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30mpg MGB

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gray Graham Moore
CAMBRIDGE, CAMBRIDGE, UK   GBR
firstly, i don't have one....

but I thought i would start this topic following a recent comment made by one of our respected regular contributors ... that it is possible.

so many threads talk about power, but not many about economy.

I would very much like to hear your collective comments on build approach for a 30mpg MGB. one that's performance respectable. and without going mad on Carrillo con rods....

several folks have commented that MGB's are usually run rich. I installed a lambda sensor at quite modest cost and it is interesting to see how readings change - although how they translate to mpg (rather than power) is less obvious.

wondering what the big avoids are - 270 cams for example? twin SU? and where the mods SHOULD be targeted.

i realise that fibreglass here, aluminium there will always help, but diminishing returns usually determines that most of the gains come form well targeted changes. so i am thinking street car, street cost.

looking forward to hear what you have..

G

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riley1489 Avatar
riley1489 Gold Member Bruce H
Great White North, QC, Canada   CAN
1953 Jaguar XK120
1959 Riley 1.5 "King George"
1973 MG MGB
First off a good, clean solid motor, with good compression,
A distributor curve to match the above, ignition timing set to just before pinking. Carburetors set/adjusted properly.

Don't install oversize/over wide tires, keep correct air pressure in them. Correctly adjusted brakes and good condition wheel bearings. If a tourer keep the hood up. grinning smiley

The above will set you on or better to your goal.

B



Check your ego Amigo!

Steven 67GT Avatar
Steven 67GT Steven Rechter
Imperial Beach, CA, USA   USA
With what Bruce said I get 30mpg (US gallon).with stock 18V motor.



There are no bad days at the beach.

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tvrgeek Avatar
tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
I guess a complete MegaSquirt ignition and EFI system is a bit heavy handed, but it works.



Cogito ergo sum periculoso

Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
My roadster gave 32MPG (impg) on a trip stock and it does exactly the same with a worked engine and supercharger. I do the same long weekend away with the mgs from our club every year, for the last 16 years. Meet at the same servo to fill for the trip and compare notes as we go. Only driving at around the speed limit, and a rally at the venue but no fast stuff. Most of the cars are stock and a couple slightly worked. Mine is the only SCed. Its like a mini comp and sometimes, not always, mine is best. ( we all get around 30 mpg) Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine early in 2016 with high comp pistons and a few other nice bits. Started on the body late 2016 and found Its a lot of work and expense starting from scratch. Did the work myself, mechanical, body. paint etc all except the interior trim.
Finished and going well, great to drive and quick. Now has a nice 3.07 LSD.



Edited 1 time(s). Last edit at 2018-04-15 05:47 PM by Denis.

mgv8glen Avatar
mgv8glen Glenn Towery
Dover, DE, USA   USA
I can do 30mpg with the DVG weber (am going to the Austin Marina 1.75 S.U carb.), the rivergate kit with 280 ZX turbo 5 speed (.745 5th.). lighten flywheel, (20lbs), true 9-1 compression (have to use midgrade gas), 185-65-15 tires. Years ago I went from Dover De. to Oshkosh Wi. & back in 98 to 100 deg. temp. & I did 31mpg with the A/C on high.

HiPowerShooter Avatar
HiPowerShooter Gold Member James Booker
Lake Winneconne, WI, USA   USA
1973 MG MGB
First, it's impossible to define a "30Mpg" MGB...or any car really as a standard.

Habits, speed, weather, load etc...will all have an effect on the average(I'm assuming you're talking about averaging 30MPG) fuel economy. It's especially true of low HP cars such as these. An extra 200lbs in the passenger seat and 100lbs in the trunk will have a noticeable effect whereas the same load in something twice or three times the power will see much less of it.

You'd REALLY need to be a "balloonfoot" to AVERAGE 30Mpg on a consistent(not just one or two tankfuls) basis. You'd be basically empty and probably not live in hilly terrain.

I can average that and a bit more when I'm driving to my place up north and are just basically cruising at 62mph for 150mi each way. One or two stop lights but that's about it.

Overall, MY car is a 26-28 ON AVERAGE ride. That includes a combo of highway/city. I've been tracking it for the last two years. I never raise the top so it's pretty much all fairweather/top down driving. The engine isn't lean...plugs are where I want them so far as color. I have very good performance and no complaints really.

I really don't see these cars gaining much more over an extended period sample timeframe. IIRC that's about what they were designed to see new.

