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[lotus1967 0]

Just want to say thank you to whomever it was that included a comment in a post that small engines were designed to run on Hi-test gas. I had been using Reg (87 oct.) which seemed to work find, but after seeing that post changed to 93 octane. Now on my 3rd. tankful, and what a difference. Much smoother, but also noticable increase in power. RPM's barely drop when engaging the mower. Next door neighbor even commented over beers after finishing our lawns that the motor "sounded" different.

Curious now to see if it lowers consumption enough to offset the slight cost increase, but really don't care.

Again, thanks to whomever you are.

[zieg72 209]

After reading your post for $.20 per gallon higher I tried it today on my 520H. I couldn't believe the difference. I know I consumed less gas unless my gas gauge quit working. The engine did sound different and seemed to have more power in the tall grass. I am going to put back on the 60" deck next cutting and see how well that works. Thanks for the post.

[gwgdog66 23]

:omg: I was skeptical, but tried it last weekend. My 16 HP kohler did seem to run smoother, and if my watch wasn't fooling with me I ran 15 minutes longer on the full tank then I was on regular unleaded.

[Coadster32 793]

Shouldn't we be putting lead addative in these, as to not burn out the valves?? These were designed before unleaded came out. Yes it might run better, but as what cost? When a two stoke motor comes to the end of the tank and runs on straight gas, it runs great, but...

[Confused99 2]

When a two stoke motor comes to the end of the tank and runs on straight gas, it runs great, but...

A 2 stroke will never run on straight gas even if it an injected motor. It will lean out right before it completely runs out which isn't good for it either.

Jason

[dkopp 1]

Careful here guys, octane rating is not a measure of how much energy is in the fuel, but only how resistent it is to detonation within the combustion chamber. Higher octane fuels actually burn more slowly than lower actane fuels. What you may be experiencing in your engines is not more energy but more torque due to the fuels burning slower and causing the expanding gases to push longer on the piston as it travels down the cylinder. I've known too many people who claim that more octane equals more horsepower. It depends on the engine design and the speed of operation.

[wh500special 2,055]

Careful here guys, octane rating is not a measure of how much energy is in the fuel, but only how resistent it is to detonation within the combustion chamber..

Yep.

I wish I would have seen this topic sooner, but somehow overlooked it.

Higher octane fuels DO work better in some air cooled engines because they resist knocking better. The smoother sound you hear is likely the result of decreased knocking. I used to have a D180 with a Kohler k532 and it seemed to run best on 89 octane or higher. Most of my other stuff doesn't seem to care but I continue to use 89 in my Echo two stroke engines since the manual suggests I do so.

Octane is actually an empirical measure of the ignition temperature of a fuel. Higher octane fuels will not auto ignite (ignition due to sufficient heat and oxygen in absence of a spark) until significantly higher temps than low octane fuels. Because air cooled "lawnmower" engines operate at temperatures in excess of a typical water cooled car engine, the higher octane fuel is less prone to premature detonation.

Because higher temperatures are needed to light the higher octane fuels off, they tend to burn less completely and actually can pollute more when used in an engine not designed for them. That's the slower burn mentioned above.

When the spark plug fires and the flame front starts to propagate thru the cylinder much of the power stroke will have been completed before the flame gets to the furthest reaches of the cylinder. Higher octane fuel in a low octane engine might not get touched by the flame front fast enough to burn off before the power stroke is over. This unburned fuel will carry out in the exhaust where it may or may not burn.

This tendency to incompletely burn the fuel that is at the outer reaches of the cylinder is also why the trend has been to increased numbers of small bore cylinders rather than to just keep punching an engine out for higher displacement. Diesels work a little differently and a large diameter cylinder there isn't as detrimental...

On the intake stroke of the piston the engine takes a gulp of air thru the carburator. As the air flows thru the carb, atomized fuel mixes with it and the whole charge travels to the cylinder.

As the engine comes up on compression the air/fuel mixture waiting inside the cyliner is rapidly compressed. This rapid compression raises the temperature considerably and primes the fuel mix for ignition by the spark plug. The fact that the air and fuel are thoroughly mixed and are already sitting there at close to their ignition temperature means that the combustion process during the power stroke is pretty closely matched to the speed of the piston travelling downward.

