how just 5 measly gallons of race fuel dilluted into 10 gallons of average joe 93 octane gas, netted me the additional two days (~120-150 miles) fuel economy all three times I tested it. My mind is blown.

 

[Aluminsx]

Your test is interesting to say the least. It was always my understanding that anything over the octane that your car needs is a waste. I'm curious if you do the test for a longer period would you see the same results? Maybe worth a shot.

 

[bngl3rt]

Why not name the additive? I'd love to try it...

 

[davidf]

Careful on the additives. They can damage the 02 sensors if used to often. Occasional is ok but every fillup is pushing it. I replaced my share of 02's on my GN from over using 104plus. It even coated up the valves. Use it in moderation.

 

[tiki240]

for science, I have purchased another 5 gal. of 110. and I will add 10 gal of shell V-power 93. I shall report back in a few days!!

 

[jond]

Stock ECU right?

 

[tiki240]

Stock ECU right?

Correct.

 

[Vega$ NSX]

I said this before here in this linked thread, but regarding octane in general:

Keep in mind octane does not equal more power. 100 octane gas does not have any more "power" than 89 octane gas. The octane rating only measures the resistance to detonation of the fuel or how much the gas can be compressed before detonation.

So let's examine that in detail for a second. Let's say our NSX requires 91 octane. This is determined by knowing how much air and fuel is mixed (air/fuel ratio) and the compression ratio the car is tuned for. If I require 91 octane, it means, I've tuned the engine to not detonate at the given air/fuel and compression ratio. If I put 89 octane in, then air/fuel and compression ratios will not match the octane. As the gas gets compressed, it will spontaneously ignite before the engine is at proper stroke. When that happens you get detonation and you will hear pinging or knocking which is bad for your engine.

Now on the flip side, if I put 100 octane in, the engine won't generate any more power than at 91 octane. It just means I have greater protection from detonation/knocking/pinging. The car will be running at the same air/fuel and compression ratios so nothing will change. Now, if I retuned the engine to accept the 100 octane (usually done by increasing the air ratio, changing timing and/or compression) then I can take advantage of the increased resistance to detonation and squeeze more power out of the engine. However, that would mean I couldn't go back to 91 octane without fear of detonation/knocking/pinging unless I had an ECU that could reprogram on the fly for different octane ratings. For example, my NSX is turbo boosted and I have a boost controller with a HKS F-Con controller. My tuner (Factor X) tuned my car for different settings for different boost level and octanes. I have a setting that is good for 100 octance race fuel and I'm able to push 14 lbs of boost. However, if I can't get 100 octane, there is a setting I switch to that is good for 91 octane. However, I can only push about 9 lbs of boost and my power output is a lot less. If I were to run 91 octane on the higher boost setting, I would probably detonate and damage my engine. However, if I were to run 100 octane at the lower boost setting then the car would run fine, but only at the lower boost settings and reduced power levels.

The common reason people think increased octane improves performance is because most higher octane (91) cars today have anti-knock sensors. What these cars do is detect knocking/pinging due to low octane fuel and retard the timing, air/fuel ratios etc. among other things to protect the engine. In other words, it retards performance to match the lower octane gas because it is safer to lower the performance than have engine damagine knocking/pinging. But that means the engine is running at partial capacity, which not only robs power, but decreases efficiency and fuel milage. So when the driver then increases the octane, the engine goes back to running at optimal performance. The driver thinks he's getting more performance, because the engine is running at full performance at the correct higher octane, rather than the derated performance at the lower octane.

So in regards to octane (and octane alone) you should not have noticed any change in performance and gas mileage unless you had your engine management system re-tuned to accept the higher octane by adjusting the timing and/or air/fuel ratios to take advantage of the higher resistance to detonation that the higher octane offers. As for any additives and their effect on performance, I can't say as I do not know what additives you used. However, in my opinion and experience I have not found any standard additives to offer any significant performance enhancements.

- - - Updated - - -

I suspect it's not the octane or the additives, it's the 10% ethanol. Ethanol has less energy density than gas. So what that means is that when you fill up your tank with 10% ethanol, you have less total energy density than a full tank of 0% ethanol gas. The 110 octane isn't what's helping, it's the fact that you replaced the ethanol with more gasoline. I would assume you would have had the same effects if you went with 100% 91 octane gasoline with 0% ethanol. Try it and see if it works.

