Pump gas


20 replies to this topic
  • dunecj2a

Posted January 27, 2005 - 06:26 PM

#1

There is a 76 station here in town that sells 100 unleaded out of the pump for $4.50 a gallon. :cry: Do you guys think that has any benefit over 91 out of the pump :cry: What about a 50/50 mix or is it not even worth it. Stick with 91 or what? I have seen a bunch of U4 and leaded race gas posts but I can't afford $10 a gallon and don't want to spend extra $$$$ if its not worth it :cry:

  • Chills

Posted January 27, 2005 - 06:30 PM

#2

Good Q dune, Im my opinion, just stick with Super!!

  • bushy

Posted January 27, 2005 - 06:34 PM

#3

No improvement with 100 octane.

Even U4 isnt even that great for the money unless you really NEED all the power you can get. For the regular rider 91 or 93 octane pump gas is fine.

  • big t

Posted January 27, 2005 - 09:16 PM

#4

I agree with other guys stick with 91 or 93.

  • Chills

Posted January 27, 2005 - 10:17 PM

#5

A shed of Light...

In my experience guys, and I PM'ed Dune this....The only time you really have to run HIGH Octane fuel is when you have a race motor with high compression. If you have a motor like that and don't run the high octane stuff, you run the risk of Pre-detonation. By running a higher octane this reduces the chance of pre-detonation on combustion. Yes, Higher octane gas runs cleaner, but also Hotter.
I learned this the hard way when I was using pump gas (Super) in my Sea Doo Jet boat with a Rotax Motor. Because these things aren't high compression, and don't need all that extra octane, even the Manufacturer says to run 87/89 in it otherwise its a waste of money, plus it will run cooler and better. Sounds kinda backwards, but true...

  • MichiganMXer

Posted January 28, 2005 - 06:16 AM

#6

I've found that my 01 is more susceptable to the "bog" down low on 91. I put 100 in mine and have had no probs with any bog or popping, it just runs better/cleaner on 100. $4.50 is a little steep, I'm $3.50 for 100. So its easier for me to rationalize the difference in cost.

  • Jetsprint2

Posted January 28, 2005 - 09:58 AM

#7

I've found that my 01 is more susceptable to the "bog" down low on 91. I put 100 in mine and have had no probs with any bog or popping, it just runs better/cleaner on 100. $4.50 is a little steep, I'm $3.50 for 100. So its easier for me to rationalize the difference in cost.

Different fuels require different jetting. If you jet and/or adjust the fuel screw properly your bike will run fine on 91. Save your money for other mods. :cry:

  • John_Lorenz

Posted January 28, 2005 - 10:15 AM

#8

There is a 76 station here in town that sells 100 unleaded out of the pump for $4.50 a gallon. :cry: Do you guys think that has any benefit over 91 out of the pump :cry: What about a 50/50 mix or is it not even worth it. Stick with 91 or what? I have seen a bunch of U4 and leaded race gas posts but I can't afford $10 a gallon and don't want to spend extra $$$$ if its not worth it :cry:


Thats al I burn in my 2000, the benifits, Starts 1st 2nd kick hot or cold. Never fouled a plug, never pings, runs like a raped ape

  • grayracer513

Posted January 28, 2005 - 10:29 AM

#9

I've found that my 01 is more susceptable to the "bog" down low on 91. I put 100 in mine and have had no probs with any bog or popping, it just runs better/cleaner on 100. $4.50 is a little steep, I'm $3.50 for 100. So its easier for me to rationalize the difference in cost.


Different fuels require different jetting. If you jet and/or adjust the fuel screw properly your bike will run fine on 91. Save your money for other mods. :cry:

That's correct. Just remember that it's the fuel, and not the octane of the fuel that makes the difference in performance. There are a great many variables in fuel formulation, and octane is raised and/or lowered by an equally great number of chemical means. Your best bet is to determine how much octane you need, and select the best performing fuel you can find for the money that at least meets that minimum. It's faulty reasoning to assume that because a fuel has a higher or lower octane, and the engine runs better or worse, that the results are due to the octane number. They simply aren't. It makes no more sense to follow that line of thinking than to assume the improvement is due to a higher price, or the color of the pump that it comes from. The octane just happens to be one of the only things you can be aware of that might be different between two gasolines.

