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Discussion Starter #1
Does anyone know the diameter of an underdrive pulley vs. a stock one for a 89TII motor.
Thanks
 

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Discussion Starter #3
I agree. I'm trying to figure out if mine is stock.
Thx

Sent from my LG-H918 using Tapatalk
 

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question re underdrive pulley

what happens with the groove in the back for the power steering belt
is it also underdriven or still the same ??

would the 120 alt still be an advantage over the 90a alt with the u-d-p on the 120 a one?
 

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bigger alternator . heavier mass to turn...
if you are looking for power. i would go with the lighter alternator.
:)

us miata racers hunt down the lightest alternator of the bunch and the lightest starter option of the bunch.

we are weight weenies though
 

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ok something to consider -I'm building a street /road course project , not a drag car

would the underdrive pulley vs lighting issue be better / worse or still same, with LED projector headlamps and their associated hardware ??

should add , I have am electric water pump already so the pulley might be redundant anyways

I'm most curious as to how much the voltage supply actually drops in real time

I've already planed constant voltage supply /fuel pump controler and constant voltage for the ECU add on's so I'm really only interested in knowing if the pulley would screw things up needlessly

(my truck alternator started failing and the ABS light started coming on
replaced alt .. ABS light went out and stayed out
only difference .. voltage became constant again ..)
 

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tryingbe doesn't, I never had an issue with a 120amp alt at night. Though I had my headlights relayed as well. Also porting the water pump and shaving every other fin off helps the motor spin up faster, and reduces cavitation in the cooling system.


1st thing I do is throw on a UDP, port and mod the waterpump and an aluminum flywheel. Makes the motor way more fun and rev happy without losing torque.
 

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I have to say not all underdrives are Aluminum . i have a steel version , although it is a vintage very early version .
 

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you are missing the point . i get what your saying but they aren't all aluminum . do your home work ,for the parts you plan to use . Here are the pulley dimensions you seek . from outer to inner-107 mm , 111 mm , 72 mm the steel version is most likely a FM part as we used alot of their turbo parts in the 90's .
 

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tryingbe doesn't, I never had an issue with a 120amp alt at night. Though I had my headlights relayed as well. Also porting the water pump and shaving every other fin off helps the motor spin up faster, and reduces cavitation in the cooling system.


1st thing I do is throw on a UDP, port and mod the waterpump and an aluminum flywheel. Makes the motor way more fun and rev happy without losing torque.

ok thanks
sounds like it's a no harm in trying kind of thing
 
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