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

[dom14]

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.

I'm getting an AFR gauge kit(still waiting for it to arrive), so hopefully that's as closest as I can get to a dyno tune.
Once I'm 100% happy with at least one of the ancient Nikki carbies on mine, I'll pay a visit to a local dyno.

I think, If I have a way to introduce some kind of drag on to the stationary running engine/wheels, it can be tuned "well" at home. :D

[dom14]

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.

No bother. Just take the timing light with ya in the back.
It only weights 200 grams or so. It won't make any difference. But, your mother-in-law in the backseat will. ;) :D

With the AFR, Gunson & timing light, I'm hoping I'll be a tuning guru in near future. :D

[Patrol'n]

Hey Dom,

I've been running 98 in my GQ rb30 wagon almost exclusively for the past 2 years or so, pretty much unless I cant get it and have to go for standard. (I try and chuck a bottle of octane booster in if possible when that happens). My family mechanic recommended I run it instead of standard.

Plugs are a great colour and condition, engine runs well, particularly since the rebuilt carby went on! Engine sometimes pings ever so slightly on standard but not on 98. (It did once briefly ping on 98 with the aircon on a hot day under hard acceleration, hasn't happened again though so I figure a bad batch of fuel that day)? I could probably advance the timing a bit more on 98 but prefer to be able to use standard 91 if I have to. Talking about the old nikki carb, getting a professionally recoed unit has to be one of the best things I've done to the old girl!

[dom14]

Hey Dom,

I've been running 98 in my GQ rb30 wagon almost exclusively for the past 2 years or so, pretty much unless I cant get it and have to go for standard. (I try and chuck a bottle of octane booster in if possible when that happens). My family mechanic recommended I run it instead of standard.

Plugs are a great colour and condition, engine runs well, particularly since the rebuilt carby went on! Engine sometimes pings ever so slightly on standard but not on 98. (It did once briefly ping on 98 with the aircon on a hot day under hard acceleration, hasn't happened again though so I figure a bad batch of fuel that day)? I could probably advance the timing a bit more on 98 but prefer to be able to use standard 91 if I have to. Talking about the old nikki carb, getting a professionally recoed unit has to be one of the best things I've done to the old girl!

Thanx mate.
I remember you wrote before about the improvement you got from rebuilding the carby.
I, on the other hand, have been as adamant as ever and been "fiddling" on my own and when the carby's gone over it's lifespan, I would consider buying a new one or EFI conversion. :D
I just got an AFR gauge kit to help me with tuning carby & ignition better.
I should've been using 98RON whenever I drive it on petrol, being a dual fuel vehicle.
Cheers