5 blade to 11 blade fan question

[deftom]

Hi all,

After discovering a seepage between cylinder/head (posted here: https://forums.pelicanparts.com/911-engine-rebuilding-forum/1119832-cylinder-head-leaks-need-your-opinion.html)

I made all the check to ensure that the engine was ok (checking compression leak, retork nuts, verify mixture, check ignition).

And I decided to install an 11 blade fan instead of the 5 blade on.:




I noticed 3 things:
-better cooling (that was expected)
-less noise
-less performance

For the last point, I wasn't expected that much. And I guess by having less noise it amplifies rhe feeling of having less horse power.

So my question is simple, dontou have any idea of how many horse power do I loose when I changed the fan?

Thanks!

Regards;

Thomas

[Nditiz1]

0 HP lost

[walt]

Since you checked compression I would verify all your plug wires and distributor cap are fully seated.

[917_Langheck]

Difference in flow volume between 5 and 11 blade fan is 9% at stated rpm. Lots of discussion on hp gain/loss and cooling in old threads.

[Bill Verburg]

997doesn't have a fan 993tt may be the what was meant

IF the 5 blade fan pully is retained the ratio is 1.8 and flow will be 1539 l/s 21.7% more air flow @6000 than stock

[917_Langheck]

Originally Posted by Bill Verburg

997doesn't have a fan 993tt may be the what was meant

IF the 5 blade fan pully is retained the ratio is 1.8 and flow will be 1539 l/s 21.7% more air flow @6000 than stock

Well Sir, fair points, but you'll have to take that up with Mr. Anderson's publisher. They still didn't catch those details in their 3rd edition of the Performance Handbook (that pic is directly from the volume).

It really would have been better to also have used the same rpm figure as a constant instead of a relative variable.

[deftom]

Hi All,

Thank you for your feedback.

So from what I understood, the difference of performance should be from 0 to close to nothing.

So the lack of power is probably due to a engine that it is less noisy.

Thanks

[deftom]

Originally Posted by walt

Since you checked compression I would verify all your plug wires and distributor cap are fully seated.

What should I expect ?

[917_Langheck]

BTW check the number of fan blades used here: https://robbreport.com/wp-content/uploads/2017/08/83.jpg

In those old threads I previously spoke to, power loss/gain is not necessarily 0, but also not necessarily large, but measurable, or at least calculable. I believe Grady Clay put up a series of numbers on the subject.

[deftom]

From what I remebered, After a certain number of RPM, having less blade is more efficiency (from Henry Schmidt if I do remembered).

I also read that from 5 to 11 it consume 3/5 HP. But I am not sure about those information

[sean m]

Originally Posted by deftom

From what I remebered, After a certain number of RPM, having less blade is more efficiency (from Henry Schmidt if I do remembered).

I also read that from 5 to 11 it consume 3/5 HP. But I am not sure about those information

And here I thought that going to 11 blade fan from a 5 blade simply reduced the heat on the engine and oil.
Certainly never thought of a drain on power. Learn from Pelican every day.

[Nditiz1]

Until someone has taken their car to a dyno with evidence of 3 consistent pulls with the 5 blade and 3 consistent pulls with any 11 blade I will find it hard to believe a 3/5 hp loss.

[Balisong]

I have a 5 blade still on my 76. I have purchased an 11 blade but haven’t installed it yet.
The worst temps I see in summer are 210 degrees.

[deftom]

Originally Posted by Balisong

I have a 5 blade still on my 76. I have purchased an 11 blade but haven’t installed it yet.
The worst temps I see in summer are 210 degrees.

It is like you regarding mine. But I suspect that even if the oil temperature doesn't go that much, 5 blade does not cool well head which cause the engine to expand more.

[deftom]

Originally Posted by Nditiz1

Until someone has taken their car to a dyno with evidence of 3 consistent pulls with the 5 blade and 3 consistent pulls with any 11 blade I will find it hard to believe a 3/5 hp loss.

You are correct, And I hopped tath someone did that... but apparently not.

So I suspect the loss of power is essentially because the engine make less noise

thanks

[stownsen914]

Engine driven fans do consume measurable hp. We can infer this from the SAE vs DIN hp ratings that Porsche used to do back in the day. DIN allowed for hp measurement to be done while driving the ancillaries from another source. For an early 911, the only ancillaries were the alternator and fan (I assume they tested a non-AC equipped engine).

Consistently 20 hp different between DIN and SAE ratings on early 911s, which I take to mean the fan + alternator consumes ~20 hp at peak hp RPM.

Hard to imagine there's enough of a difference between a 5 vs 11 blade fan to be noticeable to the butt dyno.

[wazzz]

Originally Posted by stownsen914

Consistently 20 hp different between DIN and SAE ratings on early 911s, which I take to mean the fan + alternator consumes ~20 hp at peak hp RPM.

A 70 amp alternator would hardly consume 2 hp when fully loaded at highest RPM. That leaves 18 hp only for the fan. That is high power loss.

[stownsen914]

Yeah they consume substantial hp at high RPM. If someone has better info, I'd love to see it.