I finally got my HO Alt installed...

[jco1385 5,000+ posts]

couple questions.

1. when at idle, my stock voltmeter is very low but if i touch the gas it shoots up to where it needs to be. is this normal for a HO alt? the pulley on this one is smaller than stock so maybe thats why? (i have not put the DMM on it yet)

2. i've noticed that my sub seems to have that extra "umph" on the lows. am i hallucinating or could it be true? lol

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[audioarsonal 10+ year member]

Your voltage should be at least 13.7-14.7 at idle.There are a couple things you need to take into account when upgrading to a HO alt.The size of the alt pulley,the size of the crank pulley, and the idle rpm of the vehicle.

 

[tez4life Premium Member]

couple questions.
1. when at idle, my stock voltmeter is very low but if i touch the gas it shoots up to where it needs to be. is this normal for a HO alt? the pulley on this one is smaller than stock so maybe thats why? (i have not put the DMM on it yet)

2. i've noticed that my sub seems to have that extra "umph" on the lows. am i hallucinating or could it be true? lol

Agreed with the first poster about the voltage.

That extra "umph" is the system supplying correct voltage to your MTX amp, and allowing it to do its thing. Ive run several MTXs similar to yours and they like power.

Glad its sounding right, got to check it out sometime.

 

[jco1385 5,000+ posts]

Agreed with the first poster about the voltage.
That extra "umph" is the system supplying correct voltage to your MTX amp, and allowing it to do its thing. Ive run several MTXs similar to yours and they like power.

Glad its sounding right, got to check it out sometime.

it's definately on point. i'm getting ready for the USACi meet in a week //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

might be building the type X box this weekend. you got any corner clamps by chance?

 

[jco1385 5,000+ posts]

and as far as pulley sizes... where the hell would i find out that info? i'd say this pulley is ~1/2 inch (in diameter) smaller than stock. thankfully my tensioner took up the slack. i was thinking a new belt was in order

 

[dman4486 5,000+ posts]

smaller alt pulley would increase RPM of the alt....not decrease....and you need to look at the test curves of the alt to see how much power it produces at lower RPM's

some HO alts do not turn on till the motor reaches 1200rpm

 

[jco1385 5,000+ posts]

smaller alt pulley would increase RPM of the alt....not decrease....and you need to look at the test curves of the alt to see how much power it produces at lower RPM's
some HO alts do not turn on till the motor reaches 1200rpm

i know this. and i don't have a graph. i got this alt from a guy on here. i got the alt and a box. that is all

and it does seem to pick up around 1200 rpm

 

[dman4486 5,000+ posts]

IMO....If you are not getting voltage at idle, it sounds like the smallest pulley you can find would be best

 

[jco1385 5,000+ posts]

where should i look to find one?

 

[audioarsonal 10+ year member]

The size of the Alt pulley is relative to the Crank pulley size.Yes the smaller the pulley the bigger the ratio.But if you have an alt for a full size truck with an 8" crank pulley and a 2" alt pulley this wouldn't be the same ratio for one with a 6.5" crank pulley.Most alts turn on at 2400prm alt speed.So with an 800rpm idle speed and a 3-1 ratio alt to crank that would work.But if the crank pulley is smaller then the ratio becomes less then 3-1.So either the idle rpms need raised or a smaller alt pulley is needed.

 

[dman4486 5,000+ posts]

when I worked at Advance Auto, we kept a large box of them in the back...free for whomever needed one, all shapes, sizes and belt types

we let people go digging

 

[audioarsonal 10+ year member]

^^^I doubt he'll find a smaller Alt pulley.

 

[dman4486 5,000+ posts]

^^^I doubt he'll find a smaller Alt pulley.

we had some pretty d@mn small pulleys....just large enough to get the nut inside

 

[jco1385 5,000+ posts]

well this is from a 01-04 mustang 3.8l. i have a 97 3.8l engine. not sure on crank pulley ratio and all that jazz.

what should i do, other than just keep the engine rpm up? any other options?

 

[dman4486 5,000+ posts]

well this is from a 01-04 mustang 3.8l. i have a 97 3.8l engine. not sure on crank pulley ratio and all that jazz.
what should i do, other than just keep the engine rpm up? any other options?

without a larger main pulley or smaller alt pulley, idling up is the only option