I've been running without the ducting for over 55k miles, I've been expecting the alternator to fail at any moment, but it keeps going despite the foul weather in the UK. Last summer I drove through large qualitites of flood water that would be well over the alternator cooling duct, this had no effect either.

 

Here's the duct I got from the link above. I bought 4 feet and have just over a foot left over. The perspective in the pic is skewed, it really is 2.5" in diameter. Not sure how you'd get 3" duct through the opening by the LCA.

 

Guys good information, how many feet should I order?

 

SCAT tubing might be a good alternate choice: very flexible and durable, and is available in 2-1/4 inch diameter which might be an easier fit.

Link:
http://www.aircraftspruce.com/catalog/appages/scat.php


HTH.


Bob

 

3 might do it, but splurge for 4.

 

as some of you know, i lost an alternator by sucking up a bunch of rocks, not thinking that the alternator actually sucks air in from the duct. (the stock duct had been destroyed so i just pulled it off. (and left the temp sensor in the wheel well)

what i found was that in my shed pile of parts, the heating and ac ducting was looking pretty good. IN FACT, its the perfect diameter!! fits snugly on the alternator inlet, and goes up to the wheel well area. easy to join the existing duct holding the temp sensor.

i would order this stuff from 928 intl. it will be cheaper and its the correct size! (and more durable than the original duct work that comes on the alternator from the factory)

mk

 

this is what i pulled out of my alternator when i ran it for one race without the duct. it sucked in rocks and took out the winding. I ended up loosing the battery by the end of the race, still finishing, but loosing several positions. all because i thought the duct work wasnt needed! big mistake!
all you need is a small rock to get sucked in and at near 6000rpm alternator speeds, a little rock can get in the alternator and do some real damage.

Mk

 

The duct on my 81 was shredded when I bought the car. I also am missing the alternator adapter. Does anyone have a pic of the complete setup and the routing of the duct. I too need to replace mine. Jason

 

The blades on the alternator do pull cooling air through the duct.

 

Is the 2 1/4" tubing a better fit?

 

yeah, a little late bill!!!!

anyway, i forgot what the rpms on the alternator are, but i think its more than 1:1 off the crank pulley. might even be 1:1.5 if so, thats at least 6-9,000rpm.

the alternator does have a little centrifugal blower design.

anyway, the ductwork for the heating and AC stuff works great. its all the ducting under the dash. It fits the alternator perfectly.
mk

 

Oh, it's alot more than that. Compare the alternator's crank pulley size (5") to the alternator pulley (2"). So, that's 1:2.5!

 

The right size is 2.5" and it is snug.

 

thats right , i was thinking of the little crank gear. thats right, its a big diameter belt pulley, running a little alternator pulley.

so, 6000rpm would be near 15,000rpm!!!!! a little vacuum cleaner!!

Mk

 

so, where do we get underdrive pulleys that we can replace the stock stuff with? that should be easy.

mk