Tech:Engine/K Series/Fuel

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K motors were designed to run on leaded petrol, which had a Research Octane Number (RON) of about 95. Leaded petrol has been outlawed almost everywhere in the world now, because it pollutes the environment and is good for your motor but bad for you. Japan got rid of leaded fuel in 1972.

Leaded Replacement Petrol

As of 2002, all petrol pumps in Australia now flow LRP, or Leaded Replacement Petrol. LRP is allegedly governed to be 95 RON.

Unleaded Petrol

Is it safe to use ULP in a K motor without valve additive?

-- Original Message --

From: Gail Ryan ([email protected])

To: Super Jamie ([email protected])

Sent: Wednesday, July 24, 2002 10:09 AM

Subject: Product enquiry

Thank you for enquiry that has been forwarded to the Toyota Customer Relations Department.

With the information you have supplied the 3K-H engine production year 1966 - 1974. If this vehicle was produced after Feb 1972 you may use unleaded petrol. And there is no modification required.

Regards Gail Ryan

So basially, yes, as long as it was made after 1972. If you like, you can squirt in the little 50c "Valve Master" or similar tube that petrol stations sell, but I doubt it's necessary. Anyone who tries to get you to spend thousands of dollars having hardened valve seats installed in your motor is ripping you off. These cars have an aluminium head, by design, they must have hardened steel valve seats or you'd drive around the block once and your motor would be fucked.

Because of the lesser RON of normal ULP (between 88 and 92) your Corolla may ping if you use this petrol, you may like to retard the timing to about 5-6 degrees if this becomes a real problem. Or, you could use Premium Unleaded (usually 95 RON) or one of the brand name petrols (BP Ultimate, Shell Optimax, etc) which have a RON of 98. Good fuel like this will also make your car slightly more powerful, compared to running a lesser fuel, so you'll get better mileage, or more power if you're a leadfoot :) As higher octane fuel is slower burning, the timing must be advanced to recognise a performance gain. On stock motors, I run 12 degrees with BP Ultimate.

Theoretically, if you're running unleaded petrol, you're supposed to get a catalytic converter installed in your exhaust system. Whatever.

Other Fuels

BP and Shell distributors sell a 100 RON fuel, which is usually around $2/Litre. You could also run nice leaded Avgas if you like (and can get your hands on it).


There have been a few Corollas around running on LPG. I'm told this stuff is really good for your motor both in the smooth running and the way it doesn't pollute your oil. There are two basic designs of LPG systems, you want to get the one with what's called an Air Gas Valve Mixer, companies such as Impco and Gas Research make parts like this for performance systems. LPG also has an advertised RON of 110, though this seems to have dropped in recent years. If you can afford the system (tank, lines, converter, mixer, piping) then go for it!

Octane Boosters

These formulations raise the RON level of your fuel, and are designed for use in Unleaded. The only one that works more than 1 or 2 RON is one called "104+ Super" which is in a black bottle and about 32 bucks. There is a lesser formula of the same name, in a red bottle, about 25 bucks. I can't see how they would be economically worthwhile if you're considering adding one every tank.

You can also buy drums of Methyl Benzine (also known as Tolulene) from fuel distributors. The going price seems to be about $40/20L. Mix this at a ratio of 1 part Tolulene to 7 parts Petrol. Wear really thick protective gloves and a gasmask, this stuff is really carcinogenic (it gives you cancer BIG TIME). If you run a richer Tolulene ratio, your motor will go really hard but you'll burn out your valves and seats pretty quick.