[slowbird]

Originally Posted by R 70 Judge

Non-racing application but going from a 160 amp alternator to a 320 amp Mechman alternator costs me like 2 miles per gallon in my Tahoe. It definitely has a significant draw.

Wow that's a lot of mpg to lose

[PAUL K]

Originally Posted by slowbird

That's interesting that you saw no difference.
I remember my dad having issues throwing belts on the Firebird one time, it would throw the belt probably somewhere between the 330 and 660, with the belt it ran mid 12.6 when it threw the belt it picked up a tenth to mid 12.5s. I know that the water stopped also but I'd think the fan would be worth more than the pump?? Maybe not?

Was the PS pump belt still turning? Maybe it helps more on a low horsepower combo .... It would be a larger increase in power percentage wise.

[PAUL K]

Originally Posted by slowbird

Wow that's a lot of mpg to lose

X 2

[Sirrotica]

My emergency genset is 5000 watts, or 41.66 amps, it has a 13 HP engine on it. Would it get by with a 5 HP engine, absolutely not.

When the electric fans kick on at a modern car idling, the engine lugs down 150 to 200 RPM before the computer idles it back up.

You can only do so much work with a certain amount of energy expended, whether it's being direct driven by belts, or it runs a generator that spins a motor. If there is much less HP being taken by electric fans, then they're not doing the same amount of work, moving the same amount of air. It's going to be pretty difficult to say that an electric fan moves the same amount of air as a belt driven fan because every electric fan manufacturer doesn't use the same formula to determine CFM.

We do know that in a street driven Pontiac V8 will seldom run cool with most electric fan systems, but when you go back to a belt driven fan it will run cooler. You're clearly moving more air with the belt driven fan, it's apples to oranges.

You don't typically gain any energy advantage by running a fan with an electric motor, if it's actually doing the same amount of work as a belt driven one. I don't know of a laws of physics that you gain energy by using a different mode of energy transmission, be it fluid/hydraulics, electric, or mechanical drive, such as a belt.

I don't see that you can do the same amount of work, with less energy being expended, or less drag on the engine. There is no free lunch.

[slowbird]

Originally Posted by PAUL K

Was the PS pump belt still turning? Maybe it helps more on a low horsepower combo .... It would be a larger increase in power percentage wise.

No he always took the power steering belts off to race, that was .06-.07 itself I believe.

[25stevem]

Let’s not forget some facts here gang!
Other then headlights and 2000 watt sound systems electric fans eat up the most current out of a Alternator.
But your fans should not need to run for that long atleast in a street car once your above 30 mph, I mean if your cooling system does not need to be crutched by having the fans running at that point.

[krisr]

Originally Posted by 25stevem

Other then headlights and 2000 watt sound systems electric fans eat up the most current out of a Alternator.

Not with todays cars/electricial loads. Some fuel pumps will take 20amps to run which is why most new stuff will PWM a pump, plus new cars run electric power steer pumps. Hell even IGN1A coils can chew up to 10A per coil with a LOT of dwell & boost. Radiator fans typically chew 12-15A each and again, today they PWM them.

[25stevem]

Yes, but the OP I don’t think is talking about a new production car, so once again a thread here has gone of the rails for the sake of chewing the fat.

[Half-Inch Stud]

Originally Posted by Goatracer1

To generate 140 amps at 13 volts requires 2.44 hp. Volts times amps divided by 745.7 equals HP.

Yes. And the Alternator efficiency (at cruise) is booked at 65%. I think more HP is lost during Accel.

[Stan Weiss]

Originally Posted by Sirrotica

My emergency genset is 5000 watts, or 41.66 amps, it has a 13 HP engine on it. Would it get by with a 5 HP engine, absolutely not.

I don't see that you can do the same amount of work, with less energy being expended, or less drag on the engine. There is no free lunch.

5000 watts = 6.7x HP

5 HP = 3728.5 watts

Then add friction to the process and a safety margin.

Stan

[Stan Weiss]

Originally Posted by slowbird

No he always took the power steering belts off to race, that was .06-.07 itself I believe.