The increase in power you might be perceiving is probably a result of your engine having been down on power due to knocking on the low octane fuel. Ignition of the fuel before the power stroke of the engine contributes nothing to the rotation of the crankshaft and - in addition to potentially eroding metal within the engine - is detrimental to performance. If the knocking stops with 89 octane, moving up to 93+ octane fuel will gain you nothing additional. In fact, becuase there is less energy per gallon of high octane fuel than low you will actually experience a decrease in fuel economy.

So, why do some auto engines demand higher octane?

Higher compression - or turbo/supercharged - engines compress their intake air significantly more than a low-compression engine. The more highly compressed air will preheat much hotter than a low compression engine and the fuel is more likely to autoignite before the spark plug fires it off in a controlled fashion. To run on low octane fuels, computer controls in those vehicles often retard ignition timing and vary the amounts of fuel injected into the engine. And they run at much lower output and are prone to knocks.

Higher compression ratios equate to higher expansion ratios (the combustion gases can expand more) and the engine is capable of performing more work per stroke than a low compression engine of equal displacement. I guess the generic term here is "high performance".

Tetraethyl lead (TEL, TE-Pb) was added to gasoline as a means of raising the octane back in the days before we realized that the lead particulates in the exhaust might cause health problems to pump jockeys, mechanics, and people who lived along side roadways. All the lead was intended to do was raise the octane so that higher compression could be employed in engines to increase their outputs or efficiencies.

When health and environmental concerns forced the removal of lead from motor fuels there became a need to either find another octane improver or decrease the compression of the engines so that they would run acceptably on lower grade fuels. Those were the days when a 400 cubic inch engine decreased in power from 300 HP down to 175. Lower compression and low octane fuels necessitated the change.

As better additives became available (MTBE and Ethanol) octane ratings began rising again and power outputs began a slow march upward.

As a side note, typically a service station that offers more than one grade of gasoline really only has 2 types of fuel in the storage tanks - high octane (say 93) and low octane (87). These are blended proportionally at the pump to achieve whatever is posted - 88,88.5, 89, 91, etc. If you think your engine will optimally perform on 91.3 octane you can buy the appropriate amounts of high and low and blend it yourself.

i digress...

When the lead disappeared it became more widely recognized that a side benefit of the TEL was that it provided some lubricity to the valving surfaces. Both intake and exhaust valves run at high temperatures and the fuel the encounters their surfaces on its way in or out of the cylinder is prone to burning on the surface of the valve. Lead doesn't burn well so essentially plated out as a sacrifical surface on the valves and preserved their mating surfaces. It did not take long for alloy chemistries to change to accomodate the lack of lead.

But leaded fuel did stay available into the early 1980's to continue to service the aging fleet of vehicles on the road. Because the lead particulates in the exhaust will render the catalytic converter useless, lead was eventually eliminated from the supply entirely. Looking back, this was one of the few times I think things went pretty smoothly when it comes to government intervention in business.

Don't use lead additives. You don't need them and you really don't want to be breathing the exhaust products from them if you care to avoid brain damage. I am more than willing to sacrifice an old engine than poison myself or the world around me in the interest of saving a valve or two. It's kind of like allowing your kids to ride in the back of an open pickup truck on the interstate - you can do it, but you shouldn't.

The catalytic converter also does another thing that is directly related to controlling knocking within a car engine. In order to run smoothly and without excessive pre-ignition/detonation/knocking almost ALL engines are set up to pump more fuel into the combustion chamber than there is air available to burn. The added fuel - which passes thru unburned - actually is used as a coolant to keep combustion temperatures as low as practical. Air, being 78% nitrogen, will oxidize at high temperature to form Nitrogen Oxides (NO, NO2, "NOx"). That oxidized nitrogen will result in "smog" and low-level Ozone pollution.

The excess fuel cools the chamber and decreases the NOx formation. The unburned fuel is easily oxidized to CO2 and water by the catalyst. Accompanying this oxidation is a reduction of the NOx back to Nitrogen (N2) and a second oxidation reaction of Carbon Monoxide (CO) to CO2. Three "redox" reactions in one catalyst hence the "Three Way Catalyst" name.

Bacause the catalyst needs to be hot to function properly you have no doubt noted the odd odors that come from the exhaust of a cold car - even a brand new one that is properly in tune.

back to our small air cooled engine....

To keep combustion temperatures low, our engines tend to be tuned to use quite a bit more fuel than they actually consume. You can "lean out" an engine a touch if you elect to run on higher octane fuels but it will make starting difficult.

