98RON & older engines

[dom14]

Hey Guys,

I decided it might be better to use 98RON on mine(GQ RB30 carby, dual fuel).

I thought ignition timing compromise between LPG and petrol can be set to a better minimum
with LPG being higher octane than regular 91RON petrol.

Is this a good idea?

If so, do I need any "upper cylinder lubricant" or is it just an old wive's tale?

Mine is a 1990 model GQ.

Thanx

[garett]

petrol wise no. at that age it should have hardened valves and seats(feel free to correct me on this one). i ran 95 ron in the old laser (carby 1989) i want further on a tank so it worked out cheaper than 91. but i had to re-tune it to suit the fuel.

[GeeYou8]

The RB30 is not an older engine, it came out in the Holdens as their first unleaded petrol engine, the upper cylinder lube is to compensate for the lack of lubricating lead in old engines built to run on leaded petrol.
Graham

[dom14]

The RB30 is not an older engine, it came out in the Holdens as their first unleaded petrol engine, the upper cylinder lube is to compensate for the lack of lubricating lead in old engines built to run on leaded petrol.
Graham

Ok, cool. If I understood you guys correctly, I should just put 98RON and tune the ignition timing accordingly.
That's it?!

Thanx

[Throbbinhood]

Sounds right to me.

Only consideration would be if/when you head out bush, 98 isn't always available. I keep mine on 91 for that reason, it's out bush too often to be bothering re-timing it every time.

Also one of the reasons I've avoided turbo'ing it.

[Plasnart]

Hi Dom. I was told by a motorcycle mechanic not to run 98 in carby engines. He said it leaves residue in the carby as the fuel/air mix doesn't ignite as hot as injected systems. So for my 1989 road bike its only 91 RON. I know totally different engines but the philosophy might be googleable.

[UncleFrosty]

Thanks for pointing this out @dom14.
I feel a 'speriment coming on for mine around town as I only used 98 on long trips, and hadn't considered I may be better off running it all the time due to dual fuel setup...

[billyj]

@Plasnart if thats what he is telling you i suggest finding a new motorcycle mechanic.

as to doms original question yes 98 octane will allow for a much better compromise setting between petrol and gas, as for remote travel you can get pretty potent octane booster additives which could be easily carried to give regular 91 octane a bump up if required

the rb30 is/was designed as an unleaded engine (being an alloy head it has to have hardened seats) so is fine without the upper cylinder lube

if you want to get the most out of it just bump the timing up on petrol until it pings under load then drop it back down by a degree or so

[mudnut]

@Plasnart if thats what he is telling you i suggest finding a new motorcycle mechanic.

as to doms original question yes 98 octane will allow for a much better compromise setting between petrol and gas, as for remote travel you can get pretty potent octane booster additives which could be easily carried to give regular 91 octane a bump up if required

the rb30 is/was designed as an unleaded engine (being an alloy head it has to have hardened seats) so is fine without the upper cylinder lube

if you want to get the most out of it just bump the timing up on petrol until it pings under load then drop it back down by a degree or so

That is how I timed the engine after a mechanic changed out the timing belt and the engine was pinging under load. It was only after I had to renew the head gasket because a couple of fire rings had cracked, it was explained to me that silent detonation had caused the engine to run hot and caused the cracks. If I was to tune the engine to run properly on RON 98 I would get it dyno tuned, but that is just me.

[billyj]

a dyno would the the perfect world way to do it but going a couple of deg back from the point of pinging shouldnt be a problem provided that the af ratio is right, if its running lean then it will be hot and burn things up