crazy280 Posted December 5, 2007 Share Posted December 5, 2007 I was reading the HybridzFAQ web site ("http://jeromio.com/240z/faqdraft/index.html") and something didn't make sense to me: "1: How much increase in power is there by installing an electric fan(s) in place of the stock motor driven fan? No hard numbers but the stock fan performs work by moving air so you can gain some horsepower (probably a small amount) by moving that work to an electric motor. One thing to be aware of: the stock fan pulls a lot of air. If your cooling system is marginal at idle or low speeds on a hot day, then stick with the stock fan until you fix your cooling system issues. 2: How much more horsepower can I get from a lightened flywheel? None. Chassis dynos can erroneously report reciprocating mass decreases as horsepower increases. A lightened flywheel does not increase the amount of fuel or air an engine uses so it can't possibly increase the horsepower of an engine at any specific rpm. What a lightened flywheel does is allow the engine to rev faster, which means you can get to the horserpower you have sooner and thus accelerate quicker. Remeber, acceleration is a factor of horsepower and weight." What I don't get is "part 2". I could be wrong here, but my take is this: yes, a lighter flywheel doesn't increase fuel or air, so it doesn't produce any *gross* horsepower, but that doesn't mean it won't increase *net* horsepower. After all, an electric fan won't increase fuel or air either, but according to the site: "the stock fan performs work by moving air so you can gain some horsepower (probably a small amount) by moving that work to an electric motor". In other words, some of the gross horsepower was being wasted pushing air with the fan, and now that horsepower is being transmitted to the wheels. So is the engine performing work by moving the weight of the flywheel? If so, shouldn't removing that weight also free up some lost horses (at the wheels)? The chassis dyno readings verify this (and I don't believe they are "erroneous increases"). Are there any physics people on here that can explain this to me? Quote Link to comment Share on other sites More sharing options...
Guest TeamNissan Posted December 5, 2007 Share Posted December 5, 2007 The less weight or items for the engine to drive the less drain there is on the engines hp. Lightening any of the drive train won't add hp to the motor but rather allows more of what the engine was already making to the wheels. Lets say it takes 5hp to drive a fan, if you go to a electric fan then thats 5hp you just gained. Same goes for lbs lost, its easier for the motor to spin a 10lb flywheel then a 40lb flywheel so w/e hp it took to spin that extra 30lbs is now gained. There IS VAST amounts of lit written about the topic. So obviously there is much more to it then I just described. Changing the rotating mass will not only change hp but other engine characteristics as well. You should get the gist now though, as far as your questions are concerned. Quote Link to comment Share on other sites More sharing options...
Thumper Posted December 5, 2007 Share Posted December 5, 2007 I was reading the HybridzFAQ web site ("http://jeromio.com/240z/faqdraft/index.html") and something didn't make sense to me: "1: How much increase in power is there by installing an electric fan(s) in place of the stock motor driven fan? No hard numbers but the stock fan performs work by moving air so you can gain some horsepower (probably a small amount) by moving that work to an electric motor. One thing to be aware of: the stock fan pulls a lot of air. If your cooling system is marginal at idle or low speeds on a hot day, then stick with the stock fan until you fix your cooling system issues. 2: How much more horsepower can I get from a lightened flywheel? None. Chassis dynos can erroneously report reciprocating mass decreases as horsepower increases. A lightened flywheel does not increase the amount of fuel or air an engine uses so it can't possibly increase the horsepower of an engine at any specific rpm. What a lightened flywheel does is allow the engine to rev faster, which means you can get to the horserpower you have sooner and thus accelerate quicker. Remeber, acceleration is a factor of horsepower and weight." What I don't get is "part 2". I could be wrong here, but my take is this: yes, a lighter flywheel doesn't increase fuel or air, so it doesn't produce any *gross* horsepower, but that doesn't mean it won't increase *net* horsepower. After all, an electric fan won't increase fuel or air either, but according to the site: "the stock fan performs work by moving air so you can gain some horsepower (probably a small amount) by moving that work to an electric motor". In other words, some of the gross horsepower was being wasted pushing air with the fan, and now that horsepower is being transmitted to the wheels. So is the engine performing work by moving the weight of the flywheel? If so, shouldn't removing that weight also free up some lost horses (at the wheels)? The chassis dyno readings verify this (and I don't believe they are "erroneous increases"). Are there any physics people on here that can explain this to me? Yes a flywheel does free up flywheel horsepower or rear wheel horsepower, but not crank horsepower. But as you decrease the acceleration of an engine (say in a higher gear) the benefit is very minimal. So lets say in second gear you go through it in 2 seconds and you would gain (estimate out my butt) 15hp but when you are in 4th gear and it takes 8 seconds to go through it then you only gain (1hp). Once again though you don't increase the power output of the engine you just free up the power. Just like roller rockers. Better or worse? Quote Link to comment Share on other sites More sharing options...
