First off datspeed, sorry for the thread hi-jack.

Dodgeman, I hope you didn't think I was having a go at you you, I just have a weird way of bringing my point across...

Anyway, I agree with your statement about it pumping the maximum amount of air at below 3000 rpm. However viscous fans have even more weight hence inertia to overcome than stock direct drive fans. It's almost like adding another flywheel to your car, with the difference that it now has "paddles" that tries to stop it from turning. One can literally hear/feel the difference, in my Mazda 2.5 TD for instance, between when it's coupled and when it's not. There is quite a difference in the speed at which the motor can spin up.

Other than that they still don't pump air as efficiently as thermos, because of the way they are "mounted" in relation to a thermo. Probably the biggest reason I dislike them, is because they are unreliable, I have very rarely seen any of them last for much longer than a 100K. They tend to either lock up or disengage altogether, with obvious consequences. That's also reason why I would then choose a stock fan over them...

Then onto the reason I would still choose a thermo over any of the above. With a thermo you can control your engine temp to within 5 degrees of variation, which is very, very good for engine life. You can't achieve this with a stock fan or a viscous, no matter how hard you try.

For instance we live in a country where the difference in temperature between winter and summer could be as much as 20 degrees, up to 30 and more in some places. If you now have a stock fan, or viscous for that matter, in the winter months it's constantly cooling the engine when it shouldn't. So you end up with an engine that never reaches it's working temperature.

I have alot of faith in the car manufacturers. they are very clever people and I'm sure that if they thought a thurmo fan worked any better they would use one. I might be wrong but I don't know of any new north south engined car that uses a thurmo fan. They use viscous fans because you don't need any fan all of the time and when they freewheel they cut down on the noise which is probably why you think your car revs better without one. Thurmos are used as an easy alternative when the radiator isn't at the end of the motor as in east west configeration. If you want to find out how much power it takes to spin a fan then look at a house or even a ceiling fan, they use very little power and only require a very small motor and they are much bigger than an engine fan. Try stopping a housold fan, it dosn't take much.
Thats what I recon anyway.
olboy

becuase a thermo fan costs a lot more to manufacture than a engine fan...

also an engine fan is more reliable becuase it has no moving parts or electricals

but as was said the thermo can be swiched off and that is where the power advantage is

from experience in playing with 4x4 you can get a range of fans for bigger motors and putting one that has more blades seriously affects power and revability... so if thats noticable then there should be gains to have on our smaller scale


getting back to topic.....

electronic ignition is one i forgot... best to get an elec dizzy for ease and tidiness... but they arnt particularily easy to get

p.s. i just noticed the stuff about ceiling fans.... i would love to see you try to stop one spinning at 3000rpm...(no i wouldn't)

Quote:Mate, I did not think for one instant that you were having a go at me & I appreciate your reply.

I guess that I look for a different kind of 'performance' in my dotage than I did when I was a nipper & the performance characteristics of a viscous fan, often called an Air Conditioning fan, fit my driving style.

I will differ on the assumption that the fan controls the engine temp though as this is the job of the thermostat & the radiator temp can be 1 degree above freezing, but the engine itself at normal operating temp if the thermostat is doing its job properly.

Quote:

True that...

thanks. with side drafts it shifts latter due to insufficent vaccum. but, i was considering a shift kit (stage 2). so maybe side drafts are the way to go.

thoughts?

Dual sidedraughts with a stock cam? Probably not the optimum combination. Even a single sidedraught can easily be too much carb.