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Avgas


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machinerage

 
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Avgas

Wed Jun 11, 2008 12:38 pm » Post: #1 » Download Post

any downside to using a low lead fuel in a two stroke engine?
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Andy
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Wed Jun 11, 2008 12:53 pm » Post: #2 » Download Post

Other than detonation?
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scottvor

 
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Wed Jun 11, 2008 4:41 pm » Post: #3 » Download Post

Are you referring to 2 stroke engines in general or the NSR? If specifically NSR, I don't think you'll see any performance benefits unless you adjust timing, up compression, and/or decrease squish clearence. The crankshaft won't complain about a little lead bathing once in a while.
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Barry_MC21

 
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Wed Jun 11, 2008 9:18 pm » Post: #4 » Download Post

Andy wrote:Other than detonation?


I think your confusing low lead with low octane. Wink

Low lead fuel won't cause detonation.

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Andy
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Wed Jun 11, 2008 10:01 pm » Post: #5 » Download Post

Usually low lead fuels go hand in hand with low(er) octane, but yeah, OK! Smile
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Barry_MC21

 
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Thu Jun 12, 2008 8:45 am » Post: #6 » Download Post

Avgas is also known as 'Avgas LL' (LL = Low Lead).

I think thats what he was getting at, maybe? Seeing as all pump fuel is now lead free. Wink

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Last edited by Barry_MC21 on Thu Jun 12, 2008 8:48 am; edited 1 time in total
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Barry_MC21

 
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Thu Jun 12, 2008 8:48 am » Post: #7 » Download Post

Sorry, double post.
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fontyyy

 
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Thu Jun 12, 2008 4:17 pm » Post: #8 » Download Post

Lead in fuel not only helped with wear on valves in 4 strokes back in the days of 4* (and 5*), it also raised the octane and thus decreased the chance of detonation, allowed for higher compression and more advanced timing, all good for both power and reliability.

Some people here have seen some very good results with the NSRs running tuned engines on unleaded 97 RON (84 MON) pump fuel, though I've read you'll have trouble finding stuff even that good on the forecourt in the US.
However, if the extra octane is there and you tune your engine to use it you'll see more power.

100LL Avgas has a RON of 116 and a MON of 102 (thanks to Stu Jones, works at BP for the RON figure for Avgas) and around 5 times more lead than 4* ever had. It is "low lead" only by the standard of 100/130 Avgas and Bluegas (old 80's/90's leaded race fuel, who remembers GP mechanics wearing breathing apparatus?).
50%/50% Avgas and pump unleaded mix is considered (rather optimistically) by the ACU to be 102 RON which is spot on the limit for a race bike here.

There is always talk of whether Avgas is a good cheap race fuel when it's use is discussed and I don't know enough to really comment with much authority.
What I do know is plenty of people with 250 proddy engines making very good power are using both neat Avgas and 50/50 Avgas/unleaded and plenty of others are running it without problem in place of proper leaded (and very expensive) race fuel in GP 250's running pre 1999 setups.
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machinerage

 
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Thu Jun 12, 2008 8:55 pm » Post: #9 » Download Post

thanks for the replies. to be more specific, i am concerned as to whether or not lead deposits within a cylinder could cause any damage.
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scottvor

 
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Fri Jun 13, 2008 7:53 pm » Post: #10 » Download Post

That won't be a problem.
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