mk1-forum.net

Had some Dyno-Time today and found out that the Engine is now delivering 6HP more without the Fan on the Waterpump...

Fanfaniracing wrote: ↑Sat Mar 29, 2025 9:50 pm Had some Dyno-Time today and found out that the Engine is now delivering 6HP more without the Fan on the Waterpump...

I found the fans needed between 3 and 5 HP to drive them, it depends on the revs and the particular fan.

Fanfaniracing wrote: ↑Sat Mar 29, 2025 9:50 pm Had some Dyno-Time today and found out that the Engine is now delivering 6HP more without the Fan on the Waterpump...

As a matter of interest, which fan did you use for this test?

I had the 11 Blade Fan 12G2129 on on the first Test.

Without the Fan the Engine frees 6HP more but i had the electric Fan on.

Next Time i will try without any electric consumer on...

Fanfaniracing wrote: ↑Sun Mar 30, 2025 11:18 pm I had the 11 Blade Fan 12G2129 on on the first Test.

Without the Fan the Engine frees 6HP more but i had the electric Fan on.

Next Time i will try without any electric consumer on...

But isn't the more important power figure the bhph-value?
formula: power [bhp] * engine lifetime [h] = power hours [bhph]
Probably not a very high figure in your instance

Now your asking i just figured out it's 11'000km i first tested the engine on the dyno in 2020 and it's still going strong.

I must admit i didn't use cheap ingredients though...

Since i always service it properly with fresh Oil min. once a Year also colant ect...

Fanfaniracing wrote: ↑Sat Mar 29, 2025 9:50 pm Had some Dyno-Time today and found out that the Engine is now delivering 6HP more without the Fan on the Waterpump.

Worth bearing in mind that the power sucked by most aerodynamic drags is proportional to the cube of the speed. If a fan follows this rule then 6HP at (say) 6000rpm would mean 3.5HP at 5000rpm, 1.75HP at 4000rpm, and 0.75HP at 3000rpm. Be interesting to see if the two power curves bear this out, or if fans are somehow exceptions to the rule.

In racing, every lost HP is crucial, even at the top end of the rev range. On the other hand, most mere road-going mortals are probably losing little by keeping the stock fan.

MagicWandWoody wrote: ↑Thu Apr 03, 2025 12:14 pm

Fanfaniracing wrote: ↑Sat Mar 29, 2025 9:50 pm Had some Dyno-Time today and found out that the Engine is now delivering 6HP more without the Fan on the Waterpump.

Worth bearing in mind that the power sucked by most aerodynamic drags is proportional to the cube of the speed. If a fan follows this rule then 6HP at (say) 6000rpm would mean 3.5HP at 5000rpm, 1.75HP at 4000rpm, and 0.75HP at 3000rpm. Be interesting to see if the two power curves bear this out, or if fans are somehow exceptions to the rule.

In racing, every lost HP is crucial, even at the top end of the rev range. On the other hand, most mere road-going mortals are probably losing little by keeping the stock fan.

The Power going in to driving the fan is also pretty much proportional to the volume of air that it moves too.

An alternator will also pull HP while driving an electric fan.

Ronnie wrote: ↑Thu Apr 03, 2025 7:22 pm An alternator will also pull HP while driving an electric fan.

None of the fans I've seen on the big sellers' websites say what power they are nor what fuse they use, but the size of the wires in the pics suggests currents no more than 25A-ish. That's only 300W (0.4HP) which - compared to the power of the water-pump fan - illustrates why it's not up to keeping the engine cool alone. Alternator marginal [in]efficiency means something like 0.6HP of engine power would be absorbed when the fan is on.

OTOH the water-pump fan's power at idle revs (900rpm for sake of argument and using the same cube'd calc from above) would be about 1/50 HP... illustrating why the water-pump fan can't keep the engine cool on a hot day in traffic. Picking up the revs to 1500rpm would increase the fan's power to about 1/10HP so - counterintuitively - suggesting a theoretical way to cool the engine on a hot day is to not let it idle. (Please don't beat me up if that turns out not to work... it's all hypothetical and, not having a temp gauge on my car, I won't be the one testing it.)