MPG

P

phil

New Member
Hi, I know this is probably a stupid thing to ask having just purchased a V8..
What MPG do you guys get out of your V8's, and other varients for that matter.. What modifications can be made to increase MPG? For me, I don't mind if performance suffers, as long as reliability doesn't. I was wondering if a single carb conversion was possible?
 
Hello Phil,

If the vacuum advance on the distributor is working as it should, then 16 to 18mpg suburban driving is fairly normal, and anything from 21 to 25mpg is possible country driving.

SU carburettors can be tuned for either economy or performance which gives them the edge over other carburettor designs. Single carburettors can be used along with a different inlet manifold which will yield more power, fuel consumption will typically increase.

Ron.
 
I can't remember whether your's is manual or auto, Phil. An auto should do just the right side of 20mpg unless you do a lot of town driving which might pull it a tad under 20. A long motorway run could see up to about 25. The 4 speed manual adds around 3mpg to these figures.

To improve on these figures the key issue is to raise the overall gearing. For either the auto or manual this is easiest done by fitting an SD1 type LT77 5 speed manual box. Vaultsman has recently completed an excellent thread doing just this. If you want to stay with an auto the easiest swap is to fit a ZF HP22 as fited to range rovers etc. Hold off on that for a couple of months as Ian Wilson is about to try out a gearbox specialist in Doncaster.

Once the gearing is sorted, next up is to sort out the induction system and exhaust, both of which are extremey restrictive. Sorting the induction system is very easy, see:

http://www.classicroverforum.com/viewtopic.php?f=5&t=6727

The exhaust is more expensive, requiring a decent manifold and then a new system to match.

Unfortunately the heads are not far behind. So you'd probably want to add either SD1 or 4.0 / 4.6 stage 3 heads and an RP4 or stump-puller cam. Driven gently that will improve economy markedly - but can you resist the extra horses we've liberated?

Ron and I are both in agreement that there is no particular problem with the SU's until you start winding the revs up a long way. If you do that you first need a much better inlet manifold.

There are quite a few injected cars around using Range Rover systems. Injection per se won't help either economy or power unless the breathing and heads issues are addressed at the same time - which they often are. For me it would be the last item on any shopping list, not the first.

Rather than spending serious money this way, first step is to make sure you are getting the best out of what you have. The V8 is very sensitive to plug leads, so a set of Magnecors are an early investment. Fit along with electronic ignition and a decemt coil. There are numerous notes on how to set up the carbs and check that the distributor is operating correectly.

Hope that gives a bit of food for thought

Chris
 
Hi Phil, we have just come back from the Rover Rally in Beamish, it was a 155 mile each way trip mainly on the motorway. We were doing 65 to 70 mph most of the way their and back and got about 24 mpg in our 3500s. Not sure what mpg is around town never really checked, but the only problem with the Rover is it keeps pulling to the left, it always seems to be as we approach a petrol station :D . The sheer enjoyment of driving it outweighs the cost of the fuel, at the moment anyway :wink:
 
On a long run, I've found my 3500 with LT77 gearbox, SD1 heads, Mallory dual point distributor and Holley 390 carb can get 28-30MPG (UK) over a 200 mile round trip of 90% motorway miles (sitting at 70mph), the rest being round town. Around town, or above 70MPH, the MPG drops significantly. That's on standard 95RON unleaded. Can't complain at that :)
 
Woo, lots of options then, so if this were to be done on a budget, what would the mods be that have the most significant effect? I'm assuming a single carb?

Mine is an auto..
 
phil said:
Woo, lots of options then, so if this were to be done on a budget, what would the mods be that have the most significant effect? I'm assuming a single carb?
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Not a chance, well set up HIF6's will always be more economical, and you won't have the big outlay to start with. I'd go for electronic ignition and an electric cooling fan, and make sure that all the rest is in the best condition possible. (Leads, plugs, filters etc.)
 
What about LPG conversion? Not sure what the cost of conversion would be - maybe around £1000??? I guess it depends on whether or not you do the installation yourself using a kit and even then you would have to get it inspected by an approved LPG fitter. However, like any other expensive mod's, you would have to be doing a reasonably high mileage if you want a return on your investment?

LPG is roughly half the price of unleaded and almost as efficient. So, in effect your a nearly halving your running cost. Its like getting 40-50mpg from a 3500 V8. If you do a high mileage, it's hard to imagine a better way of reducing fuel costs (other than getting out and pushing the car :D )?

With my 2200TC in standard form, I can usually rely on getting 25mpg. On a long run it's 25-30 and around town 20-25.
 
Hi Phil

I average around 25mpg in 3500S. That's mostly commuting to and from work on A roads and I don't often get stuck in town or traffic. It goes up to about 28 mpg on a longer run. I'm running with HIF6s, electronic ignition and Magnecor HT leads. To a degree mpg wasn't really a consideration when I got my car and my company pays for all my business fuel, which is a bonus :D . All of the above are great suggestions but the one major impact on fuel economy is the way you drive the car. I know it's difficult to resist the temptation to push it, especially when Mr Exec in his modern Audi or Beemer is right up your @rse but if you imagine that the go pedal is a money spending machine and the harder you press it the more money it spends, it changes the way you drive. In the days of fuel at 70p a gallon when these cars where first launched, fuel economy wasn't an issue. These days it certainly is. There are lots of good guides on how to drive more efficiently and it can be a fine balance between efficient driving and not p1ssing everyone around you off because your driving like the proverbial nun. For example, from a purely energy efficient viewpoint every time you have to use the brakes you're converting expensive fuel produced energy into heat at the brakes. Not ideal because you want that fuel energy to be used soley to propel you forward. Just by maintaining a bit more of a gap to the car in front you can see what's happening and anticipate sooner. That way you can adjust your speed by easing off rather than having to react with the brakes. It makes a surprising difference in the long term. Don't take my word for it though, try it for yourself (once you've got through the stage of marvelling at the noise of the V8 is it winds up of course :D)

Dave
 
JVY said:
LPG is roughly half the price of unleaded and almost as efficient.
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I think that's a bit optimistic as it only has about 70% of the energy value per litre. So you have to be losing a fairly large proportion of the power or the mileage.
If anyone wants a cheap conversion, I'll be removing a kit from a Land Rover in a month or two. It's pretty ancient and hasn't run for a while but might provide a starting point.
 
