Longer Fan Belt Revisited - Cheap Hp?

[DeutschMark]

I was searching the archives and came upon a thread that discussed using a longer belt such as a 9.5 or 10 x 750 belt, slowing the fan slightly for reduced parasitic loss. 7hp @ 5500rpm was claimed.

Mufflers and clever HP gains

Here in Michigan, the highest I've ever seen my oil temperature was just under 210 degrees. This was on a 3 hr trip in 90+ degree humid weather with the A/C on. On a cooler day at the track, I never even reached 200. I think I could get away with this here, where the climate is cooler most of the year.

Does anyone have any experience or comments on increased head, cylinder, or oil temperatures?

[Grady Clay]

DeutschMark,

Yes, it costs power to keep the engine cool. Contrary to your proposition, there is a net power gain with increased cooling.

Oil temperature is a poor indicator of the important temperatures in the engine. In fact the oil temperature is the coolest in the engine. The critical areas are head and cylinder temperatures. These effect the power by limiting the air/fuel charge in the combustion chamber. Even more important the high temperatures shorten the life of the engine.

When you hear complaints of worn valve guides, the reason is excessive temperatures.


If you want to increase power for DE, try the “Rubbermaid Solution”.


Here in Colorado we have thin air (barometer 24” Hg) and it gets hot & dry in the summer. This has us at the forefront of engine cooling. Here it is critical. At sea-level it is merely VERY IMPORTANT.

Porsche reduced the cooling (’75->) to meet German noise requirements. The effect was to give 2.7s, SCs and Carreras too little cooling. All of these need the 1.82:1, 245 mm fans IMHO.

This is the reason why we (all Porsche racers) were at a disadvantage in the ‘70s against the Datsun 240s. They had water cooled heads and could use 14:1 CR. 10.3:1 was pushing it with air cooled heads.

The water cooled 911s have this better under control. Well, maybe.

Best,
Grady

[DeutschMark]

Thanks Grady. My oil temperature stays low much of the time and I'm surprised how cool the engine feels after a spirited drive. Hopefully this means a long service life before a top-end rebuild is necessary.