Just curious, why would Pontiac use a base V8 fan(4 blade, 19 inch, 25/16 pitch) on the Ram Air cars but use the flex fan on the regular 400's?

For the GTO Ram air, same fan part # used as the 2 barrel. 400 used a 5 blade, HD/AC used 7 blade and could be ordered as an RPO code.

I would speculate...

Maybe power savings 4 blade over 5. I have been out of the loop for awhile but will throw out HD cooling system with a 4 blade versus a smaller core and a 5 blade.

Good question... always wondered the same thing.
While the 4 blade is correct for RA, it doesnt cool our car as well as the 5 blade.
I tried all three of these and the flex fan does the best job.

To go along with Banshee's comment, if they designed it with the idea that the mileage one would get is primarily 1/4 mile at a time...

Also we should remember that issues with cooling weren't particularly a problem "back then". My dad owned one of the original 65 RA cars..Verdoro 4 speed, black top, redlines. He told stories of driving it from Detroit to Cherry Point NC through the turnpike at 70. With a 3.90 rear one would think overheating would be an issue...but best he can recollect, it was not.

I would debate new water pump divider plates, grommets, radiator and new car had a part to play. As well, I would say fuel back then with lead and 8 grades up to 116 octane had a part in proper cooling.

Here is an entertaining read from 1968.

http://books.google.com/books?id=mykDAAA...p;q&f=false

Remember these are Research octane numbers; today's pumps deliver (R+M)/2.

Octane in today's fuels is sufficient for most engines, but lack of lead and different vapor pressures and the addition of ethanol has made any direct comparison impossible.

Both numbers (MON/RON) are compared in some instances within the link provided.

My 67 ran cooler on 110 leaded versus 100 unleaded. Those were the only two options I had.

That's a good article.

Leaded always seems to run cooler, unless you put it through a catalytic converter. I watched a late '70s Chrysler catch the back seat carpet on fire from a lead-clogged converter years ago.

I believe the main reason they used the fixed 4-blade on the RA cars is because of the steep rear gears. With speed limits of 70-80 mph, many Americans drove for hours on end with 3.90 or even 4.11 gears at those speeds. We would never do that today, but back then, it was not uncommon to be at 3800-4000 rpm for an hour straight. A fixed blade fan would still be cooling at this rpm, a flex fan would have the blades flattened, and the clutch fan would be nearly freewheeling.

That original-owner POCI 400 point perfect '68 RAI in the area here has a 5-blade. I'll have to ask the owner about it.

Wants to be "that guy".

It is quite a nice car! If you have Pontiac Enthusiast, It was featured last September.

Definitely an interesting perspective, thanks for sharing!

Wishes he were that guy too...I'll have to settle for my 400.

When the topic comes up of "which fan is better at cooling", the answer is the clutch fan. It has the most blades, they're all fixed pitch, and the fan uses little to no horsepower above 3500 rpm because it freewheels (or nearly freewheels). Because they're so good at cooling, all a/c cars got clutch fans, from Pontiacs to Chevys, Oldsmobiles to Buicks.

But sometimes people note that if the clutch fan was SO good at cooling, why didn't Ram Air cars get them? Well, it's because of the steep gears. Those clutch fans would be over 3500 rpm at only 50 mph with 4.11 gears and small 14x6 wheels, so Pontiac wisely chose to use the fixed blade units. The fixed blade versions used a lot more horsepower, but they did prevent overheating (well, most of the time anyway!).

Sometimes they offered a clutch fan as an option, but it usually cost the customer, and many didn't want to spend the money. My old 1965 GTO came with a stainless steel blade clutch fan, and the car had 3.23 gears.

By the early 1970's, coolant recovery tanks came into play (1971), and steep gears and high octane were gone, so nearly all cars had clutch fans.