I've rebuilt the carbs, rebuilt the head, added oversize intakes, replaced the deep dish pistons with shallow and bumped the CR up to about 9.7-9.8:1 by decreasing combustion chamber volume...did a little porting work but that didn't increase my MPG much...only a little performance.

Just keep it tuned and maintained...don't think there's really any secret.



"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...

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Rod H. Avatar
Amity, OR, USA   USA
1964 MG MGB
1968 MG MGB GT
I used to get 30mph (US gallons) with both my MGBs on highway trips. The roadster has done a bit better a few times.



I can't understand why people are frightened of new ideas. I'm frightened of the old ones. John Cage

'63 MGB
'68 MGBGT
'80 VW Vanagon Kombi
'09 Mazda 3 with 5 speed manual

course2kid Jeffrey Johnson
Fountain Valley, CA, USA   USA
1979 MG MGB "Lucy (Lucifer)"
Denis, out of curiousity, have you ever checked your mileage on a tank where you are just doing around town driving?

I only get about 22 mpg, but, for any given tank, most of the driving is 15 minute hops around town with lots of red lights and a few stop signs plus maybe 1/4 of the tank spent on the freeway going 65 mph. I should note that, because I live south of LA in the vast suburban sprawl of 45 mph, multilane city streets, I generally accelerate fairy hard off every stop light and spend more time idling in traffic than folks that live in less congested areas.

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mgv8glen Avatar
mgv8glen Glenn Towery
Dover, DE, USA   USA
I use my GT year round & run a 195 thermostat year round) & I have seen 15-18 mpg in the very cold going to & from the shop @ 2 miles each way through town. With a BIG piece of cardboard covering sometimes all of the Radiator to keep heat in the car & the temp gauge close to the normal I will do 27mpg on a trip, in the cold ( 15-25 deg.).

Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Jeffrey I live in the sticks and my nearest neighbor is a mile away so definitely no comparison. The odd time I get to the city it would be similar to yours. The traffic in our cities is bedlam. I stay away from them as much as I can and if I have to go I use my truck. Really love the view in the rear vision mirror on the way home. Also we use imp gal which is bigger than the US gal. Actually we use metric. Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine early in 2016 with high comp pistons and a few other nice bits. Started on the body late 2016 and found Its a lot of work and expense starting from scratch. Did the work myself, mechanical, body. paint etc all except the interior trim.
Finished and going well, great to drive and quick. Now has a nice 3.07 LSD.

RAY 67 TOURER Avatar
RAY 67 TOURER Ray Marloff
Fort Bragg, CA, USA   USA
1967 MG MGB "My Girl"
I've got a supercharged 1865 cc engined '67 B. Slightly modified for higher compression and better head breathing. It's got an LH overdrive 4 synchro transmission and regularly delivers 28 to 30 mpg. Very reliable and a blast to drive! RAY

course2kid Jeffrey Johnson
Fountain Valley, CA, USA   USA
1979 MG MGB "Lucy (Lucifer)"
Thanks Denis!

chris Avatar
chris Platinum Member Chris Roop
Pendleton, OR, USA   USA
My 30+ mpg @ 70 mph car was an early 70's (72?) that was built as a stock car excepting the wheels and engine. It had o/d which helped. The engine may have been an earlier block, but was outfitted with HC pistons, 18v rods, pushrods, and lightened lifters sitting on one of the last Crane fast road cams before Crane folded. The head was ported and polished by Sean Brown (and is featured on his website). The carbs were the new ones from Burlen and came perfectly adjusted; imagine that! The distributor was rebuilt and recurved by Jeff Schlemmer. Exhaust was the big bore stainless from the company that Moss used to sell, I forget the name. And, it ran on regular gas.
This may have been the one with .060 pistons.



Edited 1 time(s). Last edit at 2018-04-16 10:46 AM by chris.


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gray Avatar
gray Graham Moore
CAMBRIDGE, CAMBRIDGE, UK   GBR
perhaps it's something to do with your long roads, but after an imperial to US conversion, most folks i have conversed with are generally more in the 23mpg (28 imperial), and that concurs with the absolute best i got over 2 tanks (per-supercharger) after driving sooo carefully for 3 weeks.

whilst i totally recognise that driving style contributes a lot to which way mpg goes, there is still quite a difference - 30%. if i suggested i had a 36(i)mpg MGB, folks here would be in disbelief.

G

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