I am confused on which water pump

I have a 71 Skylark with a 455. In 71, did the A-body's get the short nose or long nose water pump? I currently have the long nose and need to replace it. I always thought the fan sat in the fan shroud a little too far.

 

Yes, thanks Larry. I realize this, as I can going through my box of different pulley, ugh. I just assume purchase another long body, so to your point, my existing pulleys line up. Is the fan suppose sit fully inside the shroud? or should some if the fan blade be sticking out? I do have a correct 71 455 shroud

 

Ah.....so I probably need a short nose pump...….but then I need to find different pulleys. is there a benefit to fan blade being half in half out as opposed to the way mine is?

 

71 up used the long pump, which shroud are you running? And I just completely read past that info ha, but if you have the 71 shroud you should run the long pump, I've parted out several factory 455 cars and the 70's had the short and the 71+ had the deep pullies to accommodate the long pump

 

Jay - you've also got a little variable in the length of the fan clutch shaft. My car is a long shaft pump, with a legit 71 Shroud and the correct Hayden 2705 clutch, and my fan still sits just flush with the edge of the shroud. Has never affected cooling in any way, but i cant help to come to the conclusion that all long pump cars sunk the fan in the shroud some...

 

Thanks Gentlemen. I have a 1234484 shroud, which I believe is the 71 shroud. I don't suffer any cooling issues especially with the 180 degree stat. My pump developed a squeal, and since I have to replace I thought I would make it right. But if 71 got the long body then that's what I will replace it with. Thanks for the fan article. Mine definitely sits flush with the shroud, perhaps Rhett you are correct. My clutch fan shaft is too long.

 

Take a look at pics of the Hayden 2705 clutch - the correct clutch will have a shaft thats about the width of your thumb...

 

From Larry's link -



they state
"If you have a fan shroud, the position of the fan blades in the shroud is very important to maximize airflow. Looking from the side of the engine, the fan blades should be half in and half out of the shroud.
If the fan is too far inside of the shroud, it won’t pull as much air through the shroud as it could. Instead it will create turbulence inside the shroud, spinning the air, but not efficiently pulling it through. If the blades are not far enough inside the shroud, the fan will pull air from around the shroud rather than through it."


I am going to disagree with them slightly on this based on my knowledge of ducted fans - as long as the front of the fan blade is not forward of the shroud WHERE THE CIRCUMFERENCE IS MEASURED to get your 1" clearance .. then I believe you are fine, NO MATTER WHAT is sticking outside the shroud at the back side.

I believe what they are saying is that if the front of the fan blade is into the area where the shroud "necks out" and increases in diameter .. then you are creating turbulence and just beating up the air.

.. think of the later years 350 shrouds in the big cars .. the fan was wayyyy inside this huge duct with nothing out the backside.

I modified their picture below to illustrate what I was saying .. as long as the front of the fan blade (yellow line) is behind the lip of the shroud where it necks down to the constant circumference part that the blades circulate in (Green Arrow).. I think you are fine.

In fact, I would say the ideal location is slightly back from this line but having as much of the blade inside the shroud as possible.

I have a friend who has been a senior design engineer at Northrop Grumman and I will run this past him but from everything I know .. what is outside at the back is insignificant to efficiency

 

I confirmed what I stated above with my engineer friend - as long as the front of the fan blade is not protruding forward of the constant circumference part of the shroud, then the fans' location inside is best if all of it is inside the shroud. The fans' locations should not be positioned based on "half in / half out" for optimum airflow and there is no benefit to having part of the fan outside the rear of the shroud.

.. he did state after studying the above picture, that huge airflow losses are occurring with a 1" spacing between the fans' tips and the constant circumference shroud wall and this more than negates any efficiencies gained by trying to optimize the fans' location fore / aft (as long as it isn't protruding forward as detailed above). I told him that was mostly needed due engine movement from torque. He said that tolerance (from fan tip to wall) is measured in thousand's of an inch in aerospace applications, accounting for centrifugal growth of the blades .. and each thousandth less than contact has measurable efficiency losses.

 

I can't speak with any authority about aerospace.

I expect that automotive cooling fans are not shaped the same as "aerospace" fans. Automotive fans blow as much or more air OUTWARD (radially) as they do in-line (axially). The benefit to half-in-half-out is that the shroud doesn't block the radial flow thrown off the fan.

I've seen as much as 2/3 out, 1/3 in working very well.

Yes, if you can 1) restrain the engine motion in the rubber mounts, and 2) minimize body flex with proper frame-to-body mounts, reducing fan clearance to the shroud can improve flow considerably. Realistically, about 3/8-1/2 inch all around the fan is the best you can hope for unless you've got solid engine mounts and an unusually rigid body/frame.