Post by
float_6969 »
https://forums.nicoclub.com/float-6969-u780.html
Mon Mar 16, 2015 5:16 am
If you want to twin-charge because you think it's cool and you have the means, then I say go for it. If you really think you could hit 200Nm @ 1000 rpm with ANY supercharger, you're on the wrong path. That kind of low end torque requires leverage that you're only going to get from a long stroke or lots of cylinders. You can't throw boost at something turning that slowly and compensate. Have you ever tried to run in 5th gear at a really low rpm, like 1500? Do you remember what the engine sounded like? If you then threw 7psi of boost on top of that situation, the engine would grenade itself, VERY quickly. We're not being contrary or negative here. The issue is physics. Torque comes from leverage. Leverage come from the length of the lever, and some force acting upon it. The easiest way to make lots of torque is to have a really long lever. The lever in the case of a piston engine is HALF the stroke. Let me repeat that, HALF OF THE STROKE. If you have a really short lever, and you're trying to make a lot of torque, then the only option you have is to use A LOT of force. When you use that much force, you can start to have issues with the materials you're using for the lever. Steel and aluminum and only handle so much bending action before they start to fatigue. To help you get a feel for what we're dealing with here, lets do some math.
200Nm~145 ft/lbs of torque
The stroke of the CA is 83.6 mm, which is equal to 0.2742782 feet.
The leverage used to create torque is only half this distance, so 0.2742782/2=0.1371391 feet.
To create just 1 ft/lb with a lever that long, you would have to place a 7.291866433424166 lb weight on the end of that lever.
So to re-iterate, a lever of 0.1371391 ft with 7.291866433424166 lbs placed at the end of it and the other end of the lever attached to a rotating shaft will create 1 ft/lb of torque. The length of the lever is fixed (0.1371391 ft), so the only thing we can do to change torque is to increase weight. So create 145ft/lbs, we simply multiply our weight by 145.
7.291866433424166 lbs * 145 = 1057.320632846504 lbs.
You would have to place a weight of approximately 1057 lbs on a lever 0.1371391 ft long to create 145 ft/lbs of torque. That's a MASSIVE amount of weight. Honestly, the idea that it's possible at any RPM is amazing. Now to be completely fair here, I'm assuming that we have 0 (zero) RPMs and only one cylinder. In reality, we have multiple cylinders and RPMs, which changes things a bit because once you start spinning something, it has energy in it from the combustion cycle before, so we don't have to make the full power every time, and the faster you spin it, the more energy you have from before you pass on to the next cycle. That's the important part. Making 145 ft/lbs on a CA given any RPM isn't hard to do. Making 145 ft/lbs given any number of cylinders, or stroke on the crankshaft isn't hard to do. But if all you have to work with is an engine with a short stroke and not very many cylinders and lower RPMs, that number becomes VERY hard to achieve. And the more you lower the RPM, or raise the torque, the worse the problem gets. Eventually you hit a limit where the properties of the materials that you're using are not capable of supporting the force that's applied to them, and they fail.
Honestly, if you're REALLY set on lots of low end torque, you should look into a custom hybrid electric system. Electric motors make 100% of their torque at 0 (zero) RPM and don't have the inherent limitations that all piston engines carry.