What's the deal with high octane?

[Bimminator]

Can any one shed some light on the issue of high octane? My mechanic friend told me that my 1990 535i was designed to burn high octane fuel. I have since read some info that suggested that having been sold in Canada, or North America for that matter, the car would have been set up to run on regular and that it would have to be tuned to burn premium. I have noticed that the engine sounds better with premium but will it harm my engine as I doubt the previous owner did anything but routine maintanance.

Thanks, Shawn

[632 Regal]

with out a performance chip you need to run at least 89 octane. With a chip you have to use at least 91

[JonE]

It will run even better if you add an EAT chip with at least 91 Octane! When my '90 535i had the stock chip it ran 87 Octane with no problems, it's what was the required fuel octane. Now with the EAT chip I run about 92 Octane and the chip manages to produce more horsepower and torque as it optimizes the timing for higher octane fuel. I also get better gas mileage with the EAT chip.

[paul p (chi-town)]

with out a performance chip you need to run at least 89 octane. With a chip you have to use at least 91Uh, sorta.
Dunno bout the M20/30 but the M60 takes midgrade (tho honestly it’s a rip-off, i simply get 93 for the better detergents), and the M50 takes premium.
As important is the quality for a given octane. Pay for brand name now or Techron (or more) later.

94 530iT&A ‘Helga’ (for sale...soon) --- 92 325i ‘Rolf’ (blown clutch) --- 91 Volvo 745T ‘Thor’ (13psi :D).......”Hang up & Drive!” (http://homepage.interaccess.com/~motria/pablosgarage.html)
”Bet that phone call doesn’t seem that important now, eh?” Nov 20, 2004

[bahnstormer]

if u have 9.0:1 compression like the m30 does it'll run on water =]
hehehe jk

but yeah the new honda s2k has like 11.5 to 1

and in europe the alfa's have upwards of 12:1....lucky bastards with 97 octane
at every pump =[

[Jon K]

if u have 9.0:1 compression like the m30 does it'll run on water =]
hehehe jk

but yeah the new honda s2k has like 11.5 to 1

and in europe the alfa's have upwards of 12:1....lucky bastards with 97 octane
at every pump =[


They don't have 97 octane at a pump, they have 97 or 98 RON... equivalent to 93 octane

[BigKriss]

yeah. same in australia.

[Kalevera]

Yes...like the owner's manual, and almost everybody else says, it's fine to run an m30 on regular/87. If you have a performance chip, it usually needs 91+ (that's the main reason why I don't have one...esp with the price of gas right now).

best, whit

[Bimminator]

Thanks for all the input I guess I was initially burning 93 for the cleaner fuel (ethanol blend) to help prevent carbon build up etc. but I haven't installed a chip yet so I guess I'll stick to 87, particularly because they are predicting high 90s upwards of over a dollar a litre for regular for gas this summer. Have I potentially done any damage burning 93 for the last six months or so?

Thanks great forum by the way interesting topics.

[peks]

dont think you can really damage it by running premium

[Paul in NZ]

i ussually run 91 ron but the car definetly runs better on 96 or 98 ron(smoother),and i get about .5 liter better economy per 100 ks,all standard.

[niall]

the guys at work say that 91 octane is bad stuff,
i know you yanks can run yours on it, but in the uk or
Oz they reckon to run at least 95.

i run my bimmer on bp ultimate only, im not
a jew when it comes to fuel,

also we have taken a feew late model jags out
on test runs and they ping and rattle
like hell when they have **** fuel in them

[Interceptor]

and in europe the alfa's have upwards of 12:1....lucky bastards with 97 octane
at every pump =[
Well, here in Europe we have 95 & 98 on every gas station (less than 95 hasn't been around for a decade or so). Note that this is the RON/ROZ fuel rating, not AKI, used in the US.

[genphreak]

the guys at work say that 91 octane is bad stuff,
i know you yanks can run yours on it, but in the uk or
Oz they reckon to run at least 95.

i run my bimmer on bp ultimate only, im not
a jew when it comes to fuel,

also we have taken a few late model jags out
on test runs and they ping and rattle
like hell when they have **** fuel in them
I second that BP Ultimate ONLY...

I have a std chip program in my E34,so use standard at the moment, but I know that BP Ultimate stuff is the go- have used it in other applications a lot with great results.

