I was planning on installing a mini alternator. But all I can find is
55
amp in the mini's. Will 55 amp suffice with fuel injection and
electronic
injection. I was thinking 100 amp but that may be an over kill.
Bob Mears
Supermarine Spitfire
55 amps should do it Bob.
--
Paul Lamar ...No rotor no motor.
My alternator is a 60 amp Delco recommended by the local alternator
shop. 8.5 lbs, internally regulated. It actually puts out up to 75
amps under load.
I'd like to use an underdrive pulley for this alternator, since it
will
be spinning at around twice its design speed if the stock pulley is
used. I found the stock RX8 water pump pulley is 5-groove, and about
the right diameter, including the center hole. It is normally bolted
to the water pump, while the stock (Delco) alternator pulleys are just
held in place with friction. If I used a couple of large washers, is
there any reason this pulley wouldn't be OK for the alternator?
Scott Gettings
You can figure the torque on the alternator Scott.
75 amps at 14 volts is 1050 watts. 746 watts per HP so that
is 1.4 HP. Given 80% efficient that is really 1.75 HP input.
Now you need to know what RPM the alternator puts out 75
amp and use the formula HP = T X RPM /5252 or
T = (HP / RPM) x 5252 Lets say 2 foot pounds for 6000 RPM. Bolt
the washers on and keep the alternator from turning and
apply a torque wrench.
BTW guys you can save some current drain and extend your alternator
out range by using the high pressure MSD roller vane fuel pump
instead of
the highly inefficient Walbro type pumps. My guess is you can save
about
5 amps or so. I will have more info on this shortly as I will be
testing
both.
The Walbro type pumps are ubiquities in just about
all new cars as they are very very cheap to make. Probably about $20
as all
they are is a small DC motor and an injected molded plastic vane.
Mazda sells them for an extraordinary $400 retail while the MSD
positive
displacement roller vane pump is $109 retail direct from MSD.
Paul Lamar ...No rotor no motor.
Scott that is a nice size alternator. Where did you get it from? Can
you
tell me the depth of the unit from the rear casing to the front face?
Thanks
Doug
I spent a lot of time looking around in various places, but ended up
going to a local alternator shop and telling them what I wanted:
1. 60 amps
2. Internally regulated (but not computer-controlled)
3. Light as possible
4. Reliable
5. Reasonably priced
6. Standard shaft size so I could get a larger aftermarket underdrive
pulley if needed.
The guy came back with a Delco early 90's GM 4 cyl engines-- the
numbers on it are: 1101171 D61A 7B19
8.5 lbs
The case itself is 4" from front to back, but it is 5.75" from the case
rear to the end of the shaft (the front of the pulley).
The case is 4.5" in diameter.
Scott Gettings
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