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]

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

 

[patprimmer]

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

 

[drwebb]

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!

 

[patprimmer]

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

 

[Rob45]

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.

 

[evelrod]

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

 

[oab]

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.

 

[Joest]

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

 

[jeremy4v]

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.

 

[Kamikaze]

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.

 

[rchanke]

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.

 

[76GMC1500]

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.