Once I get a chip-mod I will only use that.

btw; a tip.. ;) never, never never use Shell premium, not even for a top-up... it doesn't mix with other fuels.

:) GP

[Rory535i]

I second that BP Ultimate ONLY...

I have a std chip program in my E34,so use standard at the moment, but I know that BP Ultimate stuff is the go- have used it in other applications a lot with great results.

Once I get a chip-mod I will only use that.

btw; a tip.. ;) never, never never use Shell premium, not even for a top-up... it doesn't mix with other fuels.

:) GP

I second second that! BP ultimate is wicked stuff. Add a bottle of octane booster and you're around the 100 octane mark. makes one hell of a difference to 91!

[Jon K]

I second that BP Ultimate ONLY...

I have a std chip program in my E34,so use standard at the moment, but I know that BP Ultimate stuff is the go- have used it in other applications a lot with great results.

Once I get a chip-mod I will only use that.

btw; a tip.. ;) never, never never use Shell premium, not even for a top-up... it doesn't mix with other fuels.

:) GP


LOL... PEOPLE... LISTEN... in the USA we have OCTANE, 87, 89, 91/92, 93, and 94... then 100, 104, 110 race fuels. You guys have 95 RON. 95 RON is about 89 or 90 OCTANE. Our cars are no different than yours. You guys have a different numbering system.

[Rory535i]

LOL... PEOPLE... LISTEN... in the USA we have OCTANE, 87, 89, 91/92, 93, and 94... then 100, 104, 110 race fuels. You guys have 95 RON. 95 RON is about 89 or 90 OCTANE. Our cars are no different than yours. You guys have a different numbering system.

well on the bp ultimate pump its says 98 OCTANE hence the "ultimate". regular is 91 and premium is 95. i understand the whole RON thing. i've used fuel additives which say they will increase RON by ten points which works out to be 1 or 2 octane points or whatever.

[Rory535i]

well on the bp ultimate pump its says 98 OCTANE hence the "ultimate". regular is 91 and premium is 95. i understand the whole RON thing. i've used fuel additives which say they will increase RON by ten points which works out to be 1 or 2 octane points or whatever.

unless i'm wrong...

[632 Regal]

http://chemistry.about.com/cs/howthingswork/a/aa070401a.htm

[BigKriss]

in australia we have 91 RON, normal unleaded, 95 RON premium unleaded and 98 RON, (BP ultimate, shell optimax and mobil synergy 8000). these 3 fuels are the only 98 ron fuels i know of. Our petrol ratings are 4 points higher than petrol in the USA. eg their 87 petrol (regular) is out 91 fuel, their 91 fuel is aussie 95 fuel (premium).

Nothing in australia is below 91 ron or over 98 ron. I normally go with shell optimax. the m30 engine does not have a knock sensor, so any octane that your running over what is specified will not give you more power, it will just decrease the risk of detonation.

i run my eat chip with 98 ron most of the time, never tired 91 ron, ran 95 ron a few times with no problems at all. I had my powerchip in before that. I ran 91 RON once or twice through a crappy servo, it did ping. as soon as i realised this ****, i drove the car gently and i topped up the tank with 98. No worries :)

[JAlfredPrufrock]

I used to run 87 but noticed an improvement in mileage by running 93, so I've kept at it... I figure it will be less of a sticker shock at the pump when I switch to an EAT chip.

[granit_silber]

http://chemistry.about.com/cs/howthingswork/a/aa070401a.htm


From that site: "This fractional distillation process yields approximately 250 mL of straight-run gasoline for each liter of crude oil."

250mL = ~8oz.

1 liter is roughly 32 oz. meaning that there is a 4:1 loss ratio of crude oil!!!

Seems like we could figure out a way to lessen that ratio.

-ashley

[632 Regal]

From that site: "This fractional distillation process yields approximately 250 mL of straight-run gasoline for each liter of crude oil."

250mL = ~8oz.

1 liter is roughly 32 oz. meaning that there is a 4:1 loss ratio of crude oil!!!

Seems like we could figure out a way to lessen that ratio.

-ashley

that they use that much for a gallon of gas but the rest isnt wasted. They use the leftovers to make other chemicals and fuels. They even use petrolium in the manufacture of medications (eeek!). Im pretty sure that every drop is used for something or other kinda like cattle or pigs. What I didnt know but just learned from reading that link is that straight fuel is only about 70 octane and they have to use all them additives and antiknock agents to make it useable in cars and stuff.

