There seems to have been quite some interest in Don' Arnott's article 'Back to Basics' (June 2007 Enjoying MG) & Vic Butler's comments 'Engine bay heat' in the letters coloumn (August's copy) with poor running, especially from modified/tuned 'B's. From our workshop experiences this is all so common & can be down to many factors but worn camshaft lobes/followers are certainly very common, causing all sorts of problems! The choice of camshaft when desiring more power, torque or just an improved tickover seems challenging with the wide range of profiles available for most 'A' & 'B' series engines as used in Midget & MGB. Our experiences show that it is the camshaft profile that really determines the engine chacteristics. The standard cam & mild road/fast road such as 714 & 715 offer little in the way of refinement. More duration with these tuned profiles causes an erratic tickover, hotter combustion temperatures & all the problems & fustrations associated, such as fuel evaporation causing missing & poor starting when hot & jerky throttle action in slow moving traffic!


Our advise after 18 years of experimenting with different set ups would probably be a choice of two camshafts for road use. The first is a high lift type eg the 718 or even Leyland's 770 (especially good with 2ltr engine) where the tickover is a little lumpy, less so with 718 & better still with electronic ignition, superchip or ignition management system but not erratic & offering a very good spread of power throughout the rev range, free revving to 6500rpm. With larger capacity engines, gas flowed, ported, large valve cylinder head & 45 DCOE Weber or 1 3/4" SU's, freeflow exhaust manifold, big bore exhaust & performance distributor results show some 40%+ more usable power. Scatter cam profiles are also available offering further increases in power but the tickover suffers again. The noise though great with stage of tune in a 'B' with hood down motoring is not our choice in a GT unless combining track days as interior cockpit resonation & boom is normally too much for one's other half on anything but short journeys.

Another choice is a mild road cam. We use one different to others with less duration than 714 but with more lift than 715 & 6.This gives a tickover similar to an Austin Cambridge (my dad had one which i learnt to drive in) or a Morris Oxford with marginally better torque & power than a standard 'B' cam. Everybody seems to love its characteristics when compared to the standard & tuned profiles as it feels so much better than the figures suggest. The other benefit is that it runs as smoothly with standard SU's as it does with larger 1 3/4" carbs or Weber 45, with choke operation noticeably smoother too. This cam is so versatile, it tolerates a range of ignition timing & the engine is not prone to run-on unlike standard & other cams. Engine run on (pre ignition) is made worse with an erratic tickover. If you turn the engine off with the revs on a slight increase the engine will run on but has tendency not to if catch when revs are dropping. Good tip is to depress the clutch pedal just a little as turning the engine off as a small amount of drag lowering the revs a fraction can stop run on. We also use this mild cam with or supercharged spec, with standard 18V cylinder head,exhaust & cast iron manifold its giving similar gains to stage 2 tune with just 5psi boost & 99 octane super unleaded, halting modern turbo diesels from out-accelerating the evergreen 'B'. Even with 2-3 psi boost the benefits are very noticeable on the road. Higher boost over 6psi requires either compression changes or a better solution water injection, allowing for greater power gains of 50%+ with a flat torque curve & the smoothness & quietness that a tuned or stage 2 engine will never give. Further lift with roller rockers & higher boost is always very tempting before diminishing returns sets in but with the proximity of the two centre exhaust valves on these cylinder head's generating more heat &generally poor flow characteristics it is best not to ask for too much & push the boat out too far for road use!

As for fuel consumption this is normally determined by set up & how driven but generally speaking things being equal the use of standard carbs or supercharger seems to return similar fuel consumption with better results with supercharger set up on a run followed by twin 1 3/4 " SU's & Weber returning the least.Obviously this needs to be put into context regarding added performance & cost of modifications etc. With CO & HC emission levels the Weber emits the least at tickover followed by the single 1 3/4" supercharged carburettor,twin 1 1/2 " SU's & 1 3/4" special tuning SU's last. At the end of the day if you really want your engine to scream you need both lots of duration & lift from the camshaft, there's just no substitute as we can't unfortunately modify for variable valve timing. So in conclusion tuning parts do offer benefits for everyday road use, it is just so many seem to mismatched, incorrectly set up, ignition advance curves too step, incorrect carburettor needles etc & some horrible camshaft profiles spoiling what is an otherwise good engine in a great car!

Russell Lloyd