Depending on how clean your engine is on the inside, the ambient temperatures you're working in, or how hard you're working the engine the octane rating of the fuel you use can be of some importance. For my applications it seems that 89 octane pump gas (with ethanol) has always been sufficient to control knocking. Anything above that is just a waste.

Your mileage may vary,

Steve

[dkopp 1]

Nicely put Steve.

[DwellingBoar 0]

That was very informative. Very interesting to read. Now i have more knowledge than before. Thank you. :omg:

[wallfish 15,970]

Steve

At first your post looked to be long winded but it turned out to be very interesting with some good information. Thanks for taking the time to share your knowledge.

[zieg72 209]

I went with 89 octane today and got great results. I got everything mowed with less than 3/4 tank of gas. I had some deep stuff to go through, didn't have to slow to a crawl and the engine power gauge never went past 70%. Next cut will be with the 60" deck, we'll see how that one goes.

[Jedakiego 0]

I worked gas pipeline for awhile. When shops unload at a fuel depot they dropped off 89 and 93 octane pump fuel, Kerosene, Jet fuel (Refined Kerosene) and Diesel.

When they are pumping fuel from one area to another (Florida has Pipe Lines from Tampa to Orlando and From Tampa to Ft Myers.) There is nothing keeping the fuel apart except the pressure they pump at causes the specific gravity of the different fuels to form a wall between the fuels keeping them separate. When these "heads" (the area where one type stops and one begins) get to the tank farm they can stop the flow from the previous product and switch to the new product only loosing a few gallons (usually less than 300 gallons) which are diverted to a holding tank. This tank can see a mix of ALL of the fuels pumped and any leakage or fuel recovered from spills, maintenance etc. Also they will dispose of use lubricants, motor oils and other petroleum produces into this tank. With no pressure being present they can send this through a centrifuge type mixer and come up with a mix that stays together under pressure. It will have it's own specific gravity and octane number. They will then set aside an amount of fuel based on these numbers to send through the mixing process and the send it down the pipeline. It is many times trucked back to the original location and it is then tested, additives are added if needed and it is sold as 87 Octane.

There are only 2 fuel suppliers that DO NOT do this, BP (amoco) and Shell. These companies use a specific fuel for 87 octane.

Some other info that is interesting. BP fuel is oxygenated with chemicals to burn hotter and cleaner and this mix is dependant on the areas smog requirements and can vary greatly within a short distance. We found this running our crate motor late model and having over heating problems in specific areas of the south east.

Shell gasoline is the most consistant fuel state to state AND Shell also has the highest MON (Motor Octane Number) across all 3 of there grades of gasoline. Motor Octane Number is a better measure of how the fuel acts under load and is generally about 10 points lower than the RON (Research Octane Number) that is posted on the pump. A higher MON a fuel has the better the performance will be with it.

A way to test what you need it to check the exhaust temperature. If you are running 87 and the plug looks good check your exhaust temperature. Then run 89 octane and check your plug and exhaust temperature. IF the temperature of the exhaust gets hotter it is due to unburnt fuel from the cylinder burning in the exhaust which tells you that the octane number is to high for your compression. Cherry red exhaust is from a rich condition in the exhaust not the lean condition that is typically thought to cause it. Rich in the exhaust can be to much fuel in the chamber OR to high of an RON octane number not allowing it to burn in the cylinder. Typically anything under 9:1 you are safe with 87, Under 10:1 89 and 10:1 and SLIGHTLY above 93 octane. This can very GREATLY with chamber shape, timing, temperature and engine condition. (oil getting past the rings will cause ignition problems and cause knock as will carbon buildup in the cylinder.)

[Nick 13]

Something I dont think has been mentioned is fuel quality. Now Ive heard that it all comes from the same place but also that the bargain brands, like sams club and wal-mart, are of a lower quality. The additive packages used might be part of the problem also.

On a truck forum I often saw information from a person who had done extensive work with engine tuning. What he said was that while fuel quality can vary by location, or even between stations, some brands generally do not have the same quality and can also have a slightly lower energy content than other brands. So I assume staying with the same octane but changing stations might do more for performance.

edit: I see Jedakiego just mentioned something similar about fuel quality. Guess I should have typed faster instead of watching the TV. We had a local station that would buy any fuel he could find, even stuff in an old holding tank. While there one day the attendent had to change the pumps external filter because flow had slowed down to much. He said "I just changed that...it must be full again". :drool:

[04fxdwgi 0]

Working in the fuel distribution industry a while back, all the different labeled fuels came from the same tanks, just had different additives added at time of loading. You could see Exxon, Shell, all of them, lining up at the same pumps at any given time.

