Higher the Octane the better?

[RainmanEverson]

There's a Sunoco station here in town that sells 100 Octane "GT" gas... GT gas, sez I? "Yeah, I've got a GT, that's the gas for me!"

I filled her up (twice now) and the stuff makes a pretty big difference. But I got to thinking, the chemical properties, the difference in the combustion, is there a down-side to putting SUPER-de-DOOPER premium gas in this rocket ship?

Who's got an intelligent opinion about this?

I will say this much... the family sedan is an '06 Chrysler 300 SRT8. Having spoken to a GEN-YOU-WINE Chrysler motorsport engineer, up close and in person, he wholeheartedly endorsed running the WAY high-test stuff with no problems, and that high octane gas makes a VERY noticable difference in how the SRT8 runs, no doubt about it. Nevertheless, that's probably a terrible comparison, considering the difference in compression ratios, etc.

All in, I remain...
The Rainman

[hugoscheuer]

IMHO, unless the knock sensors are causing the spark to be retarded on 93 octane, the only difference in adding octane beyond that point, will lose power, as the additive to create the higher octane has less energy than the gas itself.......
That loss however is so minor, that it can't be felt in the seat of the pants.

Rusty 06 GT

[dshealey]

There's a Sunoco station here in town that sells 100 Octane "GT" gas... GT gas, sez I? "Yeah, I've got a GT, that's the gas for me!"

I filled her up (twice now) and the stuff makes a pretty big difference. But I got to thinking, the chemical properties, the difference in the combustion, is there a down-side to putting SUPER-de-DOOPER premium gas in this rocket ship?

Who's got an intelligent opinion about this?

I will say this much... the family sedan is an '06 Chrysler 300 SRT8. Having spoken to a GEN-YOU-WINE Chrysler motorsport engineer, up close and in person, he wholeheartedly endorsed running the WAY high-test stuff with no problems, and that high octane gas makes a VERY noticable difference in how the SRT8 runs, no doubt about it. Nevertheless, that's probably a terrible comparison, considering the difference in compression ratios, etc.

All in, I remain...
The Rainman

I am surprised you can tell any difference. Higher Octane is only useful to prevent pre-ignition, or pinging when the compression is high. Octane additives themselves have absolutely NO positive impact on "power", and since the additives used to increase Octane level actually slow down the ignition speed a slight decrease in total power is the norm, although it would likely take instrumentation to measure it. It is not something the average person could "feel". Higher Octane level than needed to prevent pre-ignition depletes the wallet faster, but does not make the car faster.

In newer cars it is not so easy to tell if the octane level of the fuel used is too low, since the knock sensors on most cars change mixture/timing to adapt to less than optimal fuel. In the older cars, the pinging on heavy throttle at lower RPM is the indicator.

If you use lower octane fuel in a modern high compression car, the ECU will make the necessary changes, decreasing power output, and then if you put in higher octane the ECU will monitor and make changes again, and if the engine is capable of more power with the mixture/timing changes allowed by the higher octane you will likely feel it.

On the LT however, you will hear pinging if the octane is too low, since there are no knock sensors. The ECU on the LT can only make mixture adjustments based on the Oxygen Sensor reading of the exhaust gas, and timing adjustments based on a "map" of temperatures/throttle setting/RPM.

[jayjacobson]

There's a Sunoco station here in town that sells 100 Octane "GT" gas... GT gas, sez I? "Yeah, I've got a GT, that's the gas for me!"

I filled her up (twice now) and the stuff makes a pretty big difference. But I got to thinking, the chemical properties, the difference in the combustion, is there a down-side to putting SUPER-de-DOOPER premium gas in this rocket ship?

Who's got an intelligent opinion about this?

I will say this much... the family sedan is an '06 Chrysler 300 SRT8. Having spoken to a GEN-YOU-WINE Chrysler motorsport engineer, up close and in person, he wholeheartedly endorsed running the WAY high-test stuff with no problems, and that high octane gas makes a VERY noticable difference in how the SRT8 runs, no doubt about it. Nevertheless, that's probably a terrible comparison, considering the difference in compression ratios, etc.

All in, I remain...
The Rainman
Well, not an intelligent opinion, but.....with the gas mileage (or lack of it) that the Hemi already gets, it's sad that you would need GT gas (at GT prices) to realize maximum performance. Knowing that "super" is 91 octane, Chrysler Engineers should have achieved maximum performance on it.

