Another fuel discussion

[Bixxer Bob]

After two race engine blow-ups (holed pistons) on different bikes at Brands Hatch and three, all on different bikes at Donington this weekend, we realised the only common factor was fuel.  We usually run Shell V Power 98RON mixed with avgas but the latest batch was some other cheapo 98RON from a filling station near Brands because Sy hadn't been able to get Shell on the way down.

Not having anything else at Donington we ran a mix of a little mixed fuel and straight avgas.  Sy started last on the grid and won his class (aircooled 500cc), also beating all but three of the aircooled 750s so it looks like we've sorted it; but is seems not all RONs are what they are cracked up to be.... 

[threepot]

I notice a difference with V Power,especially in the Super3.

[Sin_Tiger]

I've seen that before during my cart racing day's. We reckoned it was a cross scavenge affect leaving a weak fuel region in an area that also had high load, unlike the squish band which is stronger and can pass the heat away quicker.

Part of the reason we came to that conclusion was we had recently read some research that Burmiester & Wain had done with diesel 2T's. We also noted that our second engine didn't exhibit the same issue and the biggest difference was that we'd done was port polishing, after introducing some roughness near the trailing edge of the port the problem didn't return. Not saying the fuel we were using wasn't a contributory factor of course but there was lead in it in those days.

[Chris Canning]

Oh blimey yes  :icon_wink: my 1100s is an absolute horror on stock fuel it's good stuff or nothing well sort of !! and on more than one occasion I've put good fuel in and it's run absolutely pants which told me straight away it was anything but.

[Bixxer Bob]

All the pistons holed under the spark plug, but that's not a surprise as that's the hottest spot and also the thinnest point of the crown.  And it's not really the piston that's the issue, other than cost, it's the complete strip to clean the crank bearings that takes the time and effort.

At least the crank bearings weren't damaged this time.

An embarrassing race if you're a 750 rider though 

[nickjtc]

So am I reading this correctly..... the issue is with the fact that the fuel you guys are buying which is supposed to be of a certain octane rating is in fact not? Thereby causing pre-ignition or whatever and wreaking the mayhem with the engine?

Strikes me that if this is the case your fuel suppliers have a bit of homework to do..

[Bixxer Bob]

There could be a number of reasons why the so-called 98RON isn't doing what the Shell 98RON does.

It could be contaminated; with water for example.

The vendor could be selling fuel as 98RON when it isn't.

The Shell really does have additives that make a difference.

Who knows??? 

[nickjtc]

Who knows??? 

All we do know is that the fuel suppliers ask us to drop trou and present when we pull in to fuel up.  Over here it is a joke. The fuel price stays moderately stable and then the day before a bank holiday weekend it goes up, often by 10 cents a litre.

Can't comment on fuel quality concerns because I always use mainstream vendors with big turnover.

[metalguru]

Changing the 'mix' from known qualities to unknown could have lead (excuse the pun) to a weak mixture.
We used to run 3galls pump and 2 galls av on a 500 triple Kwack but it had to be setup with different jets to std fuel.
The deposits were a lot less with the mix once sorted.

[Bixxer Bob]

There should have been no difference Nige, in as far as they were both 98RON; we always run a 50/50 mix, but the unknown is what "additives" Shell put in theirs.......