Hi,
Well Jack's right that driving better will make a bigger difference
than what fan you run, and not running an alternator is just plan
silly IMNSHO. All that said Hot Rod and a number of other mag's I
recall reading over the the past 30 years have shown in back-to-back
chassis dyno tests that a standard 4 blade "factory" fan can draw as
much as 45 HP @ 6,000 RPM. That's not to be sneezed at.
An electric fan DOES draw some power by imposing a drain on the battery
that the alternator must support, but its in the range of 1-2 HP which
means your netting 43-44 HP over a straight mechanical fan.
There is another option, subject to packaging limittations between the
engine and the radiator, a fan clutch can allow the fan to free wheel if
the air stream is below its engagement temp, saving around 20 HP and
placing no additional draw on the battery. Or, as Jack suggested, you
can trim the number of blades on the fan, but I have not seen a test done
on this aproach. Certainly on a 1275cc motor freeing up 20-40 HP is going
to register on the butt dyno wether or not it improves you lap times.
I'd install an alternator with a pully that keeps it under 17,000 RPM and
the eletric fan. Then you can stop worrying about charging the battery
between track sessions, and/or worrying about it going flat during the
session, and spend more time resting up in the lawn chair so you can drive
better in the next session. Running the Alt will allow you to run a smaller
battery, so it may well be a wash as far as weight goes.
-
At 05:51 PM 5/28/08 EDT, JWoesvra@aol.com wrote:
>In a message dated 5/28/2008 5:41:05 P.M. Eastern Daylight Time,
>TomD4760@aol.com writes:
>
>Does anyone have any data on the horsepower
>draw with the standard pulley setup on the 1275
>'A' engine?
>I'm considering replacing the fan with a switchable
>electric one run off a small auxillary battery. If anyone
>has experience doing this I'd appreciate hearing about it
>also.
>Thanks,
>Tom Deats, RMVR
>
>
>
>I don't think that is worth the effort. Why would you need an auxillary
>battery? What's wrong with the main battery? Oh... I know...you don't have an
>alternator do you?
>
>Just get a small alternator and a 2-bladed fan. You will not notice the
>difference and you won't need to charge your battery all the time.
Concentrate on
>driving well rather than trying to save a micro horsepower.
>
>Jack Woehrle
All the Best! Dave
Sr. Software Engineer/Requirements Manager/Systems Assurance Analyst
Aging Racer & Thumb Pound...er...Rule Engineer
http://www.lamehorseracing.com
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