The magic to that is if you can rev to 9000 rpm and still make power, you can use a much higher final drive ratio and effectively increase acceleration by much more than just the extra HP. 300hp at 10000rpm w/ right gearing is wayy faster than 300hp at 6000rpm with appropriate gearing.

 

Like say before. Intake, plenum, valve size, valve springs, cams, runners/port design, stroke of piston (hint why smaller engines rev higher), weight of piston/rods (why NSX uses OEM Titanium rods) and balancing of the whole motor unit.

Pretty much an engine gets build from the ground up to do this. You can take a VQ for exaple and make it rev to to 9000 rpm but it will put more strain on the motor than a motor that was design to do this.

But when you want to gain higher RPM capability/power you do it at the cost of loosing lower power/torque. You have to give to gain something.

 

Not always true. Bikes for example have a flat torque curve from 3k to 18k. It all depends on the engine, how it is designed and what kind of induction it use

 

well bikes aside. thats a different talk

 

Sometimes, there is no point to rev that high when you're not making any power. If you want to rev to 9k, you have to upgrade everything to be safe. This includes, valvetrain (springs, retainers, valves, cams), pistons, rods, knife edge crank, harmonic balancer (damper), flywheel, clutch, oil pump.

Basically, a new motor.

 

Yea, if you grind a cam to have (assuming not variable valve timing) high RPM timing, you grind it to prevent what is called valve overlap (among other things that are adjusted as well) at higher and higher RPM's the valves need to open and close faster, so if you dont have a strong enough spring to pull it back open, and your cams dont hit at the right times/angles it is possible to have both intake and exahust valves open at the same time... aka valve overlap = bad for hp. Doing this will cause the timing at low RPM to be quite a bit different as well, with less time for both valves sets to be open vs piston position, and will cause you to loose low end torque (well not always, but usually, there are tricks you can do, but since variable valve timing... it's a mute point). With variable valve timing (BMW I believe was actually the first car manufacurer to do it... starting in the 1980's, then honda with VTECH, IIRC) you can just adjust.. say the length of a silenoid on the end of the valve lifter, thus effectively changing the cam grind.. etc, there are other ways of doing it too, some manufacurers use a special cam gear that lest you change how it rotates the cam, etc. With this, it's possbile to get the best of both worlds (or well... better of both worlds) so you prevent high RPM valve overlap, while still allowing for better low end torque...

Also, think about it this way... when your pistons go up and down, they travel a certain distance, right? When you rev faster, they have to traverse that same distance in a shorter amount of time..... also, when they are going up, and then reach the top, they have to come to a complete stop, and then go back down, come to a complete stop, and go back up, etc, etc. If you have a large heavy piston with a long stroke (distance for the piston to travel) then you have a very heavy fast moving piece of metal on the end of a rod, held on by a bolt, and the more you rev, the faster it goes. AKA the more force you put on the bolt/rod. If you rev too high, and the bolt, crank, or rod cant handle it, what ever one fails first... BOOM goes your motor. So for high reving, smaller lighter pistons, with smaller strokes, better balances and stronger components are all needed... well for serious gains in RPM anyways. I mean, there is almost always a margin that is engineered into the system, but with better and better engineering that margin gets smaller, that's why engines arnt super overbuilt like they used to be, the engineering is better, so you dont have to overbuild it so you make sure it works.

In rotary engines there is a triangle that looks like it's sides are buldged out that fits inside an oval shaped combustion chamber, which has it's elongated centers pushed in... so the triangle kind of wobbles in the oval, allowing 3 complete combustion cycles per RPM per rotor. There are no valves, only ports, the motion of the rotor moving past the port pushes the exahust out, and sucks the fresh air in. Because you dont have a valve train, and no super large amounts of acceleration (aka making a piston go up, come to a stop, come back down, come to a stop, go back up, etc) you can get very high RPM out of them, but they are also usually only 1-2 leters in size... But still can put out some decent HP, just not much torque at low RPM (kinda hard to make the rotor spin, as the force comes from the expanding air pushing sideways on the rotor as it's the only way it can get the rotor to move, which has a shorter lever arm than say, a long stroke large piston engine, so you dont get much low end torque (this is because the crank goes straight through the center of the rotor... well for the most part)). The majority of their torque comes from stored energy in the rotor/fly wheel.... which is why you generally dont see rotary engines with 9 lbs fly wheels... though some people do do that.

 

That statement is downright silly to anyone who understands horsepower. What the two engines above demonstrate is one engine with a lot of torque down low, and one with less torque up high.

What does the work of accelerating a vehicle is torque, and the torque range of a 10,000 rpm 300 hp engine is very limited. (If you believe that horsepower is more important than torque fine, the explanation is the same) Accelerating through the gears you'd need twice as many gear shifts with the 10,000 rpm engine, and every gear shift means you lose time. Put a Formula One engine in a 4000# car and compared to a 6000 rpm 300 hp engine it will be a dog regardless of the gearing.


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