Octane is only the fuel's resistance to knock, and the only relationship that has to any other performance or driveabilty attributes is the method used to achieve the octane number. The chemical means of improving the octane can have an effect on performance, either for good or bad. Vaporization rates and oxygen content, as well as the energy content of the mix are just a few of the things that actually make a difference.


:cry:

  • Frostbite

Posted January 28, 2005 - 10:35 AM

#10

High octane gas actually burns slower than low octane gas, a lot of people think the opposite. To take full advantage of high octane fuel you would have to advance your ignition timing.
Engines fire before TDC so that when the piston reaches TDC the mixture is fully igniting and fires the piston back down. Let's say your engine fires 20 degrees before TDC and it runs perfectly on 90 octane gas. If you switched to 100 octane gas, the mixture isn't fully ignited until the pistion is already on the way down so you lose some of the push. You advance your timing so the spark fires earlier and the power is ready when the piston reaches TDC.
If your timing is advanced for high octane and you run low octane you risk engine damage. The mixture reaches full power while the piston is still on the way up and slams it hard, engine knock. A piston that has been subjected to this type of early firing, same effect as pre-ignition, looks like it was beat with a hammer.
My sled has 2 positions on the ignition switch right from the factory, one for regular pump gas and one for high octane. The high octane position advances the timing. Lots of guys up here order barrels of av gas and race fuel for their sleds but without the ability to change the timing it's a waste.

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  • assgasorgrass

Posted January 28, 2005 - 11:08 AM

#11

I say save your money, people get too wrapped up in high octane gas for nothing. Unless you've done work to your engine to get the benefit of it, high octane pump gas is fine.

  • FZ1426

Posted January 28, 2005 - 04:41 PM

#12

The manual on my 426 calls for 95 octane minimum. Do the math. It runs MUCH stronger when I mix leaded 110 with pump gas 50/50.

  • grayracer513

Posted January 28, 2005 - 05:18 PM

#13

High octane gas actually burns slower than low octane gas, a lot of people think the opposite. To take full advantage of high octane fuel you would have to advance your ignition timing.

No, it doesn't. All gasolines burn at very nearly the same rate within a fairly narrow range. They do flash at different points, and they do vaporize at different rates, but these factors are different than the burn rate, and different than the resistance to compression detonation, which is the only thing that octane numbers are related to.

Spark knock is the result of pressure induced detonation of the fuel charge. An engine first compresses, then ignites the fuel charge. Following ignition, the cylinder pressure continues to rise as the fuel BURNS, and the flame front spreads across the combustion chamber. As the flame spreads, the remaining fuel and air in the combustion chamber is subjected to increasing pressure levels which can cause the spontaneous detonation (the simultaneous ignition and combustion of all remaining fuel at the same instant, as opposed to a wave of flame) if the fuel's octane is not high enough. If this detonation occurs late in the flame cycle, it only creates the annoying, and possibly power robbing "knock", or "ping" most of us have heard before. If it happens earlier, it can be extremely destructive, sometimes bending rods or breaking pistons. The rate at which the fuel actually burns is not related to octane, and this myth is the result of an over-simplified means of explaining the phenomena of compression knock.

Spark advance is how the timing of the rise in combustion pressure meets the piston as it begins downward on the power stroke is controlled. It is based on the recognition that the point of ignition must occur before the piston arrives at TDC in order for the optimum pressure to be applied to push the piston downward, driving the crank. The optimum point at which spark should occur depends on the speed of the engine, and the rate at which gasoline burns. Gasoline will burn at the same speed regardless of engine speed, so ideally, a system should be, and usually is, in place to increase the spark advance as speed increases, so the flame will be able to keep up.

While it is true that a low octane fuel can be compensated for by retarding the timing, thereby avoiding the knocking, a considerable amount of power will be lost due to the fire being started late. By the same token, there is no power to be gained by running the timing further advanced on a premium fuel, because even though it may not ping, the combustion pressure will rise too soon and work against the piston on the way up. This was correctly noted in the earlier examples of automotive engines with the abilty to detect knocking and correct for it on the fly. Cars built for premium fuel will tolerate regular, but loose power. Cars built for regular can run premium, but gain nothing.

