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MG MGA - Observations on comfort and economy

Forgetting about fans and fuel lines ...the last two days have been the first major outing up into the Snowy mountains for a long time ....and since then I have done many mods incl. fitting a hard top and the Judson.. So far only one way going up into the hills ...
I did a close measurement of fuel economy ..filled up close to home and just refilled in Jindabyne , NSW . Refill took precisely 33.1 litres.
On the car milometer I had covered 288 m and on the gps 266.6 m...converting latter to km gives 426 .
Car was therefore doing 7.76km/100km or 36.4 ukmpg or 30.4 us mpg .
Very pleased....the way I have set up the Judson seems to have improved the economy ....but not too much extra umph. I also read that the hardtop improves economy.
..and on the latter subject the cockpit was a lot more comfortable....I like driving open in cool or coldish weather ..but when over 30c on a long drive BBQ yourself...
Neil Ferguson

Brilliant. I've driven those roads and to be honest I can think of few better ways to spend a day or a litre of fuel.
A Bowie


They look impressive figures but it is very difficult to judge mpg precisely on the one tank load. Just the odd litre or two difference in fill-up can make a huge difference. Was the level PRECISELY the same after each fill up? i.e. did the pump cut-out click off at the identical level etc? A true average reading can only be judged after a dozen refuels or so. The single reading will be just a guide, and brought down significantly with urban driving. I have a spreadsheet on my consumption since 2006. It averages out at 23.78 mpg (UK). A typical run of your length gave me 32.77. However, at the time it only increased my average from 24.01 to 24.21. When I look in detail at the figures I can spot the times when the tank has not filled to the same level.

Out of interest, can the supercharger improve consumption if the foot is not always flat on the floor?


Steve Gyles

Steve..agree the more the merrier. However I am well aware of how small descrepancies alter calculations. I fill to a visible mark in the tank pipe ( very slowly towards the end) and I use gps plus cross check with Google for distances.. The info is fairly good and surprising given the topography.
I also drove to and from Melbourne not so long ago ( post Judson) and recorded about 40 mpg over that nearly 1400 km trip using same measuring standards.
Re Judson and economy I have two comments..
I discarded the basic fixed jet Holley that came with the Judson kit and use a large much more modern SU. . I designed a new manifold to attach. It to the compressor and read up a lot about correct velocities for entrainment to get the x section right. I also used a cylinder viewing scope and tried a fair number of needles before ending up with one that kept reasonable cylinder colours over a engine speed range..
The compressor is always working and reducing vacuum even when the hoof is not on the floor ( unlike a turbo) and I believe could increase efficiency by better air/ fuel mixing and also better cylinder burnt gas sweeping .
So yes I do believe a supercharger and good carb set up can improve efficiency .
I got about 30mpg with my old twin set up.
Ps not too much urban driving done where I live . Roads are not like Europe . Eg on the drive from Melbourne to Narooma where I am living there is only one set of traffic lights in the last 400 km ...A pedestrian Crossing in Narooma .
Neil Ferguson


That certainly accounts for the good MPG. My long journey was on the M55, M6 and M25 motorways with about 5 miles at both ends of urban driving. Surprisingly only 2 sets of traffic lights and one pedestrian crossing, but there any comparison ends - many traffic queues and thousands of cars and lorries.

I have spent countless hours over the years toying with the fuel/airmix, timing etc. car goes like a rocket but never bettered that 33 mpg. I just put it down to enjoyment.

Steve Gyles


Do you have a drawing for your new manifold? Would like to add it to the Judson modifications on my site. They go MUCH better with the SU than with the Holley, and I too noticed a MPG improvement. But performance wise mine goes like a scalded cat - a before and after test drive with a friend just amazed him with the change in performance.
dominic clancy

Dominic.....will dig it out when I get home . It is only ok for RHD cars as steering interferes on Lhd .
The Skinners Union carb design is a miracle. And way ahead for its time . The continuous orifice size adjustments over the whole speed range make it arguably as good as EFI ..if it is set up well.
It may be fading memory but I never did get the super umph I expected from the Judson and the boost has not been higher than 3psi . I have a booster gauge in the cockpit.. It is boosting ok but not in a neck breaking way. When I have the time I am going to take the unit off and reset everything. ..but it was a pig getting it in.
Neil Ferguson

Given I find nothing obvious re supercharger I wonder whether it needs to spin change pulley . When you have a chance could you measure your drive and supercharger pulley diameters...
Neil Ferguson

Will do. The trick to getting it in is to mount it as a unit. That is to say, mount the carb and carb manifold to the bottom of the unit first. Fit the head manifold to the head. Then you put the three bolts through the head manifold and gasket and get a second pair of hands. Slide the whole unit into place, making SU you have the jockey assembly in a position to clear the radiator neck and push down to later tension the belt. At this point you can offer the unit up to the head manifold and your other hands can then start the threads on the three bolts. On my car (LHD) I can rest the heat shield for the SU on the steering column and start the front bolt myself, then pivOt on that to start the rear one.

dominic clancy

Dominic..many thanks for advice..I need it.

