--What Type of Gas?--

[CB1_Boost]

What type of gas/fuel does everyone use for their CB-1??

Out of 87, 89, and 91..I've been using 91 Octane. (ethanol free)

Post up which you use and why?  Positives / Negatives?

[REgina CB-1]

91 - it makes me feel warm inside

[ptlcb1]

110 octane goes in mine... Oops, my bad, thats not one of the choices...

[CB1_Boost]

Harr Harr..    you gotta track bike.  So what would happen if you poured pump fuel in it?  and I'm assuming it really needs the 110 octane or it'll under perform?

[tcd2004]

Harr Harr..    you gotta track bike.  So what would happen if you poured pump fuel in it?  and I'm assuming it really needs the 110 octane or it'll under perform?

Owners manual says to put at least 91 in it, I usually try and find 93.

[ptlcb1]

My guess is that it will under perform.  I have always used 110.

[Drewski]

98 (RON) - "Superunleaded". We only have 95 and 98 here i think.


What's the compession ratio on your track bike ptlcb1? Or is that "Top Secret"

[ptlcb1]

I would say "top secret", because that sounds pretty cool, but honestly, I do not know.  The engine in the race bike only had about 8600 miles on it when I took it to get the head ported and installed the RR cams.  The mechanic that performed the work did ask me what type of fuel I was using.  I am clueless when it comes to engine internals.     All I know is that after the work was done, the bike was much faster!   

[kneepuck]

I've been using the cheap stuff to no ill effects. But my motor is bone stock.

[Drewski]

I would say "top secret", because that sounds pretty cool, but honestly, I do not know.  The engine in the race bike only had about 8600 miles on it when I took it to get the head ported and installed the RR cams.  The mechanic that performed the work did ask me what type of fuel I was using.  I am clueless when it comes to engine internals.     All I know is that after the work was done, the bike was much faster!   

You still have the stock pistons and unskimmed head?

[ptlcb1]

Yes, stock pistons and the head has been ported.

[clarkdw]

Manual actually calls for 86 or higher (R+M)/2 (Research + Motor)/2 which is what is displayed on the gas station pumps in North America OR (Research Octane Number) RON of 91 or better. I always use 87 because I checked the power output on a dyno using 87 and then 94 and low and behold more power on the 87.

This was not entirely unexpected by me because we have done a lot of work on Honda 4 stroke Go kart engines and they show similar characteristics. The combustion chamber and piston shape are designed to take advantage of the very different burn characteristics of the low octane fuel. The faster burn of low octane requires a more open type chamber with little or no quench area like heads designed for high octane. On the Go Kart engines we could make the high octane fuel work better by milling the heads to create a quench area. This worked even with keeping the comp ratio unchanged. I suspect that the increased turbulence in the chamber caused by the quench helps to allow a more complete burn of the high octane and hence more power especially in the peak torque rpm range. Fattened up the torque curve so to speak.

Long and short of this is that unless you have substantially changed the compression ratio or the shape of the combustion chamber then you are probably better off using low octane. I didn't check 89, 91, or 93 on the dyno but my educated guess is that if you go more than 89 you are giving up some hp.

98 (RON) - "Superunleaded". We only have 95 and 98 here i think.

I believe that this is the approximate equivalent of 89 and 93 if converted to (R+M)/2

[Lyrad]

Thanks thats good to know!! I will try the 87 for a while to see if there's any difference, I've been putting 91 since I got it.

[baard]

Using low octane is fine, as long as it's not too low. I mostly run 95 RON. I'd be interested in knowing the difference between the gas you get in north America and what we get in north Europe. Most pumps here only have 95 and 98 RON, although some are starting to offer cheap(er) 92 RON. There should be no difference in their burn characteristics, but higher octane can handler higher pressure and temperature without detonating. I've never heard or of or experienced higher power output on lower octane. Quite the contrary; if the engine has an active control system it will perform better on higher octane, with more power and less fuel consuption.

However I have no reason to question the power output you've recorded, clarkdw, which is why I'm really curious as to what's in your petrol.

The CB-1 does not have extreme compression or poweroutput, but still, using too low octane will destroy the pistons and maybe even valves and bearings, so be careful...

(I think I have a picture somewhere(no promises) of a piston from my 2-litre turbo run at 2.6bars of pressure (thats 36psi), when someone, by mistake, put 95RON in it. It was built for 98RON exclusively and the results were not suprising although deeply frustrating)

[clarkdw]

There is little or no difference in the gasolines other than in winter when oxygenating compounds are added to fuels in northern climates to ease starting. The 95 RON fuel is very similar to what we in North America would call 87 octane. Just two different ways of describing the characteristic of tendancy to detonate. Research Octane Number RON is a theoretical calculated value and is what is shown on pumps in many countries of Europe. Motor Octane Number MON is a measured value determined in the lab by running the fuel in a single cylinder engine with specific characteristics and measuring the resistance to detonation. The value shown on the pumps in North America is the average of the two (RON + MON)/2.
As far as the burn characteristics are concerned, ther are very marked differences in the way the low and high octane fuels burn. It is harder to ignite the high octane and when lit it burns much slower. The flame front in the combustion chamber moves slower away from the ignition source and in a chamber where there is not a lot of turbulence or "swirl", usually created by a quench area, the burn can often be incomplete leading to less hp and higher emissions.

In the case where there is an active system using knock sensors etc. I agree that the engine will make the maximum amount of power available from that fuel in that configuration of engine. However, if the engine is designed for low octane fuel to begin with then no extra power will be seen by running high octane. What you WILL be able to do is safely use lower octane fuel in an engine designed for high. The active system will keep the engine right on the edge of detonation and so obtain maximum power up to but not above the design octane number. Using a higher octane fuel than the engine design is meant for, VERY rarely increases power and quite often gives a negative effect. It is all about combustion chamber, piston shape and comp ratio.

Very unfortunate that you didn't have an active system on your turbo as it would have saved the engine. I also suffered many burnt valves on my Mini Cooper 'S' years ago all caused by not always being able to find the 104 octane fuel that was only available at Sunoco stations at that time.

The CB-1 was designed for 87 octane fuel (as rated in North America) or 91 RON as you see the pump so I have no fear of losing an engine that way.