Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 911 Technical Forum


Reply
 
LinkBack Thread Tools Rating: Thread Rating: 1 votes, 5.00 average.
Author
Thread Post New Thread    Reply
Functionista
 
manbridge 74's Avatar
 
Join Date: Jul 2011
Location: CO
Posts: 6,577
Every June I take five minutes to switch to 131mm from the 116mm. Then when colder temps hit I switch back. When I want to get oil to the front cooler in winter or keep temps above 180F I’ve been known to partially block the deck lid grille.

No issues with overspeeding alternator.

__________________
Jeff
74 911, #3
I do not disbelieve in anything. I start from the premise that everything is true until proved false. Everything is possible.
Old 02-13-2018, 08:07 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #21 (permalink)
Registered
 
burgermeister's Avatar
 
Join Date: May 2007
Location: Springfield
Posts: 2,125
Garage
I have been trying to make sense of the various pulley sizes and speed ratios quoted in this thread and in the 5 vs 11 blade fan thread.

The pulley sizes listed seem to be the outer diameter of the pulley. Using those numbers "raw", one ends up considerably below the advertised ratios.

Now, the belt does ride a few mm down in the pulley groove. also, the belt has thickness, so the effective radius where the belt acts is going to be someplace between the top and bottom surface of the belt. I measure 3-4mm for the 1st number (belt top surface below pulley outer radius), and the belt thickness for a 10x belt is 6mm, so another 2-3mm below the top surface of the belt.

Subtracting 10-14mm from the advertised pulley diameters gets one close to the advertised ratios, but not actually there. Here is what I come up with subtracting 12mm:

Fan Dia Crank Alt Pulley belt (10x) Ratio (spec) Alt Ratio Fan tip speed at 6800
65-74 245 116 95 710 1.3 1.25 109.3
76-77 245 131 83 725 1.8 1.68 146.2
78-79 226 126 80 725 1.8 1.68 134.9
80-89 245 127 83 710 1.67 1.62 141.3
90-98 279 145 100 775 1.6 1.51 150.1


Anyone have any idea where the extra ratio (1.6 vs 1.5, 1.8 vs 1.7) comes from?
__________________
'88 Coupe Lagoon Green
"D'ouh!" "Marge - it takes two to lie. One to lie, and one to listen"
"We must not allow a Mineshaft Gap!"

Last edited by burgermeister; 05-13-2020 at 10:58 AM..
Old 05-13-2020, 10:54 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #22 (permalink)
Registered
 
burgermeister's Avatar
 
Join Date: May 2007
Location: Springfield
Posts: 2,125
Garage
Apologies for the garbled text ... apparently spaces and / or tabs don't post. Here is what it looks like in the editor:

__________________
'88 Coupe Lagoon Green
"D'ouh!" "Marge - it takes two to lie. One to lie, and one to listen"
"We must not allow a Mineshaft Gap!"
Old 05-13-2020, 10:58 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #23 (permalink)
Moderator
 
Bill Verburg's Avatar
 
Join Date: Dec 2000
Posts: 24,278
Garage
Quote:
Originally Posted by burgermeister View Post
Apologies for the garbled text ... apparently spaces and / or tabs don't post. Here is what it looks like in the editor:

I believe that you have some errors

Here's what I got using only factory specs for the fans

__________________
Bill Verburg
'76 Carrera 3.6RS(nee C3/hotrod), '95 993RS/CS(clone)
| Pelican Home |Rennlist Wheels |Rennlist Brakes |
Old 05-13-2020, 02:49 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #24 (permalink)
Registered
 
burgermeister's Avatar
 
Join Date: May 2007
Location: Springfield
Posts: 2,125
Garage
I think I found the error in the calculated ratios ...

On the alternator pulley, the belt rides 3-4mm below the pulley circumference. On the crank pulley, it is only 0 - 1mm below the pulley circumference. Making the correction, the ratios (admittedly incomplete and rounded off) end up almost on the money.




I did leave the turbos out of the picture - thanks for including them Bill!

So ... how fast do the racing folks spin 993 motors? In other words, is there overhead in the 993NA fan to spin it faster without causing fatigue issues in the blades?

The 993TT fan turns faster - I think it has straight blades. I wonder if that was done for durability reasons - more even stress from centripetal acceleration? In which case that answers the previous question with a "no".

It is pretty easy physically to run the 993NA fan faster - the 10x760 alternator belt fits in the fan belt's place with an added 4.0mm spacer (I have the single belt conversion hub). That represents a 2.0-ish ratio - almost certainly too much for the fan to handle in the long run. I drove it around for 40 some miles, it worked fine with a bit more fan noise, but I did not take it above 5000RPM.

I have a kit car with a 993 motor that runs warmer than I'd like during track days. It has a huge oil cooler and no room for anything bigger. It seems some folks have had good success cooling the engines down a bit with more airflow. Also, the 993TT used increased airflow - also suggesting that more airflow is probably a good thing.

__________________
'88 Coupe Lagoon Green
"D'ouh!" "Marge - it takes two to lie. One to lie, and one to listen"
"We must not allow a Mineshaft Gap!"
Old 05-14-2020, 06:22 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #25 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 12:15 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2020 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.