 

[tiki240]

I said this before here in this linked thread, but regarding octane in general:



So in regards to octane (and octane alone) you should not have noticed any change in performance and gas mileage unless you had your engine management system re-tuned to accept the higher octane by adjusting the timing and/or air/fuel ratios to take advantage of the higher resistance to detonation that the higher octane offers. As for any additives and their effect on performance, I can't say as I do not know what additives you used. However, in my opinion and experience I have not found any standard additives to offer any significant performance enhancements.

- - - Updated - - -

I suspect it's not the octane or the additives, it's the 10% ethanol. Ethanol has less energy density than gas. So what that means is that when you fill up your tank with 10% ethanol, you have less total energy density than a full tank of 0% ethanol gas. The 110 octane isn't what's helping, it's the fact that you replaced the ethanol with more gasoline. I would assume you would have had the same effects if you went with 100% 91 octane gasoline with 0% ethanol. Try it and see if it works.

Fantastic response sir! I would love to get my hands on some pure gasoline as I too suspect that the increased economy is a result of less ethanol infused fuel being used. I still however, have a hard time swallowing a gain of 120-150 miles to 15 gallons fuel mixture. I would love to try this test with a full 15 gal of 0% ethanol gas, but there are only 2 stations within a good 6 hours of me that sell it, and the travel to get to/from either of them would throw another unaccounted for variable into the mix, further skewing my yeilded results.

 

[Old Guy]

First off, 110 octane rating for the racing fuel seems very high for an unleaded racing fuel. Is this an R+M/2 value, some kind of Blended Octane Value (BOV) or a RON value?

Depending on what the racing fuel is made from, you could get an improvement in fuel consumption just because the racing fuel has a higher energy density. E10 gasoline has an energy density of about 31.7 MJ/l. If (a big if) the racing fuel was primarily toluene or xylene, it would have an energy density of about 34.9 MJ/l. Based upon this, your 10 gal E10 / 5 gal racing fuel mix might have an average energy density of around 32.7 MJ/l which might yield about a 3% improvement in fuel consumption. This is no where near the improvement you are reporting.

BOV octane calculations are a little flakey and do not match up that well with numbers from test engines; that said, the BOV on your fuel mix would net a BOV octane rating of about 97.6 assuming that the 110 number for your racing fuel refers to an R+M/2 octane value. An octane number of 97.6 is way beyond what Honda recommends and I would not expect it to provide any material benefits above 93 octane fuel for a stock engine. However, your car is a 1992 and may (almost certainly) have some carbon build up in the combustion chamber which is raising the effective compression ratio of the engine (above design) and is generating a requirement for a higher octane fuel. In the absence of the higher octane fuel, your ECU may be retarding the spark to avoid detonation which is going to have a negative effect on both performance and fuel consumption. Running the higher octane fuel mix may be alowing the ECU to return to its normal spark advance settings. Have you ever tested the compression on the engine to determine whether it is 'in spec'?

In support of this hypothesis, I offer up the example of my winter driving 'mule'. Its an 87 turbo Volvo with Volvo's overboost kit. When it was new, the engine would run happily on 87 octane fuel (or at least operate within the limits of the ignition system's ability to retard spark and avoid detonation). Over the years, it got to the point where I had to switch to 91 octane fuel to avoid detonation under wide open throttle (and yes the detonation sensor was working properly). Over the same period, I would do periodic compression tests and I observed that the compression test results were getting higher as the engine aged, presumably due to carbon build up in the combustion chamber. I must admit that I did not notice a spectacular improvement in fuel consumption with the 91 octane fuel; however, there was a material improvement in performance.

Anyway, its just a hypothesis!

 

[Vega$ NSX]

Fantastic response sir! I would love to get my hands on some pure gasoline as I too suspect that the increased economy is a result of less ethanol infused fuel being used. I still however, have a hard time swallowing a gain of 120-150 miles to 15 gallons fuel mixture. I would love to try this test with a full 15 gal of 0% ethanol gas, but there are only 2 stations within a good 6 hours of me that sell it, and the travel to get to/from either of them would throw another unaccounted for variable into the mix, further skewing my yeilded results.

