Breaking the barrier

[max-it-out]

No , not the sound barrier or 200 mph....the 30 mpg barrier.

Anyone done this with a tank full , say 10 gallons on a real road trip ?

With my last E I got 24 mpg on a trip back from Scotland once , so , I`m thinking : engine in good condition , fuel injection ( + 2 mpg ) , 2.88 rear axle ( + 2 mpg ) , tyres pumped up to max safe level ( + 2 mpg ), wing mirrors removed/folded back .Then choose the warmest possible Sunday morning ( warm air is less dense so less air resistance ) and try to maintain a steady 40-60 mph using the brakes as little as possible.Add up all those savings and the magic 30 mpg looks possible.

With my present E this looks like a faint prospect indeed , as last time I checked it was using a gal. every 17 miles on average

[cactusman]

Best I've managed was 24mpg on a trip to Suffolk and back....normally hovers around the 18-19-20 mark...

[malcolm]

I normally get 22/23 mpg but once got 27 on a run between service stations on a long motorway journey.

[christopher storey]

Consistently, on both of mine, over a 25 year period, I have achieved 23 mpg. However, I am not a hard driver these days, so I would think that anything between 20 and 23 is acceptable. If you are only getting 17 in normal driving, then I would surmise that you are over-rich, as this is what consistently happens to those who use say UO needles instead of the standard UM

[Nick]

Mark,

I thought your handle was max-it-out for speed. But perhaps it's for mpg !

My average is 23mpg over 19,000 miles. On 4 occasions I've got 29 and a bit, but I suspect my high mpg's are more likely due to uncertainty in the data. No wing mirrors. Standard engine & carbs.

What's the point in trying to get high mpg through careful driving ? It's a sports car !

Nick

[Robbiee]

[max-it-out]

Consistently, on both of mine, over a 25 year period, I have achieved 23 mpg. However, I am not a hard driver these days, so I would think that anything between 20 and 23 is acceptable. If you are only getting 17 in normal driving, then I would surmise that you are over-rich, as this is what consistently happens to those who use say UO needles instead of the standard UM

Unfortunately I still have the twin Strombergs and 3.54 diff.I took one of the plugs out and it looked ok - pale grey/cinnamon , not sooty black.

Is it the case that 3 SUs are always going to be better , or can the Stroms be made to function equally as well ( I have removed the secondary throttles ) ?

I notice the my inlet manifold seems more convoluted , there doesn`t seem to be a straight flow through as in the case of the SU set-up.

[MarkRado]

What's the point in trying to get high mpg through careful driving ? It's a sports car !

Nick

[MarekH]

I've actually hit and passed 40mpg - in cash terms - with my v12 which runs both petrol and lpg via my fuel injection system. That's in excess of 20mpg in the real world, but as lpg is half the price of petrol, the economy doubles.

"45mpg" should be achievable with a standard camshaft if I were to detune the top end performance a bit.

kind regards
Marek

[christopher storey]

Unfortunately I still have the twin Strombergs and 3.54 diff.I took one of the plugs out and it looked ok - pale grey/cinnamon , not sooty black.

Is it the case that 3 SUs are always going to be better , or can the Stroms be made to function equally as well ( I have removed the secondary throttles ) ?

I notice the my inlet manifold seems more convoluted , there doesn`t seem to be a straight flow through as in the case of the SU set-up.

The straightforward answer is that, yes, the 3 SU setup will always be superior to CDs . However, there are those who can still get acceptable results which , whilst not quite as good as SUs, should not be disappointing. However, your mpg problem may be more associated with the 3.54 axle which is highly likely to cost something like 10 -15% compared with a 3.07 . However, even with that axle, I think you should be doing quite a lot better than 17mpg

[Nick]

Sorry if I came across as a bit glib previously, but the saving from 17mpg to 22mpg is about £100 over 1000 miles. The cost of changing carburettors and or diff would take a while (~10 to 20 years depending on your annual mileage) to recover.

Can't deny that the extra distance between fuel stops (75 miles) would be attractive.

Nick

[malcolm]

Can't deny that the extra distance between fuel stops (75 miles) would be attractive.

Nick

That's the main benefit to me. I get around 250 miles safely before topping up. Useful when you're touring smaller regions of Spain and France and not sure where the next decent fuel supplier will be.
It also lets me know the car is set up about right if it goes well and produces 22/23mpg

[max-it-out]

I `ve heard of racing versions being fitted with a " long range fuel tank " , a bit like the old Spitfire ...I used to carry an ancient metal Shell petrol can in the back until it started to leak ( incidentally , saw one for sale on TV for nearly 100 quid ...wish I hadn`t thrown mine out now ).
On a side note , assuming one fitted FI and took the car along to a RR for tuning , could you ask to have it set up for maximum economy or , max performance ?

I suppose in theory , they should both be at a peak when all ( or as much as possible ) of the fuel is burned to produce energy.

[max-it-out]

Sorry if I came across as a bit glib previously, but the saving from 17mpg to 22mpg is about £100 over 1000 miles. The cost of changing carburettors and or diff would take a while (~10 to 20 years depending on your annual mileage) to recover.

Can't deny that the extra distance between fuel stops (75 miles) would be attractive.

Nick

Nick , you are absolutely right of course , with the low mileages many of us do , it would take decades to repay the cost.

[johnetype]

Is it the case that 3 SUs are always going to be better , or can the Stroms be made to function equally as well ( I have removed the secondary throttles ) ?

The straightforward answer is that, yes, the 3 SU setup will always be superior to CDs .

Define superior. If in the context of this thread we're talking about mpg, two carbs will always be more efficient than three. Jaguar moved to Strombergs precisely because they were able to meter fuel more accurately to meet emissions requirements and that means better mpg.
For absolute power, yes three SUs win but twin Strombergs on a manifold with the secondary throttles disabled will give the best mpg.

[max-it-out]

Is it the case that 3 SUs are always going to be better , or can the Stroms be made to function equally as well ( I have removed the secondary throttles ) ?

The straightforward answer is that, yes, the 3 SU setup will always be superior to CDs .

Define superior. If in the context of this thread we're talking about mpg, two carbs will always be more efficient than three. Jaguar moved to Strombergs precisely because they were able to meter fuel more accurately to meet emissions requirements and that means better mpg.
For absolute power, yes three SUs win but twin Strombergs on a manifold with the secondary throttles disabled will give the best mpg.

Not doubting your claim here , but , just a couple of points to bear in mind -

1) Mine are fixed at manufacture ( not tuneable )
2) Mine don`t have the vacuum capsule

[johnetype]

Changing the distributor to one with the UK mechanical advance curve along with a vacuum advance capsule will give a significant mpg improvement.

[max-it-out]

Thanks John , that sounds like the most cost-effective solution....I assume the vacuum produced in the inlet manifold is the same with both types of carb.

[MarekH]

Mark,

The amount of vacuum is a function of how much the pistons go up and down less how open the throttle butterfly is. All the caburettor does is add a bit of atomised fuel into the mix.

Also Stromberg carburettors came in two varieties:- one had adjustable needles from above and fixed jets from below; the other type had a fixed needle above and variable jet from below.

kind regards
Marek

[max-it-out]

So you seem to be saying that all the Stromberg CD s as fitted to US spec cars can be adjusted.Other people I have spoken to said they were sealed at the factory and the mixture strength can`t be adjusted . I hope you are correct because I quite like the idea of trying to get them to perform as well as possible.

Unfortunately , whilst instructions are provided in the driver`s handbook for adjusting SU s , nothing is said about the Strombergs .

Thanks again , this forum is a superb resource and I learn something new almost every day.