My mother had her Merc A-class converted to LPG earlier in the year, and so far it's done 6k with absolutely no problems. We've checked the MPG as well, and it's only dropped by around 0.7MPG, but it is a modern system with direct injection. I think with LPG systems you really get what you pay for. We got ours done locally, because we'd seen the standard of work was high. I'm quite regularly at the garage with the Rover, and as a result, they show me some of the cars that have come in from other places, because the owners weren't happy. Some of the work churned out by people on the LPGA register is appalling. It's really quite worrying. Remember that if you are converting a car to gas, it's no longer sufficient just to have a certificate made. Instead, you must take the car to a member of the LPGA who will put the car on the register at a cost of £50.
 
Neil Castle, who runs a LT77 equipped 3500S, texted me the other day to say he has accomplished 30mpg during his weekly motoring (he drives from West Sussex to London two or three times a week).

The car is on standard ignition but has rebuilt carbs, electric pump etc.

Very impressive.

I've driven a couple of 3500 autos which appeared to do 25mpg+ on long trips. Including, I suspect, my Three Thousand Five, which appears
not at all gassy, and broadly comparable with the MPG I used to get from my 2200 auto.
 
FrazzleTC said:
My mother had her Merc A-class converted to LPG earlier in the year, and so far it's done 6k with absolutely no problems. We've checked the MPG as well, and it's only dropped by around 0.7MPG, but it is a modern system with direct injection. I think with LPG systems you really get what you pay for. We got ours done locally, because we'd seen the standard of work was high. I'm quite regularly at the garage with the Rover, and as a result, they show me some of the cars that have come in from other places, because the owners weren't happy. Some of the work churned out by people on the LPGA register is appalling. It's really quite worrying. Remember that if you are converting a car to gas, it's no longer sufficient just to have a certificate made. Instead, you must take the car to a member of the LPGA who will put the car on the register at a cost of £50.
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My BMW 328 Tourer has the modern multi-point Prinz LPG system. I've now done around 30k miles on it and must have got the installation cost back thrice over. LPG is a bit of a fiddle, and not for everyone, but it's the difference between me being able to get out and do business and not being able to justify it. I find it very scary putting petrol in a car, when you're used to £0.77 a litre.

My car does the equivelent of 45-55mpg if I was running on petrol. Power output not affected in any appreciable way.
 
My fear for anyone with LPG is this, enjoy while you can because as soon as it becomes really popular watch the price increase. Ibought a diesel car for the first time a few years ago as diesel was a hell of alot cheaper than petrol, what's the price of diesel compared to petrol as diesel cars have gained popularity. Same will happen with LPG. Governments don't you just love em!
 
For someone in Nick's position LPG is great, but for a 'nice days out car' the £1000 conversion cost will buy you an awful lot of petrol.

Don't worry about the cost of the fuel - enjoy your day out and the journey too. It will put a smile on your face every time and that's got to be worth it, hasn't it?
 
Don't forget to keep the tyres well inflated, even an extra few psi will reduce rolling resistance and improve mpg. Also don't carry loads of stuff with you, the big difference between town driving and steady cruising is getting the car moving, so leave the tools and mother-in-law at home :LOL:
 
Nick ,can you show us some figures on recovering the cost in 10K miles ?
Is the conversion transferrable from car to car?
 
happy days said:
My fear for anyone with LPG is this, enjoy while you can because as soon as it becomes really popular watch the price increase. Ibought a diesel car for the first time a few years ago as diesel was a hell of alot cheaper than petrol, what's the price of diesel compared to petrol as diesel cars have gained popularity. Same will happen with LPG. Governments don't you just love em!
Click to expand...

This really hasn't happened in this country though. Certainly LPG is very popular on mainland Europe, but it's still very much a minority thing here, which is another pain as you can't get it everywhere - the nearest LPG to my house is in the middle of Guildford and about 7 miles away.
 
DaveHerns said:
Nick ,can you show us some figures on recovering the cost in 10K miles ?
Is the conversion transferrable from car to car?
Click to expand...

Being the master mathmatician I obviously am not, I've just done some sums:

Petrol at the moment here is about £1.38 a litre = £5.90 per gallon
LPG is about £0.74 a litre = £3.12 a gallon.

My old BMW does about 29mpg on petrol. So 10k miles = 344 gallons of petrol. Total cost at today's prices £2029.60
And does about 24mpg on LPG. So 10k miles = 416 gallons of LPG. Total cost £1297.92

Saving of £731.68 on LPG over petrol over 10k miles at present prices.

My conversion (mates rates) cost me £1400, so I roughly got it back over just under 20k miles, and have now done 35k miles on it.

1206 gallons of petrol (35k miles) = £7115.40
1458 gallons of LPG (35k miles) = £4548.96

£2566.44 saving over 35k miles.

Not as major as I initially thought, but still highly worthwhile if doing a lot of distance. The other factor is I have to put £10 worth of petrol in it every 10 days or so to start the car. It switches to LPG automatically when I've done a few hundred yards from cold.

The kit on my car is completely removable, but if I do eventually sell it it'll probably stay in there as it adds to the value of the car.
 
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