Big Valve BHP

[Mick6186]

I have been reading the book ' Lotus, the Elite, Elan, Europa' by Chris Harvey and have found a passage which I hope somebody can clarify. In a section regarding the release of the Big Valve engine the passage talks about the valve sizes, cams & carbs of the engine and states " In this form it gave 126 bhp at 6500 rpm when measured at the propeller shaft ( rather than at the end of the crankshaft), which compared favourably with the SE engines 101 bhp at 6250 rpm when taken at the same source".
Bearing in mind transmission losses through the gearbox ( which I believe can be in the region of 8-10%) this passage suggests the Big Valve engine produces considerably more than the accepted 126 bhp when measured at the crankshaft.

[msd1107]

If the transmission is in top gear, the only losses are bearing losses, which are quite minimal.

If the transmission is in gear, you have two gear mesh points, plus extra bearing losses.

The greatest losses are in the differential, which, being hypoid, has sliding losses and can amount to as much as 4% or so.

If you are interested in minimizing losses, roller bearings can be replaced with ceramic rollers. Races can be ISF processed (as can rollers). All sliding points can be ISF processed. Gear teeth also, or even RF85 (http://rf85.com/F1RaceTEck.pdf) at greater cost. It just depends on how much money and labor you want to throw at the problem.

The same process can be extended to the engine. You can pick up quite a bit of HP, but the process is complicated and expensive and different people take different paths. Just look at F1, which had a largely frozen engine spec for years but had regular performance improvements.

I rather suspect the 126 HP figure is a corrected BHP figure taken at the crankshaft. Lotus would hardly want to publish a lower net figure.

David
1968 36/7988

[au-yt]

The engine in my Sprint was rebuilt by QED and with the reciept was a dyno sheet with a recorded 127hp.

Graeme