Leaded or unleaded - That's the question, Need advice on which type of fuel to use.. Options

[reineg]

Hi there, Laymen and Experts alike!

I have recently acquired a 914/4-70 with a newly built engine. Up to 2.2litre and some extra horses to boot. But now to the question:
The car has got new cylinders and pistons from Pelican Parts, but I do not know much more about the engine. So do you guys (and gals) reckon it would be safer to use modern fuel and add lead, or shall I just go for modern fuel and not add lead?

What is most detrimental to the engine; to add lead to an engine that doesn't need it, or not to add lead to an engine that requires it?

Appreciate any and all thoughts on this..

[wonkipop]

Hi there, Laymen and Experts alike!

I have recently acquired a 914/4-70 with a newly built engine. Up to 2.2litre and some extra horses to boot. But now to the question:
The car has got new cylinders and pistons from Pelican Parts, but I do not know much more about the engine. So do you guys (and gals) reckon it would be safer to use modern fuel and add lead, or shall I just go for modern fuel and not add lead?

What is most detrimental to the engine; to add lead to an engine that doesn't need it, or not to add lead to an engine that requires it?

Appreciate any and all thoughts on this..

here is my take.
lead was in fuel ostensibly to prevent engine knocking. pre detonation.
it came about when manufacturers starting producing higher compression engines in the post war years.
if i am not mistaken earlier low compression engines in say the 40s, 50s and even early 60s did not need leaded fuel.
this was certainly the case in australia.
back in the 60s and 70s there were two fuels.
standard and super.
older cars with lower compression engines ran on standard.
it was lower octane and did not necessarily need or contain lead additive.
super certainly had it. in addition to being higher octane.

there is also a view that the lead additive in some way lubricated the valves or valve seats. but i think thats more of a misunderstanding.
by preventing pre detonation you got less wear on the back of the exhaust valves.

vw engines (and 914 engines) were already engineered a bit more sturdier when it came to the valve train due to being air cooled. at least that is what i have always been led to believe.

the octane requirements for the earlier engines and all the european versions is to do with the higher compression. the problem with early unleaded fuel when first introduced was they could only produce it with lower octane ratings. so they had to lower the compression ratios in the US cars. thats basically all they did with the US market cars from 73 on. lowered the CR. and of course. lowered the power.

but by the time we get to the 90s the fuel companies had formulated higher octane rated unleaded. so CR went up again.

i believe a european spec 914 with the higher compression ratios is fine to run on unleaded so long as you have the correct octane rating.
you want to avoid pre detonation is all.

remark by other poster regarding ethanol percentage formulated fuel is spot on.
you want to avoid ethanol added fuel if at all possible.

[Superhawk996]

but by the time we get to the 90s the fuel companies had formulated higher octane rated unleaded. so CR went up again.

Adding context, compression ratio went up in the 90s more as a function of OEMs being able to use knock sensors as a result of the sensors themselves becoming cheaper and the ECU processor speeds increasing.

When you can sense the onset of knock and vary timing in response, you can take more risk with compression ratio. Higher compression ratios are more fuel efficient and were better able to meet Fuel Economy regulations. They also produce more horsepower, a win for everyone.