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Extract from October's MGCC publication - Safety Fast

From the Sweated Brow

by Gerald Sweatman

Well, here we are again with another thrilling episode in the saga relating how to get more M.G. miles for your money. The unkind would say "sell the CGT automatic" but that's not the particular challenge I'm looking for! Develop and improve on what one has, must be the M.G. enthusiast's way of life. Besides which, once the smooth quiet pull of the lusty "six" has been experienced, it's not willingly given up.

In No.1 of this series the development of improved fuel economy was described via basic timing and fitting of the "Stromberg" spark converter. Since that time a full 36,000 mile service schedule has been carried out, with no noticeable effect on fuel economy. I took my own advice (No.3 in this series) and used the "clickadjust" tool plus feelers to confirm that there was but one thousandth of an inch of wear on seven out of the twelve rocker pads, so no cause for concern, and also to compare the points gap setting with the "Remax" gauge versus a dwell meter. The dwell as found was 37 degrees (6-cyl. spec. 33-37 degrees) and the feeler was on the tight side. Correcting for proper "feel" gave a dwell of 35 degrees, so the top bush wear in the distributor was within acceptable limits as the feeler gauge method gave the correct dwell result. That's one less thing to have to spend on.
In case you should wonder what that particular fuss was about, it has been known for a car to stop due to such extreme wear in the top distributor bush that the cam was incapable of opening the points inspite of them being correctly set by the static feeler gauge method. The dwell meter, being used while the engine is running, picks up all the errors. The car in question was not an M.G.. You would never allow this sort of thing to happen - would you?
A previous epistle urged the keeping of detailed records, and from mine something interesting has shown up. For a while I was puzzled by the differences between m.p.g. results on the outward and return legs of a long day journey, or by the difference between identical journeys (route, loading, and max. speed) made on successive days when weather conditions differed. Three cases illustrate this:
1. Shuttleworth return. 245 miles. Cool day, p.m. max. just under 60 deg.F.2-up, no luggage. a.m. outward: 28.9 m. p.g., pm return 22.5 m.p.g..
2. Abingdon return. 252 miles. Hot day, climbed to 80 deg.F by noon, p.m. almost 90 deg.F max. 1-up, no luggage. a.m. outward 27.63 m.p.g., return 22.57 m.p.g..
3. Droitwich return. 427 miles. Outward: p.m. max. 65 deg.F., wet. Return:p.m.max. 73 deg-F, dry. 2-up, with luggage. Outward:27.17 m.p.g., return next day was at 24.45 m.p.g.. Being thick, it took a while, but then the penny dropped. What seemed to be showing was the difference in ambient weather conditions in terms of the running efficiency of the engine as between the relative cool of the morning and heat of the afternoon, or between the two days of the Droitwich run, which were both made commencing at 1.15 p.m..

Then another penny dropped. It gets pretty darned hot under the bonnet of the "C". Just how hot was demonstrated by a fast test run at an indicated water temperature of 180 deg.F and a shade air temperature of 76.deg.F. A pocket thermometer taped in free air close to the air cleaner inlet went full scale 130 deg.F and then right on to the end of its capillary! A quick wander through some calculations showed that if air could be drawn into the engine at 76 deg. instead of a minimum of 130 deg F, a gain of 10.4% in air density and therefore in weight of charge drawn into the engine per unit time, would be obtained. In order to obtain this air pumping performance with air at 130°F an engine of 3215 ccs. would be needed instead of 2912 ccs., or alternatively a supercharger giving 1.58 pounds of boost would be needed! Hence, the "cold" fresh air induction arrangements which one sees on performance cars, and also the reason for intercoolers on turbos.
There seemed to be something to be gained for nothing if a "cold" air inlet could be arranged. About four inches in front of the "C"s air cleaner inlet is a blanked-off hole in the radiator diaphragm panel, used on U.S. spec. models for a forced air cooling inlet to the carburettors, so this blanking plate was removed. A small but definite improvement in fuel consumption was obtained.
Results to date are:
1. Period from purchase and
prior to any tuning:
4018 miles at 22.36 m.p.g.
Brooklands test run 20.05 m.p.g.
2. After re-set and tuning of
ignition and carburation:
3102 miles at 23.36 m.p.g.
Brooklands test run 21.95 m.p.g.
3. After fitting Stromberg
ignition device:
2441 miles at 22.52 m.p.g.
Brooklands test run 24.55 m.p.g.
4. After opening cold air inlet
to carbs:
423 miles at 25.75 m.p.g.
Brooklands test run 25.27 m.p.g.

This result is encouraging and hopefully one more small gain has been secured. The consistency and therefore value of the test runs as predictors seems to be confirmed. Future plans are to test Molyslip, then try Carbonflo (or whatever it is called now) to see if there are any benefits with leaded fuel by slowing down the flame front, in addition to those obtained from the Stromberg's high frequency series of sparks. This follows up on the letters of Reg Dennis of Farnham (July '94 and May '95 letters).
Finally, an electric fan will be tried although I think that this will very likely result in a speed restriction in very hot whether. During 1995's heatwave, motorway running at 70 m.p.h. at a shade air temperature of 90 deg.F pushed the engine gauge to 200 deg.F which is quite far enough for a 10 p.s.i. system in which plain water will boil at 239 deg.F. Something must be kept in hand for cavitation, scale fouling, and hot spots. At 70 m.p.h. the shrouded cooling fan is running at 5400 r.p.m. and it's hard to imagine an open electric fan providing more - if as much - cooling air flow, although removal of the fan shroud might just allow more air flow over the whole core. Elimination of continuous power drain and fan howl, and control of temperature surge at traffic checks would be worth-while benefits.
The road test (1968) consumption at 65 m.p.h. was quoted at 25 m.p.g., which is now being beaten on long runs. Just how poor fuel consumption can be, under adverse conditions, is shown by a series of runs of between 6 and 10 miles in length made at only 14.63 m.p.g., and a series of between 10-20 miles in length made at 20.33 m.p.g.. It just goes to show how long it takes to warm up an engine and transmission thoroughly.

Now, I wonder about water injection........
Gerald Sweatman.

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