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Sad but funny observation

 

Silver Member
Username: Boopers

Lima, Ohio United states

Post Number: 143
Registered: Jul-04
so I'm sitting in my car at a stoplight listening to a song, and I just happen to look at my tach.... well when the music hits the tach drops a bit, pretty obvious that that means something bad, no noticeable dimming of lights though, only 1/2 volume too. guess that upgrade in alts is getting to be more of a need now, not later, type thing.
 

Silver Member
Username: Johnnylemoine

LaPlace, Louisiana United States

Post Number: 156
Registered: Aug-04
yeah I'd say. Thats wierd.
 

Silver Member
Username: Southernrebel

Louisiana USA

Post Number: 230
Registered: Mar-04
anytime your tach drops, your loosing ALOT of voltage...lol

i'd say you really need an HO alt.
 

Silver Member
Username: Fishy

Tamarac, FL USA

Post Number: 492
Registered: Sep-04
It simply means your alternator is putting a higher load on your engine when the bass hits(which makes perfect sense, the extra energy has to come from somewhere), not necessarily a bad thing unless it stalls your engine completely. :P I bet if you rev it up a bit you won't notice much if any change in rpm.

-Fishy
 

Silver Member
Username: Fishy

Tamarac, FL USA

Post Number: 494
Registered: Sep-04
Actually a higher output alternator can put MORE load on your engine at stoplights potentially making your "problem" worse. Personally, if your getting good voltage(no dimming lights) I don't think you have much to worry about.

You got a lil 4 banger in that vehicle?

-Fishy
 

Silver Member
Username: Boopers

Lima, Ohio United states

Post Number: 149
Registered: Jul-04
rofl, not even, it's a supercharged 3.8l :-) and the tach doesn't drop a whole notch, just like 1/4 notch, so like 10 rpm or so.... was just disturbed by that, figured it meant my alt was kicking it up a notch.
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 2235
Registered: May-04
10 rpm, or 100? 10 sounds a little low to be considered anywhere near a problem, the idle itself will fluctuate more than that.
 

Silver Member
Username: Fishy

Tamarac, FL USA

Post Number: 496
Registered: Sep-04
How much does your idle change when your a/c compressor kicks in? If its about the same I wouldn't worry none.

Remember unless you have massive amounts of torque your engine doesn't develop much HP at low rpm so any extra load will have more visible effects at idle.

-Fishy
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 2237
Registered: May-04
Really, horsepower is nothing but a measurement of torque x rpm. 400 lb ft of torque at 3,000 rpm of 8,000 rpm will be the same, horsepower will be higher with a motor making it at 8,000, but it'll still "feel" like 400 lb ft of torque, just like a 200 hp V8 will feel more powerful than a 200 hp four cylinder because the torque is actually higher over the RPM range, the V8s RPMs will just be lower than the four cylinder at peak horsepower. It's the torque that moves things, burns tires, turns accessories, etc :-)
 

Silver Member
Username: Fishy

Tamarac, FL USA

Post Number: 501
Registered: Sep-04
Yep, all "low end torque" means is lotsa "low end" horsepower or horsepower that is readily available at low rpm.

The formula for rotary power is simple. Its simply Torque times Radial Frequency(w=2*pi*f) or

P = T*w = T*2*pi*f = T*2*pi*RPM/60

-Fishy

 

Bronze Member
Username: Sixstar

Post Number: 62
Registered: Aug-04
Is it neccessarily the engine being strained? The tach is almost certainly electronic, and just might be fluctuating due to lack of power getting to it.

I would get out of the car and listen to see if the revs actually drop.
 

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 4544
Registered: Dec-03
Fishy is right.
when the bass hits, a large spike of current is drawn from the alternator, which puts strain on it.
this in turn puts more load on the engine which causes the RPM to drop just a bit.
it's more noticeable because you're at idle, and the alternator isn't in it's charging state, so its only putting out 12VDC.
above about 900rpm, you'll put out 13-15 volts as a charging bias, and this will supply better current to the system, and RPM shouldn't be as noticeable.
also, consider adding a capacitor to the system if you want the drop to be less noticed.
the cap will supply current for brief demands, then slowly recharge, thus smoothing out spikes in demand on the alternator. It won't replace a need for a larger alternator if lights are dimming etc.. but it will help smooth out spikes and handle little things like you're seeing.
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