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378 More on cooling a V8 engine bay Tony Lake (Flamenco Red 2489) from Northamptonshire has sent in some useful comments on the cooling issues raised in the recent note by the Canadian V8 enthusiast, Barrie Robinson, with his modified MGBGTV8. (Apr 08) We know that the times when the Factory MGBGTV8 cooling system is challenged are during sustained full throttle performance at low speed or when idling in traffic. In top gear at or near full throttle at speeds as high as one can achieve in the UK the system will cope because of very high ram air volume through the radiator. In lower gears climbing steep hills at wide open throttle for sustained periods cooling is found wanting, but it is very ambient temperature dependent. The electric cooling fan position in front of the radiator is a disadvantage for ram air supply as the fans offers quite a significant restriction. Also a pusher fan it is less effective than a puller fan located on the engine side of the radiator. The radiator grille is also a restriction as is the rubber bumper assembly. Some wind tunnel work in Australia on a Ford Falcon with an in line six cylinder engine reported that the cylinder block itself is another restriction causing a dead zone for air flow through the centre of the radiator, data showed that the cooling air velocity was about zero at that point regardless of vehicle speed. The MGB V8 layout will be no better and probably slightly worse. If you add in the limited space around the engine and lack of escape routes for hot air, then we should not be surprised that in hot weather the cooling system is a little stretched. Also anybody with K&N air filters has had to fit smaller needles to restore A/F ratio which means a small increase in maximum power, so putting more load on the cooling system at full throttle. The engine in Barrie Robinson's MGBGTV8 is modified: reprofiled camshaft, 10.0:1 CR, Edelbrock manifolds and four choke carburettor, say a 20% increase in flywheel horsepower over a standard Factory MGBGTV8 engine. Without knowing the actual performance or specific heat rejection at rated load and speed one cannot calculate the total heat rejected to cooling water but it is reasonable to assume a 20% increase over a factory engine in line with the likely increased power output. This neglects any efficiency improvements that result from lower pumping losses brought about by better breathing. The power required to maintain equilibrium on a level road at part throttle will be the same as a Factory MGBGTV8, his |
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challenge is keeping the engine cool under sustained full throttle conditions. Barrie has made some significant modifications that will reduce under bonnet temperature, the ceramic coating on the inside and outside of the exhaust manifolds and pipework will push some of the heat rejected to exhaust further down the exhaust system but it will still have to escape somewhere, more of the waste heat will emerge in the exhaust gas itself. The holes in the wings are a good escape route for cooling air. The aluminium radiator is interesting , this is a popular performance modification in the US and offers a strength advantage over copper/brass designs. Because of this the tube size is larger and they are spaced further apart with lower internal restriction for coolant and greater flow area for cooling air. It will reduce water pump suction restriction and allow more coolant flow round the block and more air through the radiator. The shorter water pump is a master stroke because it frees up the space to fit an electric puller fan which in turn unblocks the area in front of the radiator. His report also shows how important the radiator pressure cap is, that and some ethylene glycol in the coolant shifts boiling point to 120degC. I can't see a recuperator bottle in the engine bay, that is good idea to catch any coolant loss in the event the pressure cap lifts. In operation the package developed by Barrie Robinson is going to be pretty effective under full load conditions on steep hills compared with a Factory MGBGTV8, so it will be interesting to hear how he gets on travelling the "road to hell". Perhaps he can tell us about: gradient, road speed, engine speed, for how long full throttle was sustained, gear selected, engine temp, ambient temp and most of all whether his electric fan is ever active and also what actually happens in stationary traffic. For we Europeans the acid test this year will be the Swiss meeting (European Event of the Year 2008 in Switzerland) with plenty of overheating opportunities in the Alps.
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