octane

[Robert Haller]

Alright, correction to my previous post. I was thinking Dan was referring to 89 octane. It's J.D. I should be agreeing with. It's89 octane for me now on!

[MartyA]

OK Bob, steal my thunder! I was just going to brag about getting 41 mpg over the weekend on my 78E. Darn...

It has only been a short comparison of a couple hunnert miles, but I feel that I get slightly better acceleration with the regular 87 octane, but but the mpg goes up a little with the 92. Also I observed my plugs were a little lighter color with the 87. Sort of a light tan, with the 92 they are a light grey.

Again, this is a very short observation.

[Dan Timberlake]

detonation = too rapid burning of gasses at ends of combustion chamber. Makes audible ping, or heavy knock if severe. A little probably doesn;t do much damage. Damage is visible as aluminum flecks on spark plugs and erosion at edge of piston, or cracked plug insulator nose. It is caused by end gasses getting too hot and burning too fast or too soon. High compression, hot inlet temp, high engine temp, advanced timing, low octane all can bring it on. The rapid pressure rise hammers parts like crank, rods, head gaskets. Heat transfer into head, spark plug and piston is much greater during periods of detonation. "Knock sensor" listen for knock and retard the ignition timing to kill it.

Pre-ignition - when air fule mix ignites by itself before the plug fires because of sometihing glowing hot in the combustin cchamber. Since this by definition is advanced timing there is a good chance any combustion cycle started by pre-ignition will end in detonation.

Damage can be hole in middle of piston.

[webbcraft2150]

I can run "regular" in the winter, but have to go one grade higher during the summer. We have consistent 95+ days and no humidity during the summer.

[2fast]

Re: Mogas and aircraft engines...

You can save a lot of gas with the correct craft. The aircraft I fly uses no fuel at all, infinite MPG (after release)! Just need a little sunshine.

Originally posted by Bill
Bob Udy wrote:When I got my '56 Tri Pacer approved for car gas there were two companies that could issue the certificate which is based on both the engine and airframe. I think I paid $1.00 per HP, or $150 for my old Piper. In my case, and perhaps your boss' 182, they were originally designed for 80/87 Avgas, so regular Mogas is closer to the original spec than the 100 low lead that's sold at most airports. OTOH, local stock car guys like to use the 100LL in their race cars!

Marko wrote:Actually, piston engine aircraft run very slow compared to motorcycles or high performance cars. At high RPM the prop tips could go supersonic and cause all kinds of problems. My plane runs at about 2600 RPM flat out at sea level.

Gary LaPook, or any other recip drivers, please correct me if I got any of the details wrong.

[chopper]

normal pump gas in uk is 95 to 98 octane.

[jimg1au]

octane

same in australia unleaded std. premium 95 and 98octane also a gas for older cars lead replacement.my xs runs on all 4.my boat runs on unleaded 70hp yamaha.most cars built after 1986 run on unleaded.
jim garvey
xs1100rh/midnight
xs1100rh

[captjerry]

Hi Mick and Jim,
In the U.S. I cant swear to it but I believe we use a different
formula for determining octane now. I think it was in 75 we
switched to all unleaded in our cars, leaded fuel was still
available in the early 80's but I cant recall the last time I saw
leaded gas in a gas station.
Octane use to be determined by Research Method, it was a single
number which was posted by the manufacturer.
Sometime during the 70's they came up with a new method of grading fuels which actually lowered our octane number which supposedly was more accurate, we see on all our pumps
(R+M)/2
Which translates to Research Method + Method Octane Number divided by 2........
What does this mean???? Hell I dunno...its late....Im at work and bored
Just a long way of wondering if in the UK and OZ ya'll measure octane in the same method as over here.
Cheers

[Robert Haller]

Originally posted by MartyA
OK Bob, steal my thunder! I was just going to brag about getting 41 mpg over the weekend on my 78E. Darn...

You know Marty, the more I think about it, the more I think that 50 mpg must have been a miscalculation. I have never exceeded 41 mpg before or since, and normally I get around 36.

[BigDaddy]

I have a Cougar w/ 11.5/1 compression and it requires a min of 104 octane, to not ping (runs real nice on aviation fuel)...I would think w/ these bikes 87 octane is a little low, I always use 91.

[MartyA]

One of the brags about these engines was the 'semi-hemi' head design, swirls the gas well, allows good combustion. I have heard old Yam diehards claim the XS could run on anything that burns.

[Nulle]

I use the blended at 88% and seems to run good.

[fusionking]

I nearly always use the best grade they have. It isn't like we're talking about a lot of money. You can harm an engine by running too low grade of fuel but there isn't much down side to the good stuff. Besides it is possibile to not hear your engine detonate over wind , pipes and God only knows what else and also it could only be doing it on just 1 or 2 cylinders at random. then you didn't save jack #@%$ !!!!!!!! IMHO .......... Garry

[BrianB]

running poor with higher Octane

I was reading thru this thread because last week, I went and filled my Tank full with the higher Octane gasoline which I beleive was 93. I usually use the lowest at 85 or so. It runs great with the lower Octane but put in the higher just because. Well I had a harder time starting it and idle and low RPMs it ran like crap. I have ran that tank out and went back to the lower octane and it is running great again. Why would it perform better with lower otcane than higher?

[81xsproject]

Talk about resurrecting the dead . 91 is as high as it gets were I am. This was discussed recently at great length. If I remember correctly, higher octane is only needed to suppress pre-ignition due to high compression. So if it ain't pinging with the low stuff you are good to go. As for running worse with the good stuff, I believe that the other conclusion of the discussion was that the compounds used to raise the octane produce less energy per volume than the gasoline it is replacing. But, I am not expert and some folks swear that running the good stuff helps. I have never noticed a difference.