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24K views 20 replies 11 participants last post by  kuhlka 
#1 ·
So I did some research and found couple fun video explaining the differences.

I have a question to ask for a few of you fellow (same car) owners but before I do I will lay down what I understand.

I am a total noob at cars so lower your standards for me.
While driving my brz, I noticed that when I change my gear above 4 RPM, I felt the car getting push or pulled even more. (note: i started driving manual in December so I made gear change at 3 RPM)
So according to those video I watched, I must have been very close to the trq peak? hp peak?
what does this mean? Torque 151 lb-ft @ 6,400 rpm (I got it from the subaru website)
 
#5 · (Edited)
This means that the engine produces 151 lb-ft of torque when it is spinning at 6,400 rpm (revolutions per minute). This figure is the peak torque, or the maximum amount of torque that this engine produces. Basically torque is what gets you moving, and helps you accelerate, so the higher the torque the faster the car will be accelerating.

At different RPM, the engine produces different amounts of HP and Torque, as seen in the chart.
Text Line Plot Slope Diagram
 
#10 ·
Every motor is different, and will have a different HP and Torque curve. There are tons of different variables that contribute to what the maximum HP and Torque numbers are, where they peak, and at what RPM they intersect. So, to answer your questions, there is nothing magical about the RPM where torque and HP are the same, it just is what it is, and it's different for each different motor. I don't know the technical reasons for why there is a dip in the torque curve around 4k RPM, I guess it's just a unique characteristic of this particular motor.
 
#12 ·
think about it this way.

torque is the rotational force that to motor can apply. meaning if you were to attach a 1 foot radius pully onto our motor, you would be able to pull up 151 lbs when it is spinning at 6400 rpm. this max weight that can be lifted changes at different rpm based on the curve posted above.

horsepower is a unit of power (amount of force in a given time), which is a function of torque and rpm. this means that when the engine is spinning faster, you are applying this torque force faster, thus applying more power.

where you can really capture this advantage is through a transmission. you are applying a lot of force very quickly (at high rpm and full throttle) but you reduce the speed with the gearbox and effectively generate more force on the wheels in the lower gears. this is the primary reason that you feel more acceptation force at the top of lower gears than at the top of higher gears.

I think the cause for the torque dip in this motor is because of the way the valve train timing is set up. we have variable timing that optimizes the timing for different rpms, but it drops a little during part of the transition period... just a guess here though.


I hope this kind of answers your question


Sent from AutoGuide.com App
 
#15 ·
The most important info to use from the HP/Torque curves is where you want the engine speed to be when you want the most torque and/or HP; i.e. where you want to shift when you're really trying to go fast. For example, these curves show why it's so frustrating to be limited to 4,000rpm during the break-in period; you end up shifting just as the power dips. Now that I'm out of the break-in period, I'm experiencing the fatter part of the power band up above 4,000rpm.
 
#16 ·
I think the drop in torque after certain RPM is due to dominating effect of parasitic losses (rotational inertia of the rotating components, friction losses etc). Same reason why power drops. At what RPMs it happens depends on the design and working parameters of the engine.

An engine can be designed to provide high torque in a narrow band or low torque in a wide band by making changes in the intake-exhaust system, cam profiles and timings.. depends on the application for which the engine is intended.
 
#20 ·
OK. I did wonder why that flat spot occurs smack in the middle of the rpm range. Looks like this engine is designed to be suitable for stop and go City traffic and also for hammering down an open and bendy road. It should be fairly easy to avoid that dip in the torque. Looks like a typical variable valve timing torque dip (really it is a torque increase at the higher rpm that creates the dip so as to keep the torque curve as flat as possible). If you compare the torque curves for the old Cayman 2.9 v the Cayman S 3.4 you will see a very similar dip in the torque curve and more pronounced in the S. What is really happening is the engineers are seeking high torque at high rpm using variable valve timing and that is the crossover point between low overlap low lift valve timing and high lift high overlap valve timing.

Before variable valve timing became so common you would never see 150 lb ft from a normally aspirated 2.0 litre engine from any manufacturer. You would need at least 2.5 litres to get that kind of torque in the "old days".
 
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