  • Rich_Rohrich

Posted January 28, 2005 - 08:36 PM

#14

Gasoline will burn at the same speed regardless of engine speed,


While the "laminar" flame speed of a fuel won't be influenced by engine rpm, there isn't anything laminar about engine combustion. :cry:

Higher engines speeds reduce the overall burn time by virtue of additional turbulence in the combustion chamber, less time available to lose heat to the surrounding chamber surfaces, higher flame speeds, and increased mixture density. As a general rule, the first half of combustion 0-50% burned, flame speeds rise in direct proportion to rpm, while the 50-100% burned time flame speeds rise exponentially with rpm. As an example Honda has shown in some of their research a flame speed of 45 m/sec at 8000 rpm, with an increase to nearly 200m/sec at 16,000 rpm on a small bore test engine. In engines with narrow valve included angles, and efficient combustion chambers these factors can offset the reduced time available for combustion to take place, and retarding the timing will actually produce more torque. By monitoring RPM and throttle opening (which influences Manifold Absolute Pressure or MAP) it's possible to have a smarter advance curve that more closely follows the actual requirements of the engine, rather than just advancing with RPM. Full engine management systems monitor additional parameters to take this control to a higher-level still.

As we get closer to EFI based full engine management systems on bikes we'll see the simple advance curves of the past fade away. :cry:

If you'd like to see the Honda paper I referenced it’s:
SAE paper #700122 Research and development of high-speed, high-performance, small displacement Honda engines

It's kind of a classic paper and has a ton of really interesting information in it that is still relevant today.

  • grayracer513

Posted January 29, 2005 - 08:37 AM

#15

Higher engines speeds reduce the overall burn time by virtue of additional turbulence in the combustion chamber, less time available to lose heat to the surrounding chamber surfaces, higher flame speeds, and increased mixture density. As a general rule, the first half of combustion 0-50% burned, flame speeds rise in direct proportion to rpm, while the 50-100% burned time flame speeds rise exponentially with rpm. As an example Honda has shown in some of their research a flame speed of 45 m/sec at 8000 rpm, with an increase to nearly 200m/sec at 16,000 rpm on a small bore test engine. In engines with narrow valve included angles, and efficient combustion chambers these factors can offset the reduced time available for combustion to take place, and retarding the timing will actually produce more torque. By monitoring RPM and throttle opening (which influences Manifold Absolute Pressure or MAP) it's possible to have a smarter advance curve that more closely follows the actual requirements of the engine, rather than just advancing with RPM. Full engine management systems monitor additional parameters to take this control to a higher-level still.

As we get closer to EFI based full engine management systems on bikes we'll see the simple advance curves of the past fade away.

Thanks, Rich. I knew there were influences that actually changed the flame speed dynamically, but what I knew about them I thought would unnecessarily complicate my already pretty lengthy post. My focus was to try to steer people away from connecting octane number with any characteristic of gasoline that it isn't actually connected to, and that fuel octane isn't the primary influence on ignition timing. The Honda research is new to me. Thanks for the reference to it.

The point about monitoring throttle opening is dead on, of course, and is the reason I have never been a fan of unplugging the TPS on these bikes. It puts the ignition module back in the "stupid" mode, where it follows only engine speed. The stock setup on modern four-strokes with a TPS IS an example of smarter timing control, not as complex as EFI systems, but far better than simple RPM based timing, and it's a shame to disable it. Contemporary EFI systems monitor RPM, throttle position, atmospheric pressure and temperature, manifold pressure and temperature, engine temperature, exhaust oxygen content, and mass air flow, and are capable of compensating for changes in weather and altitude on the fly. They can adjust the fuel mixture and ignition timing on a per ignition stroke basis for each one of eight or more cylinders individually at speeds beyond red line, and are one of the main reasons cars like the Z28 can produce the kind of power they do now and still pass current smog laws. When bikes get to that point, hang on! :cry: :cry:

  • grayracer513

Posted January 29, 2005 - 08:43 AM

#16

The manual on my 426 calls for 95 octane minimum. Do the math. It runs MUCH stronger when I mix leaded 110 with pump gas 50/50.