I agree those are definitely on the high end of expected results but the NSX really wasn't designed to handle any ethanol at all. The NSX's I know who run E85 (33% less energy density) use a ton more fuel than I do running 100 octane race fuel (like for like turbo boosted cars). So much so they have the next size larger fuel injectors.

Too bad you don't have a more local source of pure 91. However, if you have the cash and an insatiable curiosity, you could try using 100% race fuel (or at least the same volume of race fuel vs. 93+10% ethanol mix) and seeing the results. In theory, you should get even greater fuel economy/range than the 1/3 race-2/3 93+10%, although it's not a linear relationship.

Also, keep in mind the temperatures. I have no idea where you are located, but it is my understanding that ethanol is MUCH more reactive to temperature than gasoline. I can't remember warmer temps are better or worse, but you might be able to research it and see if there was a correlation to your findings. Keep up posted, very interesting topic! :smile:

 

[tiki240]

The 110 I am mixing in is actually leaded, and simultaneously the same reason I have never run it with just the race fuel. The leaded 110 fuel by itself would in all probability do more harm to my o2 sensors, oil, and catalytic converter than net benefit to fuel economy. I also find your fundamental logic to be sound with regard to the higher-than-spec compression ratio and possible retardation of ignition timing without elevated octane fuel. I am being extremely careful with how I operate the car this tank because I would hate to throw off such a fascinating (to me, at least) "study". Of course, Fuel economy is not why any of us bought our NSXs, but if as stated in my original post, there is a measurable/feel-able performance and/or economy boost within little to no difference in operating costs, Id happily spend an extra few dollars if it meant not only would I be driving for longer without a fill-up, but enjoying the car all the more.

I made sure to use 10 Gal of Shell 'V-power' as it is the "best" pump-fuel readily available, so this tank should be enough to at least give a reasonably definitive answer one way or another. Another thought, it could also be the sum of all the factors combined rather than any one aspect. The cold, more dense air from the current season, + a clean fuel delivery system, new spark plugs, fresh oil, new air filter, not getting stuck in traffic, not winding the motor out to redline, not braking unnecessarily, using the best available pump fuel, mixing in a more energy-dense leaded fuel, the ignition timing being able to to return to factory-tune, and not having the windows down making the car more aerodynamically slippery, etc.... essentially, generating a 'perfect storm' scenario for operating conditions.

One way or the other, I am excited to report the results after the next few days.

 

[Old Guy]

An obvious caution with the use of leaded racing fuel. Even though you are diluting it by 66% with the addition of the Shell gas, you may still have very high concentation of TEL (lead) in your blended fuel mix. This will depend on how the racing fuel was formulated to get the high octane rating; but, adding lots of TEL is generally the cheapest way to increase the octane. Your blended mix might have a TEL concentration that is higher than the premium leaded fuels available pre 1975! During the combustion process, TEL forms metallic salts which messes up spark plugs, O2 sensors and catalytic converters (the switch to unleaded fuel has been partially responsible for the extended service intervals that we now have on items like spark plugs). It used to take more than 1 tank of leaded gas to bugger up a catalytic converter; however, I have no sense as to how sensitive O2 sensors are to fouling by TEL. Given the price and hassle associated with their replacement (at least on my OBDII NSX), I would not be inclined to experiment too much with the use of TEL fuel. Also, if you live in an area that requires SMOG certification, you could be in for a nasty and expensive suprise at your next test.

Your test ideas are interesting; however, I suggest avoiding the use of leaded fuels as it will limit the experiments long term application to 'street legal' cars, although I admit that it is going to be pretty hard to get really high octane numbers without the use of lead. A popular way of boosting the octane rating is with the use of toluene or xylene. Toluene has an R+M/2 of around 104 and xylene is slightly higher. Most commercial gasoline already has a significant component of toluene (15-30%) in it so it is not an 'alien' substance and should not present any material compatibility issues with the fuel system or problems for O2 sensors or cats as long as you don't go crazy with the blend ratio. Toluene and xylene are available at paint suppliers and places like Home Depot. The price per gallon at Home Depot probably makes it unrealistic as a fuel additive; however, I have heard that if you are prepared to purchase it in a 5 gallon pail from a wholesale paint dealer, you can get it for less than $10 per gallon. Clearly, this is going to be a lot more expensive than using racing gas and I suggest toning down your blends a bit. 1 gallon of toluene with 14 gallons of 93 octane gas would give you a BOV of about 93.7. A 2 gallon: 13 gallon ratio would give you a BOV of about 94.5.