91 is recommended for the LT. My LT ran perfect on 87. No difference at all. I didn't "hot-rod" the bike, however.

[RainmanEverson]

... for your replies. Premium gas here in N Fla is 93... and it runs just sweet on that lotion. The Hemi is a different matter. Put 100 octane gas in that beast and there's a huge difference.... anyway, this was about the scooter and I'll leave it at that, again, thanks guys...
Rainman

[ClearwaterBMW]

[COLOR=DarkSlateBlue]There's a Sunoco station here in town that sells 100 Octane "GT" gas... GT gas, sez I? "Yeah, I've got a GT, that's the gas for me!"



hmmmmm
i'd find some independent lab to test that "GT GAS"
i say..... bull doo doo
no one sells 100 octane gas

how much/gallon?
why WOULD they sell it?

sounds J-ville fishy to me :histerica

[ClearwaterBMW]

The Hemi is a different matter. Put 100 octane gas in that beast and there's a huge difference....

seriously, exactly HOW can you "FEEL" the difference in your HEMI with 100 octane gas?

the computer in THAT vehicle ought to prevent any discernible difference as well, quite frankly

[messenger13]

On the LT however, ...
91 is recommended for the LT...
Umm...would you two mind staying on topic here? The man is talking about putting 100 octane fuel in a real bike...not that silly old LT, that's yesterday's news with yesteryear's technology. :rolleyes: :D


But I digress...

I run 87 while going from tank to tank (LD touring), and 89 when in the city or ripping up the twisties. I have yet to hear any pinging, nor do I feel the need to even put 93 in my GT. 100 octane would just be a waste of money, IMO.

[mneblett]

I am surprised you can tell any difference. Higher Octane is only useful to prevent pre-ignition, or pinging when the compression is high. Octane additives themselves have absolutely NO positive impact on "power", and since the additives used to increase Octane level actually slow down the ignition speed a slight decrease in total power is the norm, although it would likely take instrumentation to measure it. It is not something the average person could "feel". Higher Octane level than needed to prevent pre-ignition depletes the wallet faster, but does not make the car faster.

In newer cars it is not so easy to tell if the octane level of the fuel used is too low, since the knock sensors on most cars change mixture/timing to adapt to less than optimal fuel. In the older cars, the pinging on heavy throttle at lower RPM is the indicator.

If you use lower octane fuel in a modern high compression car, the ECU will make the necessary changes, decreasing power output, and then if you put in higher octane the ECU will monitor and make changes again, and if the engine is capable of more power with the mixture/timing changes allowed by the higher octane you will likely feel it.

On the LT however, you will hear pinging if the octane is too low, since there are no knock sensors. The ECU on the LT can only make mixture adjustments based on the Oxygen Sensor reading of the exhaust gas, and timing adjustments based on a "map" of temperatures/throttle setting/RPM. I agree with all the above -- plus, lower octane stuff lights off easier when cold, i.e., easier starting when the temps fall.

[Ted Shred]

hmmmmm
i'd find some independent lab to test that "GT GAS"
i say..... bull doo doo
no one sells 100 octane gas

how much/gallon?
why WOULD they sell it?

sounds J-ville fishy to me :histerica

Ummm ...you shouldn't make statements that clearly aren't true. The Sunoco stations here sell 100 octane fuel. It's about 5.50 a gallon. People buy it for high performance vehicles that they might race at the local tracks. You can also buy 100 octane at most of the tracks out here. If you have the proper equipment it can make a difference. Stock vehicles that are tuned and built for "pump" gas like the GT aren't really going to run any better on the higher octane fuel....

[RainmanEverson]

... that's a good question, one I asked myself too. I filled up the motorcycle and took it over to the GA field and paid $4. for a fuel analysis. 100.035 octane.

I'd be glad to take the performance question for the SRT8 off line, if anyone's interested.

Again, thanks a lot for your responses. One thing I noticed on the motorcycle. Now and then when I'm coming off the gas abruptly, I get one or two very minor backfires.

