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Leaded vs. Unleaded Gas
7

Leaded vs. Unleaded Gas

Leaded vs. Unleaded Gas

(OP)
I have a Yamaha WR426F with a fourcycle engine with a 12.5:1 compression ratio. Yamaha specs that the minimum octane rating is 95 and must be an unleaded gas. Most all pump gas within this area does not exceed 91 and does not work well at all when used with an octane boost additive. Race fuel is readily available but the leaded versions are much cheaper and have still higher octane ratings than the unleaded. Yamaha states that leaded gas will harm my engine,,, is this true and if so why and how?

RE: Leaded vs. Unleaded Gas

3
I don't know if motor cycles have catalytic convertors, but lead certainly kills the catalyst.

Adding Tolulene or Xylene will increase the octane rating. To the best of my knowledge, this is a technique used by oil companies to make premium unleaded.

This link will give you a wealth of information on internal combustion engine fuels

http://blizzard.rwic.und.edu/~nordlie/cars/gasoline.htm...

Regards
pat

RE: Leaded vs. Unleaded Gas

(OP)
Thanks Pat, the above link does have a wealth of knowledge. And no the motorcycle engine does not have a catalytic converter, but is in the simplest form ie. carb, single cylinder and open clear breathing exhaust. So where can the damage occur (valves, cylinder, exhaust packing)? From what (heat, deposits, corrosion)?
The link also makes reference to the troubles of blending unleaded with leaded fuel, which I didn't completely understand???

RE: Leaded vs. Unleaded Gas

The only problem I can see is deposites, and I relly can't see that being aproblem. One of the problems in running old engines on unleaded is the lack of deposites that lubricate some parts and prevent erosion of the valve seats.

The problem with brewing your own fuel, is that burning fuel is a chemical reaction, and as you mix the chemicals, they may interact in a way other than as expected. Normally with the major hydrocarbon components, this is not a problem, but with various additives it can create unexpected side effects. This is unlikely, but not impossible.

Some time ago (probly something like 8 or 10 years) i mixed premium unleaded and leaded 50/50, and got a better result than either on its own in that the mixture prevented pinging whereas the pure as from the pump fuels did not. I discovered this one day as I needed leaded, but could only get unleaded, so I topped it up to get to the next station.

Some years later, the reverse was true. The mix pinged while the premium unleaded did not.

First time was on a very hotrodded old air cooled VW with 10:1 static compression ratio, but as it had steel valve seat inserts, and was well and truely pre polution controls, it could run on either so long as the octane was OK.

Second time was a 350 chev in my ski boat, also with 10:1

Regards
pat

RE: Leaded vs. Unleaded Gas

Adding toluene or xylene to a pump fuel will normaly raise the octane, by how much, depends on what is there to start with.

It does burn dirty and increases black deposites on plugs, chamber and exhausts, and if to much is used this can be a problem due to loading up of plugs. There might already be a lot in the premium unleaded you are buying.

Sorry the answer is not straight forward, but the situation is not straight foward.

Regards
pat

RE: Leaded vs. Unleaded Gas

I agree with pat, i don't see any problem using the leaded. Maybe YAMAHA's intention was that leaded fuel will leave deposits inside your engine (valve seats etc.) that will reduce engine efficiency and might cause in the long run an engine failure. Anyway, this is not the case in the WR since you'll born the deposits in high RPM's (and power...) ...
If you decided to go for the leaded please keep me informed

RE: Leaded vs. Unleaded Gas

This may seem too simple, but re-check that 95 octane requirement and see if it refers to pump octane,research octane(R)or motor octane (M).Pump octane is R +M /2. A 95 research octane requirement will be more like 93 pump octane. I realize that this is still higher than the 91 pump octane available in your area, but it may be high enough to run OK in your motor.Also, try different brands of the 91 octane gas.That posted pump octane rating is a minimum and the actual octane may run a bit higher from brand to brand.

RE: Leaded vs. Unleaded Gas

swall gets a star for beating me to the punch.  The technical term for "pump octane" is Antiknock Index (AKI).  My Suzuki calls for 91 RON minimum, and runs just fine on 87 AKI, which is no surprise if you understand the difference.

Geez, 12.5 is a big ratio for a factory machine!

RE: Leaded vs. Unleaded Gas

Sounds like the lawyers wrote the owners manual for you.  IMHO this was only added to the manual so that the bike would be 50 state legal.  California is really starting to ratchet down on off-road bikes, which is why there isn’t a whole lot of development going on in the 2-stroke bike world any more. I run leaded race gas in all of my atv & motorcycle engines, race and non race, and have no problems.