[632 Regal]

if you found "that" interesting check this out:

Petroleum ether is a list II watched chemical due to its use in clandestine drug labs. Most chemical supply stores won't even sell you watched chemicals because of the stigma attached to them. However it is a very useful solvent commonly used and for personal use all you need is a small bottle.

Ether can also be extracted from starter fluid but you'll need a fractal distillation apparatus or you might as well be huffing gas. An acid base water extraction will not suffice contrary to popular belief. Using water will remove some contaminates but it will not remove hexane and upper cylinder lubricants so don't even bother.

Ether can also be synthesized by reacting ethyl alcohol with sulfuric acid which megalomania has described here: http://roguesci.org/megalomania/synth/synthesis2.html#ether

Neither methods are as hard as they seems, you just need to learn something about chemistry and pay some money for lab equipment.

As for what it is like, it smells like gasoline (and if you use it so will you), and the high basically lets you think at the speed of light. If all the world happens at once and time is only an illusion ether helps you wake up from the illusion. For about 5 or so minutes.

For dosage if you the first rag you inhale only sets the stage. You do not need to huff it or deprive your brain of oxygen in order for it to work, just breath it in between normal oxygen breaks. When the first rag is no longer wet breath another one to begin your journey.

I also highly recommend using whip-its at the same time (nitrous oxide, whipped cream) as it will make the trip much much much more powerful.

It's also easy to hallucinate and hear voices one ether, at least to the well trained eye and ear. This is largely because nothing will make sense and you will be in another reality, reality being described as what we our senses tell us and how our brains interpret it, ether heavily changing the latter. The glare on the window can become a vast gigantic barren wasteland.

It's good times, I've been meaning to dump a gallon or so into my cars carpet and go driving around my town like Hunter S Tompson.

Ether is also extremely flammable so don't do stupid things around it like smoking. Try doing a hair spray flame thrower with a can of starter fluid (it'll be over a yard long). When people talk about meth labs exploding they're usually talking about ether exploding. Old ether or ether exposed to air can also form an explosive peroxide. Respect the chemical.

Oh yeah and as a final note put red or blue food coloring in the bottle of ether when you get it so some fool doesn't think it's water and gets a nasty suprise. Well my friend drank a bunch and everytime he burped he got high, but still that can't be good for you.

[CheapCheap1]

Very interesting discussion & informative info...
Anyway, beside the octane #, is there any way to find out the "sulfur content" in each (brand) of gasoline?
Thanks a ton,
CC1

[632 Regal]

The sulfer issue is pretty ellusive. I stole this from some site, probably find more on it.

In many areas, sulfur levels to vary from one retailer to another. Unfortunately, many gasoline retailers don't provide information on the sulfur levels in their gasoline, and so it may take a little research to find out how much sulfur is in the fuel you're buying. Here are some gasoline sulfur levels that you can use as a basis for comparison:

Sulfur Level, in ppm Example
500 Average gasoline sulfur level in many parts of North America
80-150 Typical sulfur levels seen in "lower" sulfur gasolines offered by some retailers.
30 Maximum sulfur level permitted in California, and some other U.S. states. Soon to be the maximum sulfur level permitted in many countries beginning in the next 2 - 5 years.

In Canada, the Canadian automaker's association has introduced an "Automaker's Choice" program that identifies fuel with a maximum sulfur level of 150 ppm. Currently, you'll only find this logo on the pumps at a few MacEwen stations (owned by Irving). Beginning in July, 2002, all gasoline sold in Canada will be required to have a maximum sulfur level of 150 ppm. As of January 1st, 2005, that maximum will be lowered to 30 ppm.

[JonE]

Yes, EAT chip in M30 requires 91AKI and whatever the RON equivalent is. My neighbor and I recently figured out that with the approximate 1.5 mpg increase I get with the EAT chip that the cost of running premium is almost a wash, therefore, having the EAT chip should not cost significantly more in fuel for those of us running M30 engine. Advantage is better mileage and better performance. Of course this does depend on each grade of fuel's going price/gallon. To me, even if it is close, it is still worth having the smoother running, better performing EAT chipped car!