Rainman

[ClearwaterBMW]

Ummm ...you shouldn't make statements that clearly aren't true. The Sunoco stations here sell 100 octane fuel. It's about 5.50 a gallon. People buy it for high performance vehicles that they might race at the local tracks. You can also buy 100 octane at most of the tracks out here. If you have the proper equipment it can make a difference. Stock vehicles that are tuned and built for "pump" gas like the GT aren't really going to run any better on the higher octane fuel....

you boys in cali sure are fancy folk...... :)

no one sells 100 octane gas around here...
and i live in an area which houses about 3 million folks :p

i dare say that 99.999999999999% of the people who buy the 100 octane gas at some Sunoco local to you:
1. don't have the "equipment" to have it make a difference
2. wouldn't know the difference in the first place :)

ah.....
cali and excess.... now THERE'S a new concept......... :rotf:

[jayjacobson]

seriously, exactly HOW can you "FEEL" the difference in your HEMI with 100 octane gas?

the computer in THAT vehicle ought to prevent any discernible difference as well, quite frankly
100-103 octane "racing" gas is not uncommon. Many road racers and boat racers use it. But, their engines are highly modified and need it.

Having to use it on a brand new factory vehicle to achieve max performance is a shame, however. Especially when that vehicle is already a gas guzzler!

[jayjacobson]

you boys in cali sure are fancy folk...... :)

no one sells 100 octane gas around here...
and i live in an area which houses about 3 million folks :p

i dare say that 99.999999999999% of the people who buy the 100 octane gas at some Sunoco local to you:
1. don't have the "equipment" to have it make a difference
2. wouldn't know the difference in the first place :)

ah.....
cali and excess.... now THERE'S a new concept......... :rotf:
No, were just "pee-ons" like everybody else.

Now, about that excess......

[jayjacobson]

....I'd be glad to take the performance question for the SRT8 off line, if anyone's interested.....Rainman
Not necessary, Rainman! Who says you have to stay on topic?

[ClearwaterBMW]

No, were just "pee-ons" like everybody else.

Now, about that excess......LOL
i just wanted to see if you were paying attention :)

no offense intended, i assure you

[ClearwaterBMW]

Having to use it on a brand new factory vehicle to achieve max performance is a shame, however. Especially when that vehicle is already a gas guzzler!i would SURELY agree with that

[jayjacobson]

LOL
i just wanted to see if you were paying attention :)

no offense intended, i assure you

No offense ever taken, of course. Paying attention....nah!

[jayjacobson]

Quote:
Originally Posted by dshealey
On the LT however, ...

Quote:
Originally Posted by jayjacobson
91 is recommended for the LT...

Umm...would you two mind staying on topic here? The man is talking about putting 100 octane fuel in a real bike...not that silly old LT, that's yesterday's news with yesteryear's technology. :rolleyes: :D


But I digress...

I run 87 while going from tank to tank (LD touring), and 89 when in the city or ripping up the twisties. I have yet to hear any pinging, nor do I feel the need to even put 93 in my GT. 100 octane would just be a waste of money, IMO.
OOHHHH, I see! Now, we have to stay on topic?!

We can't cuss or use four letter words. We can't call other members names. What's next?!.....posts that have to make some sense?

[ClearwaterBMW]

What's next?!.....posts that have to make some sense?
if THAT happens.... i'm leaving :p

[jayjacobson]

if THAT happens.... i'm leaving :p
Yes! Thank you, Greg!

[George_S]

I am surprised you can tell any difference. Higher Octane is only useful to prevent pre-ignition, or pinging when the compression is high. Octane additives themselves have absolutely NO positive impact on "power", and since the additives used to increase Octane level actually slow down the ignition speed a slight decrease in total power is the norm, although it would likely take instrumentation to measure it. It is not something the average person could "feel". Higher Octane level than needed to prevent pre-ignition depletes the wallet faster, but does not make the car faster.

If you use lower octane fuel in a modern high compression car, the ECU will make the necessary changes, decreasing power output, and then if you put in higher octane the ECU will monitor and make changes again, and if the engine is capable of more power with the mixture/timing changes allowed by the higher octane you will likely feel it.

A car or motorcycle can see a performance benefit from higher octane (lets call it "premium gas") fuel. And the "average" driver or rider can certainly tell the difference. Just because the vehicle's computer retards the ignition when lower octane is used, in order to prevent pinging, that doesn't mean its not giving a performanace boost with premium fuel. It's just not doing any harm with regular. But performance can and mostly will be lower with "regular". There IS a difference in the two instances.

I'll give a couple of proofs- Lexus and Toyota sedans share the same engines. Lexus engines operate at a higher compression ratio, and as such, give an approximately 5% greater net horsepower with that compression and premium fuel. The Lexus manuals also state that you'd need to use premium to get that horsepower increase, altho using regular gas will do no harm, you just won't get the stated HP.