crazy280 Posted December 5, 2007 Author Share Posted December 5, 2007 Thanks Thumper. Good to know! Quote Link to comment Share on other sites More sharing options...
johnc Posted December 6, 2007 Share Posted December 6, 2007 Chassis dynos do not measure horsepower, they measure the ability of a vehicle (engine, transmisison, driveshaft, differential, halfshafts, axles, wheels, and tires) to accelerate a mass. The horsepower number comes from a conversion calculation. Anything that you do to increase the efficiency of the vehicle's ability to accelerate the mass will show up in the conversion calcualtion as an "increase" in the horsepower number, even though the engine is using no more air or fuel. Its acutally just an increase in accelerative ability of the vehicle - which does mean the vehicle will accelerate quicker. But its not making any more horsepower. Engine driven cooling fans are different because they are performing work (moving a fluid - air) at a steady state rpm so the engine must use some fuel and air to get that work accomplished. A flywheel doesn't perform any work at a steady rpm, so lightening it doesn't reduce the work (and air/fuel) requirements of the engine. Quote Link to comment Share on other sites More sharing options...
bjhines Posted December 6, 2007 Share Posted December 6, 2007 On a chassis dyno you can "increase" the HP numbers by doing some simple cheats. Align the drive wheels straight, Use smaller, harder tires remove the brake pads remove the accessory belts disconnect the exhaust remove the aircleaner and a dozen other things that can increase your dyno numbers but have nothing to do with streetable horsepower. Quote Link to comment Share on other sites More sharing options...
crazy280 Posted December 7, 2007 Author Share Posted December 7, 2007 Thanks Johnc, I think this part explains it for me the best: Engine driven cooling fans are different because they are performing work (moving a fluid - air) at a steady state rpm so the engine must use some fuel and air to get that work accomplished. A flywheel doesn't perform any work at a steady rpm, so lightening it doesn't reduce the work (and air/fuel) requirements of the engine. It makes sense because once the flywheel is at rpm, its just kind of getting a free ride, whereas the fan is using the same energy all the time. So taking weight off the flywheel is just reducing the mass that the engine is accellerating, similar to taking weight off the vehicle (which explains the accellerative benefit), but no actual hp increase. Thanks for the wisdom guys Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted December 7, 2007 Share Posted December 7, 2007 I notice there is always reference to using an electric fan as freeing up HP. It does not free up as much as you would think when its on, it takes a few ponies to drive an alternator under load. Some of the fans out there draw major current. Evan Quote Link to comment Share on other sites More sharing options...
Zmanco Posted December 7, 2007 Share Posted December 7, 2007 It's my guess that the premise of a lightened flywheel increasing hp comes from those who measure on inertia-based dynos. Oversimplifying, inertia dynos determine the hp by how fast the drum's speed is increased by the car. Anything that lowers the rotational inertia of the drivetrain will result in a higher reading on this type of dyno, although won't necessarily mean that the engine is making more power. In fact, taking weight out of the wheels/tires, or putting on lighter brake rotors, would have the same affect. Funny how no one says that lighter wheels increase hp? Maybe that's an idea for a new brand of wheels Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted December 7, 2007 Share Posted December 7, 2007 It's my guess that the premise of a lightened flywheel increasing hp comes from those who measure on inertia-based dynos. Oversimplifying, inertia dynos determine the hp by how fast the drum's speed is increased by the car. Anything that lowers the rotational inertia of the drivetrain will result in a higher reading on this type of dyno, although won't necessarily mean that the engine is making more power. In fact, taking weight out of the wheels/tires, or putting on lighter brake rotors, would have the same affect. Funny how no one says that lighter wheels increase hp? Maybe that's an idea for a new brand of wheels Having gone from boat anchors to light rims before, your dead on. My suspension performed better as well. IMO lighter wheels are probabally a better (but more expensive) way to go! Evan Quote Link to comment Share on other sites More sharing options...
