Electric Fans and Horsepower Losses/Gains
#11
#12
efans are easily in my top three list of mods.. right up there with $1200 re-gearing, and $375 custom tune SCT.... go figure, the efans ran me around $150 total, and if I weren't so **** about wiring, I could have gotten out of it for $70ish...
the delivery right off idle is real and present... right where you need it.. I could care less about RPM's above, say, 1500, the punch is right off the line, and the truck never got over 195* in any situation again..
the delivery right off idle is real and present... right where you need it.. I could care less about RPM's above, say, 1500, the punch is right off the line, and the truck never got over 195* in any situation again..
#13
#14
I'm using the Cherokee recall fan. I need a better fan shroud for better cooling.. Using the AC adds about 10-15+ degrees and then if in traffic for too long she'll slowly creep up to 210... other wise she does awesome... I have it just mounted to factory shroud which is probably reducing the effectiveness of the fan greatly.
#15
I read the results myself from the link, and while they were an interesting read, the alternator test did not mention the use of an electric fan.
While 65 amps would be plenty for a cabureted street rod with an HEI ignition, standard lighting, and small stereo, MPI vehicles draw more than 65 amps after startup to run the various onboard systems. If they didn't we wouldn't need 120 - 160 amp alternators.
While I'd be willing to believe that an electric fan setup (dual fans) likely draws less alternator HP than a oem clutch fan..I'd want to see the test. If you can find such a test, it would have more merit.
While 65 amps would be plenty for a cabureted street rod with an HEI ignition, standard lighting, and small stereo, MPI vehicles draw more than 65 amps after startup to run the various onboard systems. If they didn't we wouldn't need 120 - 160 amp alternators.
While I'd be willing to believe that an electric fan setup (dual fans) likely draws less alternator HP than a oem clutch fan..I'd want to see the test. If you can find such a test, it would have more merit.
But, I will give you a hint. An alternator under zero load draws zero power from the motor. An alternator under full load draws the maximum power from the motor. So, given that a 60A draw costs 3 HP, and you have a 180A alternator drawing 120A of load, adding six 10A fans, or three 20A fans, or two 30A fans, will cause an increase in parasitic loss of ______ HP?
And my 2nd gen 96 RAM came with the standard 85A alternator, like every other RAM of the year that didn't add the optional high output alternator. Dodge did not feel that truck "needed" a 120-160A alternator "to run the various onboard systems" or it would have come with one standard. Plus, that alternator, like all automotive alternators, cannot put out anywhere near 85A at idle, yet the truck mysteriously still runs, the lights mysteriously stay lit, the heater mysteriously throws heat, and the stereo mysteriously still plays music. And there are plenty of computer-controlled cars sold today, in 2012, with 65A alternators.
The truth is the ECM systems don't draw that much power. They operate @ 5V (industry is moving to 3.3V), whick means every 1A @ ECM voltage requires 0.41A @ 12V . Most Factory Repair manuals won't even mention the draw, as it's considered insignificant. Anecdotal evidence suggests 3A @ 12V or so ... that's the parasitic draw of a completely shorted ECM on a car battery. The rest of the system ... ignition, spark, etc ... is identical to a carbeurated, coil and electronic distributor engine, which is lower than a points, coil and distributor engine.
Last edited by Johnny2Bad; 12-14-2012 at 07:08 AM.
#16
The only time my fans even come on is when I'm just sitting still idling for a long time. The only time there is parasitic drag via alternator from the fan is when the fans are actually running, or perhaps within a moment or so of them turning off as the battery gets topped up. ie most of the time my efans presents no load at all to the engine. It's a great tweak imo.
That's also why if you want the lightest, most efficient cooling system, you should look at quality fans such as SPAL (there are others; just an example) who give complete specifications. The "advertised" CFM ratings you see are at zero pressure drop ... in other words simulating driving when you don't need a fan. It's actually the CFM rating of the fan with no radiator in front of it.
I suggest that you want to know the CFM rating at about 5~7 inches of pressure drop, which takes into account the presence of a radiator in front of the fan, and is as close to typical of stop-and-go traffic situations when you actually need the fan as you're going to get. If you have a 3 or 4-row rad, the pressure drop could be higher than that even. (Adding a row, the 2nd row is 1/2 as efficient as the first, the 3rd is 1/2 as the 2nd and 1/4 as the first, and so on. Each additional row has the effect of making the rad less like a mesh and more like a piece of plywood for airflow through it and pressure drop behind it). With almost any rad, once actually installed in a vehicle, the bottom 1/4 or so does mostly nothing and the top 1/3~1/2 does most of the cooling. Cross-flow rads are the most efficient.
That low pressure drop value will also be the point where the current draw is the highest, and you want to know that number as well. Some fans have zero CFM under those conditions.
The above is all you really have to go on ... nobody ... not even OEMs ... have figured out how to measure the pressure drop behind a radiator with any accuracy in an actual road-going vehicle. They get all excited if the dyno-equipped wind tunnel, the road test, and the computer simulation are within +/- 10% 10 times out of 20, and that's after doing speed compensation that could be 15 MPH different between each test method (ie wind tunnel with dyno @ 30 MPH = road test @ 40 MPH). That would be considered "state of the art" results, and they don't get it often. Nor have they even settled on what tools to measure the pressure with ... every OEM uses different methods, and none are very consistent nor has one method stood out as better than alternatives. They're all equally bad.
I have an experimental fan system I am going to try in another vehicle, assuming I can find the room, which I think I can. Not going to spill the beans just yet (and maybe never) but so far it looks promising on paper. There is data that says it works, but with HVAC and Aircraft, not automobiles. I have never seen a car with this system, although with some levels or racing you never actually know what they're doing. The real world tests will prove it one way or another though. There is a lot of experimenting but little science to engine cooling. When 21st century computer modelling only gives you a good guess, you know the state of knowledge is, at best, only half there.
Last edited by Johnny2Bad; 12-14-2012 at 08:54 AM.