Bonneville America Forums Forums Technical Forums Performance Mods HP vs Torque

So...I searched and didnt find a discussion based on the HP vs Torque subject.
With my recent posts about a couple of different engine upgrade kits the thing that has be thinking is HP vs Torque. Im no expert on this...but heres my thought. Feel free to confirm, deny and comment in any way.

HP is nice and is usually what is bragged about but I think I want Torque. Torque is what gives you the ability to get mass moving.
What I dont know is when HP turns into torque or vise versa. Theres got to be a balance with internal combustion engines and in particular our parallel twins (I say this cause I know electric motors are low HP and very high Tq and not relevant in this discussion).

When does an increase in HP become more important than torque?
When does HP turn into torque? When does the opposite happen?

So....what are you thinking? What do you know?

I have wonder the same myself...I found this which seems to explain things in a techie/non-techie way

http://www.vettenet.org/torquehp.html

Now I understand whay my sportbike could out run my harley (when I had them)

BHP is a product of torque x RPM. The higher the torque you can produce at any particular revs the higher the BHP figure at the same revs.

When modifying an engine, if you can keep your torque up as the revs get higher, you will increase your peak BHP figure.

Thanks for the link. I started to read through the explanations and thought, "Cool, I'll finally understand this stuf." Then I read further, where I found a counter-argument from someone else questioning the smarts of the first guy. Even the geeks disagree! There's no hope for guys like me, I guess. If the bike starts, and if it goes when I twist the right grip, then I'm happy.

Torque is the important figure. HP is calculated from torque.
PieMan's assessment is correct.
See my sig line, Hp and torque are ALWAYS equal at 5252 rpm.

Well done Zdenko for starting this one.

We did have a brief discussion a fair while ago now about this subject but there were many more 790cc bikes on here then and for some reason, lots of them prefered HP. Go figure.

Now that 865's are probably on a par or maybe even a majority, any discussion mightn't get kyboshed.

Personally, I've always been on the torque side of things and particularly after doing some reading of my own. The best way I look at it is "pull back factor when you are cruising along and want to overtake a truck or something".

In other words you don't want to have to kick down a gear, you just want to pull back on the throttle and go right. Good torque is the one that gets you past quicker.

I also know that Ramsound has always been onto this one for a good while now and his dyno figures and explanations back this up.

Thanks for the link Jim, I'll read it later on tonight at work

I had a few conversations today that helped put some things into perspective for me...

From a freind that races SCCA -
HP is used to get down the straight, Tq is used to get moving out of a corner OR in combination with HP when passing.
From a friend whos dad builds race motors for boats -
Tq gets a load moving, HP keeps it moving. Transaltes into...Tq when passing and HP when to keep passing.

So...both answers are similar but also not specific.

I know there is no right or wrong answer. HP and Tq go hand in hand and always effect one another.

The old Harley saying "Torque moves the pork"

an old timer drag racer told me "torque gets you down the track & hp is how fast you get there".

Both are important since they are different sides of the same coin.
But when doing a dynamic (inertia) dyno run you are measuring Power "the rate at which work is performed or energy is converted" vs rpm at the rear wheel RWHP. The Engine torque is then calculated by the formula Torque = HP X 5252/RPM and expressed as torque or load at engine crankshaft.
So the actual rear wheel torque depend on the engine RPM and all the different gearing ratios in the drive system.

Our bikes 50 - 55 Ft lbs at crankshaft will be something like 600 - 700 ft lbs at rear wheel at 7400 rpm in 1 gear.

Hasse

I like where I'm sitting for HP, I would like to get my torque up several more ftlbs though. Cams will help.

I was just thinking how close some are getting to cracking those elusive dyno numbers of: 80hp and 60ft/lbs of tq.

Is it possible or are we just having ourselves on?

I mean, if Roadworthy ends up getting his cams on, will this be the X factor required to finally cracks the code???

I think if I was a betting man, I know where my money would go.

Any other punters out there???

Oh well. This quest for more and more power is addicting and a bit crazy. I remember being quite happy with the bike when it was new. I thought it had plenty of power, but it's easy to be "bitten" and I must admit I was. Big question now is what each extra HP and each extra ft-lb will cost. And are they worth it? Probably, but it never seems to end...

Thanks Z, I forgot that one. Well, the winter is long...

HP vs torque discussions are usually based on older designs from the pre-CAD days. Intake, internal engine and exhaust were treated as separate systems, so torque curves tended to be round or even pointy shapes. Engines were tuned to move the peak torque up or down the RPM range to get lots of low end torque with less high RPM power or lots of high RPM power and little low end torque, even though the actual peak torque was very nearly the same.
Now, with computer matching of component characteristics torque "curves" can be, and often are, flat from just off idle to redline. Add in such modern concepts as computer controlled variable valve timing and constant velocity intakes and you have torque and power delivery from the same engine.