6.5 Precups - Power -OR- Economy?

[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

[65TD]

Take an air boat for instance.

In 4" of water over marsh grass she glides along with ease.

Put it in sand it's not going to move well and it takes a lot more throttle.

Surprisingly it acts about the same in very tall wet grass and reeds.

In the case of sand it's just the friction on the bottom. Requires more volume of air. In the tall grass it's more the obstacles preventing the free flow of air that requires a lot of power.

In both it seems it's not as much the weight of the prop as it is the airs resistance to movement.

[JohnC]

One benefit to having a fan clutch that does not disengage completely is that it provides airflow for the intercooler and AC condenser even when the engine temperature is under control...

[baker2acre]

Shouldn't the exposed frontal area of our trucks handle that heat load at speed?? The only time that would not be so would be at low speed manuverings?

[TurboDiverArt]

One benefit to having a fan clutch that does not disengage completely is that it provides airflow for the intercooler and AC condenser even when the engine temperature is under control...

That's probably a good point. With the A/C on it would probably have to lock up the fan or command it to be on very frequently to generate airflow in around town driving. With the A/C off the clutch might do great for mileage but might deliver poorer mileage with the AC on. Maybe if you wired the fan to the compressor or something so that when the compressor turned on, so would the fan. I don't think you would want the fan locked up the whole time the A/C is blowing.

Art.

[65TD]

Electrics you see used in production all come on with A/C. Some have two fans. One of the two fans may be dedicated to the A/C and the other fan could still be off.

By the way almost all electric fans I have seen were on vehicles that did not have an option. Either due to motor alignment or positioning in the vehicle, or lack of room.

Also I pretty much run my A/C all the time if needed. If it's hot, or if the windows are fogging up. In humid areas it's needed a lot.

[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?

[DmaxMaverick]

With an air operated clutch, like on the OTR's, I am not aware of any significant repair issues. Another TDP member more exposed with this will have to chime in. I've been around them since they were first used, but have never seen one in need of repair. Perhaps that's my unique experience, or a testement to their reliability. For the application we are discussing, an electromagnetic may be a better option. The use of an air operated clutch would require an air source. The A/C compressor clutches are generally reliable, and will see similar power transfer with either a fan or A/C compressor. They are common parts and not very expensive. Some enginuity will be needed, but a clutch could be fabricated that will work. I've thought about this for many years, but never put it to practice. Maybe it's time.

[TurboDiverArt]

Money wise I'd think a lighter fan might be a better option. Building an electric clutch (like an A/C compressor clutch) might be too expensive to sell commercially, what would the pay off be? I think when I replaced my A/C clutch the price was somewhere between $200 and $300 for the part from NAPA. A fan would be cheaper I

[arveetek]

I know electric fan clutches are available for the 5.9L Cummins. I remember an episode of Two Guys Garage when they installed one on their Dodge truck. I don't know if there are any available for the other light duty engines or not.

I think the electric clutch is the perfect answer. You get the best advantages between the electric fans and the oem fans. Another benefit is the ability to manually engage the fan and let it run when you want. If you're approaching a large hill and you'll know the engine will get hot before reaching the top, you can flip a switch and engage the fan to get the maximum cooling before you get into trouble.

Casey

[ronniejoe]

The clutches used by motorhome chassis manufacturers should work. I saw some electrically actuated fan clutches on GM 8.1 L gas engines during an interview with the Workhorse Chassis folks. Should probably look up what they are using.

[baker2acre]

Jim,


How would compression ratio play into this... I.E. Higher CR + Smaller Cups+ Low Boost or Low CR + Big Cups + High Boost or any combination of... ? Would any combination offer the best fuel economy?