Is delivering half as much torque twice as fast the same thing? (effectively)

mke said:

In reply to alfadriver :

No, you could easily  run 15 psi boost to double the torque and you can tune the peaks to any rpm you please...mostly.  A 2.5l turbo deisel might well be designed for 3000 rpm all day everyday vs an NA 2.5l type S engine designed for what 8k.  Its just a thought experiment, not real because nobody would be likely to put a skidsteer engine in their car...but hp is hp.

...but its just a thought experiment.

That would imply that the turbo would add nothing at 8000rpm. Or even 5000rpm.  Makes no sense.  

Then comparing a 2.5l turbo diesel that revs to 4000rpm to a NA gas engine that revs to 8000 rpm where both make the same power...  I can't understand that, too.  The engines would be the same, at all.

I get that it's a thought experiment, but there's attempts to think about it in reality, so one must bring a dose of that in.  So it's really impossible to say "all things being equal".  If all things are actually equal, 500hp = 500hp, simple as that.

alfadriver said:

That would imply that the turbo would add nothing at 8000rpm. Or even 5000rpm.  Makes no sense.  

It means the engine has a redline below that.  Most industrial engines redline around 3600. I have an old flathead Lincoln V12 with what was a skyhigh 3800 redline.  Aircraft engine are like 2500 as are many truck engines.  The goal is to extend engine life and/or reliability by limiting cycles.

Again, I agree with you that this isn't a very realistic thing because nobody would want to build 2 identical cars with engines designed for wildly different purposes... they certainly could be built but 1 or both versions would suck.

In reply to mke :

So that's just less of "all things being equal".  

So you are talking a Camaro vs a Honda 2000.  Sorta since the Camaro weighs more. 

The real question is how much area is under the torque curve for each because that is what you need for the calculation of which would give the better acceleration while bench racing, ceteris paribus.

jharry3 said:

The real question is how much area is under the torque curve for each because that is what you need for the calculation of which would give the better acceleration while bench racing, ceteris paribus.

Yes.....but that assumes perfect gear ratios.  Area under the WHEEL torque curve is more real.  Same way you calculate you're optimal shift points, simple excel sheet with the torque curve and the final drive ratio in each gear, when the wheel torque in 1st drops below the wheel torque in second (at the new rpm) or you hit redline you shift.

alfadriver said:

In reply to mke :

So that's just less of "all things being equal".  

Right, its not a real situation you'd ever actually run into....you can create it, but it gets a little silly.

These thought experiments fall apart because of all the variables.  In two situations where you have the same power output, the same amount of work is getting done in the same amount of time by the motor.  I keep typing out and deleting a longer answer but the answer to the actual question stays the same.  The rest is why that point doesn't strictly matter.

ProDarwin said:

Well, one way around the synchro problem is to put a primary reduction in the trans to bring the gearset down to normal speeds (I know the S2000 has one, not sure if it is before the standard gearset though).  However, this is A) an extra gear required and B) multiplies torque to the rest of the gears.

I looked into this today at work.  The S2000 trans is very interesting.    It doesn't have a reduction gear, what it does have is a unique design that more or less looks like a front wheel drive trans, or maybe a normal rear wheel drive trans backwards.  

Instead of the input shaft being a simple spud that drives the countershaft, that drives the main gears, and the synchronizers couple the gears to the output shaft, the S2000 trans has an long input shaft with some of the synchro hubs on IT.  One of the hubs is on the countershaft, as well.  Very much like a transverse unit.  The difference is, instead of the countershaft being geared to the ring gear on a differential, it is geared to a spud shaft whose only purpose is apparently to make the output inline with the input and the same rotation direction as the engine.  Again, kind of like the INPUT of a RWD trans, except there is no coupler for a 1:1 passthrough.

Kind of ironic that Honda made the perfect trans for a reverse rotation engine,  and then needed to put that spud shaft in the end because the F20C is not reverse rotation.

Wish I could find the copy of the British publication Bike from the early oughts where, as an experiment, they took 10 experienced riders, a new CBR 600F? and set about putting them off around a road course.  Then, they gave them an identical bike with modified cams and fuel delivery which was only capable of around 80 bhp on the dyno (compared to well over 100 stock) but with far superior torque.  Essentially just moving the power band down in the rev range.  9/10 riders agreed the modified bike had way more suds and was much faster.   

But Honda couldn’t SELL a bike with only 80 bhp.

alfadriver said:

I would much rather have a 500hp/ 250lbft motor over an 250hp /500lbft motor.

All day long.

Power can be geared to make any torque, torque can't be geared to make any power.  Conservation of power is pretty important.

If I were putting bread on the table by winning races I would agree.  In a real world road car—not so sure.  It’s the main reason TDI owners can’t wipe that stupid smirk off their faces.

Or I suppose the 500 hp “peaky” engine could be fun in the real world too as long as you had 29 gears and a robot to do the shifting for you :-)

I’m exaggerating of course.  Some V12 Ferrari’s closely match your 500/250 and I’m sure they’re loads more fun than any TDI.  They are also quite a bit lighter and more race oriented than what I would consider to be a good road car.

your third paragraph was technically spot on.

Knurled. said:

ProDarwin said:

Well, one way around the synchro problem is to put a primary reduction in the trans to bring the gearset down to normal speeds (I know the S2000 has one, not sure if it is before the standard gearset though).  However, this is A) an extra gear required and B) multiplies torque to the rest of the gears.

I looked into this today at work.  The S2000 trans is very interesting.    It doesn't have a reduction gear,

My understanding was that there is a reduction there aside from the main gears.  If you look up S2000 Gear ratios on the google, you'll see a "Secondary gear reduction" of 1.16 (AP1) and 1.208(AP2)

https://en.wikipedia.org/wiki/Honda_S2000

In reply to ProDarwin :

That's probably the gear ratio between the countershaft and the spud shaft, meaning all of that is happening at the very end of the trans, not the input.   Those numbers sound to me like at least one of the tooth counts is prime (29/24 is 1.208, and 29/25 is 1.16.... bam!) which is Good for gears because it guarantees that every tooth will contact every other tooth with no harmonic pattern. "Hunting" gears versus "non hunting".

In other words, that gear ratio exists because a ratio needs to exist.

I just realized/remembered:  Subaru also does it this way.  They have a similar ratio (and DIFFERENT ratios amongst different models...) for the gear going to the center differential.  Or maybe it was the gear coming from the center diff to the driveshaft.... it's been a long time since I've had a Subaru manual trans apart.
 

Audi doesn't have a gear, because Audi driveshafts are reverse rotation, going clockwise as you face forward.