The V8 Owners Forum -

ok bit of an odd question, well 2 questions.

is there much difference in fuel economy between older carb engines to EFI, and any newer injection systems installed?

and also how good are V8's compaired with other engines?

imo bigger engines do not drink more fuel than small enless you use the power, in my car, goign from 60 up to current 143 its actually better on fuel cause i went from carb on to k series injection which is pretty good on fuel.

now i get about 40mpg, tryign to work out how badly V8 is gonna munch fuel, hopefully wont make much difference on day to day driving.

tho fuel economy comes 2nd after speed


Ralph

From 20 to 30 mpg maybe 35 but if you get that its pointless having a v8 they can also get as low as 15 if your stepping on it. Very wide range of figures but also a wide ranging question as the engine could be mild to wild. EFI will give you the best economy but a well set up carb can also be very good.
Bigger engines can use more fuel in traffic running as they simply use more fuel just to run.
Are V8's better than other engines, depends on what way you mean?

katanaman wrote:From 20 to 30 mpg maybe 35 but if you get that its pointless having a v8 they can also get as low as 15 if your stepping on it. Very wide range of figures but also a wide ranging question as the engine could be mild to wild. EFI will give you the best economy but a well set up carb can also be very good.
Bigger engines can use more fuel in traffic running as they simply use more fuel just to run.
Are V8's better than other engines, depends on what way you mean?

when i said if they where as good, i ment as good on fuel, other than that they are way better, just lissen

i know that if i boot it everywhere i am obviously gona use more fuel cause "power dont come from no where!".

what kinda cars get 35mpg? cars only weighing in at about 950 with a V8 so should be dam sight better than range rover lol.

weight i think is the main factor on fuel economy anyway, yes a V8 will drink more but i wouldnt imagion tick over is a very big persentage of fuel used anyway.


Ralph

EFi should be better on fuel than a carb.

The problem with the Rover V8 is that it's a very old design so it's not as efficient as a newer design.
Also, compared to a 4 cylinder engine, it's got twice the friction from the pistons, big ends, little ends and valve gear.

If you get more than 30mpg in a light car, I would consider that darn good!

I get 12-15 in heavy cars on LPG.

Chris.

My 5 litre TVR just touches 30mpg on very steady cruise on the motorway.
On local runs it's around 19mpg.

When I'm actually using the car as intended it's best to not ask.

I get, on avaerage, about 10mpg, but that's from a 4.2 AJPV8 and I do mostly short, urban driving so my MPG sucks. If I mix it with a few mway cruises I can expect more like 17-20 average, I think.

I'm just building up a 3.5 RV8 whcih will have efi, probably with megesquirt or emerald ecu, and maybe a pair of turbos. Whether that will give better mpg remains to be seen, but it will be going in a scimitar to start with, which won't be too heavy.

Last year on a 70mph motorway cruise got just on 30 mpg

But I've had it as low as 6!

Ian

i think i'll be lucky to see double figures when mine's running!

so looks like no V8 is capable of more than 30 then!

i will find out in time i guess!


Ralph

I can get 32/33 on a sensible run with a 290hp 3.9 on injection, with a mid sized car, and 3.7 gears!!

I can get 32/33 on a sensible run with a 290hp 3.9 on injection, with a mid sized car, and 3.7 gears!!

That's only because you partly run it on MY liniment fumes

Ian, you need to check what you write mate,

My 1974 Rover 3500 (P6B) at its best returned just under 27mpg following consistent 70mph running.

Just prior to being replaced, the engine was returning 21 to 22mpg under similar conditions.

Now, my new 4.6, running with twin SU carburettors, needles carved to suit, regraphed distributor, high torque camshaft and running through a 3 speed auto returned 29mpg during consistant 70mph running, and that was only some 7000 miles into its life.

My P6B sounds awesome too, very very deep, and loud, like a very loud Discovery or Range Rover with a 3" exhaust

Ron.

As an example of a more modern V8 the wife's XK8 regulaly gets above 24 to the gallon mostly around MK (round about every 1/4 mile) add in some open road driving it is about 27, put it on a run up to glasgow we see 29 to 30 to the gallon (pretty rapidly) it weighs about a ton and a half and it is an auto.
Mike