5-blade flex fan vs. 7-blade clutch fan for better cooling and possible HP gains
 

I’ve checked some previous threads under this forum for more details, but didn’t have much luck so I’m tossing this out there…

I have a ’69 Custom S (non-A/C) which originally had a 350ci/2bbl, so it had the stock fan shroud and 4-blade fan with ~1 5/16” spacer.

- Years ago I upgraded to the 19” 5-blade flex fan (Ames P154FK), and it not only helped with cooling on my 400ci, but I also picked up a few 10ths at the track. It was definitely a worthwhile upgrade!

Now I’m looking to upgrade to the 18” 7-blade clutch fan (Ames PF154GA) and heavy duty clutch (Ames P154G) for perhaps better performance and cooling benefits:

- I’m using a 3-row radiator, 50/50 coolant/water mix and a Robert Shaw 160 degree thermostat (recently changed from 190 degree.)
- The 400 runs at ~190 degrees and up to ~210 in traffic on hot 90+ degree days. It does not overheat, but I want to see about having the engine run cooler because I drive it to the track and it gets "heat soaked".
- Current 5-blade fan is half-way in and half-way out of the fan shroud, as it should be for best air flow as per Jim Hand (who also recommends using a thermo clutch fan for best results.)
- For the new 7-blade fan, I would still use the same fan shroud, ditch the spacer and bolt the fan & clutch directly to the water pump as it’s 1 5/8” from flange to fan.

1) Would there be additional cooling benefit with the 7-blade clutch fan vs. the 5-blade flex fan?

2) Is there any evidence of any gains in horsepower and/or torque from going to the clutch fan since there would be less resistance when the fan is not needed at higher speeds?

Thanks for any advice!

Jim.

Pics of 19" 5-blade flex fan (current), 18" 7-blade fan and heavy duty clutch...

anytime you can increase air flow there will be a cooling benefit.

cant confirm the power gain question but makes sense that less resistance will increase power, by how much is anyones guess without real testing.

7 blades will pull more cfm than 5 blades and only improve cooling, at least theoretically.

Fan
 

I have run both the factory original 5 blade flex on my bird and a 7 blade with clutch fan.
I will say the whole cooling system is more then just the fan.
Just the 7 blade and clutch were no help till I installed an AC pulley
Setup with 8” crank and 6.5” water pump pulley.
Along with a new cold car radiator I never see higher then 180 during a long highway run and
The heat of summer. 170 around town with 170 thermostat.
Stat was checked and cracks open at 165-167 and is fully open around
185-190. This is with a STD fan clutch from Napa with no mods done to it.
Yes

It’s a whole system.

Gerry.

Thanks everyone, good input for sure! I think I'll go ahead and pop for the new 18" 7-blade clutch fan, mainly for any additional cooling.

I'm probably done racing for the season, but can follow up with some empirical road testing once I get the new fan installed.

Thanks 68 Firebird, I'll investigate the different sized pulleys next if needed...

Any further input is welcomed!

Jim.

Every time I think about going to an electric setup in my car I look at the stock "Maxi 3 Core" rad , stock shroud, stock 7 blade fan and stock clutch. Then I realize how well this has worked over the years.zero issues..all the way from 300hp to 600hp..same cooling system.

Only problem I see is that a shroud for the 5-blade 19" fan is going to be a little large when you drop down to the 18" fan. Think you can flip a coil on whether the 7-blade potential for moving more air will be offset with the poor fit in the shroud.

I had the H.O. fan with the proper shroud and it worked well supplying cooling for my added AC system except at very low speeds. I converted to the 19.5" 7-blade AC fan, proper shroud, and SD clutch and it will idle forever with the air on without the temp climbing.

How's your water pump? Is it clearanced properly? Coolant flow affects all avenues of cooling; hi and low speeds.

Yrs ago I asked the best rad shop owner around here what he thought about a 7 blade with a clutch . Response was …it’s GM s best design, don’t mess with it. A cooling system is a sum of its components, good rad property clearanced pump and shrouded fan.

Sounds like my local guy..40 plus years in business..he knows what works.

David Freiberger did a episode on engine masters - pretty sure the clutch fan was okay, but the flex fans were...horrific - but don't quote me! Find the episode..

Thanks for the replies, all!

Yeah, I forgot to mention that the water pump is a FlowKooler Hi-Flow #1649 from Summit with the accompanying divider plate (see attachments). I replaced the stock pump back in March 2018 and I vaguely recall doing a cursory check for clearance while also ASSuming the newer divider plate from FlowKooler would have it clearanced properly?!

The engine has never overheated, but it does get to ~210-215 degrees in traffic on hot 90+ degree days with the 19" flex fan along with the original/stock fan shroud used on the 350ci (no A/C, so it had a 4-blade fan) which I replaced with the 400ci. My goal is to reduce the operating temp so that the engine is not so heat soaked after an hour+ drive to the track.

Thanks for the pointer, I will search for that Engine Masters episode!

I now have the 18" 7-blade fan and clutch from Ames (#P154GA, #P154G 1964-76). The catalog did not offer a 19" clutch fan, so I went with what was available. I just need to find time to install it. I will provide some empirical testing feedback once I get it installed. However, now that the weather is cooler, the real test will be next summer...

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