TQ vs. HP

Which car would win in a drag race?

  • Car A will win because it has twice as much torque.

    Votes: 213 51.8%
  • Car B will win because the engine spins faster.

    Votes: 80 19.5%
  • The cars will tie.

    Votes: 118 28.7%

  • Total voters
    411

Kiwi_ME

Veteran Member
Joined
Jul 3, 1999
Location
New Zealand
TDI
2015 Cross Polo 1.2 TSI 81kW, ex '03 Golf TDI, '82 Rabbit Diesel
jnecr said:
Max torque at the wheels for any gear is acheived when the engine is producing MAX TORQUE
Correct, and furthermore, to figure out the theoretical shift points for getting the most work out of your engine you need to place your start and finish engine RPM's for each gear such that ...

Edit: I was incorrect, as TDIMeister says it's the highest time-average HP value you can keep while running thru each gear. The work done is the integral of HP over time.
 
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TDIMeister

Phd of TDIClub Enthusiast, Moderator at Large
Joined
May 1, 1999
Location
Canada
TDI
TDI
The above two posts are correct. But for any given speed my car is running, if I had the choice to run a shorter gear or a taller gear (the portions of the graph where there is an overlap of curves from two or more gears), and my objective was to accelerate as quickly as possible, I would choose to ride on the curve that is sitting highest up on the vertical axis for each given speed.

Take a specific example from the graph, driving at 75 MPH: in 4th gear, I am riding just before the point of peak engine torque. But I would get faster acceleration if I were to instead run in 3rd hear (higher up the vertical thrust axis) even though at that point the engine is actually developing less torque. The gear is doing nothing magical here. The point: at 75 MPH, is the car accelerating faster at the torque peak (4th gear), or is is it possible that the car can actually accelerate quicker at some condition where the engine is actually developing less torque?

It's all a question of frame of reference, and Diesel drivers say torque is almighty because most are conditioned in their (our) driving style to stay in the same gear as much as possible. In that case, sure, more torque equals more acceleration. But if we're in a drag race, we have to put that hubris aside, and row the gears more, which means getting the absolute highest acceleration at any given time; at any give speed at which the car is travelling; and at any gear.

This occurs ONLY AND ONLY at the part of maximizing engine power! End of discussion! :D
 

Bob_Fout

Oil Wanker
Joined
Sep 5, 2004
Location
Indiana
TDI
2003 Jetta - Alaska Green (sold) / 2015 GTI 2.0T
Would we benefit from a tranny with more than 5 or 6 gears like we have now?
 

jnecr

Veteran Member
Joined
Oct 9, 2004
Location
Raleigh, NC
TDI
2014 BMW 328d
no, we won't really be helped anymore than we already are. You could do a little tweaking to make it more race oriented (drag or otherwise) but the differences won't be that great...
 

jackbombay

Top Post Dawg
Joined
Mar 12, 2002
Location
Diesel knows best
TDI
A4 Jetta
TDIMeister said:
For one of them I think I'll just copy Jackbombay's question at the top of this thread verbatim :p
Sweet! I got a question into the TDI club quiz without even intending to. I better get it right, although I fear that the correct answer might have gotten lost in the minutia thought, the pound of bricks is heavier, right?


03_01_TDI said:
its all about gears.
 

TDIMeister

Phd of TDIClub Enthusiast, Moderator at Large
Joined
May 1, 1999
Location
Canada
TDI
TDI
By Jove, I think we've got it! High fives and beers all around :). It's quarter to one a.m. in my time zone. Sheesh, almost 100 posts in a single thread in about a 24 hour span.

I'm beat. HAve a good evening, all.
 

Mad_Matt

Well-known member
Joined
Dec 19, 2005
Location
Clarksburg, MD
TDI
15 EcoDiesel Jeep
Torque VS HP

It's funny how I put the 2 formulas for HP and Torque in this post on page 2 or 3. The Facts get so convoluted in long winded posts. The Higher revving engine will win the race all other things being equal. Your trying to make thins much more complex than it has to be. Life is all about the KISS principle. Keep it simple. Enjoy the commentary.
 

nicklockard

Torque Dorque
Joined
Aug 15, 2004
Location
Arizona
TDI
SOLD 2010 Touareg Tdi w/factory Tow PCKG
Jack, we can do better on the visual

Throwing out ideas:

How about making a 3 dimensional plot of x,y,z: RPM, T, acceleration.

Acceleration graphed as a function of RPM and torque. For some reason the HP curve just doesn't measure up visually. I can't get a feel for the relationship to torque--moreover it doesn't convey the QUALITATIVE nature of that torque. IOW: it lacks that context (for me anyhow.)

I'd have to graph it in SigmaPlot. Excel sucks for 3-d plots, but Sigmaplot is only available on my work computer. I roughed it out on paper and the 3-d shape looks like a mishappen orange slice, bulging at ~3700 rpm and flattening to a thin wedge then point at the idle end.

TdiMeister, anyone: ideas?
 

Kiwi_ME

Veteran Member
Joined
Jul 3, 1999
Location
New Zealand
TDI
2015 Cross Polo 1.2 TSI 81kW, ex '03 Golf TDI, '82 Rabbit Diesel
nicklockard said:
For some reason the HP curve just doesn't measure up visually. I can't get a feel for the relationship to torque--moreover it doesn't convey the QUALITATIVE nature of that torque. IOW: it lacks that context (for me anyhow.)
I think those thrust curves in each gear vs vehicle speed are best to show what torque is all about. You can feel that directly in the driver's seat.

But you don't feel "power" unless you hold your head out the window into the wind. And as for "energy" or work done, only in that realization that you and your car have reached your destination and spent fuel doing it.
 
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jackbombay

Top Post Dawg
Joined
Mar 12, 2002
Location
Diesel knows best
TDI
A4 Jetta
nicklockard said:
Throwing out ideas:

How about making a 3 dimensional plot of x,y,z: RPM, T, acceleration.
Would the acceleration take drag into account? Or would you figure it on more of a "power to the wheels" basis? I think the latter would be a good way to graph relationships you want to illustrate.

100 posts in 24 hours, the Vtec must have kicked in there for few hours :p
 

jnecr

Veteran Member
Joined
Oct 9, 2004
Location
Raleigh, NC
TDI
2014 BMW 328d
nicklockard said:
How about making a 3 dimensional plot of x,y,z: RPM, T, acceleration.

Nick, you don't happen to have dyno sheet with actual data instead of the graph do you? Don't dynos put out a spreadsheet type output as well as a graph? It seems to me that they would have to...
 

nicklockard

Torque Dorque
Joined
Aug 15, 2004
Location
Arizona
TDI
SOLD 2010 Touareg Tdi w/factory Tow PCKG
That's what I was hoping to find in the picture server here somewhere...you need the numbers (in reasonably close increments) to build the spreadsheet for graphing. But hey...we're moving to newer, bigger labs and offices this week.... I've got to pack :)
 

n1das

TDIClub Enthusiast, Veteran Member
Joined
Jun 11, 2002
Location
Nashua, NH, USA
TDI
2014 BMW 535xd ///M-Sport, 2012 BMW X5 Xdrive35d, former 3x TDI owner
jackbombay said:
You have 2 identical cars with the exception of the engine and the transmission, the engine and trans of both cars are the same weight though.

Car A has an engine that produces 420 lb/ft of torque at 2500 RPM for an output of 200 WHP and it has a CVT tranny that has no losses and it maintains a constant engine speed of 2500 RPM under all conditions.

Car B has an engine that produces 210 lb/ft of torque at 5000 RPM for an output of 200 WHP and it has a CVT tranny that has no losses and it maintains a constant engine speed of 5000 RPM under all conditions.

Which car would win in a drag race?
I'm gonna think outside the box for a minute...

I say NEITHER car will win since they won't go anywhere because they are producing POUNDS PER FOOT (lb/ft) as stated in the problem, not torque (ft-lbs). :D Neither of them will get off the line since they aren't producing any torque (ft-lbs). :D

There's a BIG difference between foot-pounds (ft-lbs), feet per pound (ft/lb), and pounds per foot (lb/ft). :rolleyes:

:D
 
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bareass

Veteran Member
Joined
Dec 29, 2005
Location
Windsor Ontario Canada
TDI
`02 Jetta 74K
if its makeing the same wheel hp.. then wouldn't the tdi win bcause its hitting that power earlier and with more torque??. it seems to me that if you have the same power its more of a race to that power.. and tdi's have less the half the distance to go
 

Bob_Fout

Oil Wanker
Joined
Sep 5, 2004
Location
Indiana
TDI
2003 Jetta - Alaska Green (sold) / 2015 GTI 2.0T
The other car simply revs to its power band before launch.
 

nicklockard

Torque Dorque
Joined
Aug 15, 2004
Location
Arizona
TDI
SOLD 2010 Touareg Tdi w/factory Tow PCKG
n1das said:
I'm gonna think outside the box for a minute...

I say NEITHER car will win since they won't go anywhere because they are producing POUNDS PER FOOT (lb/ft) as stated in the problem, not torque (ft-lbs). :D Neither of them will get off the line since they aren't producing any torque (ft-lbs). :D

There's a BIG difference between foot-pounds (ft-lbs), feet per pound (ft/lb), and pounds per foot (lb/ft). :rolleyes:

:D

Literalist! :p
 
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