Hp/torque/engine size

[barend]

Can someone explain to me in layman's terms what the relationship is between these three and other pertinent output info? I.e., what is more relevant, Hp, torque, compression ratio, bore and stroke, displacement? Or(/and) does this relate to driving style and area (e.g. Florida Flat or Colorado curvy)

thanks

 

Oh, I'm wondering 'cause I was surfing the web and found what turns out to be a 1200, 65 Hp engine with I think it said 71ft/lbs (R1200CLC) and since I haul a sidecar and would like to continue doing so, is this something I should not consider or is it a possibility

[Redneck]

hp is how fast it will accelerate the load torque is how much it will constantly pull. As a general rule the longer the stroke the more torque and at a lower rpm. There is no substitute for cubic inches.That 120 will be a dog compared to your venture.

[dingy]

Torque is King.

 

Torque is the force that the piston develops on the crankshaft.

 

Torque is what develops HP. HP is the most often talked about number in part due to torque numbers have to be taken into context of the rpm range over which it is developed.

 

This is not to imply that HP numbers are meaningless, they aren't. You need to know if the HP rating talked about is crank or RWHP. Crank HP is an almost arbitrary number that a manufacturer puts on their motor. It is determined , as the name implies, at the end of the crankshaft. This number disregards any degradation of HP by things such as water pump, alternator, transmission losses. What is meaningful is the RWHP (rear wheel HP) after all drive train losses are factored in. Crank HP is always higher than RWHP so it is the advertised rating.

 

Stroke length vs bore is a major factor in RPM potential. Short stroke motors (stroke is less than bore) will rev higher than an equivalent sized long stroke.

 

Engine size is not always a determining factor of output. Other factors such as intake style( carburated, EFI, turbo) can greatly influence output.

 

Compression is not a good gauge of potential. For a given motor, increasing compression is a source of more HP, but turbo equipped motors run at a lower compression ratio than an equivalent carburetor motor and deliver more power.

 

This probably doesn't go very far towards explaining this though.

 

Google is your freind, just search on those three terms or something like "HP torque displacement relationship" and you will find a lot of material.

 

Gary

[MiCarl]

Really simplifying:

 

Torque gives you an indication of the ability to accelerate. Horsepower gives you an indication of ability to go fast.

 

With a side car you're probably more interested in getting that extra weight moving than in going fast so you'll care more about torque.

 

There is another variable that you might care about which is the torque curve. Does the engine produce lots of torque at low rpm, or does the torque peak when the engine is running faster?

 

As a rule longer stroke means the torque is highest at low RPMs. For accelerating from a stop and putting around town you'll do lots less shifting with a long stroke. This is why big twins (which have long strokes) are popular for cruising.

 

For better mid range response and more reliable acceleration at freeway speeds you'd probably be happier with an engine like you're looking at - moderate stroke that brings the torque on at mid-range rpms. That's the reason engines like your example show up in touring bikes. These engines tend to be V fours or boxers (Goldwing, BMW).

 

A very short stroke engine won't produce a lot of torque and then only at high rpms. This would not be a good choice for a hack. These engines are always in line fours.

 

So the only variables you care about are torque, horsepower and the torque curve. Ideally your torque spec will say xxft-lb@yyrpm so you know at what rpm torque is peaking. Where the rpm isn't listed you can use to stroke length to give you an idea if the torque peaks at low or higher rpm.

Edited March 27, 2011 by MiCarl

[RandyR]

So whats your goal? to reliably haul around the sidecar at legal speeds and enjoy the ride and scenary? Or to be the first one to the next gas station?

 

Half the sidecars I see (well maybe used to see is more accurate) on the road are attached to BMW airheads. That tells me that the first scenario is likely covered by an R1200 irrespective of the touted engine specs.

[barend]

I have no problem hauling a$$ (and enjoying it) with my '83 on the slab but that is really not the primary concern. I am concerned about the second gear and cracked frame issues mine may (will?) have. I am at 39K miles now so theoretically it may be another couple of years, but I don't have the knowledge to fix that myself so perhaps prudence would dictate I start looking at a possible replacement.

 

Thanks for the feedback guys! It'll be awhile before this happens and I need to start saving. Between now and then maybe I can find a airhead somewhere I can borrow to see if I like the ride.

[jlh3rd]

torque is a measure of how much work you want to do....ie., moving lbs. per foot ( work = force x distance )( and it's not ft/lbs.)....so you wanna move your 900 lb machine .........now , how quick do you want to move it.? depends on the horsepower.........you can put a 40 hp motor in your machine and gear it to produce enough torque to move it, but , you will not go very fast.......put a 100 hp motor, and with properly spaced gearing, you'll be able to produce the torque you need, produce the torque faster, and maintain it longer ( power curve) to accelerate your machine quicker and to a higher speed.....

by varying bore, stroke, induction, exhaust...you effect the hp/tq produced....then gearing helps you apply the torque where you want it to get your machine moving......and then using hp to keep and get it moving faster...........

when i'm in the mountains climbing,...i want torque........when i'm in the flats, i want horsepower

[KiteSquid]

I am at 39K miles now so theoretically it may be another couple of years, but I don't have the knowledge to fix that myself so perhaps prudence would dictate I start looking at a possible replacement.

 

Two options for you:

 

Befriend a venturerider in your area that loves to work on bikes... feed them and repairs will come.

 

 

Buy a second Venture Royal to use as a backup. IMHO they are inexpensive and if you find a low milage unit it can be very rewarding.

[OldBear]

Remember that the R1200CL is a completely different motor than say an R1200R, RT or GS. The C series were built as "cruisers" and are well known in BMW circles as being low powered. While a C will certainly pull a hack, it will not move it with the authority other BMW 1200 twins will. Check on BMW sites for the differences in HP and Torque. Caveat Emptor.

[Snarley Bill]

horsepower, rpm, and torque go hand in hand. cubic inches mean nothing. volumetric efficiency does. for example, an r-6 yamaha which has 600 cc's, or roughly 37 cubic inches. will produce 107 hp. at 15,500 rpm at the crank, and has very little torque at the crank. if you have an old stationary engine that has 10 hp. and 50 ft. lbs. of torque at say 500 rpm. and may displace 150 cubic inches with 1 cylinder. it will not come close to the r-6 engine which when geared for the same output rpm of the crank speed of the stationary engine, will produce a tremendous amount more torque. it is all about converting horsepower and rpm to torque. an r-6 engine, due to it's high horsepower and efficiency will produce considerably more work in a given amount of time then the high torque stationary engine. moral of the story is, high effieciency in an engine, meaning maximum hp. per cubic inch rules the roost. i always believed there was no substitute for cubic inches, when in reality there is no subsitute for engine efficiency and gearing. the japanese have rewrote the book on engine efficiency. the bigger the displacement of an engine the harder it is to obtain volumetric efficiency, because air can only move so fast. a small cylinder can be filled with an air and fuel mixture much faster, and more efficiently than a large displacement cylinder. so there

[MikeWa]

Easiest way to remember.

Torque measures the force applied.

Horsepower measures the movement.