fan blad style differences - why ?

[Warren F.]

I was wondering why there was a different style fan blade used between the LS5 and LS6. Was the 5 blade style used for less drag and power loss on the LS6, obviously both fan styles would work. Thanks, Warren

[Joe L.]

Re: fan blad style differences - why ?

Warren------

The 1971 LS-5 and LS-6 did not use different fan blades. BOTH used blade assembly GM #3991420. The 1971 LS-5 WITH A/C did use a different blade assembly, though. This blade assembly, GM #3992095, had a greater blade pitch and specially configured blade end tips to reduce noise.

[Warren F.]

Re: fan blad style differences - why ?

Joe: Thanks for the explanation, I wondered about this for years. I've forgotten, is the "pointed blade fan" a 7 blade or 5 as well?

[Joe L.]

Re: fan blad style differences - why ?

Warren------

The standard fan, GM #3991420, is a 5 blade fan. The LS-5 with A/C fan, GM #3992095, is a 7 blade fan.

[Warren F.]

Re: fan blad style differences - why ?

Joe: Thanks, again! Is the reason for the AC style fan to increase air flow and will it be a more efficient fan for cooling purposes?

[Joe L.]

Re: fan blad style differences - why ?

Warren-----

Yes, the A/C fan blade provides increased air flow, primarily as a consequence of its increased blade pitch. The increased blade count also provides some additional airflow, but not as much as the increased blade pitch. The unique configuration of the tips was added to reduce noise that the increased blade pitch resulted in.

These 71-73 GM #3992095 fans are long-since discontinued and are diffcult to find, even used. They sell for $500+, if you do find one.

For improved cooling performance on 71-75 Corvettes you can use fan blade assembly GM #342715. This is a 17-1/2", 7 blade fan.