6.5 Precups - Power -OR- Economy?

[Robyn]

The fan is a big boat anchor for sure. Unfortunately the little electric units wont even come close to pulling the wind the direct drive units do.

I am faced with a serious fan dilema in my Hummer Kit in that the room up front for the radaitor is not enough to allow for the factory unit. Its gonna get a small aluminum unit in front as well as a small aluminum unit under the truck in the rear with a set of electric fans. Gawd I hope it works.
Total cooling area will be more than the one factory unit BUTTTTTTTTTTT.

[DmaxMaverick]

About that fan thing.......

The "27 HP" it takes to turn the fan is at full rated RPM. It is substantually less at lower RPM's. The marketing of the alternative kinda' left that part out. Also, power requirements increase exponentially with increasing RPM, so at 50% rotational speed, it is much less than 50% of that 27 HP.

The engine driven fan is many times more efficient than any electric setup.

Both fan types use power from the acc. drive belt. The electrics lose efficiency through the alternator, wiring, battery, and motor(s). The engine driven fan loses efficiency only due to its mass and operation period. It is "clutched", but is never really "off".

Sure, it takes more HP to turn it. And it turns when it doesn't need to. There is a better alternative than electric, if you goal is efficiency.

If you were to reduce the mass and capacity of the engine driven fan to near the capacity of an electric, it would be much more efficient, except........when it doesn't need to turn. A thermostatic controlled on/off clutch would also have to be used. Electric, like the A/C clutch, or air operated, like OTR applications would work well. The viscous coupling (fan clutch) will have to go. A remaining drawback is the low engine RPM operation.

Now.......
If an electric fan is capable of keeping a 6.5 cool, a similarly capable engine driven fan would be more efficient. Electrics have generally about a 50-60% capacity of the OEM fan. So, if you were to reduce the capacity of the engine driven fan to near that of the electric, it should be more efficient. The capacity can be reduced by downsizing the mass, and rotational speed. If it doesn't work, then the electric would not have worked under the same conditions.

There are still other factors to consider, like water pump speed, climate, and load, but I think the maximum efficiency can be had w/o an electric fan. Perhaps a combination of both. An electric for lower, and engine driven fan for higher RPM's. The OEM fan was designed to work (or supposed to) while operating at the maximum capacity of the truck, so it has to be overdesigned for less than those conditions. An electric fan alone would be no match under the same conditions.

[65TD]

27 HP is a ridiculous number to assign to this.

If you examine the power required to replace this 27 HP with alternator output you can convert to amps.

1 hp = 745.699872 watts

27 * 745.69 = 20133.63

watts / volts = current

20133.63 / 12 = 1677.8025

1677 amps of current to provide 27 HP.

So lets say the electric fan is drawing 25 amps or less than 1/2 hp.

Cruising down the highway at 45 mph your truck may produce 50 hp. 27 hp for the fan and 23 to get down the road. So our electric miracle fan is going to save millions.


Loss of power in electric components considered it could take roughly 100 amps of electricity to produce 1 hp of electric fan power.

[baker2acre]

DmaxMaverick...

I see your point, to a degree. However in this condition I must respectfully disagree. I think your comparison isn't apples to apples... or well it may be but in an orange basket. In the setups that use the electric powered fans they are thermostatically controled!! Meaning if not needed they can be turned OFF. In this situation where mileage is the goal the ability to turn a power requirement OFF would be invaluable!! This is why our oems have clutches... but they still draw power when off. Apples to apples I agree that an electric unit is less efficient when operating, but in a 500 mile cruise where an electric fan may come on for... let's say 50miles of that 500 while the oem unit has been operating in full or partial mode for the entire time. Also, I'm sure that the OEM setup could be reduced in size and or speed to lessen it's draw but you will in turn reduce it's effectiveness by the same measure. The electric would still be there when you do need it.

[DmaxMaverick]

DmaxMaverick...

