Hot Spark and NASCAR Sunoco Premium

[twistedwankel]

All things being equal on my 81 GS750EX with 25,000+ miles.

All I did was finally get the stator to make juice near 14Volts making the engine run better and get one tank of the Sunoco Premium as opposed to Hess or Raceway. The gas costs the same I just had to go a couple miles farther to get it.

49.2 mpg highway as opposed to a personal best of 43 in the last 3 years. Same rider same roads same FL hot temps same lead hand.

Now I have to try that with my car/truck. That's pushing a 14+% mileage improvement which is astonishing to me.

Especially at $3.25/gallon. Like we might as well live in UK. (It's like $8/gallon there but hopefully all VAT?)

:shock: Ok. I know that there is no gas savings in taking my bike to the store as I'm gone for 2 hours and use up 1/2 a tank of gas compared to my pickup truck with which I'm home in 15 minutes. I just think this is cool to go farther and smoother and faster for less.

[chuckycheese]

Octane

I can't imagine higher octane gas will give you better mileage in your bike. Maybe it's better quality gas!

[bonanzadave]

I can't imagine higher octane gas will give you better mileage in your bike. Maybe it's better quality gas!

This is on another recent thread. Higher octane yields no better mileage, and sometimes worse.

[Steve]

Just for fun and games, try the same ride with Sunoco Regular (87 octane) and post the results.

Expiring minds want to know. :shock:


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[Red Rocket GS1100]

My experiments

I had been using premium fuel thinking that the bike would respond better. Recently I began putting the regular octane gas in and suddenly the bike runs smoother with less noise and better pickup. Maybe coincedental...but I'm stickin with regular octane from now on. 8-)

[twistedwankel]

I can't imagine higher octane gas will give you better mileage in your bike. Maybe it's better quality gas!

All the gasolines I've used/referred to are Premium at 93 octane supposedly? So definately just a "better quality" gas. And a hotter spark? I was getting some knock with 87 octane under accelleration so switched to premium some time ago and it went away. 89 octane midgrade didn't make any difference with the knock.

But in the interest of clarity I will next time fill up with 87 octane Sunoco NASCAR's only fuel and see what the miles are.

Having done more than my share of car racing I agree with the comment that "premium" gas can slow you down because they put in additives that "slow" the burn in today's fuel with a big spark advance. No more lead. With the spark knock and O2 sensors in modern cars they "hear" the ping and retard the spark and richen the mixture so under hard accelleration is the only time it would affect fuel economy with the lower octane.

My 26 year old bike doesn't have those features so I hear the knocks. Bet the newer FI bikes do - but I never asked.


Second tank of Sunoco Premium 93 Octane no Ethanol finally used up and 48.2mpg with probably 50 miles of straight highway @ 70mph which I didn't so the first tank. So that's pretty good within a mile/gallon with normal for me riding. I just filled it up again with 87 Sunoco Regular so that will be the final reality for this gas??

[Steve]

It's a popular mis-conception...premium gas does NOT make more power. :shock:

That's right. 8-[ It is actually harder to light than regular gas and it burns slower. That is what makes it more desirable in a high-performance engine that would accidentally set off regular gas before the spark ignites it. Higher compression is what gives more performance. However, more compression also means more heat in the combustion chamber before the spark. Sometimes there is enough heat to set off the mixture. This is what you hear as "pinging" or "knocking", usually at low rpm with large throttle openings. Premium gas will resist ignition until the spark happens, then it gives full advantage of the increased compression.

In stock engines, this "advantage" of premium fuel is not usually necessary. And, since it is harder to light and burns slower (that is why you also have to advance the timing on a high-performance engine), peak pressure in the combustion chamber happens too late to even give as much performance as regular gas. This can lead to incomplete combustion, which also leads to increased deposits on the spark plugs, valves and pistons.

Granted, there are times when higher octane gas might be necessary. I have found that towing a trailer uphill on a warm day increases general engine temp enough that I can hear occasional pinging, so I will use a mid-grade gas for a few tanks while in those situations.


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[chuckycheese]

Gas mileage

This is a little off the mark but not by much. I have a new BMW car for which premium (91 octane) is strongly suggested. I tried using 'regular' and found I got slightly better gas mileage (with no perceivable performance difference) on 3 separate 400 mile rides, on the same road. I've never gotten a straight answer on why that might be...other than the suggestion that I'm not smart enough to figure gas mileage!8-[

Any opinions would be of interest!

[twistedwankel]

This is a little off the mark but not by much. I have a new BMW car for which premium (91 octane) is strongly suggested. I tried using 'regular' and found I got slightly better gas mileage (with no perceivable performance difference) on 3 separate 400 mile rides, on the same road. I've never gotten a straight answer on why that might be...other than the suggestion that I'm not smart enough to figure gas mileage!8-[

Any opinions would be of interest!

Because you have a computer in your new car that looks a zillion times per second at all the data variables to give you optimum performance/efficiency including the gear you/re in and your intake/exhaust composition. And on and on and on. Computers are amazing when it comes to a mechanical data stream. But they can't tell me when "the world" will end? I will just hope for the best concerning "my world". Hope that helps. Smaller and faster and quicker and fuzzy logic. Soon it will tell the cops to email you a ticket with the long and lat co-ordinates/time/and speeds before you get home.

Good reason for owning old stuff.

[dardoonk]

Check those stations and see if any of them are adding 10% or 15% ethanol to their fuel. Milage decreases as Ethanol is added. I don't remember the exact number, but I think that Ethanol burns at about 85% efficiency of gasoline.

[82gs1100]

a station nere me has 10% ethanol. in my jeep grand cherokee 4.0l i only get 15mpg with it. with no ethanol i get 20mpg not worth the 5 cents cheeper they charge.

[49er]

Check those stations and see if any of them are adding 10% or 15% ethanol to their fuel. Milage decreases as Ethanol is added. I don't remember the exact number, but I think that Ethanol burns at about 85% efficiency of gasoline.

IMO, the most valid point in this debate.
I recently raised the CR on my 850 from 8.8 to 10.5-1. I planned on using the stock advance, so I ran the bike on 98 octane. It performed great, with no signs of detonation under high loads. I then ran it on 95 octane. Still no detonation but a slight detoriation in performance. Not dynoed, but I could feel the difference in the amount of throttle required for a given response.
Our 2 valve GS's already run 37 degs total advance in stock spec. Why would anyone try to run more advance? They are right on the limit anyway. Yoshimura running 11.5 -1 CR on premium, managed 38 degs on his GS1000's. This extra degree was intoduced at 7000rpm.

[emjay]

Check those stations and see if any of them are adding 10% or 15% ethanol to their fuel. Milage decreases as Ethanol is added. I don't remember the exact number, but I think that Ethanol burns at about 85% efficiency of gasoline.

From what I've heard we should not run gas with Ethanol in our bikes. Any comment on that?

[Steve]

Virtually all of the stations around here have "up to 10% Ethanol" coming through the hose.

I have had no problem with <=10%, but traveling in the mid-west the last few summers, I have seen higher mixtures, and they definitely hurt performance and mileage. I would definitely avoid the E-85 that is starting to show up.


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[emjay]

... I would definitely avoid the E-85 that is starting to show up.

Now that you mention it, that is what I heard - don't run the E-85.