Back in the day. lol On my brothers '62 Olds the power steering was just over .1

Stan

[Cliff R]

Since my 455 never even thought about running hot, and was actually a PITA to get up to temps I tried switching from a clutch fan to electric a few years back.

The trade off was not worth it. You are no longer driving the fan and robbing crankshaft horsepower for cooling, but the drain on the battery and required work from the alternator offset the gains. The alternator was working so hard to keep the battery charged that I'd "spin" or "twist" alternator drive belts at the track at high RPM's. That NEVER happened with a clutch fan set-up.

I also killed the battery a few times in hot summer days idling around the pits and the cooling fan running and had slow cranking to refire the engine to make a pass. I really didn't see enough improvement in ET or MPH to offset the negatives so put the clutch fan back in place and ditched the electric fan set-up........

[J GLASGO]

On my Pure Stock drags RA4 GTO,, I put a toggle switch to bypass alternator load. No difference in et or speed.

[NeighborsComplaint]

Originally Posted by Half-Inch Stud

The math holds for : HP lost = (14.4V x 130A /0.65 efficiency) / 746

Most who have posted forgot the efficiency you mentioned. 1Hp may equal 746 Watts but an alternator is not 100% efficient so output does not equal input due to drive ratio (pulley size), frictional losses and heat.

[george kujanski]

"To generate 140 amps at 13 volts requires 2.44 hp. Volts times amps divided by 745.7 equals HP. "

More accurately, 2.44 HP is the equivalent output; the required mechanical input is more like 5HP given the efficiency of about 50%.

George

[R 70 Judge]

Originally Posted by slowbird

Wow that's a lot of mpg to lose

Originally Posted by PAUL K

X 2

I went from getting around 320-330 miles per tank to 270-280 miles per tank. It is pretty crazy how dramatic the change is. The Mechman died once a couple years back and while it was out for repair I switched back to the 160 amp alternator and my gas mileage came right back.

[Dragncar]

Originally Posted by J GLASGO

On my Pure Stock drags RA4 GTO,, I put a toggle switch to bypass alternator load. No difference in et or speed.

I have pulled the field wire and did not see a difference either.

[Half-Inch Stud]

Seems crazy how inefficient the car Alternator is rated 65%. Before knowing i would have assumed > 92%.

[lust4speed]

Originally Posted by 25stevem

...But your fans should not need to run for that long atleast in a street car once your above 30 mph, I mean if your cooling system does not need to be crutched by having the fans running at that point.

I would argue that point. My '67 GTO has a high pressure area under the engine that builds up with speed. My fan does as much work at highway speeds as idling around town. Now if I were to get busy and make up an air dam for the front of the car blocking the airflow then that high pressure area would go away and the air would freely flow through the radiator. I remember reading that Trans Am's that had the front spoiler removed would run hotter on the freeway. Sounds like they had possibly an even higher pressure area under the engine bay.

Also as said above, a fan has to move a certain amount of air to maintain engine temps. This required energy should really be close to even between mechanical and electric fans. Otherwise the no-free-lunch principle would be violated.

[Sirrotica]

Originally Posted by lust4speed

I would argue that point. My '67 GTO has a high pressure area under the engine that builds up with speed. My fan does as much work at highway speeds as idling around town. Now if I were to get busy and make up an air dam for the front of the car blocking the airflow then that high pressure area would go away and the air would freely flow through the radiator. I remember reading that Trans Am's that had the front spoiler removed would run hotter on the freeway. Sounds like they had possibly an even higher pressure area under the engine bay.

Also as said above, a fan has to move a certain amount of air to maintain engine temps. This required energy should really be close to even between mechanical and electric fans. Otherwise the no-free-lunch principle would be violated.

That is true about the 3rd gen T/As overheating without the chin spoiler. I was doing some work for a car lot that had sold a 84 anniversary edition that the owner had dragged off the chin spoiler on a parking stop. It would O/H on the highway, but not idling. As soon as the spoiler was replaced, no more problems, very sensitive to not having that piece of aero hardware in place.