I've seen the same explanation with regard to Chrysler and Chevrolet. You can read it in black and white on page 50 of the current issue (Nov. 2006) of Pop Mechanics, where they discuss the Chevy Cobalt SS.
" On those occasions when we had no option but 89-octane fuel, the SS didn't perform as briskly as with premium. Since the engine's computer rolls back ignition timing to prevent damage from lower octane gas, no harm was done. And there was no real difference in mileage. So this car offers the best of both worlds: You can run it on low cost fuel when you're not interested in going fast, and it'll haul when you can afford to."

[dshealey]

High octane fuel will in itself not give you any better performance, however, as I stated before, and you also stated, the only way it can improve performance in an engine is when lower octane has resulted in the engine controller backing off to correct for knocking, and therefore decreasing overall performance. I stand by my statement that higher octane than necessary to prevent pinging/knocking will do absolutely NOTHING to increase performance, but that lower octane than necessary will Decrease performance.

The problem is that people interpret this as higher octane being automatically better, when it is not. Higher octane than that required by the compression ratio etc. of the engine design is nothing but a "wallet thickness decreaser".

It is much like shoe sizes. Smaller hurts, correct is just right, but larger is not better.


A car or motorcycle can see a performance benefit from higher octane (lets call it "premium gas") fuel. And the "average" driver or rider can certainly tell the difference. Just because the vehicle's computer retards the ignition when lower octane is used, in order to prevent pinging, that doesn't mean its not giving a performanace boost with premium fuel. It's just not doing any harm with regular. But performance can and mostly will be lower with "regular". There IS a difference in the two instances.

I'll give a couple of proofs- Lexus and Toyota sedans share the same engines. Lexus engines operate at a higher compression ratio, and as such, give an approximately 5% greater net horsepower with that compression and premium fuel. The Lexus manuals also state that you'd need to use premium to get that horsepower increase, altho using regular gas will do no harm, you just won't get the stated HP.

I've seen the same explanation with regard to Chrysler and Chevrolet. You can read it in black and white on page 50 of the current issue (Nov. 2006) of Pop Mechanics, where they discuss the Chevy Cobalt SS.
" On those occasions when we had no option but 89-octane fuel, the SS didn't perform as briskly as with premium. Since the engine's computer rolls back ignition timing to prevent damage from lower octane gas, no harm was done. And there was no real difference in mileage. So this car offers the best of both worlds: You can run it on low cost fuel when you're not interested in going fast, and it'll haul when you can afford to."

[meese]

Now and then when I'm coming off the gas abruptly, I get one or two very minor backfires.Check your exhaust for possible leaks. Start by re-torquing the header bolts, then look for small cracks at the front header flange or just in front of the catalytic converter.

[tmgs]

There's a Sunoco station here in town that sells 100 Octane "GT" gas... GT gas, sez I? "Yeah, I've got a GT, that's the gas for me!"

I filled her up (twice now) and the stuff makes a pretty big difference. But I got to thinking, the chemical properties, the difference in the combustion, is there a down-side to putting SUPER-de-DOOPER premium gas in this rocket ship?

Who's got an intelligent opinion about this?


High compression engines and turbo/supercharged engines operating with higher combustion pressures need a higher octane. However these days the manufactures have opened up the combustion chambers so much it is much easier for a engine to run a lower octane fuel with high compression pistons, they have been able to open up the combustion chamber and still keep the velocity needed for low rpm torque with the use of 4 valve heads, it still keeps small intake ports which keeps the velocity high yet allowing a much larger amount of air in and out providing an arena for higher compression engines on regular gasoline. Which is basically why some of the jap bike had been running variable flow designed heads (an extra valve)


So, No your wasting your money, bet is if you put it on a dyno with that 100 proof <g> in it you will see no difference.

Running higher octane fuel than what is needed is just purely a waste of cash these days,

here is more than you care to know about the subject
http://en.wikipedia.org/wiki/Octane_rating

if you start searching intake velocity exhaust ports high compression octane levels you will be a pro in a few weeks if you can remember it all <grin>, I can’t!


oh one other little thing to keep in mind is running to high of octane fuel , you can burn leetle holes in the pistons although I don’t think you could ever have a issue with 100 oct in the GT engine!

