New Fuel For Old Cars

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This is to cover the basics of running an older engine on unleaded petrol. Just the basic first questions you may ask when you get the old girl home for the first time.



===My car uses PULP and won't crank if a hot start is immediately attempted straight after shutdown. I have a perfect battery, distributor and electrical leads. What is causing this?===PULP is easily ignited by anything glowing in the combustion chamber. A workaround is to flood the Engine by stepping on the gas pedal 3 or 4 times before re- attempting any cranking. The excess fuel will quench whatever is glowing in the combustion
chamber and allow the starter to spin the Engine over more easily (though it can take a few seconds for the fuel to effect the quench). Open the gas pedal progressively as you crank until the Engine fires. Treat the start attempt as if the engine is flooded (because it just has been).


===I’ve just bought an Old Holden what petrol should I put in it?===The simple answer is 98 unleaded with a fuel additive like flash lube.
The long answer is . . .

There are two problems with running older cars on unleaded petrol

1.Upper valve lubrication

2.Octane rating

Upper Valve Lubrication
The lead in leaded petrol (Super) lubricated the inlet and exhaust valves. When you run unleaded the lubrication component is not present. The result is valve seat recession (VSR). Simply put it burns out the valves and their sets, particularly on the exhaust side. You will have to pour in some additive to stop the VSR, or get the engine modified.

Octane Rating
The octane rating is the number you see on the fuel pump when you fill up, but sometimes it’s not listed. The higher the number, the bigger the bang. To be about the same as the original super, you need 95 or 98

Unleaded petrol (ULP) = 91

Premium unleaded petrol (PULP) = 95

Ultimate, Optimax ETC = 98

Optimax extreme = 100

Original leaded super = 97


===My car is a {cool old holden} do I need to worry about this stuff?===Anything before the VL commodore needs these changes to keep it running properly. To confirm you car check these web pages. If your car is NOT listed then you need to use this information.

Australian Institute Of Petroleum - Holden


===How do I stop valve seat recession?===That depends on a few things like . . .

If it has the hardened valve seats from an engine rebuild, ignore it. Just use unleaded. Check receipts for proof of the changes.

If not then you can squirt some additive in to the fuel tank every time you fill up, or you can buy a kit that will feed it automatically for about $70. You mount a small bottle in the engine bay, and top it up every few weeks. You can get them from Super Cheap ETC

If you’re going to get the engine rebuilt in the near future then don’t bother and just let it wear.

If the engines good and you don’t want to muck around with the additive, then pull the heads off and get the hardened valve seats fitted. Its a few hundred dollars for a six.


===I can’t afford the expensive petrol what should I do?===Try using the lowest fuel (standard unleaded) and if the car runs rough, is hard to start or pings under load go up to next octane rating until the car runs OK. If that doesn't work then you can have the car de-tuned for the standard unleaded but it's not the best answer. Even between brands there's a difference. My standard blue six runs terribly on shell optimax, but is fine on BP ultimate, both have the same 98 octane rating. So try different brands as well.


===If I put in 98 or 100 octane will I get a performance boost?===Only if the engine can make use of it. Being a carburettor with no computers, the engine won’t self tune for different fuels. So you’ll have to take it off for a tune up. If it’s an older motor that’s worn or has low compression from standard you won’t feel any difference and be wasting your money.


===I can still get Lead Replacement Petrol (LRP) from my service station, should I use that because it’s the proper stuff?===The general consensus is LRP is rubbish and should be avoided. It won’t matter soon because their going to stop making it.


===What if I convert to Liquid Petroleum Gas (LPG), then I don't have to worry right?===LPG has an octane rating of 100, but cars are usually set up with a choice to run either petrol or LPG. This mixing of options means the car isn’t tuned for either properly as a compromise. To keep good power ETC you should run it only on LPG and get it tuned just for LPG and use petrol only when you absolutely have too. This isn’t going to stop VSR so you need the hardened seats or the valve lube additive anyway.


===Hold on all the old taxis use to use LPG and they were OK===They would get an LPG head fitted when new. This was basically getting the hardened seats and valve guides in a complete head bolted straight on. You can still get them new from yella terra but at $1100 dollars it’s cheaper to get your existing head sorted.


===Can I buy one of those LPG heads and run it on petrol?===Yes, and you'll get a minor boost in power because of some port work they do in preparing the head.

==References==Australian Institute Of Petroleum
BP Australia
Unique Cars Magazine
Yella Terra