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Global Mod,
Mod | | | Forums66 Topics128,080 Posts1,056,060 Members48,433 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
| | THANKS!
For helping keep this great
old truck web site
on the Internet for over 30 years! and not clogged down
with Ads!  Again, thanks!
| | | | Joined: Sep 2010 Posts: 122 Shop Shark | | Shop Shark Joined: Sep 2010 Posts: 122 | Have a 261 with a 4.3 dia water pump pulley. I also have 2 dampers, one with a 6" dia pulley and the other with a 6.75" pulley. What would be the fan rpm for each pulley at engine speed of 2000 rpm. What is a "typical" fan speed? | | | | | Joined: Jul 2008 Posts: 326 'Bolter | | 'Bolter Joined: Jul 2008 Posts: 326 | Around 2800 vs 3100 RPM
IDK what typical speed/ratio should be. The only steady state RPM would be at highway cruise speeds.
SimS | | | | | Joined: Apr 2014 Posts: 924 Shop Shark | | Shop Shark Joined: Apr 2014 Posts: 924 | DcCrpm= DfFrpm
(Diameter of the crankshaft pulley)(crankshaft pulley/engine RPM) = (Diameter of the fan pulley)(fan RPM)
Both sides of the equation must balance out.
Brad
Wrench Fetcher, PhD | | | | | Joined: Jun 2011 Posts: 1,901 Shop Shark | | Shop Shark Joined: Jun 2011 Posts: 1,901 |
Give me ambiguity
or give me something else
| | | | | Joined: Sep 2010 Posts: 49 Wrench Fetcher | | Wrench Fetcher Joined: Sep 2010 Posts: 49 | I could not go larger than 6" on the damper or the pulley would rub on the motor mount. That's on a 1951 with a 235. Maybe I have a problem some other place. | | | | | Joined: Apr 2014 Posts: 924 Shop Shark | | Shop Shark Joined: Apr 2014 Posts: 924 | ... but talk forum members into hammering out sheet metal into fender patches as opposed to buying replacements? Touché.  Brad
Wrench Fetcher, PhD | | | | | Joined: Dec 2008 Posts: 1,922 'Bolter | | 'Bolter Joined: Dec 2008 Posts: 1,922 | Far more important: that's also the water pump RPM. Slow it down too much = always runs hot.
Fan speed only matters in traffic, above 35 mph you can remove the fan entirely.
The best fan design: the largest diameter turning at the slowest speed, with a shroud. | | | | | Joined: Jun 2011 Posts: 1,901 Shop Shark | | Shop Shark Joined: Jun 2011 Posts: 1,901 | .... but I never said that!!!
I said if I made one it would be the greatest patch ever and the five layers of bondo were just for enhanced rust protection... our manufacturers have sold us out but I will makes great panels for everyone!
Wheres that LMC catalog?
Give me ambiguity
or give me something else
| | | | | Joined: Apr 2014 Posts: 924 Shop Shark | | Shop Shark Joined: Apr 2014 Posts: 924 |
Wrench Fetcher, PhD | | | | | Joined: Mar 2007 Posts: 4,215 Moderator | | Moderator Joined: Mar 2007 Posts: 4,215 | Ryan, I don't know my fan speed, but I had that 4.3" water pump pulley too, at first. (261 engine) It was very obviously spinning the fan too fast. I simply slipped a larger pulley, about 6" diameter right over the smaller one, using the 4 small fan bolts to hold it in place. I have been running it for 4 years, no issues. | | |
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