[Bimminator]

I checked to see if all the bolts had been tightened today hoping that might be the cause of any leaks but they seemed tight so I don't know. While I was out there tinkering having my coffee I decided to have a go at my OBC lights as they have been out since I bought the car. I was afraid it was pooched but info from this forum led me to see that the lights could be changed. Sweet! So I started taking out screws etc. , got my radio out(that was a pain in the ass) faught with the left and right toggles on obc, pushing and pulling trying like hell not to break anything and after about half an hour the front part of the obc finially popped off and hung forward, still attached by wires. I had been trying to slide the whole unit out but I guess you don't need to. I got the three bulbs out and had to drive 40 min. to a stealership to get the bulbs as they are a dealer only item( $9.98 can. for 3) It took me 20 min. to get the bottom one in as I couldn't flip it over still being attached and all. Well let me tell you, it works! I finally have my obc back. All proud of myself I start putting everything back together and wouldn't you know I dropped a screw in an openning on the sliding luver thingy on my shifter which was broken. Scince I have dropped all kinds of change down there plus a coffee or two I start taking it apart. Talk about openning a can of worms. This all started today at 9:30 but by 3:30 everything is back together, I was able to tape the luver back together (yes Duck tape. This part is no longer available) and all is now good in world. If my wife finds out I spent the whole day tinkering she's gonna be pist! But I don't care, I got my OBC back! If I could only find some instructions to use it right.

[632 Regal]

http://home.iae.nl/users/bts/obc.htm

[Bimminator]

Thanks for the link it looks petty informative. do you think my 535i would have the same obc as a 7 series?

[niall]

first of all

Our cars are no different than yours. You guys have a different numbering system
i dont think that is true, i know with jags the uk models have
higher compression than the US models. and im pretty sure
its the same with bimmers, does the 525i US spec not
have 8.8 to 1 comp?? as opposed to 9.0 uk??
correct me on the details.

and kriss


the m30 engine does not have a knock sensor, so any octane that your running over what is specified will not give you more power, it will just decrease the risk of detonation.

not true mate. a knock sensor is there for people who run ****
low octane fuels, it retards ignition when detonation occurs.
any higher octane fuel will be benificial to the motor also
there are additives in BP ultimate that have cooling properties aswell.

[pundit]

...not true mate. a knock sensor is there for people who run ****
low octane fuels, it retards ignition when detonation occurs.
any higher octane fuel will be benificial to the motor also
there are additives in BP ultimate that have cooling properties aswell.
It depends on the engine and especially the engine management system to a great extent. Yes a knock sensor will retard the ignition timing at the onset of detonation to safeguard against engine damage. Correspondingly it will allow for timing advance as far as the higher octane fuel (and other factors) will allow which will give more power/potential fuel economy. BUT an engine that does not have knock sensing is at a distinct disadvantage when using premium. In fact many older engines that don't have knock sensing will often run less efficiently on higher octane fuel than regular unless they are tuned specifically for it (ie EAT chip). High octane fuel while providing a higher calorific output is harder to ignite. It may not burn as efficiently and completely in older engine designs. My Tarago van, (2.2 litre 4cyl fuel injection - no knock sensing) produced considerably less power and about 15% less fuel economy on Optimax (98 RON) than regular unleaded. If I'd experimented with the timing advance I may have got a some improvement but I would always have to make sure I ran 98 RON or it would suffer detonation. The timing advance in a M30 is set within the ECU chip. There is no knock sensing.

[Paul in NZ]

but the m30 will run better on higher octane Pundit??ie 96 or 98 RON vs 91

[niall]

no sorry mate this is not correct

Correspondingly it will allow for timing advance as far as the higher octane fuel (and other factors) will allow which will give more power/potential fuel economy.

a knock sensor does exactly what it says on the tin, it detects knocks
it does not know if an engine is running in any other state than detonating
or not detonating . it CANNOT advance the timing, all it can do is retard it, or not retard, it, it works like this, there is a piezoelectic element inside the sensor which generates a voltage when a vibration is applied to it, so like i said, it does not account for any other factors, maybe you have confused it with an O2 sensor

[Mobius]

it CANNOT advance the timing, all it can do is retard it, or not retard it...described in another way; 'advance until knock is detected'.

Some (more modern) engine management systems will 'learn' the best ignition map for a given situation by advancing timing until knock is sensed. In addition, some forced induction cars will continue to build boost until knock is sensed.

