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MG MGB Technical - MGB Mileage checkin

So, what are we doing mileage wise in our cars? I filled up last night before coming up the hill from SF to Tahoe: $61. I use 3 oz of lead, 91 octane at 5.10/gall, and 3 oz of acetone and if I can remember a gal of toluane in the 13 gallon tank. I ran last tank with sustained spurts over 108 mph ( so sayeth my GPS) on stretches coming back from On The Road Again Classic Restorations in Morgan Hills Calif., and kept it at 5500 RPM in OD for 3-4 minutes at a time shooting along over 100mph. The car is dead solid steady at the speed. I spend chunks of time idling at stoplights and back to dead stop in SF FWY traffic on the tank. No matter what I do, I get 25-28 MPG. I get 33-36 if I cruise hwy 75-80mpg in OD. The car is a completely head-toe rebuilt-renewed-bettered 1977 mgb roadster. 1800 4 lug punched 60 over, Burgess BVFR head, Jackson 5.5:1 rollers,new 1 3/4 SU, Peco, GB 123 dizz on curve #6 ( no det at sea level). Refabbed OD, and recently declunked the rear.Jackson rear composites and rebuilt front end/swivels with needle rollers on King pin which is dropped 1 inch vertically ( thanx I think to Glen Towery in what Virginia?) All oil is synthetic ( sorry, it works just wonderful 4 me in OD)On board wideband O2 Innovate, stays between 15 and 12. I feel the car is powerful within the moderate specification producing more efficient use of fuel, thus the mileage. I'm prepping first for EDIS then EFI down the road.
What are you fellas doing,?, at a time when we are about to see a complete national rethinking of fossil fuel use and attitudes. Just being nosey as hell again. Cheerios VIc
vem myers

All I can offer is on my 72B, that is not too well on any road toward restoration status, recently and finally went from a consistent 18mpg (using unleaded 10% ethanol blend)to 2 tanks at 23mpg. This 5mpg increase was due to adjusting the valves, followed immediately by tuning and balancing carbs and fixing a cable problem that had the choke ever so slightly closed at all times.

I've read that the 25-27mpg is a "to be expected" range for mpg.

My OD is presently out, but I anticipate my 23mpg to go up by another 3 mpg or so, as the OD does not drop the rpms all that much anyway. I'm still hoping for 30mpg on open road cruising. I know 2 midgets that are getting 40-45mpg, but they are well maintained.

I also intend to re-time the engine using the ole' 4000 rpm and high advance setting to see if this helps anything, but only after I pull distributor to clear out any gummy ole grease, etc.

I do not think the car would ever go beyond the 30mpg on the open road.
R.W Anderson

79 MGBLE with original (80K)motor and (4 speed) trannie, Moss SC, Mike Brown P&P head, Custom designed cold air intake, FastCars Front Coil over, Hoyle Rear IRS with 3.9 ratio Sierra LSD differential, 15" Panasports; I see 31MPG highway.

R.W. The 10% ethanol fuel will reduce your mpg, avoid it if you can.
John H

Unfortunately in MN there is a proposal to move to 20% ethanol. 10% was mandated across the state years ago, no one sells non-ethanol gas in MN - except for a fuel race car stations, but its spendy.

It is my understanding that 10% ethanol is national now, but some states still offer non-ethanol "enhanced" fuel.

So we're stuck with the loss of 2-3 mpg all year long now.
R.W Anderson

On a recent trip of 272 Miles, cruising in 5th at 70-75 mph most of the time, with the a/c on, I used 9 gallons - just over 30 mpg. Car is standard except for the 5-speed.

Bernie Lowe

This brings up a question I have been wondering about,
how much pollution does the 10% ethanol gas save?If it's only 10% we aren't polluting less if we have to burn 10% more gas.If it's less than this nothing but a scam.If they claim 15% then it is really only 5% accounting for the worse mileage.
patrick bailey

I've been getting about 22 city/hwy. the last time i did all highway, i got 27, but since then i've tuned the carbs and correctly adjusted the timing, so i'm hoping for an improvement.

my midget gets about 40 highway.

don g

I'm averaging about 32 mpg now and that's with the standard 4 speed. It looks like I gained roughly 1 mpg thanks to the non-ported vacuum (advance) conversion.

73 B, .020 over, mild cam, 10:1 pistons, MSD-6A, pertronix EI, Schlemmerized 25D4, Sean Brown P&P head & matched intake, HIF4's w/AAA needles & K&N filters, all smog equipment intact and on-board, Datsun 5-speed, generic tires @ 31F/33R, very heavy right foot.