RE: Leaded vs. Unleaded Gas

(OP)
One thing I forgot to mention which may be a factor is that this engine has titanium valves(?).
Guyguy may be right with any deposits being blown out since this machine revs up to 10,000 or 11,000 rpm.
Swall, I've tried all the different 91 pump gases with no success.  I currently use a 50:50 110 leaded with 91 unleaded thereby yielding a 100.5 blend which works fairly well but still runs better on straight 110!!

RE: Leaded vs. Unleaded Gas

The lead will not be a problem with titanium valves.

at 12.5 to one, I would be looking at 105 octane or more.

Unless otherwise stated, I always presume pump octane.

I agree, it sounds to me like the lawyers wrote the manual

Regards
pat

RE: Leaded vs. Unleaded Gas

I was surprised to see this post as my Son in Law races the same bike in 250cc form and asked me the same question. He is upping the displacement to 302cc and even higher CR.  I told him to use the same stuff I use, Sonoco 112 @ ~$4.00 a gal.  The unleaded race gas is sold in cans and is only 104 max. Also VERY high in cost per gal.  I have used the leaded race fuel in all my race engines for 45 years, SS and titanium valves with no problems that I can recall. The  only prob with a  titanium valve was due  to a lost lash cap---.
Incidently Don has been using 91 with additive so far and he won in the Intermediate class last week in Victorville!

Rod

RE: Leaded vs. Unleaded Gas

2
The leaded gas leaves an acid deposit which rusts the exhaust from the inside out. The lead is a major key in the Octane equation. What you want is a fuel with no aromatic hydrocarbon content. This causes soot. You want a fuel that has a low heat of vaporization for its cooling effect on the intake charge and burning speed. The lower the final boiling point, the better the cooling affect on the charge it has. Sort of like Alky in that respect. Try a VP C12. this is a fairly fast burning fuel. Most specialty fuels are good to about 8000. Above this, you need a faster burning fuel. VP also has some MR2 fuel that is oxygenated. You will make more power here. The only other fuel I'd use would be TURBO BLUE aka TRICK GAS. Again these are slow burning fuels for forced induction or Nitrous. They do however work great in aspirated motors up to 8000. So, check with the Manufacturer, I'm sure there is a better fuel for your RPM requirements if you can get away with it.  

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

RE: Leaded vs. Unleaded Gas

All hydrocarbon fuels leave acid deposites, leaded or otherwise.

Carbonic acid is formed as a byproduct of the combustion of hydrocarbons, and NOx forms when air is heated to the temps encountered in a high compression engine. NOx with water makes nitrous acids which are relatively strong.

I never had a race car exhaust rust out, as they normaly get broken or become obsolete before that happens

Regards
pat

RE: Leaded vs. Unleaded Gas

Back in the 70's before the EPA banned Lead from pump gas, this exhaust system rusting was widespread. I experienced it along with several of my friends in the 80's when we would run our street cars on leadded fuel exclusively. However, today I don't have that problem since I can't run lead on the street due to the CAT.

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

RE: Leaded vs. Unleaded Gas

Don't know if it's still used, but perchloroethylene was added to TEL to combat plug fouling and when it burns it produces notoriously corrosive HCl.  I doubt "carbonic acid" (aka CO2 dissolved in water, which it doesn't do very much at exhaust gas temps) contributes much to corrosion, despite it's much higher concentration.

RE: Leaded vs. Unleaded Gas

Shaun
1) Your modern exhaust might be made from a more durable material.
2) Your more modern engine is designed to minimise the NOx output as it is considered a major polutant. The acid produced from the NOx is a lot stronger than the acid produced from the CO2 that is still there in large quantities.
3) Your more modern fuel probably contains less sulphur, thereby producing less SOx and subsequent strong acids.

Regards
pat

RE: Leaded vs. Unleaded Gas

To start with, most of the folks posting in this forum seem to be "regulars" and I trust what I read.  Be that as it may, the facts about corrosion, and polution from ICE's is well known and has been so for hundred years. From reading the above posts one might get the impression that if you don't use leaded fuel your engine will succomb to "rust"!
Just consider that in Jan. 2001 (I think--- my famous 'memory', you know!) I rebuilt the engine in my 1930 Model A Ford after something like 70 years and a bit over 100,000 miles---funny, not a spec of rust!!!

Rod

RE: Leaded vs. Unleaded Gas

Rod

Despite what I say above, I agree, rust is not a problem in engines, as carbonic acid is weak, and the stronger acids are in lower concentrations, especially in polution controlled cars.

