[font size="1" color="#FF0000"]LAST EDITED ON 08-Feb-01 AT 09:46 PM (EST)[/font][p]Hey, I've got a set of performance pulleys from March that underdrives the accessories significantly. I also have an optima red-top battery with 900cca. Now, after driving my truck with this set up for about a month, I'm wordering if the underdriven alternator means my battery isn't getting enough charge at idle. the voltmeter stays at 14 when the car is at anything over 900rpm, but below that, it's only a matter of time before it's touching on 11/12. When I've got my stereo goin (200watt rms amp for the sub)i can see it begin to drop with each bass hit. I've noticed that the headlights and blower motor put a lot of load on the electrical system, so my voltmeter has seen 11/12 before the pulleys, but should I worry? it never goes below 11/12, but the lights will visibly dim, like when you leave them on and trun the car off. Is the battery gonna be fine, just the electrical system won't always be at 14? I was thinking about buying a higher amp alt from powermaster, but I read somewhere that alts with higher output actually put out lower at idle, true? Lemme know...

1989 F-150 : 5.0, shorty headers, Flowmaster cat-back, K&N filtercharger intake, March pulleys, "Multi-brand" performance ignition, soon to be Mass-Air...doesn't know she's not a Mustang

 

I'd revert to the stock pulleys if you want optimum charging system performance....It sounds like you need it with a 200 watt stereo!

 

A healthy altenator should put out 14.5 volts without a load (except for the engine running). You probably should be running a high amp altenator for your setup. Stock is only 60 amps and it sounds like you need to be pushing 200.

'82 F150 2WD w/351W (orig 300 I6)
Slik

 

Opinions are like a-holes, everyone's got one. Here's mine:

Ditch the underdrive pulley. If you have the stereo, you need the alternator at full power.

Get a bigger alternator. Determine size needed by adding up loads (use rms power from your amp, not peak) I bet you need at least a 125 amp alternator to run the system you got.

Add a 1 Farad cap to the system to handle the bass.

To compensate for the extra drag on the motor the new alternator will do, ditch the stock engine driven fan and get an electric fan.

That's it.
Randy

 

[font size="1" color="#FF0000"]LAST EDITED ON 09-Feb-01 AT 11:45 AM (EST)[/font][p]You see the setup I have below, and the stock alternator can't handle it at idle. I have to be going around 2k rpm or more for the alternator to keep up, but I would defintiely go with a larger alternator if you really push your system. Seeing as all my speakers are in the back seat, I don't usually run full blast.



Daywalker
92' F-250 351 4x4 xlt 4.10 5spd sprcab lngbed
Sound System: Stock Stereo, Rockford 800 watt amp, Vega 18 inch sub 400 watt rms, one Cerwin-Vega LS-12 3 way floor speaker with a 300 watt power capacity, and one Boise floor speaker with a 75 watt power capacity.

Performance Mods: K&N Air Filter.

Cosmetic Mods: Black Grill Guard, 5% window tint, bug guard, bed liner.

http://albums.photopoint.com/j/View?u=1426655&a=10683799&p=36629681&Sequence=0&re s=high

 

What never seems to be mentioned is while your worried
about your alternator and the rest of your elec system, you
are not getting the advertised peak performance and wattage
from your amps if you don't have full voltage on the system. So
there is no use spending all that money on big amps if you
compromise the output of the alternator with small pulleys.

 

I'm not so worried about the stereo being at full capacity (my girfriend can't handle the volume I can, and she's in the truck half the time), all I really care about is not killing my battery. I've already got the powermaster 140amp alt picked out and I'm just waiting for the $170. I still have the question I wrote: Has anyone else heard that high amp alternators acually put out lower at idle?

RGAZ: I was thinking about the cap too. Looks like I'll be looking for one of those as well. but about the electric fan...doesn't that defeat the purpose of getting a higher ampo alternator If I'm just gonna put more load on it like an electric fan? how many amps does a fairly inexpensive one draw?

Franklin2: Not big money here. That amp ran me $70 on sale, just a Jensen for the sub. and even at idle with 11/12 it still hits the 12" pretty hard.

Thanks for the input. Please keep in mind I'd really like to keep the pulleys, They gave me an extra 1 MPG and helped that 3000+rpm engine power. I'm willing to compromise with less than peak stereo output and dimmer lights at idle, but not with draining a $140 battery.

1989 F-150 : 5.0, shorty headers, Flowmaster cat-back, K&N filtercharger intake, March pulleys, "Multi-brand" performance ignition, soon to be Mass-Air...doesn't know she's not a Mustang

 

Run a powermaster 140 amp alt., slightly underdriven, puts out down to about 500-550 rpm @ just over 13 volts with blower on high, every lite I have lit (over 500w worth), and the A/C running, wipers on high, brakes and 4-ways on. They don't cut in until 2000 rpm at the alt. when used as a true one-wire set-up, however you have the option of using an extra wire to run the alt. anytime the ignition is on, this is what I did. My stock would quit around 650-700 rpm. The rating on it is for 140 amps, came with the pulley and is tagged as being tested with 90 amps at idle and 160 amps at 13.6 volts at full tilt, usually puts out around 14.6 or so with the normal load on it.

 

Some quick advice on the electric fan. You can gain substantial hp and mileage by installing the electric fan. You want to get the highest cfm with the lowest draw and covers the biggest area of your radiator. The best one that I have found is the Perma-Cool 16" that pulls 2500-2900 cfm with a 9 amp power draw. It costs about $90. The neat thing about the electric fan is that you don't need to have it running all the time. I have an electric on mine and it has not turned on all winter. The best setup is with a thermal switch that screws into a water port on your manifold or thermostat housing, tied to a relay that turns the fan on whenever the A/C compressor turns on, and wired to a manual switch that allows you to manually turn the fan on. If you want real cooling power, put 2 14" Perma-cools on your radiator for over 5000 cfm of draw at idle. That's a ton better than your stock fan will do.

'82 F150 2WD w/351W (orig 300 I6)
Slik

 

Thanks Chuck P., that's all I neede to hear.

Thanks for the fan recomendation too, Silk. I'll look into that.

1989 F-150 : 5.0, shorty headers, Flowmaster cat-back, K&N filtercharger intake, March pulleys, "Multi-brand" performance ignition, soon to be Mass-Air...doesn't know she's not a Mustang