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1969 Lotus Elan SE S4


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What fuel should I use and do I require an additive?

Recently purchased a Lotus Elan S4 1969 with the following mods to the engine.


Elan was fitted from new with: High Lift Cams, a 4 Branch Tubular Exhaust. Then rebuilt past it’s original ‘SE’ Specification by way of Larger Valves, Modified Cams, Fully Balanced Rotating Assembly and the Head Gas-Flowed to Optimise Performance.

Can anyone help?


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As SJSportscars sell seats for use with unleaded fuel, which suggests the originals weren't, then I'd suggest if you don't know what yours are you need to use an additive. :thumbup:


John W

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My old man has something very similar to yours by the sounds of it, 1970 elan fhc S4 SE. He's only had it about 50 years and has rebuilt it a few times with a bit of help/hindrance, it was his daily driver for a few decades. 

It's on strombergs and SE cam has a larger cored radiator, electronic ignition and We think larger valves fitted by QED a long while ago, can't tell you what the compression ratio is though and this has a large effect on octane requirements. Collective Memory less reliable than the Lotus.

As I understand it an aluminium head has to have valve inserts anyway so you should be fine with no lead/additive. As you have larger valves I expect new seats were installed at the time.

He currently runs on any petrol he can get cheap, we only have E10 locally so that is what he mostly uses with no issues noticed so far but it's kept in a dry garage and doesn't go out too much these days and defiantly not monitoring WOT performance.  

Over the years there has been a lot of fiddling with spark plugs, ignition settings, carb. Needles, carb rebuilds, etc. Had various issues like running on, difficult starting when hot etc, but at the moment it seems to run very well. I Think the deeper core fitted to the original radiator probably was the best thing, allowing it to keep cool in traffic.

As all of these twin cams are going to differ whether you choose to run on high octane vs low would be dependant on pinking (pre detonation) if you don't get pinking with low octane it should be fine. If you do then use high octane or make adjustments.

The effect of E10 on old fuel lines may also be a factor you might consider or if your car lives in a damp environment and not used much. 

Hope this helps,  although might be a bit long winded if you just needed to know its Petrol.

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  • Gold FFM

I, and many like me, only use premium E5 in our Lotus and other classic cars. Even if it's not strictly necessary. The lower ethanol content is definitely a good thing for fuel lines, carb seals etc and higher octane means you're less likely to run into problems should the timing be off for example. Given the limited mileage most classics do, the extra expense isn't too bad for some peace of mind.

As above, with an aluminum head and especially if the valves have already been upgraded, the inserts should be able to cope with unleaded.

I have made many mistakes in my life. Buying a multiple Lotus is not one of them.


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10 minutes ago, Escape said:

I, and many like me, only use premium E5 in our Lotus and other classic cars

Only use E5 for mine.

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