I'm getting a combined city/highway 31 mpg. The low in the last 1,000 miles was a shade over 27mpg on one tank with a high of 34 & change.

I've been trying out a 195* t-stat over the old 185* one, and the car hates the extra 10*. Mileage is down, and I had to retard the timing a degree and a half. Gotta fix that....

Rick Stevens

Regarding the ethanol issue, a loss of fuel mileage was not my experience. I used to add 20% - 25% ethanol to the fuel for my Triumph-engined Saab 99 to boost the octane to something it could live with. By tuning to take advantage of it, I raised my mileage from 25 mpg to 29 mpg. You need to tune to take advantage of the ethanol.

With my BGT, I get 30 mpg highway driving moderately, like 65 - 70 mph.

It's a GK engine, 1-1/2 inch twin HS4, 0.030 overbore, Delta KB cam, head ported per Burgess book (the version with a lot of cutting on the exhaust side and only cleaned up on the intake), 155 psi cranking compression, plain old points distributor, and an overdrive trans.

I expect to improve this with a carb rebuild. My shafts and bushings are worn too much for the at-idle tuning procedures to be valid.

C R Huff

When I tried gasoline with 10% ethanol back in the late 1970's, fuel economy fell by at least 5%, plus the engine had less power.

Taking it easy on the Interstate at 65-70 MPH, my 1972 MGB gives 30-34 MPG.

1925cc, 2nd generation Derrington crossflow head with a Piper 285 camshaft, twin Weber DCOE 40s, Piper Big Bore exhaust system and Aldon 101BR2 distributor.
Steve S.

I know this is a different car but my everyday runner is a Mazda 2.2turbo. I avarege around 450 kilometers to the tankfull on unleaded and can scrape 500 ks out of it on a long run but if using ethanol enhanced (10%)have never been able to get 400. It's about 4 cents a litre cheaper than straight unleaded here and with an empty tank (45 litres)you only save about $2 but it costs more to run it. This car runs an O2 sensor and adjusts it's own mixture and ign. timing so it is definatley the fuel that is the problem. Doesn't appear to perform quite as well either. Sorry it's not an MG but thought you might be interested anyway. Gary

I dont know lads, every time I see this sort of thing Im back to my usual thing of my engine using too much fuel, but I dont know. My engine runs well. Its a stock late UK spec engine, so it has twin SU HIF4 carbs, but it has a 123 electronic distributor. On a tank of fuel, Id be getting about 250 miles, maybe a little more. That would be combined driving, not stuck in heavy traffic. That works out at about 23mpg (UK gallons) or around 19mpg (US gallon).
Ross Kelly

At one time they were adding ethanol to increase the octain, this seemed to not cause problems. Now they are substituting the methanol for other additives that have been removed, this is called reformulated gas and is supposed to lower emisions. On my cars with carbs, I lose arount 20% in mpg when using reformulated instead or normal gas. My truck with throttle body injection lost 11%, multiport injection around 6%.
John H

I actually did the math on this not too long ago and I found that I was better off leaving my timing where it is and using premium grade gas. The savings at the pump do not make up for the loss in mpg. The numbers were rough and conservative but the result was still considerable. I think you lose more mpg from having to retard the timing more than lower grade of gas, but the two together you cant ignore.

I also know someone who decided to test the difference on his commute truck. He used all three grades over a month and figured the mileage for each one. Because he left his timing the way it was, he found that the middle grade of gas saved money. He was pretty clear about how bad the lowest grade was, and that it was better for the engine. Now if he had adjusted his timing for the premium grade, I think it would have won out.

I typed that wrong. He was pretty clear about how bad the lowest grade was, and that the "higher grade" was better for the engine.

Of course a lot depends on how you drive.
I have a '74 MGB GT with OD. Megasquirt EFI with mapped distributor Ignition. Engine has been upgraded with hardened valve seats; standard otherwise

Daily driving of 30 mpg and about 36 mpg on highway driving
werner haussmann

Did you know that it takes several barrels of oil to produce alcohol? Did you hear that in parts of the world people are rioting because corn is getting expensive or hard to find?

Producing ethanol fuel from corn is either a slight net loss in energy creation or a slight gain. Most estimates say its a loss, a few say its a slight gain. While it's true that it takes fuel to plow, plant, harvest and process corn to make ethanol, I haven't heard of the 8:1 - 10:1 ratio mentioned above. (Remember ethanol only has about 66% of the energy of gaasoline.)