The acids are purged from the engine in the form of gas as it runs. They collect in the water that condenses in the cooler end of the exhaust. Mufflers have always been prone to rust.

My only point was, that it is not caused by lead, so running leaded fuel won't rust your exhaust anymore than unleaded, and possibly even less as the light grey coating might just protect the surface a little

Regards
pat

RE: Leaded vs. Unleaded Gas

Back to drwebb's comments

If there is perchloroethylene in there it most definitely will form HCL which is as strong an acid as the acids formed by oxides of nitrogen and sulphur.

I am amazed to hear that perchlor is used when you consider how long it has been known that it is a castiogen. I know the lead is to, but you needed it for the antiknock and lubrication and valve seat coating.

Regards
pat

RE: Leaded vs. Unleaded Gas

Back to reality

The argument about the corrosive nature of lead really doesn't matter in this case, as I have never known a race engine exhaust to rust out before it is discarded for other reasons

Regards
pat

RE: Leaded vs. Unleaded Gas

For what it's worth, I just did a bit more research.

drwebb's comments are pretty well on the mark

Brominated and/or chlorinated hydrocarbons are added to leaded fuels as lead scavangers to convert the lead deposites to volatile lead halide salts, so as to avoid excessive build up of lead.  

The level that these are added at is critical. To much, and you get corrosion, to little and you get fouling.

Avgas specifies the chemically correct ratio, while automotive gas normally has a little more.

Once again, one of the advantages of leaded fuel was that the deposites lubricated some components, so for this to work, the lead scavangers must be in the correct proportion to leave a little lead behind.

The light grey or white deposites on the tailpipe of a correctly tuned car running leaded fuel are probably these lead halide salts. They will deposite where the temperature of the tail pipe surface is low enough for them to solidify on contact.

See the link in my post of 06/11/03 for details

Back to reality again.

The only engines I ever saw corrosion problems on were boat engines which operated in a salt water environment, or engines that were left exposed to the weather and not used for years. I am sure that the corrosion in these cases is down to the salt and long term exposure to water, and occurs no mater what fuel is used.

The only cars I ever saw with premature corrosion of the  exhaust system, were those production road cars that had a design that retained water (like the loop over the back axle), and where the manner of use never evaporated the water out of the system. In my experience, racing use blows and boils all water out of the tailpipe and muffler.

I don't see any of these problems with this guys motor bike

Regards
pat

RE: Leaded vs. Unleaded Gas

I seem to have struck a nerve with patprimmer, when I only meant to point out that ShaunT's observation that leaded fuel can be more corrosive isn't unreasonable.  Your point about stoichiometry is well taken; if all the HCl/HBr forms lead halides it won't corrode anything else.  It is excess alkyl halides that could cause problems, and this serves as another example of the balance of properties in good formulation science, and emphasizes the importance of using a quality leaded fuel.

On a related note, spray-type chlorinated carburetor cleaners are reputed to sometimes ruin oxygen sensors due to HCl formation on combustion if used on EFI equipped cars.  There are non-chlorinated carb cleaners available, but ALL 'throttle plate cleaners' are nonchlorinated for this reason.

As you note, chloride from NaCl in the marine environment is a corrosion promoter, and HCl has chloride built in to the acid, which makes HCl even more corrosively aggressive than H2SO4 or HNO3.  But I don't want to delve too deeply here for fear someone from the Corrosion Engineering board will wander by and give us all a schooling!

Probably the reason they weren't too concerned about the 'carcinogenity' of perch is that in gasoline it's contribution would be totally swamped by the much more potent compound benzene, which is still there!


RE: Leaded vs. Unleaded Gas

The nerve you struck was that I didn't do quite enough homework before shooting my mouth off, and consequently I was wr! wro! wr! not quite right. I really hate that.

The Cl- ion is certainly agressivly corrosive to many metals, but the SO4-- ions and NOx- ions are also quite corrosive. The NOx ions are often in much larger quantities in a high compression, non polution controll engine, where I expect that in any properly formulated fuel, very few Cl- ions will remain as ions in the exhaust.

I got outmy old chemistry book, but could not find the reactivity series tables. Maybe it's to long since I studied this.

Bottom line still remains that corrosion is not a real world issue with race engines.

