Fuel choice

[John]

To sum it up a bike with a compression ratio of 9.3:1 and lower is suited to 91 fuel, and if you use a 96 on it then you risk damage to your bike, and 'knocking' of the engine, am I correct in assuming so?..

while anything higher than 9.3:1 requires a higher octane fuel (96) to utilise its full capability, and if you use 96 in a 9.3:1 compression engine you risk backfiring due to un-burnt gasses exploding in the exhast ?
anyhelp/closure would be great.. cheers

What is compression ratio??
What is al thess 12.4:1,9.3:1 for?? Do i just go and fill up my '98 VTR250 with 91 ?? Do i have to add anything in my tank with the fuel??

Compression ratios indicate the compression per stroke before the spark is set - most high preformance bikes 12.5:1 up are reliant on higher octane fuel - because of the strong compression using 91 (which is more prone to compression combustion) may or may not cause pre-igniting or compression igniting, this is knocking - anything lower than than 10:1 should be more than happy on 91 in most cases anything higher just doesnt get fully burnt and you foul plugs and burn carb diaframs, remeber look at the manual run the fuel its tuned for, any lower will cause damage any higher will cause various problems in the long run, consensous is that you run the lowest ocatane that the bike is designed for.

Just on a side note, your VTR should be fine on 91, I know that the ZXR250 needs 96 to run top of its game with its 12.3:1 compression (or higher cant remeber off head)

[scumdog]

Rule of thumb: Higher the compression ratio = the higher the octane needed.

Too high an octane is just wasting your money (and at times may foul plugs)

Too low an octane? you'll kill your engine with 'pinking' - hole in pistons, broken rings, hammered out big-end bearings etc.

[Jonty]

ZXR's have a compression ratio of 12 2 according to my manual and unfortunatley do not seem to indicate what fuel to use. Very helpful indeed.

My bike is coming up 16 years old and quite honestly, I would put the cheapest stuff in available in it as i have tried all three octanes and can't pick the difference (other than the obscene price of 98)

[scumdog]

ZXR's have a compression ratio of 12 2 according to my manual and unfortunatley do not seem to indicate what fuel to use. Very helpful indeed.

My bike is coming up 16 years old and quite honestly, I would put the cheapest stuff in available in it as i have tried all three octanes and can't pick the difference (other than the obscene price of 98)

Check with your dealer but I wouldn't run low octane on an engine that high in compression.

[Storm]

So my fire breathing Gn with its HUGE compression ratio of 8.9:1 will do absolutly (note the definitive word there) no different with 96/98 than it will with 91?

[John]

ZXR's have a compression ratio of 12 2 according to my manual and unfortunatley do not seem to indicate what fuel to use. Very helpful indeed.

My bike is coming up 16 years old and quite honestly, I would put the cheapest stuff in available in it as i have tried all three octanes and can't pick the difference (other than the obscene price of 98)

Yup dude, run 96 in her/him/it - I asked heaps of mechs about it who all replyed run the highest you can, even throw in some avgas if you really want to (told by more than one mech).

I had being using 91, with the occassional compression igniting sessions at the lights :P

[scumdog]

So my fire breathing Gn with its HUGE compression ratio of 8.9:1 will do absolutly (note the definitive word there) no different with 96/98 than it will with 91?

Most likely you are correct - see post #21 on this thread too.

Always check with your 'owners manual' first but I feel you're wasting your money with the higher octanes.

[Lou Girardin]

Compression ratio is the amount that the total cylinder volume is squeezed into at the top of the compression stroke. Eg. 120 cc's is reduced to 10 cc's