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30mpg MGB

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Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Graham your old style 35 type auto even at its best has close to a 10% slip, or a hydraulic drive ratio of 9/10 in the converter. Hence the bigger diff ratio to help make it up but it does make smaller cars struggle and dose not do the mileage a favor. 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.

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pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
In reply to # 3717766 by gray 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

I would guestimate I see 30 mpg Imp on long trips but I've never checked. I know I can reduce it to about 1/2 that hooning around.

Getting 36 mpg Imp from an MGB is really remarkable. (30mpg US = 36 mpg Imp) It works out to 7.8 litres /100 kilometers... about the same as a 2017 Hyundai Accent. https://www.guideautoweb.com/en/makes/hyundai/accent/2017/specifications/l-sedan/

My Fiat 500 with its 1.4ltr multiair engine gets 7 ltr/100km average, or 40 mpg Imp... just 4 mpg better than a well tuned 50 year old MGB. That doesn't seem right... does it?

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.

Paul755 Paul H
Richmond, VA, USA   USA
1974 MG MGB MkIII
1979 MG MGB MkIV "Nemesis"
Its how you drive it. I hammer the snot out of my B and get around 18 - 20 mpg smiling smiley. If I wanted to be sensible I could probably get 30 mpg, but why ? In N.VA gas is $2:55 a gallon, I'd rather drive my B hard and have some fun than save gas money. Just my opinion only, we all have different priorities.

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njlwa Avatar
njlwa Gold Member Norm Leech
Deer Meadows, WA or S. TX, USA   USA
1974 MG MGB GT "Sea Bee "CB"
1975 MG MGB "Arby II"
2001 BMW Z3
My 67 and 74 GT get ~33MPG. Mostly Hiway both had OD.



"Some people try to turn back their odometers. Not me, I want people to know why I look this way. I've traveled a long way and some of the roads weren't paved "

spikerj Avatar
spikerj Josh Spiker
Provo, UT, USA   USA
1973 MG MGB MkIII "Little Red"
I’ve noticed my stock 1973 B gets between 20-23 mpg in city and 27 mpg on the highway.

nickj Avatar
nickj Gold Member Nick Jenkins
Novato, Marin Co, CA, USA   USA
1970 MG MGB GT
1972 MG MGB
I've never understood how so many people get better than 25 mpg from an MGB. I've had many M.G.s, and the best of them got maybe 23 mpg. And that was a Midget. 20 mpg is more normal, even with white plugs.

Years ago our club had an economy run. By driving what I would consider dangerously, I managed 28 mpg. But that was it. I just don't get it.

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
In reply to # 3717999 by nickj I've never understood how so many people get better than 25 mpg from an MGB. I've had many M.G.s, and the best of them got maybe 23 mpg. And that was a Midget. 20 mpg is more normal, even with white plugs.

Years ago our club had an economy run. By driving what I would consider dangerously, I managed 28 mpg. But that was it. I just don't get it.

A spanking new 2018 Mazda Miata gets 33 mpg highway.(US gallon) It's about a 2400 pound convertible... like a B. Hard to believe a 50 year old MGB can match it.

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.

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nickj Avatar
nickj Gold Member Nick Jenkins
Novato, Marin Co, CA, USA   USA
1970 MG MGB GT
1972 MG MGB
Adrian, I used to get 28-30 mpg out of my 1.8 Miata all day long. Computers. Hard to beat.

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
A Miata GT would be kinda cool... don't you think?

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.

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Rod H. Avatar
Amity, OR, USA   USA
1964 MG MGB
1968 MG MGB GT
Best we have ever got with our Mazda 3 is exactly the same 30mpg as with the MGBs. Driving the same way...long trips driving safely and conservatively with the traffic on freeways and secondary roads.



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

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
What I have read on this subject is that we can run leaner than a modern car at cruise because we have no catalytic converters. No idea if this is valid... just putting it out there.

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.

Rod H. Avatar
Amity, OR, USA   USA
1964 MG MGB
1968 MG MGB GT
In reply to # 3718061 by pinkyponk What I have read on this subject is that we can run leaner than a modern car at cruise because we have no catalytic converters. No idea if this is valid... just putting it out there.

Adrian

Adrian, this article might be of interest to you.

http://www.autotap.com/techlibrary/catalytic_converters_and_o2_sensors.asp



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

chris Avatar
chris Platinum Member Chris Roop
Pendleton, OR, USA   USA
Back in the 70's, I was tickled with 25 mpg out of my bug eye until I was in this shop when another guy brought his in and complained that he wasn't getting his usual 40 mpg.


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NOHOME P P
O, ON, Canada   CAN
1967 MG MGB GT "Maggie (GT From Hell)"
The MGB was rated at about 25 mpg from the factory when running US gallons. That was not bad for the day. In the hands of a skilled hypermiler, you might be able to get to 30 mpg with a stock car.

Start by moving to FL since it is the flattest state in the country.

Today's fuel has ethanol which packs less calories per gallon, so that means that all else being equal, the MGB is going to get less miles per gallon than when new. If doing this challenge, look for fuel that has no ethanol.

A set of blueprinted SU carbs is where I would start. You wont get the thing to idle lean unless the throttle shafts and fuel level in the jet is perfect. Very few are or ever were when new causing people to set the idle mix rich from the get-go. Since the SU does not transition to different circuits for different throttle positions, the rich idle mix is carried to the entire rpm range.

Have to give some thought to going down to a single carb; once again, if mileage rules over performance, the single carb will provide all the fueling you need at the lower rpm.

A rock steady ignition with a big enough spark to set-off a lean mix is a good idea. Maybe an MSD box?

Blueprinting the rest of the engine would be a big help and you might want to look into some of the anti-friction coatings that are available for the pistons.


Bumping the compression will help, but then the fuel will cost you more ( $0.60/gallon more in Ontario) so while you might gain miles, you lose dollars.

I am not clear on where a ported cylinder head would land in this game: On the one hand, removing any restriction in the pump is a good thing, but if the goal is to max out mileage, then I don't think you will be driving in any rpm range where the porting would come into play.

Maybe look into some of the miracle lubricant$ for gear boxes and rear gears. I know for a fact that the FRS benefits greatly from an expensive aftermarket lubricant in the gearbox, I put it down to less friction. Could just be a lighter wallet.

Like I said at the start... good alignment, 60 psi in the skinniest tires you can buy and some hypermiling driving techniques might get you to the 30 mpg club in a bone stock as-new MGB, but if you are hypermiling, everybody else on the road hates you and your life is probably not worth living anyways.

Pete

tvrgeek Avatar
tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
Instead or disagreeing on what a 30 MPG car is, I think the OP was trying to get something going on efficiency rather than power. This should lead to leaning the carbs, better advance curve, vacuum advance, synthetic lubes, tire pressures, gear ratios, aero issues etc.



Cogito ergo sum periculoso

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