Since doing the 160 tstat last year I've noticed that the fans of course run more often (ECM fan programming via HPP: on @ 185 F), however if they're running its usually in their low rpm mode. Still, this obviously places some extra load on the alternator.

How much power is bled off the engine by the alternator load? Any guesses? Enough to consider bumping the fan activation temp up to the next hotter setting (212 F)?

Has me wondering if the extra alternator load is negating any slight power gain from the lower engine operating temp...

Sometimes I think to much :crazy:

P.S. this is not intended to start a 160 tstat vs. stock tstat debate but I can see how it would develop into that :cry


[Modified by Lone Ranger, 10:56 PM 5/23/2003]

 

I don't think its that much... no more than 1 or 2 hp...

and to be honest, I don't think its that much.

 

The parasitic loss from the alternator is not a function of the alternator's electrical load, only it's rotational inertia, condition of the bearings, and pulley size. You're not adding any load, per se to the alternator, just time at higher load. I KNOW you're not losing any engine performance, and I don't "think" you're shortening the life of the voltage regulator in the alternator either, though I wouldn't swear to it (if you *are*, it's VERY minimal). FWIW, I have a manual fan switch so I can either let the ECM control the fans or I can. I typically leave the fans running ALL the time, and have not had any alternator problems in the 3-1/2 years I've had the car.

 

:withstupid: simple physics

 

Every watt of power that the alternator provides to the electrical system in your car comes from the engine. The alternator is not 100% efficient , so your engine supplies not only the power the alternator delivers, it supplies the losses too. At 105 amps, your alternator provides 1470 watts which is 1.97 hp, or including losses, about 2.35 hp robbed. Not only does your engine have to provide power to your fans which run more often trying to get rid of engine heat to maintain 160 F coolant, it also has to supply power to the water pump to circulate coolant which occurs at a higher rate trying to maintain 160 F. The factory thermostat allows a higher engine temperature which does not have to remove heat as much and the water pump and alternator losses are less. Not to mention lower thermal efficiency and therefore less hp at 160 F.

 

Hp is neglible & why would you care at idle - assuming your fans are functioning correctly? Electrical draw, on the CS130 (not your year) is a concern. Most of the 105 amp alternators can't keep up with a full load; ie, both fans blowing & the a/c on high for an extended idle. The fans will slow down and engine temps will climb, but for your year, that shouldn't be a problem, or if it is, check alternator output. If your concern is that your not seeing the hp you expect from the lower temps, well that'll just start a debate.

 

Now THERE's an original arguement for NOT using a 160° thermostat, at
least it's a first for me...

Too tired to check the numbers for watts and hp but I like the reasoning.

 

Into the abyss we go... okay, explain what you mean by thermal efficiency :) If you mean heat = energy therefore more heat = more energy while that is true as a law of physics I believe there are other factors at play in an internal combustion eengine that cause excessive heat to rob power, specifically higher heat increases the tendency for detonation and so timing is more likely to be decreased to compensate which causes less power to be developed. Also I believe, at least in the LT1, that the ECM sets the mixture richer when coolant temp exceeds 185 F. Someone on the forum saw this in logged data from his motor or something. The richer mixture tended to reduce power.

Also, with the standard mechanically driven water pump, how is it able to vary its drag on the motor in reaction to coolant temps? Unless you are saying that the coolant itself offers less resistance to being pumped when at higher temperatures, that I can see as being a possibility.

 

The more load you put on that alternator the harder it is to turn and that is the simple physics of it. However the amount is going to be fairly small, a couple of horsepower at most vs. full operating load and no load.

But here's my question. As soon as your wheelspeed exceeds 40 mph the fans kick off anyway. So why does it matter? It's essentially only costing you horsepower at idle.

 

I've been wondering what the fan hysteresis speed was... :cool:

 

We aren't going into the abyss, we are going into the world of thermodynamics! :D To keep the coolant at 160 compared to 180, you have to remove more heat and its the coolant that moves that heat. The coolant circulates at a higher rate (gph) and the water pump requires hp to move coolant, so at 160, your water pump draws more hp from the engine than it would if the coolant were at 180. Furthermore, the extra heat you are transferring to the atmosphere (by using a 160 stat instead of a 180) is thermal energy not available in the form of horsepower at the crankshaft. A larger portion of the heat (gasoline and air) supplied to the engine goes to the air instead of to the output shaft. Therefore it is less thermally efficient. I have quoted a test done by Continental Motors many times. They took some identical small engines (25-40 hp) and ran them for long periods at maximum hp and kept the coolant temps at various temperatures. They recorded that the engines delivered increasing hp with increasing coolant temps and the specific fuel consumption decreased (same fuel flow made more hp) with increasing temperature. They tore the engines down and measured the cylinder bore wear and the wear decreased with increasing coolant temps.

 

Actually its been said that GM's newer alternators (since the serpentine belt was introduced) are a much lighter duty alternator than the old ones. That is why it is recommended to never let an alternator bring a dead battery back up to full charge. Its been proven many times to kill the internals of these newer alternators. So I wouldn't be suprized that an alternator on a car setup with longer fan run times not last as long as one setup stock.

