Importance of RPMs?
- Thread starter efript
- Start date
The advantage is in gearing.
With the NSX, because of VTEC (variable valve timing), the engine can rev higher without the torque falling off; the torque stays relatively flat as revs rise. This means that you can rev the engine higher while staying in the same gear. And, as a result, you don't lose acceleration due to shifting to a higher gear, as soon as you do with a more conventional engine.
You can read a more lengthy explanation here.
With the NSX, because of VTEC (variable valve timing), the engine can rev higher without the torque falling off; the torque stays relatively flat as revs rise. This means that you can rev the engine higher while staying in the same gear. And, as a result, you don't lose acceleration due to shifting to a higher gear, as soon as you do with a more conventional engine.
You can read a more lengthy explanation here.
The very simplified version:
The more fuel/air mixture burnt in a given time, the more work done.
So you go large displacement i.e suck in a few huge gulps during a given time, OR
high rpm i.e. suck in lots of small gulps during the same amount of time.
F1 cars happen to be a good example. Since there are restricted to a 3 litre displacement, they turn to high rpm (18000 rpm, consuming more than 650l of fuel/air per sec.) to produce more than 850 bhp.
The more fuel/air mixture burnt in a given time, the more work done.
So you go large displacement i.e suck in a few huge gulps during a given time, OR
high rpm i.e. suck in lots of small gulps during the same amount of time.
F1 cars happen to be a good example. Since there are restricted to a 3 litre displacement, they turn to high rpm (18000 rpm, consuming more than 650l of fuel/air per sec.) to produce more than 850 bhp.
From what I understand you get more horsepower. You steal a little torque form the lower revs and place it up higher in the RPM range, you end up with more power.
nsxxtreme said:
Yes and no.
First of all, VTEC doesn't "steal torque from the lower revs". Torque at the lower revs doesn't change at all. It simply adds torque at the higher revs, to keep it from dropping as revs rise.
You do end up with more power (horsepower); that's because power is torque times revs. But that's a mathematical equation more than anything else; torque, not horsepower, is the force that moves the car. However, the horsepower figure is meaningful because it, in effect, reflects the gearing advantage of the VTEC cars.
All of this is explained in the article linked above.
Efript,
Good question. Not so easy to answer.
Basically, you can get the same power and torque from big displacement with low rpm or small displacement with high rpms.
However, big engines use lots of fuel at any speed while smaller engines can be (NOT: will be) very economical and low revs. Bigger engines are also bigger and heavier.
In the NSX, like already said above, the high revs give the car the ability to use short gearings and still achieve high speeds. My NSX is doing 4K rpm at 100 mph. Another car might be doing only 3K. To be able to do that its gearing must be longer to achieve the same speed with lower rpm.
When I look at a torque dynograph of my NSX is see that I have 90% or more of the maximum torque over a rev-band of 5500 revs (from 2700-8200 rpm).
Good question. Not so easy to answer.
Basically, you can get the same power and torque from big displacement with low rpm or small displacement with high rpms.
However, big engines use lots of fuel at any speed while smaller engines can be (NOT: will be) very economical and low revs. Bigger engines are also bigger and heavier.
In the NSX, like already said above, the high revs give the car the ability to use short gearings and still achieve high speeds. My NSX is doing 4K rpm at 100 mph. Another car might be doing only 3K. To be able to do that its gearing must be longer to achieve the same speed with lower rpm.
When I look at a torque dynograph of my NSX is see that I have 90% or more of the maximum torque over a rev-band of 5500 revs (from 2700-8200 rpm).
vtec is a different animal. I was speaking in general, you could have more low end power in a lot of hondas but honda revs the crap out of them because they know the torque can be made to make more horsepower at higher RPM's. I think you will find that even a vtec system could be made to make more power down low at the sacrafice of losing power up top.
nsxtasy said:
nsxxtreme said:
I don't think you understand the difference between power and torque, or how VTEC works. Power doesn't matter, except as a reflection of gearing. And VTEC does not affect torque below the VTEC crossover point.
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