So, a knock sensor IS a two-way street. :)

[niall]

yes but that is contrary to what pundit says, and what i said is still true,
a knock sensor knows only 2 states, and produces a current or not.
what you said is true but is not relevant in the least to e34's

[jplacson]

Ok, how does this translate to RON?

We have 92, 95, and 96 RON... manual states 95 RON... will running the cheaper 92 RON vs. 95 RON make a difference?

[Mobius]

yes but that is contrary to what pundit says, and what i said is still true,
a knock sensor knows only 2 states, and produces a current or not.
what you said is true but is not relevant in the least to e34'sI don't see how it's contrary to what Pundit said, and ya seemed to be making a blanket statement in your post, 's all. :)

Ok, how does this translate to RON?

We have 92, 95, and 96 RON... manual states 95 RON... will running the cheaper 92 RON vs. 95 RON make a difference?American AKI ([RON + MON]/2) can be roughly converted to RON by adding 5 (or to MON by subtracting 5, as the difference between the two is usually ~10).

If the manual says to use 95 RON fuel, use 95 RON fuel. More would be a waste, less could cause knocking.

[niall]

If the manual says to use 95 RON fuel, use 95 RON fuel. More would be a waste, less could cause knocking.

from my bro's M30 i am 100% sure that higher octane makes the
car run better. simple as that

[peks]

you still have your owners manual? youll find all the info in there. if you dont, buy one off ebay, you wont regret it. youll find all sorts of amazing little nuggets in there.

[632 Regal]

Im feeling all fuzzy inside now.

[Mobius]

from my bro's M30 i am 100% sure that higher octane makes the
car run better. simple as thatSo either the low-octane gas he's buying is crap, or he's got a good bit of carbon buildup.

Or maybe he has a chip and doesn't know it. :)

If an engine runs poorly on the octane it was designed for, then there's a mechanical problem that needs to be addressed.

[pundit]

no sorry mate this is not correct


a knock sensor does exactly what it says on the tin, it detects knocks
it does not know if an engine is running in any other state than detonating
or not detonating . it CANNOT advance the timing, all it can do is retard it, or not retard, it, it works like this, there is a piezoelectic element inside the sensor which generates a voltage when a vibration is applied to it, so like i said, it does not account for any other factors, maybe you have confused it with an O2 sensor
A standard factory recommended timing is based on using a specific octane rated fuel and if the knock sensing can only allow for retardation (relative to the normal factory timing) not advance beyond the 'norm' so to speak then you are correct. When the engine is not detonating the timing is 'relatively advanced' compared to when it is and the knock sensing kicks in, but not in relation to the standard manufacturers setting. However as Mobius said, there are more sophisticated systems that are more flexible in how they 'manage' and are capable of more than just knock sensing timing retardation, timing advance above the 'norm' can occur if the conditions allow it. However with very clever systems what is 'normal' anyway? They just take everything into account and constantly 'tune' the motor accordingly. Did that make sense?? Pheeeww! Glad we got that cleared up! :p

My other point being that just running any engine that is not designed or tuned to get the benefit from high octane fuel doesn't necessarily guarantee an increase in performance.

[pundit]

but the m30 will run better on higher octane Pundit??ie 96 or 98 RON vs 91
It's difficult to say. With a standard M30 maybe not a great difference. It's really a case of experimenting to determine whether you gain a performance/economy improvement as you increase in octane rating.
One needs to be careful not to trick themselves into thinking that high octane fuel will always guarantee better performance in every engine not matter what.

The same vehicles/engines are often sold into different countrys with different compression ratios and tuning settings to take into account the 'standard' quality of the fuel available in a particular country. Chips like the EAT chip remap the engine managment (timing advance etc) to make better use of an octane increase compared to the standard chip. Without this retuning much of the benefit of higher octane fuel will not be realised.

[Paul in NZ]

well all i know is this,my m30 sure feels nicer on 96 or 98 compared to 91(min reomended)and the obc has dropped 0.5 l/100kms even tho i am due for a service.

[niall]

well all i know is this,my m30 sure feels nicer on 96 or 98 compared to 91(min reomended)and the obc has dropped 0.5 l/100kms even tho i am due for a service.

i can second this for sure :)

[BigKriss]

i'm thinking that with a stock chip and the m30 engine, that at 91 RON or 98 RON the engine will produce the same power, because it's reading a standard map tuned for 91 RON.