I see your point, to a degree. However in this condition I must respectfully disagree. I think your comparison isn't apples to apples... or well it may be but in an orange basket. In the setups that use the electric powered fans they are thermostatically controled!! Meaning if not needed they can be turned OFF. In this situation where mileage is the goal the ability to turn a power requirement OFF would be invaluable!! This is why our oems have clutches... but they still draw power when off. Apples to apples I agree that an electric unit is less efficient when operating, but in a 500 mile cruise where an electric fan may come on for... let's say 50miles of that 500 while the oem unit has been operating in full or partial mode for the entire time. Also, I'm sure that the OEM setup could be reduced in size and or speed to lessen it's draw but you will in turn reduce it's effectiveness by the same measure. The electric would still be there when you do need it.

I agree, and I stated that as well. The viscous coupler will have to go. A different method of engagement will have to be used to gain maximum efficiency. The OTR applications use an air operated clutch, and it can be seen as being many times more efficient. The engine can be running, and the fan is barely moving, if at all. Engagement is obvious....squeel (clutch engagement), and roar (fan moving air). Unfortunately, the OEM fan would very likely be inappropriate for this application. It is designed to operate with a viscous coupler, and be under load all the time, just more or less depending on the clutch engagement.

I was comparing the apple to apples. The OEM fan against the aftermarket's offering. The goal is the same, and they do the same thing....move air. My reason for posting was to compare the raw efficiency between the two, all else being equal.

Other things to consider....Electric fans are expensive. Repair/replacement of electric fans is expensive. Would there be enough economy gain by using electric fans to offset the initial cost and maintenance? How many miles would it take to recover the loss? And.....how much of the truck's capacity is lost do to a lesser ability to control engine heat with heavier loads, grades or summer heat? I realize maximum economy is the scope of this argument, but it is still a truck. At what point is it no longer useable as a truck? What price for that?

[gmctd]

The 27hp is probably rated in static conditions, such as full engagement at full throttle while sitting still, as in traffic, where actual dynamic also involves forward vehicular movement at 70mph, in 4rth overdrive with TCC locked up, and a great volume of 70mph air forced thru the radiator by that forward movement.

27hp is simple scare tactics, imo

[kevin77]

The 27hp is probably rated in static conditions, such as full engagement at full throttle while sitting still, as in traffic, where actual dynamic also involves forward vehicular movement at 70mph, in 4rth overdrive with TCC locked up, and a great volume of 70mph air forced thru the radiator by that forward movement.

27hp is simple scare tactics, imo

I have a little 24hp tractor that I hooked up to a silage blower (4' diameter fan) When I get the fan cranked up, I can blow leaves 30 to 40' - it sounds like an airplane taking off - and the neighborhood knows I blowing leaves - I cannot see a fan that is about 2' in diameter taking that much HP to run.

Kevin

[More Power]

Most things in a diesel engine are a compromise. Engineering manuals that discuss the Ricardo Comet precombustion chambers say swirl velocity is key to efficiency (best use of fuel & air). I suspect the size of the port in these 6.2/6.5 precups are a compromise as well. The smaller port precups allow for designed swirl velocity when running NA and the TD precups provide similar swirl velocity when under boost pressure. Unfortunately, most 6.5TD's aren't generating a lot of boost pressure when driven for fuel economy. This likely produces a swirl velocity below optimum.

Conversely, running an engine with NA precups at 10+psi boost pressure and higher RPM could result in less than complete evacuation of spent gases in the NA precups. Just a theory.

Most 6.5's are run somewhere in the middle, which I feel would benefit from the more efficient (for economy) NA precups. If I were building another power engine, I'd use the biggest TD precups available, and would run up to 20-psi max boost pressure using one of the new emerging turbochargers that are way more efficient than the GM-x series at the higher power levels.

My hunch is that the difference in power production capability between NA & TD precups is just a few % on an otherwise identically equipped engine running up to 12-psi boost pressure. On the other hand, the fuel economy advantage could be as much as 25%.

Jim

[baker2acre]

Thanks Dmax...

I think I see where you're going now. I must have jumped the line where you ommitted the viscous coupling for a more efficient connection. I mad some assumptions and generalizations and I appologize.

I was unaware that the OTR rigs used air!! I think that's rather clever. By the way, you brought up the issue of expense and maintanance/repair with the full electric setup... out of curiosity how would the full-independant clutch system either air or electromagnetic compare? How durable are the clutches and contact surfaces?