The results of your fuel mix experiment notwithstanding, the manual refers to 95 octane by the Research method (RON). California gas pumps are labeled based on the average of the reseach and motor octanes (R+M/2). 91-92 octane by this method equates to about 95 octane RON. Your power gains were from a superior fuel, not from its octane.

  • Frostbite

Posted January 29, 2005 - 09:04 AM

#17

[quote name='grayracer513']No, it doesn't. All gasolines burn at very nearly the same rate within a fairly narrow range. They do flash at different points, and they do vaporize at different rates, but these factors are different than the burn rate, and different than the resistance to compression detonation, which is the only thing that octane numbers are related to.

QUOTE]

Hmnnnn, maybe I got some bad information or maybe I didn't use the best terminology. What I have learned and what I should have said was high octane gasoline burns more controllably and predictably than low octane gas. I do know that high compression can cause low octane gas to ignite before the plug fires, but I learned that low octane fuel produces more of a flash explosion where under the same circumstances a high octane fuel produces a more controlled (what I called slower) burn and gives more of a push to the piston rather than a whack.

My experience is from roadracing. I travelled and helped wrench for A Canadian 600 and 750 production champ. I also travelled with him when he was hired to ride Reuben Mc Murter's Team Honda superbike's after Rueben had a crash early in the year and decided to retire as rider and manage instead. The general rule was running more advance on the ignition timing with higher octane fuels beacuse the fuel burns slower so you have to light the spark sooner.
When Pascal Picotte was riding a Ducatti for Fast by Feracci they would switch between race fuels for practice and sometimes use F1 fuel only for championship races since it was extremely expensive and they practically wore chemical suits when fuelling the bike. The Ducks were fuel injected and they were constantly changing the ignition and fuel mapping chips.
This is what I have learned first at AMI, then a few years as a bike mechanic and 9 years roadracing, but I realize I still could be wrong. :cry:
I just bought a book on carb tuning and one section mentions that humid air is denser than dry air. I have done a lot of wind turbine research and air density is a huge factor in power output. It is common knowledge in the wind industry that dry air is heavier and denser than humid air. Somebody's right and somebody's wrong.

  • grayracer513

Posted January 29, 2005 - 10:56 AM

#18

When Pascal Picotte was riding a Ducatti for Fast by Feracci they would switch between race fuels for practice and sometimes use F1 fuel only for championship races since it was extremely expensive and they practically wore chemical suits when fuelling the bike. The Ducks were fuel injected and they were constantly changing the ignition and fuel mapping chips.

You're not really wrong, exactly. Higher octane fuels burn "more controllably" compared to lower octanes IF the lower octane fuel is operated near the upper limit of its knock resistance. The trouble is that there is so much more to fuel performance than octane, and octane is not necessarily connected to any of these other factors.

Changing fuels might very well require different ignition mapping for optimum performance for a variety of reasons.

Here's a good place to explore gasoline further:

http://www.faqs.org/...s/gasoline-faq/

Part three deals with the octane question in great detail, and the rest of the paper covers gasoline thoroughly, and the engineer who wrote it still knows how to speak English. :cry:

  • FZ1426

Posted January 29, 2005 - 08:15 PM

#19

The results of your fuel mix experiment notwithstanding, the manual refers to 95 octane by the Research method (RON). California gas pumps are labeled based on the average of the reseach and motor octanes (R+M/2). 91-92 octane by this method equates to about 95 octane RON. Your power gains were from a superior fuel, not from its octane.


Perhaps I'll just put it this way. It's not an experiment, it's experience. It runs crappy on pump gas, and really good with some good old fashioned leaded high octane. nuf said?

  • grayracer513

Posted January 29, 2005 - 08:24 PM

#20

Perhaps I'll just put it this way. It's not an experiment, it's experience. It runs crappy on pump gas, and really good with some good old fashioned leaded high octane. nuf said?

I can't dispute the results you got from changing from an unnamed pump fuel to another unnamed fuel, because I wasn't there, and it's entirely possible that it happened just like that. What I said was:

Your power gains were from a superior fuel, not from its octane.

...and I stand by it. :cry:





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