There are certainly some inconsistencies on how we view toxins. Chlorinated hydrocarbons are mainly banned or listed as dangerous in the minds of most of us, but many still splash benzine containing compounds around with careless abandon. Maybe it's the fact that we can buy it so easily, that we take it for granted

Regards
pat

RE: Leaded vs. Unleaded Gas

Corrosion CAN be a race-exhaust issue if you decide for example to make an exhaust pipe out of 304 or one of the other insufficiently-stabilized stainless alloys - as opposed to for example 409 and 439, and maybe 321.
What happens is that welding will make a heat-sensitized zone in unstabilized stainless where the chromium precipitates out as chromium-carbides along the grain boundaries,  and the very smallest exposure to halides, especially the Cl in roadsalt, will produce intergranular corrosion and cracking-type failures.

Proper stabilization takes the form of added Ti or Cb to tie-up the excess carbon as titanium-carbides or columbium-carbides.

RE: Leaded vs. Unleaded Gas

Okay all.  Don has done a couple of races on the 250 using  leaded race fuel and see absolutely no difference from the unleaded aside the lack of ANY knock.  Next year he is moving to "expert" class and we are now attempting to convert to methonol fuel for that 'added edge' or 'unfair advantage', we'll see. (He runs 'heads up' against the 450's)

Rod

RE: Leaded vs. Unleaded Gas

Having raced two strokes, the reason I don't use leaded fuels, is the lead deposit it leaves on the plug body causing misfiring.

Harvey.

RE: Leaded vs. Unleaded Gas

I'm surprised many that have responded to this post feel the 12.5:1 static CR is really high.  Most motorcycle, especially high RRM road bikes have about 12:1 or more CR and are designed for super unleaded (91 octane) fuel.  With a lot of power to weight, large camshafts, and proper combustion chamber design even higher compression is possible.  If you live at high elevation (>5000ft) you can also run lower octane fuel since the atmospheric pressure is less.  Take a look  at any gas pump up in Rocky Mountains above about 4500ft and you will notice that regular unleaded is only 85 octane, plus is 87, and super is 91.  

Also, I agree that leaded fuel should pose no problems with your engine, but I’d be interested in knowing how toluene works.  If I’m not mistaken, there was a lengthy discussion on its use in this forum earlier this year.  I believe Pat had some insight during that discussion.  Take a look at thread 71-41617.  

-Joest

RE: Leaded vs. Unleaded Gas

I use E85 in my race car, the only thing is you have to be able to flow 25% more fuel, you definatly have to change jets but sometimes the passages in the carb are not big enough.  I did extensive testing in college 6-10 years ago and yes Methanol will destroy the fuel system but ethanol typically will not harm the metal or seal components.  I use standard components in my carbs and everything works fine, a little marvel or sea foam oil will help with upper cyl lubrication if you are worried about it.  this is in a 312 ci ford scca car and a 468ci big block chevy drag car, I also converted a 99 5.3 chevy pickup with a whipple supercharger and a 2001 ford 5.4 with a superchager with no detonation at stock compression and 8 psi of boost.  Give it a try, the corn growers will appreciate it.

RE: Leaded vs. Unleaded Gas

Gee can you people noy buy fuel from your local airport?
110 or 140 octane it does need rejetting and is heavier on the float etc.  Tell them it is for racing and you may get some slick sponser help.
also Compression can be fooled by the use of cam overlap or cam seperation angle, We are limited to flatops in one class of racer and I use a 104 lobe seperation that brings the pumping compression way up there.
Hope this helps or gets you thinking.

RE: Leaded vs. Unleaded Gas

(OP)
After lots of trial and error I've settled on a 1.5:1 ratio of leaded 76 brand 110 octane race gas with 91 octane pump gas from 76 or Esso. This gives the best bang for the buck and still performs well. Using VP C12 race fuel worked extremely well but costs much more than 76 brand.
Thanks all for your input.  

RE: Leaded vs. Unleaded Gas

The reason the bike says to use unleaded only is because California requires the manufacturer to require the use of unleaded.  In all reality, low lead fuels like avgas are probably the best for your engine and valves.  The only reason for not running lead that I have heard is because it is rumored to damage the stelite coating on the exhaust valves.  I think stellite is only used on steel valves and I think it was only used on valves manufactured immediatly after the conversion to unleaded fuel.  I think my 1970 Honda Trail 90 uses stellite coated vavles because the exhaust vavle cost something stupid like $50.  There are a few race applications that use stellite because it is very hard, even at high temperatures.  For most applications, however, stainless steel has taken over.  I remember hearing that Yamaha no longer makes all 5 valves out of titanium and that the exhaust valves are now stainless, but I may have heard incorrectly.

Low leads are safe and many racers use them, just not in AMA because it has been outlawed.

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