Still (pardon the pun) corn-derived ethanol is more of a farm subsidy than an energy policy.

The wasteful diversion of energy to growing corn and the diversion of this food crop has resulted in food riots. There were riots reported in Mexico a year ago, and last year a number of riots were reported as food prices spiked in Haiti and other places.

Far better and more enlightened for us in the US to take advantage of our abundant energy resources awaiting development in Alaska, off shore and in the north central part of the country.
John Z

This has come up several times and the difference between Imperial and US gallons is always a crowd pleaser. Yours is about 10% less, although I'm sure there is a Texas gallon that's the biggest in the world. I have posted before but our tuned B with o/d and the ST front spoiler never drops below 25 which would be round the back lanes in a bit of a hurry through at least 35 including some main road is normal, up to an amazing 44 in cold damp conditions at an indicated 65MPH on a deserted autobahn. On that occasion I stopped the car and filled it in Holland in case the fuel gauge had failed! These numbers agree with others here in the UK and adjusted as above with US numbers. It does show just how much better cars would be if they had not gone off down all the marketing and political blind alleys that result in them weighing 2 tons and having catalysts fitted ,because of the total amount of exhaust emmisions caused by cars weighing 2 tons plus a total failure of public transport policies
Stan Best

Guys, my 74 MGB GT with a factory low compression engine with 112000 original miles on the clock consistently gets 25 miles to the gallon or roughly 30 US miles to the gallon on the low grade fuel available at the pump in around town driving. It gets as much as 32-35 miles to the gallon (CDN) or 38-40 miles to the US gallon on the highway in overdrive. With fuel in our area running at approx $6.90 per cdn gallon, the GT gets used most of the time. As if we need a reason to drive them!

Brian Smith

Werner,How do you like those harden seats?I put them in my 1972MGB(havent fired it up yet)and also Stellite valves(sp).Comments???
Rich Osterhout

I just put the hardened seats with Stellite valves on the car about 2 months ago. No complaints.

The primary reason I had a valve job is because valve #8 (exhaust) was recessing and I was getting coolant leakage at the head gasket by plug #3. Other than that it was running fine. I suspect the valve was recessing because as an experiment I was running very lean (16:1 AFR) for a 1500mi highway run.

Is the US gallon larger than the Canadian gallon? You calculated higher miles for US gallon
werner haussmann

Werner,Thanks,I just did a complete rebuild of the motor last year,and put them in because of the unleaded gas issue.Right or wrong.... Who knows??The motor isnt back in the car yet.....Getting it acid dipped and some body work finished the in she will go.Thanks again,Rich
Rich Osterhout

Thanks Werner, I did get it wrong. The figures for the imperial gallon are correct for my MGB as I get 25 mi/gal regularly around town and from 32 to 35 on the highway. The US gallon is actually smaller than the imperial measure so it would tend to show lower miles per gallon. I recently installed an overdrive and am hoping that these will improve for highway driving.

Brian Smith

27 pretty consistently with my 67 BGT with OD and stock motor with 89,000 miles.

RW Got to come across the border. You can still find a lot of premium without alcohol in WI. I figure it runs me about $1.80 more a fill up for premium.

A recent PBS documentary stated that 1 gallon of oil produces 1.2 gallons of ethanol.
Fred Doyen

Fred - if what you wrote is literally true, then ethanol (and I take it you mean corn-based ethanol) is a net waste, as ethanol only contains 2/3's the energy of the equal volume of gasoline. 1.2 gallons of ethanol would have about the same energy as 0.8 gallons of gasoline/petrol.

Are you sure you're citing them correctly? PBS would probably select the most optimistic numbers, and it might be in BTU's. But if it is gallons, then we can see why it doesn't work. Even if you do get a 20% bump in energy, it's far better just to drill directly for oil in Alaska or off shore or get it from the oil shale out West. Alot more "bang" for your gallon there, and fewer starving children.
John Z

PBS is also on the global warming bandwagon.

A 2007 study found that the average Australian walks about 900 miles a year.

Another study found that Australians drink an average of 22 gallons of beer a year.

That means, on average, Australians get about 41 miles per gallon
Barrie Egerton

Barrie - your mileage may vary!

That "average" Australian - would that include all the women, children, men and kangaroo? 22 gallons a year is less than half a gallon a week.

I think ethanol is a fine thing, just not for my car.
John Z

This thread was discussed between 11/07/2008 and 25/07/2008

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