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brendo907
Samba Member
Joined: September 13, 2013
Posts: 339
Location: North Pole, Alaska
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 Posted: Sun Oct 27, 2013 11:00 pm Post subject: Not a normal power pulley question |
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| I was thinking of a power pulley. before you attack me telling me how hot it makes the engine run let me say that i live in fairbanks alaska. It was 18 degrees yesterday and i will be seeing below 0 before too long and even down to -40 and more. Is it still a bad idea? what kind of power increase? i have a 74 super, 1600 DP engine. soon to be daily driver. thanks everyone |
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Geoffffreak
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Joined: May 08, 2013
Posts: 57
Location: Orange County
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| Posted: Sun Oct 27, 2013 11:05 pm Post subject: |
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Burr.... that sounds terrible. with teperatures that low, its probably better to run the power pulley. i dont think its too much of a hp gain tho. Maybe 5-7?
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1974 Std. 2007cc Dual 44 Webbers. (German look in progress) Family owned from the factory! |
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Aussiebug
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Joined: June 03, 2002
Posts: 2162
Location: Adelaide Australia
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| Posted: Mon Oct 28, 2013 1:57 am Post subject: |
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A power pulley usually runs the fan about 20% slower than the stock pulley. Since the stock fan uses up to 6hp at around 4000 engine rpm, the most the power pulley will give you is about 1.2hp more at the wheels, for a 20% reduction in cooling. NOT a good tradeoff, even if you live in a cold climate.
Assuming that your stock cabin heating system is working, you'll also get a lot less warm air into the cabin.
You might also find that your alternator has trouble charging the battery, especially when driving around town at lower speeds.
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Rob
Rob and Dave's aircooled VW pages
Repairs and maintenance for the home mechanic
http://www.vw-resource.com |
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brendo907
Samba Member
Joined: September 13, 2013
Posts: 339
Location: North Pole, Alaska
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| Posted: Mon Oct 28, 2013 12:20 pm Post subject: |
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| That's very true, I do like my heat |
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olspeed
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Joined: May 01, 2008
Posts: 489
Location: In the shadow of Denali, I still don't give a damn how they do it outside
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| Posted: Mon Oct 28, 2013 2:10 pm Post subject: |
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Brendo907
I only live around 150 miles south of you and I still have a power pulley that I purchased back in the 80's that was only used about a month when I tried the same thing... power wise you won't feel any difference but heat wise, well that is another story.
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brendo907
Samba Member
Joined: September 13, 2013
Posts: 339
Location: North Pole, Alaska
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| Posted: Mon Oct 28, 2013 2:20 pm Post subject: |
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| olspeed wrote: |
Brendo907
I only live around 150 miles south of you and I still have a power pulley that I purchased back in the 80's that was only used about a month when I tried the same thing... power wise you won't feel any difference but heat wise, well that is another story. |
Where are you at? Down in delta? What would you want for it? I might try it out just for fun but who knows. I just gotta finish putting together my engine I was cleaning my heat riser and had to wait for new gaskets. |
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thechief86
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Joined: January 18, 2012
Posts: 860
Location: middle tn
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| Posted: Mon Oct 28, 2013 7:43 pm Post subject: |
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is there the option of running a smaller alternator pulley as well, to keep the same rpm ratio for the fan? would it still give any gain? just asking, I still have my stock pulleys, and don't plan to change them, other than filing some grooves into it to make the timing points a little more obvious when tuning....
I already did that though, and i'm glad I did
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Aussiebug
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Joined: June 03, 2002
Posts: 2162
Location: Adelaide Australia
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| Posted: Mon Oct 28, 2013 9:58 pm Post subject: |
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| thechief86 wrote: |
is there the option of running a smaller alternator pulley as well, to keep the same rpm ratio for the fan? would it still give any gain?
:D |
That would not make any difference at all, since you'd be spinning the alt/fan at the original speed. THAT'S what uses the hp.
This type of question pops up regularly, along with "why can't I use an electric motor to drive the fan?" and stuff like that.
The problem is that to force enough cooling air through the finning, you need both flow and PRESSURE. In fact, Bob Hoover (RIP Bob) measured the pressure inside the fan shroud with the engine running hard, and found it to be about 5psi above atmospheric. That pressure together with the volume of air (21cf/sec for the 1200/1300/1500 fan and 25cf/sec for the doghouse fan) means you need serious hp to drive it - 4-5hp for the early fan and 5-6hp for the doghouse version. Try doing that with an electric motor an you are pulling about 375 amps out of the 12v battery.
Water cooled cars don't need anything like that hp for the electric fan as it does not have to produce any pressure - just a decent flow for the car at rest - the forward motion of the car itself provides most of the flow through the radiator.
Ever wondered why VW went to a wider fan belt with the doghouse engine? It's wider to make it stronger - the older belt is at it's strength limits with the smaller fan. And now that it's wider, it rides a little higher in the engine pulley groove, so it needs to be a little longer too. So you have the older belt at 9.5mm x 905mm and the doghouse belt at 10.3mm x 912mm.
The engine is quite a forgiving one and driving it with a power pulley will work, but don't expect the engine to last anywhere near as long as one with the full cooling system.
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Rob
Rob and Dave's aircooled VW pages
Repairs and maintenance for the home mechanic
http://www.vw-resource.com |
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