[zieg72 209]

I went with 89 octane today and got great results. I got everything mowed with less than 3/4 tank of gas. I had some deep stuff to go through, didn't have to slow to a crawl and the engine power gauge never went past 70%. Next cut will be with the 60" deck, we'll see how that one goes.

Well the 60" deck is back on with the mid-grade gas in the tank. Cuts flawlessly, engine sounds much better and it took about a 1/2 tank to do 1.5 acres. I am real happy I stumbled on this tread...

[W9JAB 156]

Shouldn't we be putting lead additive in these, as to not burn out the valves??

I have been using a lead additive from day one of owning my 42 year old Horse, Is it doing any good? Well it does not seem to do it any harm, the motor dose not burn any oil, and runs nice.

I also use "slick 50" in the oil, Now I know that works. My tiny teach shows a 50 rpm increase with the "slick50".

[wh500special 2,055]

Shouldn't we be putting lead additive in these, as to not burn out the valves??

No.

You can put it in, but everything I have ever read to support it's use is mostly anecdotal. My primary worry is more related to the lead in the exhaust that you and your kids will be breathing. Your gains will be minimal from a mechanical standpoint, but the tradeoff is inhaling things your body can't deal with.

I think Slick 50 has a Teflon micropowder in it. Teflon (PTFE) makes a nice dry lubricant and it probably leaves behind a resisdue after it drips down into the sump after engine shutdown. That residue can probably improve cold start lubrication.

I remember when I switched my vehicles over to synthetics a few years ago that they seemed to rev a little higher at startup when filled with synthetic. I attributed it mostly to better viscosity control at low temperatures. My suspicion is that Slick 50 has a pretty lightweight carrier oil in it that is allowing your engine to rev a little higher by thinning out your crankcase oil a touch.

When Slick 50 was the rage there were a lot of articles related to determining whether or not is was beneficial. As I recall, it was found to contribute little to improving things in automotive engines but was not detrimental in any case. The Teflon powder - although milled exceptionally fine - mostly didn't pass thru the oil filters and was promptly rendered unavailable for the engine. But w/o a filter, perhaps you do see some benefit.

It is awefully tough to beat the R&D departments of the big oil companies when it comes to improving the performance of any fuel or lubricant. Sure they make some compromises when formulating to deal with cost/benefit tradeoffs, but Pennzoil, Valvoline, et. al. put a lot of work into developing effective lubricants. Same goes for modern fuels. There are a lot of lab hours and chemistry put into each drop, so optimization above their abilities is pretty tough to acheive.

So I say use the Slick 50 if you like, but lose the lead.

Steve

[Coadster32 793]

Does the same idea hold true for the Lucas oil stuff, as with the slick50?

I see the displays on the countertops of the autoparts stores, and it looks pretty good, but... my friend swears by the stuff but I haven't tried it yet.

[wh500special 2,055]

When shops unload at a fuel depot they dropped off 89 and 93 octane pump fuel, Kerosene, Jet fuel (Refined Kerosene) and Diesel.

They are able to do this as long as the fluid velocity in the pipe is held reasonably low. High speed pumping causes turbulence which would promote mixing. If they keep things moving under what is known as "laminar flow", there will be minimal mixing between grades of fuel. This is also called "plug flow".

I suspect you might be mistaken when you speak of sending 89 and 93 down the pipe. It seems like they would only send 87 and 93. 87 and 93 can be blended in any linear proportion to acheive intermediate grades of gasoline, but if they only sent 89 as the low end they'd never be able to blend under 89.

There is no doubt in my mind that the mixture of fuels is dumped in a holding tank and is sent back for re-refining. But the chemistry of that mixture would be way off to use it as a source for 87 octane gasoline. And if they only accumulated a low amount each time a new fuel came thru they wouldn't have enough supply to maintain a steady flow of 87 octane to the gas stations.

I have been wrong before (many times), but I am guessing that your memory is fading a little on which two grades of gas were carried by pipe. Unless in FL they truck all the 87 octane from place to place but that seems like a cumbersome way to move the highest volume product.