There are lots of resources on the internet discussing the use of toluene as an octane booster which are worth exploring. If you decide to experiment with it, two words of caution. Tolune is volatile and an agressive solvent. Be careful with the vapours (flamability issues and giving you a real bad buzz if you breathe them in) and if you spill it on your paint you will probably lose or at least damage your clear coat.

With a longer term view, it would be really interesting to confirm whether your engine has a higher than normal compression ratio (either due to carbon build up or perhaps modification by a previous owner). I think that this is important as it will determine the applicability of your results to other owners. If you have an elevated compression ratio, it means the performance results that you achieve with the high octane blend are likely not going to be repeated in cars with normal compression ratios. If it turns out that you have a normal compression ratio, then something more interesting is at play here.

 

[JD Cross]

I concur with Old Guy on the unleaded fuel usage and possible damage to O2 sensors.

As far as mileage goes I've got 21 years of records going back to my first tankful.
Meaningful mpg data should likely be gathered on a long term basis.
I think in comparing a single tank to another single tank there are too many variables (temp, wind, humidity, driving conditions etc.) to draw accurate conclusions.

My NSX has averaged 22.85 USmpg since new with the best tankful at 29.0 USmpg.

In the BC lower mainland/Vancouver Island I get lower mileage because of the ethanol but on my annual drive to Alberta I will gain about 3 % in mpg.
This may be due to less ethanol in the fuel or just flatter terrain.

Jim

 

[tiki240]

Reporting back in, Had constant fuel light illuminate at 363.3 miles avg ~24 mpg. better than the usual 22.1-ish... but way off my previous results. Only discernible difference I can think of is the temps went WAY up this week from hovering in the 40s up to 68-74 three days in a row. *scratches head*... I don't get it.

 

[kaede]

In the BC lower mainland/Vancouver Island I get lower mileage because of the ethanol but on my annual drive to Alberta I will gain about 3 % in mpg.
This may be due to less ethanol in the fuel or just flatter terrain.

Jim

Side tracked a little, right now I know that Shell V Power as well as Chevron 94 is still ethanol free in Canada (At least in the GVRD). Anyone know whether or not Shell V Power is ethanol free in the US? (Washington specifically if there is a difference state to state).

 

[JD Cross]

Side tracked a little, right now I know that Shell V Power as well as Chevron 94 is still ethanol free in Canada (At least in the GVRD). Anyone know whether or not Shell V Power is ethanol free in the US? (Washington specifically if there is a difference state to state).

Kaede

Wondering how you would know that Chevron 94 and Shell V-Power 91 are ethanol free?

From the Chevron Canada website:
"BC's Renewable Fuel Standard came into effect on January 1, 2010. To meet this fuel mandate, Chevron gasolines in British Columbia may contain up to 10% ethanol."
Also from the same website:
"Oxygenated gasoline reduces fuel economy an average of 2 to 3 percent because oxygenated gasoline contains less energy than non-oxygenated gasoline."

The 94 octane Chevron may be ethanol free but it appears the other three grades may contain ethanol. The Shell website makes the same statements about ethanol in their V Power.

Could you let us know your sources?
Thanks
Jim

 

[chussey]

Meaningful mpg data should likely be gathered on a long term basis.
I think in comparing a single tank to another single tank there are too many variables (temp, wind, humidity, driving conditions etc.) to draw accurate conclusions.


Jim

+ 1

 

[kaede]

JD Cross,

On all chevron stations the 94 specific says contains no ethanol =D I can't be 100% sure but thats at least what the label says. Never send any to the labs to get it tested but hopefully they wouldn't deliberately "lie" to consumers. Next time you stop by Chevron where they have 94 octane have a look!

As for V Power, some of the newer gas stations don't have the sign up anymore, but they all used to have a label saying 87 bronze - contains up to 10% ethanol, 89 Silver - contains up to 5% ethanol, and 91 V Power contains no ethanol. Also, on Shell Canada's website (http://www.shell.ca/en/products-services/on-the-road/fuels/shell-vpower.html) under Frequently Asked Questions, locate IS V Power premium gasoline safe for all vehicles, the last point clearly states that V Power does not contain any ethanol!!!