A correction....I mentioned I drove About 1400 km with the Judson and got 40 ukmpg...I checked back and it was actually 36.5 ukmpg almost spot on with latest .
Neil Ferguson

Just got back home. For those in oz with the knowledge I drove back down from Perisher /jindabyne and the Snowies via Bombala to Pambula ..spent a night ..then drove up the Sapphire Coast Road ( not Princes ) stopping to look at the many great beaches, Tathra ocean jetty and the tremendous geology of the this near vacant forest coast..all superb.
Mga did 7.46 lt/100 km so a little better than on the way up the hills.
I just checked everything and lost about 2.0 litres of coolant and used 1.5 litres of oil ( bringing latter back to H on stick). Must be a slight water leak.
Oil consumption seems to have increased considerably . . I travelled just under 800km so consuming oil at nearly 2 litres per 1000km .What is considered normal ? Should I be concerned ? There is no blue smoke at any time .
Neil Ferguson

Dominic..My Judson Pulley wheel is 102 mm diameter at the rim.
Neil Ferguson


I have forgotten what engine you are running. It seems a lot of consumption on both counts. I guess you may be losing a bit of water through one of the hose joints as you have had them apart during your recent work. Do you run an expansion tank system?

By comparison in my 1800V I never have to top up water and oil between the annual servicing.

Steve Gyles

Steve...the water thing is most likely trivial as you indicate. I have not reinstalled the non pressurised overflow bottle yet and this may alleviate half above ..but I have a leak and will find.
Re oil .... I started owning cars in early 60s ( and motor bikes ) and they all consumed oil or leaked.....but there was a limit to the latter when it became an indication of things ugh. You have a miracle car . Pleased to see no oil drip leaks yet from mine after all the recent work and hard drive ( incl prop shaft removal from 5 speed box to remove broken grease nipple ).
Checking oil and fuel was a routine in a petrol station in the good ole days ( and is again) .
I read up loads of bumf in last few days including from the wanderlust Barney Gaylord . He seemed to indicate not to get up tight until over 1 quart per 500miles so I am just above this .
I have not had the head off my standard 1600 for 20 years .....I bet it it is the valve guides ! I feel a load of work coming on with this combined with a Judson removal and make over.
I have never had any work done on the seats post lead removal but always used a additive in the fuel..but now in the Judson lube drip. It will be interesting to see if the seats have receded at all.
Neil Ferguson


Sorry if I mislead you slightly with my oil consumption. Obviously, it does use some, but not sufficient to require a top up during the year. Certainly no leaks. My drip trays underneath are still clean after nearly 5 years in my present house. Hope you find the sources and not too much hassle! I guess it will be the supercharger out if its valve guide wear?

Steve Gyles

The water loss was trivial. The drain valve was leaking. I took it off cleaned it and greased it and replaced and has been holding . If it leaks again I will plug the hole and get a new one.
I have found a potential reason for oil loss .....When I put my Judson in I used the nozzle on the SU HIF44 for connection and hooked it up with hose to the existing draft tube ( cut short ). It had a long U tube in the hose connection and it was filled with oil so something strange has been happening. Have gone back to original draft tube arrangement and capped the SU back to basics and will see !!
Neil Ferguson

Crank is 105mm at rim, Judson pulley is 92mm at rim
dominic clancy

my 1850cc stage 1 tuned 3-bearing doesnt often get into the 30mpg area unless I drive stop driving it like I stole it!
25 to 28 mpg is the most usual figure and I am expecting a little worse when the 1950cc engine is fitted.

When I first got the car I once drove 280 miles before re-filling the tank and was a little surprised when I managed to get 9 gallons and 7 pints into the tank. I probably had only 5 miles of driving left and so it was a close thing.

So I now tend to begin looking for a petrol (gas) station when the odometer gets to 200 miles which hopefully leaves me with just over 2 gallons in reserve.

On the subject of comfort Neil, is the hardtop less hot, less noisy and more comfortable than the soft top?

Although it does get warm inside, my main issue with the soft top is the visibility out of the sidescreens. I have to duck down to see out of the side windows, otherwise I can only see as far as the edge of the road. (being 6ft 1" causing problems again)

I have even wondered if it would be possible to fit some kind of transparent panels into sides of the hood in the section immediately above the top of the sidescreens to make it safer for me to drive. They would have to be made of the same transparent flexible plastic as the rear window panel.

I would also make the rear window into a zip out panel that I could roll down to promote airflow through the cockpit.

Perhaps next years project?


Colyn Firth

Colyn..I am 6 ft 2in and from recent comments you seem to have both longer legs and a longer torso than my fair self??? is there a third portion of your body that I have not got here down under?

I have just finished a retune of the car and found it running lean ..resetting it right now using guns colour tune . I have only a single SU HIF 44 with the judson so tuning is relatively doubt my fuel consumption will increase ( and maybe a little more umfh) but not by much and ..but not compared to the throbber you drive.
I have also just bought a Gunson Exhaust CO analyser from Amazon UK ( I had a load of gift cards for this bunch for my recent birthday it for just under 100 quid delivered to Oz so pleased.) . It won't arrive until mid march but reports i have read are generally complimentary . After reading up a load on exhaust gas I expect to be looking for about 2% CO or thereabouts...see general chart I came across below. Any body on the site had any experience with one of these?

Re comfort I found sitting in the shade under the top much much more comfortable than open or soft top driving.....loads of air around ..and I was driving a long time in greater than 30c temps..My head is about 3cm from under the lid and I have to go into the foetal position to get in but once in ...snug as a bug...
Visibility about the same as the soft top ..but I have door top mirrors and find them excellent and easy to see .
The roll up rear window sounds a simple job for any car upholsterer ...the windows over the doors sound like it could look messy...

Neil Ferguson

This thread was discussed between 11/02/2016 and 02/03/2016

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