Leaded vs. Unleaded Gas 7

[rchanke]

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?

 

[patprimmer]

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.html

Regards
pat

 

[rchanke]

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???

 

[patprimmer]

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

 

[patprimmer]

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

 

[guyguy]

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 (-:

 

[swall]

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.

 

[drwebb]

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!

 

[etatv]

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.

 

[rchanke]

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!!

 

[patprimmer]

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

 

[evelrod]

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

 

[ShaunT]

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)

 

[patprimmer]

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

 

[ShaunT]

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)

 

[drwebb]

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.

 

[patprimmer]

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

 

[evelrod]

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

 

[patprimmer]

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

 

[patprimmer]

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