[hugoscheuer]

[QUOTE=tmgs]High compression engines and turbo/supercharged engines operating with higher combustion pressures need a higher octane. However these days the manufactures have opened up the combustion chambers so much it is much easier for a engine to run a lower octane fuel with high compression pistons, they have been able to open up the combustion chamber and still keep the velocity needed for low rpm torque with the use of 4 valve heads, it still keeps small intake ports which keeps the velocity high yet allowing a much larger amount of air in and out providing an arena for higher compression engines on regular gasoline. Which is basically why some of the jap bike had been running variable flow designed heads (an extra valve)


So, No your wasting your money, bet is if you put it on a dyno with that 100 proof <g> in it you will see no difference.

Running higher octane fuel than what is needed is just purely a waste of cash these days,

here is more than you care to know about the subject
http://en.wikipedia.org/wiki/Octane_rating

if you start searching intake velocity exhaust ports high compression octane levels you will be a pro in a few weeks if you can remember it all <grin>, I can’t!


oh one other little thing to keep in mind is running to high of octane fuel , you can burn leetle holes in the pistons although I don’t think you could ever have a issue with 100 oct in the GT engine![/QUOTE


VERRRRRRRRRRyyyy interesting. Since increasing the "octane, (read impuritys in the gasoline), causes the fuel air charge to ignite later than the spark is timed to, don't you think that your are losing power??? Since the flame front is delayed from its optimum....

Rusty 06 GT

[tmgs]

[QUOTE=tmgs]High compression engines and turbo/supercharged engines operating with higher combustion pressures need a higher octane. However these days the manufactures have opened up the combustion chambers so much it is much easier for a engine to run a lower octane fuel with high compression pistons, they have been able to open up the combustion chamber and still keep the velocity needed for low rpm torque with the use of 4 valve heads, it still keeps small intake ports which keeps the velocity high yet allowing a much larger amount of air in and out providing an arena for higher compression engines on regular gasoline. Which is basically why some of the jap bike had been running variable flow designed heads (an extra valve)


So, No your wasting your money, bet is if you put it on a dyno with that 100 proof <g> in it you will see no difference.

Running higher octane fuel than what is needed is just purely a waste of cash these days,

here is more than you care to know about the subject
http://en.wikipedia.org/wiki/Octane_rating

if you start searching intake velocity exhaust ports high compression octane levels you will be a pro in a few weeks if you can remember it all <grin>, I can’t!


oh one other little thing to keep in mind is running to high of octane fuel , you can burn leetle holes in the pistons although I don’t think you could ever have a issue with 100 oct in the GT engine![/QUOTE


VERRRRRRRRRRyyyy interesting. Since increasing the "octane, (read impuritys in the gasoline), causes the fuel air charge to ignite later than the spark is timed to, don't you think that your are losing power??? Since the flame front is delayed from its optimum....

Rusty 06 GT


eventually yes, it all depends on how high of octane and how the engine is designed to adjust for diffferent fuels,

basically.

it;s been known for years running a higher octane fuel than needed is a waste

[jayjacobson]

....I've seen the same explanation with regard to Chrysler and Chevrolet. You can read it in black and white on page 50 of the current issue (Nov. 2006) of Pop Mechanics, where they discuss the Chevy Cobalt SS.
" On those occasions when we had no option but 89-octane fuel, the SS didn't perform as briskly as with premium. Since the engine's computer rolls back ignition timing to prevent damage from lower octane gas, no harm was done. And there was no real difference in mileage. So this car offers the best of both worlds: You can run it on low cost fuel when you're not interested in going fast, and it'll haul when you can afford to."
Cobalt SS, haul?! The only stock 4 cylinder that "hauls" is the Lotus. Well, the Subaru twin turbo ain't bad either.

[RainmanEverson]

... I wanted (an) opinion(s), and boy, I got'em! I'm glad I asked. Brisk debate, by and large credible information and entertainment value... who could ask for more?

Rainman
:bmw:

<ok, ok, not another dime wasted on the high class schtuff.. I'll stick with 93... yeeesh...>

[jayjacobson]

....I've seen the same explanation with regard to Chrysler and Chevrolet. You can read it in black and white on page 50 of the current issue (Nov. 2006) of Pop Mechanics, where they discuss the Chevy Cobalt SS.....
Remember when we used to keep the Popular Mechanics out in the garage, under the 50 wt? Now, we keep it in the house, under the coconut oil!

[jayjacobson]

... I wanted (an) opinion(s), and boy, I got'em! I'm glad I asked. Brisk debate, by and large credible information and entertainment value... who could ask for more?
I'm not sure about the credibility; but the entertainment value!......