Most gasolines - regardless of brand - are very similar in composition. That's why you see the same fuel depot filling trucks from BP, Shell, Exxon, Casey's, Farm service, etc. Where the difference lies is in the proprietary additive packages that each label blends in. The detergents, stabilizers, etc are what the major brands hang their hat on and present the only real marketable difference b/t fuels. The additive packages are typically blended into the truck tank with the raw fuel.

It used to be that only the top octane fuel received the "best" detergent package a seller would have. But the more finicky nature of auto engines and the increased emissions controls have prompted the retailers to incorporate additives even into their lower grade fuels. The top end fuel may still get the "best", but the other two receive a fair dose as well either by direct addition or by reblending the low+high at the dispensinge point.

The detergents in the highest grade fuels can actually - over time - clean out some of the deposits that form within the fuel system of the vehicle. The lower grade fuels have enough to maintain the cleanliness of the system. This is done mostly as a means of preventing fuel system issues in customers' cars and exposing them from liability issues.

Independent shops can either buy their fuel on a contract basis from a big supplier, or can shop around each time they need fuel dumped. Many choose to contract with a single supplier for convenience and are therefore more subject to the ups and downs of the prices of national supply. Those that shop can often get a better "spot price" for their fuel which they may or may not pass along at the pump. The downside to NOT contracting with a fuel supplier is that you become last on the list of receiving your shipment when ordered.

i don't remember the actual number of "boutique formulations" of gasoline sold in the US, but there are literally dozens of location specific formulations of gasoline available. In any case you are getting the pump posted octane number, but unique additives may be added to serve some unique environmental need of a particular region. Same areas (the Northeast) forbid the addition of MTBE (an octane improver). Some areas (the farm states in the Midwest) demand that a higher percentage of corn ethanol be blended in. In winter, cold areas see the addition of more oxygenates (ethers) to improve cold weather emissions and cold start performance.

Nationally I think 5% of all gasoline sold must have ethanol in it now. That means that some gas will have 10% while some may have 0%.

This formulation difference means that midwest refineries really can't sell to other regions. And vice-versa. There has been talk of eliminating the regional/seasonal differences, but places that don't need a changing fuel supply(AZ, NM, etc) would be penalied with lower economy for no added benefit.

If the oil companies had their way, they'd sell nothing but one version of one grade of gasoline. But they aren't making the policy on this.

All that said, and all the complications we have with fuels at least it is reassuring to know that the US has the best quality supply of gasoline going. One less worry for consumers.

Steve

[wh500special 2,055]

Does the same idea hold true for the Lucas oil stuff, as with the slick50?

I have no real knowledge of any of Lucas Oil's products. They do make a surface tension additive that makes the oil cling to gears which seems like it would be ideal for gear cases, other than that though and I have no idea what they make.

Even though I'd love for you to spend your entire CT income on Lucas products and send it back to Indiana (where it is made) I have no idea even what they sell. My general feeling towards most additives is that they probably provide limited additional benefits because if they were as great as they claim to be the big manufacturers would already by adding them. EVERYTHING in life is a compromise and you NEVER "get something for nothing". Where I worry about additives is that the tradeoffs may be undetermined.

That's my opinion only of course.

Steve

[Coadster32 793]

EVERYTHING in life is a compromise and you NEVER "get something for nothing". Where I worry about additives is that the tradeoffs may be undetermined.

That's my opinion only of course.

And very well stated, Thank you for all the technical info.

[bo dawg 478]

Wow, my head is spinning after reading all this thread at once. Too much knowledge, I'm not quite sure I understand it all, but doggone it sounded great. Your the man Steve :thumbs2:

[wh500special 2,055]

Wow, my head is spinning after reading all this thread at once. Too much knowledge, I'm not quite sure I understand it all, but doggone it sounded great. Your the man Steve

Thanks.

There are a lot of sharp guys on this forum and there is a real depth of experience since so many occupations and trades are represented. I think I learn something new almost every day reading stuff like this.

Steve

[lotus1967 0]

After being responsible for starting this topic I'm feeling like I've accomplished a good thing. Great knowledge, great lessons, and great hints.

A humble thank you to all who have contributed. I never expected this.

[W9JAB 156]

Premium Gas

If you want premium gas try two Toco Bell Burrito Supremes and a six pack of Bud :thumbs2: