Simple explaination of HP vs Torque, using an FRS as an example..

[ZDan]

P(t) implies that power is varying with time. That's the problem with it. It is misleading for the case we are talking about.

If we're talking about a given fixed torque value and a given fixed rpm, P(t) = T*w is not the right way to express the equation for power. P = T*w is.

[BRZnut]

Good info, but back to a basic question I have always had...why does the FRS/BRZ have the dip at 4000 RPM and a peak at 3K and 5K??? Do other NA engines do this?? Is it a boxer thing?

[switchlanez]

Originally Posted by ZDan

P(t) implies that power is varying with time. That's the problem with it. It is misleading for the case we are talking about.

If we're talking about a given fixed torque value and a given fixed rpm, P(t) = T*w is not the right way to express the equation for power. P = T*w is.

I agree P(t) = T*w is incorrect due to its use of scalar constants on the right hand side. But P(t) = T*w is correct due to it being a vector equation. I get that it's unecessary and misleading. But misleading and incorrect are two completely different things.

[switchlanez]

Originally Posted by BRZnut

Good info, but back to a basic question I have always had...why does the FRS/BRZ have the dip at 4000 RPM and a peak at 3K and 5K??? Do other NA engines do this?? Is it a boxer thing?

I think the peaks come largely from the way the direct injection is tuned. That's why I mention people should be thankful we have the peaks instead of complaining about the dip. Because one way to rid of the dip is to take away direct injection. Then torque will be weaker EVERYWHERE.

[GotM]

Originally Posted by switchlanez

I think the peaks come largely from the way the direct injection is tuned. That's why I mention people should be thankful we have the peaks instead of complaining about the dip. Because one way to rid of the dip is to take away direct injection. Then torque will be weaker EVERYWHERE.

I think when I read through the D4S literature this is what I gathered as to why this was happening. I will need to read though it again.

These types of dips are not unique to this car. I think you will find all engines have some unique signatures. Personally I like that this curve is rather flat except for the dip.

If you really think about, in a straight line pull you will only see this dip once if your goal is max acceleration. Once you shift you will always be past the torque dip. check out this link to see how each shift falls past the torque dip in each gear.

http://www.ft86club.com/forums/showthread.php?t=24456

If you look into the date that created these graphs. The torque dip lasts about 0.68 seconds.

On a track, this may or may not make a difference.

[ZDan]

Originally Posted by switchlanez

I agree P(t) = T*w is incorrect due to its use of scalar constants on the right hand side. But P(t) = T*w is correct due to it being a vector equation.

If the right-side terms are vectors, that doesn't make them time-dependent. Vectors can be constant or time-dependent just like scalars. Dot product of two constant vectors is a non-time-dependent scalar, so still shouldn't be P(t) = T dot w.

So they I get that it's unecessary and misleading. But misleading and incorrect are two completely different things.

The representation is wrong for our case.

Can you link me to where you got it? I'd like to see the context.

[GotM]

Originally Posted by ZDan

Can you link me to where you got it? I'd like to see the context.

Wikipedia search - Power(physics) specifies it this way.

[sol740]

You've all certainly wasted a function of my time to tell my brain in nerd what my ass knows in car.


N/A 4 banger is slowish.

[Saab2Frs]

So much for "simple" explanation with everyone busting out their physics.

[Dazza]

Originally Posted by Yruyur

After reading this thread I just realized I am dumb.

I'm just really pleased I can read and wright (even if I can't spell )