A special head for the M.G.-A

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72

 

H.R.G. light alloy head gives 8 b.h.p. Increase in the middle-r.p.m. range

The  M.G.-A sports car uses the B-series B.M.C. 1.4-litre engine in twin carburetter form. As this is a “bread and butter” engine which has to serve a number of different B.M.C. makes of car it has its limitations, peak power being 72-73 b.h.p. at 5,500 r.p.m. The B.M.C. engineers realise this limit and have developed a twin-o.h.c. head for this power unit, which lifts the maximum power by 36 b.h.p. in conjunction with a slight increase in engine swept volume, at the expense of noise, increased cost and, it seems, other disadvantages, because Motor Sport  has still not been allowed to road-test one of these cars, after being told last summer that the car had proved too unsatisfactory to be submitted to us.

Meanwhile, working independently, Godfrey and Proctor of H.R.G Engineering Co., Ltd., Oakcroft Road, Tolworth, Surrey, abetted by V. W. Derrington Ltd., have produced a far more simple and satisfactory method of increasing the power of the M.G.-A  through its cylinder head.

The H.R.G. head is of LM8 light alloy, weighing half that of the standard M.G. head, or less than a normal M.G. exhaust manifold. The siamesed inlet ports on the same side as the exhaust ports of the standard engine have been changed for four separate inlet ports of the same size, on the off side. A special combustion space is employed, with slightly inclined sparking plugs towards which the mixture is projected on the compression stroke, the sharply divorced inlet and exhaust valve areas of the standard head being largely dispensed with. The exhaust porting is unchanged and can be used with the normal manifold or, more advantageously, with a Derrington three-branch exhaust system. Flat-top h.c, pistons are available, together with better quality valves and stronger valve springs. H.R.G. find it advantageous to lighten the valve end of the rockers and Derrington has in hand lightweight tappets and push rods.

To revert to the H.R.G. cylinder head, this costs £58 10s. and comes complete with special stubs for attaching the normal twin S.U. carburetters to the four ports and a special spanner for the repositioned plugs. When installed in the car the heater is moved to the near-side. The special exhaust system costs £17 10s., the h.c. pistons £12 12s.

We recently spent a day at the H.R.G. works to check the claims made for this cylinder head. First we saw an engine fitted with this head run on the test bench, complete with dynamo, Derrington exhaust manifold and car exhaust system, but no fan. The engine had pistons giving a compression-ratio of about 9.3 to 1 and the S.U.s had BF needles.

Afterwards, under exactly the same conditions, a standard M.G. head was substituted, the only other alteration being to change the carburetter needles to GS. The power increase with the H.R.G. head was 8 b.h.p. at 4,500 r.p.m. and 7.1 b.h.p. at 4,000 r.p.m. The Derrington manifold is worth about 2 b.h.p. Incidentally. the engine “ran-on” when switched off, with the M.G. head, but not with the H.R.G. head. The latter weighs 16 lb. without manifolding, the former 32 lb.

Maximum power from the H.R.G. head with Derrington exhaust system is achieved at 5,500 r.p.m., when an increase of nearly 10 b.h.p. is obtained over the M.G. head with standard manifolding.

To complete the check we spent the following day driving an M.G.-A two-seater with H.R.G.  head, special cool-air inlet box and three-branch exhaust. Although running on comparatively soft K.L.G. FE80 plugs no trouble was experienced, even when crawling through the December fog, while subsequent experiments proved that the H.R.G. head renders the engine extremely flexible, a satisfactory top gear range of 10 to over 100 m.p.h. being available, an indication of efficient carburation and combustion.

Fog hampered performance testing but on a wet road the extremely creditable time of 9.4 sec, was recorded for 0-50 m.p.h. acceleration, two-up. On a dry road this could undoubtedly be reduced to under 9 sec. as wheelspin was excessive in bottom and second gear. The speedometer was, of course, corrected for this test, being 1.4 m.p.h. fast at 50 m.p.h. The standing 1/4 mile was covered in 18.8 sec. under the same adverse conditions. These times better those of the M.G.-A coupé  by 1.4 sec. and 1.0 sec., respectively, and are but 2.1 and  0.7 sec. slower than the equivalent times for the Twin Cam 1,588 c.c. M.G.  It became necessary to change up from second to third at just above 50 m.p.h. and thereafter the car fairly surged away in third, making us wish for better visibility so that acceleration checks could be made to higher speeds. We believe that up to 70 m.p.h. this H.R.G.-tuned M.G. will beat a normal M.G.-A by some 5 sec.

The car gave no trouble while in our hands and although as noisy, crudely sprung and difficult to enter as every M.G.-A, the engine proved not only very flexible, as has been said, but smooth and free from pinking or running-on, in spite of the 9.3 to 1 compression ratio. We understand that fuel consumption is, if anything, fractionally improved, the water temperature never rose above 160 deg. F. in spite of radiator blanking and, had the opportunity arisen, we think this H.R.G.-M.G. would have come within 10 m.p.h. of the Twin-Cam M.G., comfortably exceeding 100 m.p.h. And the hard, purposeful engine noise is that of the normal M.G., not being increased by the special head or exhaust manifolding.

Those who contemplate racing or rallying in M.G.-A’s next season should investigate these mods. Already some competitors have proved them advantageous.  —  W. B.