Running 18RG on 100 octane fuel.

[JadeEstevez]

Just a quick question. How Should I tune my 18RG to run on 100 octane fuel? It currently runs on 98 but there is a servo close to where I live now and 100 octane is heaps cheaper.

[lexsmaz]

Either dont do anything & just put in the 100 octane & it will be fine & No difference or you could try & bump the timing up a bit you might be able to squeeze an extra degree or 2 of timing out of it ....

[ToyTA22]

As lezsmax said adance timing by about 2 degrees and you will need to go slightly larger jets to make the most of 100 octane, due to fuel slight higher density. my friend used to use BP 100 in his Monaro when racing his road car and we were told to put 1 cup of castor oil in with 5 litres of 100 octane due to little upper cylinder lubricant in 100 octane. It won't cause engine to smoke but will give of odd odour when high revs are used. You can buy castor oil at chemist.

[fixeruperer]

doesnt bp100 just have lead in it to pump up the octane ?, i dont know why you would need upper cylinder lube with it.

the other 100 octane pump fuels usually just have ethanol in it to pump up the octane. ethanol usually needs extra fuel, but there is so little in the 100 pump fuel, unless you are already slightly lean, you shouldnt have to touch the fuel. timing as well, 1-2 degrees, but i dont think its worth it.

[JadeEstevez]

Yeah its ethanol enhanced fuel from unitied. Filled up today as I ran the car nearly empty to try this out... Seems fine, Goes great and idles good, But every now and then (only did it twice today) on slight acceleration there is a little backfire from the carbys, Just a small pop but no hesitation. The timing is at the farthest mark on the pulley which from memory is 15 degrees BFTC?? Correct me if I'm wrong... So would advancing 2 degrees more hurt the engine at all? If I go any farther then I'm outside the manufacturers specs. Also I'm running HKS cams if that factors in at all?

HKS Cams


Intake:
10.5
288

Exhaust:
10.5
272

Sorry, New to the whole Octane thing. I was only running her on 98 because thats what the last owner recommended as it runs like shit on lower octane fuels.

Apologies if I ask stupid questions

[Dazza]

The backfire through your carbies will be from running lean. When i used to run BP100 in my gocart that i raced, i had to open the jets up a bit. I would say that an ethanol blend fuel would need the jets to be opened up even more. I would try a size bigger in the main jets.

[JadeEstevez]

Cheers Mate, I'll give it a go Hunting for jets now.

[BrianGT]

Marcus..I have no idea what type of ignition system you are running but if it's a distributor then anything you add on at idle is also added on at full advance.
For example, mine is at 9-10 degrees idle and 34 degrees all out at 4k revs....that's roughly 24 degrees of advance.
If you start at 15 degrees idle you could end up at around 39 degrees all out and that's too high.....especially if the mixture is lean.
I would be wary of advancing the timing any more than you have it which is possibly already a bit high.

[jfallen]

Just to clear up a few things: I run BP-100 (AVGAS) in my track car, it smells awesome and costs $2.70 a litre and is illegal for street use.

BP100 or BP-Race100, or more simply: 100/130 AVGAS is a highly leaded fuel (often over 0.5g/L,) is dyed GREEN, and used in aviation, while also being sold by specialty race fuel distributors on presentation of a racing licence. It is no longer available for purchase from Aerodromes for motorsport use. It also has a high proportion Toluene and Benzene in its composition, both of which are banned for on road purposes. Let it be known that AVGAS (BP100) is illegal to use on the street. The octane rating of 100/130 is a lean/rich rating, and is a Motor Octane Number (MON,) as opposed to a Reshearch Octane Number (RON.) Avgas in a lean environment has a RON of ~110 and it goes up from there as you run it richer and richer.

Leaded fuels deposit lead (and bromine,) in your exhaust. It will foul up your O2 sensor and clog up your catalytic converter with lead. Not only will the cat no longer be effective, this lead build up leads to significant flow reductions. If your friend is running it in his modern day Monaro he's a NUMPTY. If he's running it in his old one, he stands to not only have a very hefty fuel bill (@$2.70per/L,) but also cop a +$5000 fine.

100-RON fuel (often sold through United petrol stations) uses Ethanol to boost octane. It is legal for street use. If tuned effectively there are small but measurable gains from 98-RON, more so on boosted engines


As for Castor oil (which also smells awesome,) your friend really is a NUMPTY. If he's using AVGAS (proper BP100,) then the lead in the fuel is the best upper cylinder lubricant. At the ratio mentioned 1 cup (200mL) of castor oil to 5L of fuel that's 25:1, the same as most 2-stroke engines require!!! How daft is this guy? I think you need to sit him down and have an intervention. If he's using United 100RON, Castor oil has no effect other than forming varnishes and gums (especially at 25:1 in a 4-Stroke) that degrade engine performance over time. Especially so, if it's straight castor oil with no scavengers or ad-mixtures like Shell's Racing M Castor oil (which I use in my 2-Stroke Chain saw, because it smells awesome.) Castor oil forms no cushioning deposits on the valves like lead does, it is simply consumed in the combustion process. Castor oil does have an extremely high film strength, one of the best in-fact, which is why 2-Stroke go-kart and Motorcycles that spin past 12,000RPM love it, given that 2-strokes tend to be oil starved. As mentioned above I use castor oil (Shell racing M to be specific) in my Chain saw, and a few other 2-Stroke powered garden tools mixed at 25:1 (often with out of date AVGAS.) I don't have to, but most 2-Stroke oils smell really oily when burnt and I don't like that. I know I don't need to use castor oil, and it's much more expensive.

Some people (in-fact this is almost a requirement when racing) mix Castor oil at 200:1 for use in rotary motors that run on E85 that have had the factory oil squirters removed (note: that that's a fairly specific case.) Mineral and synthetic oils DO-NOT mix with alcohol fuels, castor oil does. Rotary's need oil present in the housing to lubricate the apex and side seals in much the same way piston motors need oil in the cylinder bore to lubricate the piston rings. Mixing stronger than 200:1 say 100:1 or 50:1 has no added benefit as the oil requirement is very low. It serves no purpose in preventing valve seat damage in iron headed piston engines other than smelling nice and producing varnishes/gums (which you don't want.)

Hope this clears up a few things.
Jordan

[Rodger]

Marcus

Your little pop from the carbs at light load is an indication that the Pilot Jet is a touch lean. One step up is what is needed. Then reset you Idle mixtures.
Have you got your vacuum advance disabled or is it connected?
Aim for 32-34 total advance. Check what mechanical advance number is stamped on the mechanical advance plate, double that number and add the static value as set now to give total advance. If you need to add more than 12 degrees static then you need to build in more mechanical advance so check if the advance plate has another higher number stamped on it and swap around the advance plate.

Regards
Rodger

[JadeEstevez]

Just went and checked while it's not raining. It's running 12 degrees BTDC, Not 15... My apologies, I was only going by memory.

Also, My pilot jets are 60, Should I bump them up to 65?

[Rodger]

Next size up is 62.5 then 18R-Gs on the Type T Solex used a 63.8. If you have the 65s then give them a go to see if the pop dissapears, it may then be rich.

Regards
Rodger

[JadeEstevez]

I had another set but I have put them in a 'safe place'. Anyone know where I can order jets? The carby specialist in SA can't get them -___-

[mlw077]

You can order them through Rodger.

[JadeEstevez]

Thanks mate.