Having an EAT chip and going from 95 RON to 98 RON or even higher (race fuels) would I get a power increase? I don't think so. I wish I did :)

[Mobius]

i'm thinking that with a stock chip and the m30 engine, that at 91 RON or 98 RON the engine will produce the same power, because it's reading a standard map tuned for 91 RON.Yup. Correct.

Having an EAT chip and going from 95 RON to 98 RON or even higher (race fuels) would I get a power increase? I don't think so. I wish I did :)Nope. No knock sensor makes any sort of timing adjustment based on octane impossible, unfortunately.

I wish it did so that I could have a chip, but maybe still run 87 when I felt like it.

[niall]

this is correct and incorrect,
an advance adjustment is advantageous
but not essential for a motor to run more smoothly
and produce more power, we keep covering old
ground here. the fact remains M30 will run better
on 95 / 98 rather than 91
its simple as that

[Paul in NZ]

run better yes,but there is no actualpower increase right?A chip would allow a power increase through advanced timing but higher octane is then mandatory to minimize a real risk of damage due to detonation...cos that s what chips do basically isnt it.

[Mobius]

the fact remains M30 will run better
on 95 / 98 rather than 91
its simple as thatRight. Keep talking. You just keep making more sense.

[niall]

run better yes,but there is no actualpower increase right?A chip would allow a power increase through advanced timing but higher octane is then mandatory to minimize a real risk of damage due to detonation...cos that s what chips do basically isnt it.

exactly. without a chip maybe you could see
power increses of 1 or 2 bhp, i dont know .
mybe one someone here with loads of money
can but an M30 on a dyno and prove me wrong

[niall]

get of your high horse mate
dont be a pain in the ass

[Nick.Hay]

It was suggested to my father (by our ex-dealership mechanic) that higher octane petrol has little affect on standard BMWs, as the engines are so well designed and are so efficient.

[Paul in NZ]

if the m30 is so efficient why is the economy only average?

[Rory535i]

if the m30 is so efficient why is the economy only average?

lol was thinking the same thing.

[Mobius]

if the m30 is so efficient why is the economy only average? Yeah.. I don't think I could put 'efficient' and 'M30' in the same sentence without a 'not' in front of one of them.

It's a great engine, it just lost pace with current technology shortly before it was cut off. Oh what could've been. :)

[Paul in NZ]

It's a great engine, it just lost pace with current technology shortly before it was cut off.

exactly dont get me wrong i love it.....

[Bimminator]

Lots of interesting comments and opinions etc. but what I was originally trying to get at, is there any point or advantage in using high or higher than 87 octane in my 1990 535i ][U]with stock chip[/U[B]. I was burnihg 93 initially because I thought that it would burn more efficiently and cleaner and hoped that I would get better fuel economy but I have come to realize that without a chip upgrade I am probably pissing my money away for the preminm fuel.

[Rory535i]

quess you're gonna have to come to your own conclusion out of all these posts! we can't seem to agree on one lol.

[Bimminator]

Hey thats what these forums are all about, I'm learning a lot, we all seem to have common issues with our e34s, and we sometimes differ on fix or the problem. An invaluable resource though as I can't get get any info out of BMW unless I spend $100 an hour.

[ichbin]

Basically BMW suggests premium because of the high compression. Higher octane gasoline products contain ingrediants to prevent the fuel from igniting from compression (earlier than it's supposed to) rather than ignition from the spark plug. With the lower octane gasses it is possible that you may not hear knocking but it may, stress may, ignite due to compression causing engine wear over time. This will also reduce performance. However, the concensus seems to be that with a stock BMW it doesn't really matter. They had to detune their engines so that they could be run on the lower octane fuels ie. 87. I noticed that I get better gas mileage, by a fraction, using high octane gas (bmw e23 85 735i). So there was probably some pre-ignition combustion occuring with the lower octane gas.

In conclusion: High octane fuels withstand higher pressures so if you want to be certain that your fuel isn't igniting under pressure buy high octane. High octane is expensive. If you have a Nikasil engine only use high quality gasoline with low sulfur content. Most stock BMW's will take the low octane.

I'd say if you have a stock BMW use what give you the better gas mileage as compared to the price of the gas.