However, that piece of information/statement is missing in the Shell US website. So thats why I wanted to confirm whether or not anyone know V Power in the states contains ethanol. I gas up my vehicles from the States quite often, the price for V Power over in point roberts is $1.12/L vs in vancouver its $1.40+/L.

 

[JD Cross]

JD Cross,

On all chevron stations the 94 specific says contains no ethanol =D I can't be 100% sure but thats at least what the label says. Never send any to the labs to get it tested but hopefully they wouldn't deliberately "lie" to consumers. Next time you stop by Chevron where they have 94 octane have a look!

As for V Power, some of the newer gas stations don't have the sign up anymore, but they all used to have a label saying 87 bronze - contains up to 10% ethanol, 89 Silver - contains up to 5% ethanol, and 91 V Power contains no ethanol. Also, on Shell Canada's website (http://www.shell.ca/en/products-services/on-the-road/fuels/shell-vpower.html) under Frequently Asked Questions, locate IS V Power premium gasoline safe for all vehicles, the last point clearly states that V Power does not contain any ethanol!!!

However, that piece of information/statement is missing in the Shell US website. So thats why I wanted to confirm whether or not anyone know V Power in the states contains ethanol. I gas up my vehicles from the States quite often, the price for V Power over in point roberts is $1.12/L vs in vancouver its $1.40+/L.

Kaede

Thanks for pointing out the V Power 91 info on the Shell website. I missed that and will now switch over to Shell. I've been a Chevron user for years but haven't bothered with their 94 gold as our NSX's don't need it.

Jim

 

[kaede]

Yes, next time you check out chevron their 94 supreme plus grade should clearly have a label right beside it saying "Contains no Ethanol". However, it is a tad bit more expensive than V Power. Cheers!! :smile:

 

[JD Cross]

Yes, next time you check out chevron their 94 supreme plus grade should clearly have a label right beside it saying "Contains no Ethanol". However, it is a tad bit more expensive than V Power. Cheers!! :smile:

Filled up at the Shell in Pt Roberts yesterday
Pump was marked with "may contain up to 10 % ethanol" and V-power had a 92 octane rating.
It's 91 rating in Canada no?

 

[IndependentLemming]

Fairly easy to find 91 no ethanol in the South. I have not went with any type of data testing since I only drive the car once a week (100 miles,rain or shine) and tend to be heavy footed. The "butt" dyno says no ethanol makes a huge difference and when I pay attention I think I get 1/5 - 1/4 tank better gas mileage.

 

[kaede]

Filled up at the Shell in Pt Roberts yesterday
Pump was marked with "may contain up to 10 % ethanol" and V-power had a 92 octane rating.
It's 91 rating in Canada no?

Yes, Canada's octane rating is 91. That is why I asked if anyone know if there is any difference between Canadian V Power and US V Power. Every Shell gas station in the US only has one sign stating that their fuel has up to 10% ethanol. Where in Canada they always have a little table with bronze-10%, silver-5%, V Power NO ethanol. Also, the there is no statement or mention of no ethanol on Shell USA's website for V Power. So I am guessing they do have it :frown:

On the bright side, V Power is around $1.2x'ish/Litre in Point Roberts VS our $1.4x - 1.5x'ish/Litre in Vancouver.

 

[zhaninsx]

I filled up the tank this morning with ethanol free fuel (92 octane) and have to admit there does seem to be something to this. My NSX seemed more responsive on the drive home and generally more "alive" at both low and high speed. Can't judge MPG yet as I only drove 22 miles from the station to my house and the needle hardly budged (probably because I put as much fuel as I could into the tank). My car is completely stock with no engine mods, and there was about three gallons of regular premium (with ethanol) in the tank before I filled up. When I pulled into the station, there was a Testarossa there filling up, and I passed another F-car headed towards the station when I was leaving, so it looks like other performance car owners are very aware of this. I found the station using www.pure-gas.org, which lists a decent number of ethanol free gas stations per state. I'm pretty much sold on this already and plan to drive the 7 miles out of my way to get what seems to be a noticeable performance improvement.