fhptom Posted December 8, 2007 Share Posted December 8, 2007 We just pulled the motor out of my friends racecar so I thought I would take a picture of his lightened flywheel. Just shows what a quality machinist can do for you. Tom Quote Link to comment Share on other sites More sharing options...
crazy280 Posted December 8, 2007 Author Share Posted December 8, 2007 How much does the average machinist charge for something like that anyhow? Quote Link to comment Share on other sites More sharing options...
Tony D Posted December 8, 2007 Share Posted December 8, 2007 I notice there is always reference to using an electric fan as freeing up HP. It does not free up as much as you would think when its on, it takes a few ponies to drive an alternator under load. Some of the fans out there draw major current. Evan There is the thing that nobody points out: "when it's on".... It is very unlikely that your electric fan will be on driving down the road at any speed over 30mph, or during a 1/4 mile run. And it's this time when all available horsepower is required, lettting the electric fan free up the 2-5 hp that a fan will soak up. If you look at the clutch fan engagement speeds and freewheel speeds even when the fluid coupling is disengaged, the fan is still being turned, there is no way to totally stop it it's using horsepower. On an electric, you can simply turn it off, elminating all parasitic drag. If the fluid coupling is engaged, the horsepower to drive it at locked-coupling speeds is prodigious. People really don't realize how much horsepower a fan can suck up when moving air. As an example, Ingersoll-Rand went to an electric driven fan on their air-cooled compressors (5hp motor) to give a perceived marketing advantage over a competitior Atlas Copco, who used a fan turned by the main motor driver shaft through it's compressor's gearbox. When comparing compressor total CFM output, purchasing agents would see the I-R unit 'made 25 more CFM' than the Atlas Copco did....But when you looked at total package absorbed KW, they were identical (at full load). One way or the other, the engine needs to be cooled. With an E-Fan it only cools when needed. With an engine driven fan, regardless, you are always using main motor power to keep it spinning. Also, using the battery as capacitance, the electrical load of the E-Fan turning can be dampened out as a lower overall load instead of a huge instantaneous hit to the alternator. So it's a lower drain than if there was no battery at all...same power is used, just sperada out over more time. Same as adding a large air vessel in a compressed air system---the more storage you have, the lower the hp requirement you can get away with to handle impulse loadings. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted December 8, 2007 Share Posted December 8, 2007 Also, using the battery as capacitance, the electrical load of the E-Fan turning can be dampened out as a lower overall load instead of a huge instantaneous hit to the alternator. So it's a lower drain than if there was no battery at all...same power is used, just sperada out over more time. Same as adding a large air vessel in a compressed air system---the more storage you have, the lower the hp requirement you can get away with to handle impulse loadings.Tony D, I agree with everything you wrote except this last paragraph. It would be true if the max output of the alternator was LESS than the demands of the efans. But in practice, unless every other electrical load was on (high beams, cabin fan, rear window defroster), even an older S30 alternator will have enough capacity to provide all of the power required by a typical efan. Only when the total current of all the loads exceeds the capacity of the alternator will the battery begin to provide power in a properly functioning car electrical system. I do think that we are beginning to split hairs here as an alternator outputting 30 amps at 14V will place less than 3/4 HP load on the engine. But this is a good discussion to help dispel some of the myths with regard to lightened flywheels and efans. Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted December 8, 2007 Share Posted December 8, 2007 Totally agree we are splitting hairs! However nobodies pissed yet so I consider this a valid conversation! lol. Back in the day I had a flex fan on my car with the bending blades.. that thing had to be the biggest HP drain ever. Plus it was a finger whacker! That was long before I understood such things. Evan Quote Link to comment Share on other sites More sharing options...
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