Performance Tuning the B Series Engines

1 Performance Tuning the B Series Engines. Written by Stephen Strange. There are few mysteries about the engine employed in the MGB. This is not a state-of-the- art, fuel-injected, dual-overhead-camshaft, four-valves-per-cylinder, variable-valve-timing, microchip-controlled technological wonder, festooned with interconnected sensors and switches, all linked to mysterious black boxes, and guaranteed to intimidate and befuddle NASA engineers. This is something more along the order of an archeological relic from a bygone age of motoring, something that was intended be maintained by its owners with simple hand tools and to also be produced in versions that were to be installed in farm tractors and diesel-engined taxis. In today's world of laser weapons, it seems as anachronistic as a sword.Crude, yet still highly effective in a very intimate way. Keep in mind that the design of the B Series engine was started in August of 1944 when it had become obvious that the defeat of Germany was close at hand. Lord Nuffield gathered together his three top engine designers, Eric Barham, Jimmy Rix, and Bill Appleby from his engineering staff at the Austin Design Office and gave them the assignment of creating a pair of all-new engines that would enable the company to get a jump on the competition in the postwar market. The ultimate result was the A Series and the B Series engines. The cast iron block was designed to the British Standard (BS) 1452-17 in which the coolant jacket extended down to just below the level of the piston rings when the piston was at Bottom Dead Center (BDC). Flow-cast of grey iron, the block was allowed to slowly cool so that graphite crystals would form within its matrix, assuring reasonable machinability. During the era in which the B Series engine was designed, hydraulic tappets for automotive applications were still in their technological infancy; therefore, the engine was designed to use solid chilled iron tappets. Setting of valve lash clearances was accomplished by means of a simple manually adjustable ball end and jam nut mechanism on the lever end of the rocker arm. The majority of the oil from the rocker arm assembly was allowed to drain down the pushrod passages in order to lubricate the upper ends of the tappets and then through two holes respectively positioned in the bottom of the tappet chest between cylinders #1 & #2 and #3 & #4, thus bypassing the lobes of the camshaft. This simple approach offered the designers the opportunity to wisely leave the camshaft exposed to the crankcase so that its lobes could be lubricated by a pressurized spray of oil emitting from the lower ends of the connecting rods. This desire to lubricate the lobes of the camshaft and the lower sections of the tappets dictated the thickness of the connecting rod big end. Adequate bearing support was then achieved by using a large diameter big end design. The engineers at the factory prudently decided that because the rather stout Renold camshaft drive chain had an even number (52) of 3/8”pitches (spaces between links), the sprockets were both given an even number of teeth, 20 for the drive sprocket on the crankshaft and 40 for the camshaft sprocket. This prevents any single roller of the chain from contacting the same sprocket tooth each time it makes a consecutive circuit, thus preventing uneven wear and consequent vibration, as well as prolonging the drive system's lifespan. Its Heron-type cylinder head incorporated the pistons into the overall combustion chamber design by featuring concavities in their crowns. It also made use of Weslake- patented combustion chambers, which were a marked advance beyond previous technology, allowing for superior air flow characteristics and fuel-air charge distribution while 2 permitting excellent flame propagation. The incoming fuel/air charge was directed toward the spark plug and away from the hot exhaust valve, minimizing the possibility of preignition and allowing less ignition advance to be used. The siamesed intake ports, like some other features of the engine, were largely the result of production economics. By using siamesed intake ports the intake manifold could be of efficient, yet simple design and thus still be relatively inexpensive to produce. In addition, the pushrod passages could be neatly situated between the ports, thus keeping the cylinder head and block as compact and light as possible. The placement of both the intake and the exhaust manifolds together on the same side of the cylinder head meant that only one mating surface needed to be machined, and fewer manifold mounting studs and their attendant threaded bores were required. It also allowed the distributor, oil filter, and generator to be placed on the opposite side of the engine for easier accessibility, thus greatly simplifying maintenance. There are also some distinct engineering advantages to this approach. By placing the intake ports with their cool incoming fuel/air charge next to the hotter exhaust ports, this area of the cylinder head is better cooled than it would be in a crossflow design, precluding warpage by enhancing heat transfer from the exhaust valves and thus extending their lives, although this configuration allows more heat to accumulate in the walls of the intake ports. This condition of radiant heat being detrimental to fuel/air charge density, it consequently reduces power output potential. Due to the relatively small surface area of the roof of the combustion chamber, the undersquare (small-bore long-stroke) configuration gives better thermal efficiency and thus better fuel economy, as well as providing a greater surface area on the exterior of the cylinder walls in order to minimize the heat transference problems inherent with the cast iron material that was chosen for the block to be cast of. It also gives better scavenging effect, thus extending the powerband. By requiring an inherently larger volume crankcase to accommodate the long stroke of the crankshaft, power-robbing "Pumping Loss" could be minimized. The cylinders were of the Wet Liner type, being directly exposed to coolant flow over their entire exterior surface area inside a large coolant jacket. The bore centers of the later larger-displacement versions of the engine could be located the same distance apart as those of the earlier, smaller displacement versions of the engine so that the later engine could take advantage of the designer's intent that it have an inherent "developmental stretch" in order to give later larger-displacement versions the potential to be produced on much the same tooling, thus keeping both Research and Development costs, as well as Production costs within reasonable limits. A high capacity Holbourne-Eaton positive displacement eccentric rotor oil pump was provided to supply the crankshaft bearings. These were 1.125" wide for the front, center, and rear bearings, and .875" wide for the intermediate bearings of the five-main bearing version of the engine. They all had diameters of 2.125", a full .125" greater than that of the previous 1622cc three main bearing version of the engine. This produced an almost unbreakable crankshaft with lots of overlap between its journals and counterweights. The main bearings were provided with exceptionally heavily gusseting as a diesel version of the B Series engine was to also be produced. This imparted exceptional rigidity to the block. The oil pump was driven directly from the camshaft by helically cut gears, minimizing noise output. Although the B Series engine design is truly a compromise, it is a brilliant one that modern mechanics recognize as being one that was far ahead of its time when introduced. It was further improved with the introduction of its five main bearing version. Certainly there were other new engine designs that were even more advanced in the mid-to-late 1940s, but this one was intended to be available in cars that ordinary people could afford to own and operate. In those days, that made it special, and its designers had every reason to be proud. 3 During an era when full race engines struggled to reliably produce 1 BHP per cubic inch, when the 18G Series arrived in 1962 it boasted 95 BHP from a mere 110 cubic inches, giving it a specific output of .864 BHP per cubic inch, and this was an engine that could reliably be used as a daily driver! In its heyday, it was impressive indeed. Pretty fantastic for a relic whose design is well over a half of a century old! A true classic engine for a true classic car! Everybody who is about to rebuild the tired engine of their MGB entertains the thought of improving upon the power output of this classic engine design. However, nobody wants to end up with a temperamental beast. Properly built with quality components and knowledgeably modified, an enhanced-performance version of this engine should last as long as an engine rebuilt to Original Equipment specifications. It should also be reasonably reliable enough to be used as an everyday car. Since you are rebuilding the engine, this is a good opportunity to do it the Peter Burgess way. As a former professional mechanic who has built custom engines, I can assure you that I have thoroughly read both of Mr. Burgess' books "How to Power Tune MGB 4-Cylinder Engines", as well as its companion volume "How To Build, Modify, And Power Tune Cylinder Heads," and that his theories are both sound and logical. His reputation as the MGB engine tuner is well deserved. His books should be in every MGB owner's library. His website can be found at http://www.mgcars.org.uk/peterburgess/ .

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