 

Here is my take on it, and take it with a grain of salt, the Alternator on the car is working all the time and truth be told its AC voltage ( 3 phase AC actually) and cant be stored so if your not using it its wasted, you lose a tiny amount of power as it goes thrue the rectifier ( diode) and voltage regulater ( which does create heat), for the 1 or 2 hp you lose from it dont worry about it, unless your car will only ever see a 1/4 mile strip and if thats the case remove it and run battery power alone. ( Total loss system)

i fail to see how there is any extra load on the alternator based on its output, once you take into account the total drag on the bearings,brushes and other moving parts of the sytem the load should stay fairly constant its only how much power the system is pulling from the alternator that changes.

the only power loss i could see is if you were pulling more amps from the system then the alternator could provide( then your on battery power) at that point you may have small computer glitches to the onboard computer or worse yet to your ignition system causing a weaker spark and hurting engine HP because of that.if thats the case jump to a high power unit from the car audio guys and dump a 200 or 300 amp alternator under there and never worry about it.

anyway thats just MY view on it. take it or leave it




[Modified by Delta, 9:21 AM 5/25/2003]

 

If you didn't take high school physics, then sign up for the next evening class. If you did, then why didn't you stay awake?
The alternator supplies electrical power (watts) and it does so by converting mechanical energy (input shaft torque and rpm) to electrical energy (volts and amps). The more electrical equipment you turn on, the more amps the alternator has to deliver and therefore the more torque is required at its pulley. The conversion rate is 746 watts per horsepower. A 105 amp alternator putting out its maximum current is delivering 14v x 105 A = 1470 watts. 1470 watts divided by 746 watts per HP = 1.97 hp. Alternators are about 80% efficient, so the input shaft hp will be 20% more , or 1.2 x 1.97 hp = 2.46 hp.
Why anyone thinks that the alternator shaft ONLY needs to be turned with bearing loss and windage loss torque and it will put out rated current does not understand the law of conservation of energy.

 

Okay, but under this theory the hotter an engine runs the more power it makes and that isn't the case with piston engines. They make better power when cool. 1/4 mile racers are always looking for ways to cool their motors down before a run so as to make better times. They've even been known to ice down their intakes to try and get the air charge cooler.

 

Right, I can't agree with the theory that the heat in the radiator is horsepower. Once the heat is in the coolant it is simply waste heat. The water pump also doesn't pump signifcantly harder to move 160 degree water than it does to move 180 degree water. The thermostat is there simply to set the MINIMUM temperature of teh coolant. Granted there is an optimal temperature point inside the combustion chamber but getting rid of the extra heat in your radiator doesn't cost any more power. If X amount of air is moving through the radiator that is constant, changing the thermostat will simply allow the coolant mixture to get cooler, it won't slow the car down.

I'm not going to pretend to know what the optimal combustion chamber temperature is but we must all understand that there is a practical limit. You can't always say "colder is better" or "hotter is better" There is a point of diminishing returns somewhere and there is a physical limitation as well.

Overall keeping the engine cooler will result in a cooler intake charge that will make more power but the temp of the intake charge is not the same as the combustion temperature and that needs to be kept in mind as well.

 

When you waste heat, you also waste horsepower. When you transfer heat from the burning fuel/air in the cylinder, that lowers the cylinder pressure and then also the hp. The rate of heat transfer is directly proportional to the difference temperature between the cylinder walls and the burning charge in the cylinder. The lower temperature your coolant is, the larger is the temperature difference and the more hp loss. 38% of potential hp is lost in the exhaust gases, and 36% of potential hp is lost in heating the block and coolant. 6% of potential hp is lost in engine friction. Go to google and check out," thermal efficiency of internal combustion engines".

 

... from CorvetteZ51Racer

My faith in your schooling is waning.

jfb has it nailed. Power is power. You have to produce it somewhere.
If you make a run with your headlights on high then you will run slower.
The A/C system is a good example of electrical load. It's an electromagnetic clutch that engages the system. The coupling requires quite a bit of power (equal to the parasitic loss of the compressor).

So who here runs 1/4's with the A/C on?

 

OK now back to the question how much elec. draw in amps is required to run i.e. a/c,both fans, a/c blower, lights, and the radio at the same time......I burned down my alternater last summer.......120 amp ........the repair shop said if you pull more than 60 amps for a continuose time the alternaters created heat will fry it .....he said any alternater what ever amp is designed for maximum load for short duration only..........he told me to bring my car in and he would check the draw but I never did........I'm supercharged so I have to run both fans even on the freeway.......anybody know? :cheers:

 

Go to Sears and buy their clamp on DC ammeter ($49.95). With all the loads you mentioned off, record the current, then turn on all the accessories and record the current. Subtract the 1st recorded amps from the second and you will know the current drawn. Multiply the total current reading (second reading) by the battery terminal voltage and multiply by 1.2 (for efficiency, assuming 80%) and divide by 746 and the answer will be the hp your engine is supplying the alternator.