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Get the most MPG

Published: 28th May 2013 - 0 Comments - Be the first, contribute now!

Get the most MPG
Get the most MPG
Get the most MPG
Get the most MPG
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No, we’re not discussing the nation’s finances, but your classic’s fuel efficiency! Here’s how to improve it – and your wallet…

Did the price of fuel restrict you driving your classic last year? While typical annual mileages are low it’s still annoying to pay so much for a day’s drive – even in a much-loved classic. And, of course, some oldies weren’t exactly economical when new, let alone now!

If you read Stuart Bladon’s column last month, on the famous Mobil and BP Economy Runs of the 1960s and ‘70s (of which he scored several classic victories), you’ll know that quite remarkable mpg figures could be extracted from even exotic cars, by way of careful tuning and considerate, but not sluggishly slow driving.

Because many classics aren’t used much, they are often allowed to slip out of tune because the process is so gradual that you don’t appreciate the drop off in power and economy. If you’re new to classics then you may not realise how things can slip, due to lack of proper, regular servicing.


Start with what should be an essential check for any car, looking at tyre pressures which can rob a car, old or modern, of almost 5mpg! Under-inflated tyres cause extra drag so keep them to recommended settings but don’t over inflate. Modern radials can save fuel but on the other hand older ‘crossply’ tyres are slightly ‘taller’ in profile meaning higher gearing; we’d go for the former and enjoy longer tyre life and better grip as compensation.

Any wear or play in the suspension can affect the steering alignment, which again causes unwanted drag, so more fuel is used, plus this leads to faster tyre wear at the same time. Have it checked.

Binding brakes also waste fuel and this fault is not uncommon on an old car, especially if its only rarely used. Disc brakes, by their nature, bind slightly, but don’t accept this from drum brakes; free them off otherwise you can kiss over almost 10mpg good-bye.

A cold engine is a wasteful one and thermostats do lose their efficiency after a time. Fitting a new one (try a ‘Winter type’ that has a higher opening temperature) can work wonders plus make the heater perform better at the same time.

Most older cars also feature a fixed fan, which again is inefficient by cooling the engine when not needed. An electric replacement is the best answer but you could also experiment by removing the old fixed blade that’s probably fitted and running without it. Don’t worry, usually you’ll only experience overheating worries when stuck in a major traffic jam (so keep it in the boot to be safe!).


An off-tune engine really wastes fuel – and we’d wager that many classics are doing just that, possibly due to their infrequent use causing owners not to bother spending time and money getting the engine in tune.
During the mid-1970s BP conducted a ‘Pound Stretcher’ test and handsomely proved that a good ‘tune up’ could yield as much as 23 per cent extra fuel economy (see table).

Assuming that your engine is in good health – a compression test will reveal the truth – most DIY types can ‘tune’ an engine as it’s quite straightforward.

However, to do it properly is time consuming as it’s not just ‘plugs and points’ but also carb float levels, choke and throttle cable adjustments, balancing multi carbs, checking distributor wear and so on.
You can buy semi-workshop tools to help, such as dwell meters (c.b. points setting) and a strobe light (ignition timing) but we’d sooner seek out a marque specialist (who also may know some useful dodges for your engine) or old school garage that has electronic engine tuning facilities.

Once connected up to your engine it will check every aspect of the engine and find faults that you couldn’t determine manually plus save wasting money buying unnecessary parts. That said, such equipment (and we saw a complete ‘Sun’ system from the 1960s for sale at last year’s Beaulieu autojumble for under £200-ed!) is only as good as its operator and many experienced mechanics can do equally well with basic tools and a good ear.
But, be sure to do something because your car needs it! A study by Champion (Spark Plugs) in the mid-70s showed that out of the 5400 vehicles it ‘spot checked’ 58 per cent had poor c.b. points and more than half suffered from an over-rich mixture wasting fuel.

But that’s just pennies thrown away when you compare it to a staggering 25 per cent which had the ignition timing out by so much that a piston burn out could have well resulted!

You can go a stage further than the recommended settings and have your engine finely tuned on a rolling road under driving conditions and loads to optimise its fuel and ignition settings, gaining added bhp and mpg as a result. However, this is likely to cost around £100.


Believe it or not, performance tuning an engine can improve its economy because you’re making the unit more efficient. Weber and Zenith carburettor replacements were popular before fuel injection came along (they are still available as well) while cylinder head tweaks, paying particular attention to the exhaust valve and ports gas flow, proved pretty beneficial for economy and power.

Actually, a good old fashioned cylinder head decoke and valve grind will probably work wonders, too. It’s more tedious than difficult, and all you need are basic tools and a torque wrench to tighten down the head afterwards. However, a leisurely weekend spent doing this is worthwhile – in fact, on Economy Runs, a good many competitors did this to gain an advantage, even on cars with less than 5000 miles from new!

Other modifications worth considering include electronic ignition because it does away with conventional c.b. points. Since these contacts make-and- break millions of times between maintenance intervals (making and breaking 176 times a second @ 5000 rpm would you believe!) they naturally wear in service and the important gap closes up. An electronic ignition uses an infa-red beam so the ‘gap’ remains constant and so keeps the ignition in top tune.

You can play around with smaller carb jets and needles to gain added mpg but bear in mind this will naturally hinder performance and can, if you drive hard, lead to overheating and piston burn outs, depending upon engine.


Of course you can’t talk about fuel economy without mentioning LPG conversions. It’s not so much that they make fuel go further, because actually LPG is less efficient and so mpg suffers! No, the benefit is in the cost
at the pump. LPG conversions are popular with certain juicy classics such as Jags, Rollers etc, and it does enable low cost classic days out. However, installations can run into thousands and while DIY kits are available, it really should be left to professionals. On some older engines, the cylinder head valve seats may need to be replaced, although an unleaded conversion does the same thing.

The system has to be checked and certified periodically like a domestic set up and this is not appreciated by many motorists. Boot space is compromised and you can run into touring problems when carrying LPG, if you have to use tunnels.

We Reckon...

Every little helps, as the advert says, and you can make your fuel go further if you put the effort in.
A thorough service and tune up remains the most cost-effective route and intelligent economy- minded driving costs nothing.

But any mods, conversions and indeed major repairs need to be balanced against their initial outlay and the miles you intend to cover in your classic.

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