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MG MGB GT V8 Factory Originals Technical - Fuel mileage

I clocked my mileage to and from the V8 convention over the weekend (way too many cool cars!) and I was averaging about 21 miles per gallon on my fuel injected 3.5L. I was a little disappointed in that, as I was expecting around 26+ considering how light the car is. What are other people getting both with injection and carburetors?


Every time Iíve checked my mileage I got 16 miles per gallon with a 3.5 liter Buick and a four-barrel carburetor using the stock rear end. I only got 18 miles per gallon with the original four-cylinder motor.
George Champion

That's actually pretty great Justin. My 4.2 carb'd only gets about 15, if that.

My mileage varries by how heavy my foot is. Carbed 302, with 625cfm carter, 14-19mpg
Larry Embrey

Bog standard factory V8, except for tubular headers, and single cherry bomb s/s exhaust and K&N filters with richer needles.
When I first bought the car average miles around town 15-17 miles per gallon, and lucky to get 19-20 m.p.g on a run(50-75 m.p.h)
A year later after changing P.O's incorrect type of H.T Coil, and spark Plugs, and some sympathetic (empathetic?) tuning, the old girl does 22 m.p.g around town and 30 m.p.g on a good run. (The Co2 emmissions have also dropped from over 8% to 2.6%)
top speed on the clock between 135m.p.h and just over 140 m.p.h(with sebring light covers)
All very good but now the body is crying for attention!!

Of course that 30 MPG Imperial is 24 MPG U.S.
George B.

Last month I ran a good ck. on my hot wire F/I 4.2 on a 1200 mile run & I did a 24.5mpg.When I had a carter 400 on her she would only do 21 My 3500 in the 74.5 with a Carter 400 afb would give me 25 to 26 & the 72 roadster with the 4.9 with a LOT of power & 10.5 comp. will give me 30 mph on the run to the Roadster factory BUT around town 14-15 is all David, you will never get good mileage for you have NO vacum advance on your distributor & that is 3 to 5 mpg! Juston what is your total adv. say at 3,000 rpm? It should be 36-39 or you will get poor gas mileage.
Glenn Towery

"Factory" GT V8 with John Eales 220 bhp engine on SUs, set up on both engine dyno. and rolling road.

17 to 18 mpg (UK) around town and short trips. Average 25 mpg on longer runs say crusing 85 mph not exceeding 95 mph, a few more mph say crusing 95 tops 110 mph drops consumption dramatically - probably down to about 20/22 mpg.

My RV8 was MUCH worse until "chipped" by John Eales, particularly in consumption from a cold start which was (I estimate) less than 10 mpg until fully warmed up, usually 6 to 8 miles. This contributed to 14 to 16 mph overall.

Now chipped I guess it's doing somewhat better than the GT V8.

Nigel Steward


Mine's an EFi 3.5 with RV8 headers, single SS silencer, and 15" wheels with 3.08 Rover diff.

I manage 30 (Imperial) MPG on Motorways, but the gearing is quite high (approx 1000rpm per 30 mph), and overall fuel consumption averages mid twenties (Imperial)

I don't know how this compares with US gallons.

Michael barnfather


4.5 with Holley 15" wheels with 3.08 Rover diff.

20 mpg summer 18 winter (Imperial) Mixed bag commute outside lane motorway speeds.


It's amazing the disparity amongst cars here. I'll check my vacuum advance at 3,000 rpm's and see what's happening. I'll also double check my timing and make sure all is good there. I guess I'll stop whining about my 21 miles per gallon. I'd have a heart attack if I were only getting 14!

So now here's the better question: What's causing the disparity?


Apropos to naught; MPG Imperial X .8 = MPG U.S. An Imp. 44 gallon barrel = a U.S. 55 gallon drum.
George B.

I usually get about 28 (UK) from my factory V8 but on the run back from Le Mans this year I was driving with a lighter foot than normal because of a marginal cooling problem, but still keeping up with the traffic, and got 322 miles from one tank which is 34 mpg! Averaged 31 over 1000 miles overall.
Paul Hunt


Fuel injected cars seem to be the most economical, Holley the worst, with SU's somewhere in between.

A lot must depend on driving style,and road conditions, most of my driving is fast motorway/dual carriageway (I've done over 5000 miles since April),and I expect to do over 250 miles between fills .

Michael barnfather

Justin, it takes a steady pedal on the highway to get the mileage.

I put 1741 round trip miles on my MGBV8 including the thrashings on the Grattan Raceway & the autocross course. VERY happy to report nothing broke. :)

My mpg ranged from 22.75 to 25.9 running 70-80 on the interstate. The tank that included travel to and from the racetrack & over an hour of racing returned 13 mpg.

Note: the 2 tanks that Dan Masters ran thru on the drive home only managed 19.5-20 mpg. Hmmm, wonder why? :) :)

Round trip from outside Washington, D.C. to Grand Rapids, including the side trips was 1091 miles. With a passenger, 2 sets of luggage, a 215 with mild cam, 1404 Edelbrock, 195/65/15 tires, 3.70 MGC rear, T-5 with .63 5th gear, milage was 24 to the gallon. Ran one tank, 214 miles with the A/C on full blast, 23.8 MPG for that tank.
Jim Stuart

When I did the 24.5 m.p.g. I was running from 65 to 90 m.p.h. with the A.C. on high!
Glenn Towery

This thread was discussed between 19/08/2002 and 21/08/2002

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