I am far from a gear head, and most complex mechanical machine frighten and confuse me...however I am betting someone can explain to me how some engines (motorcycles in particular) can have smaller displacement yet more horsepower. Examples:

The 2015 Yamaha MT-07 had a 689CC engine yet only produced 74 HP.

The 2015 BMW F800GT had a 798 CC engine yet only produced 90 HP.

The 2015 Triumph Street Triple had a 675CC engine but produces 104 HP.

How can the third bike have the smallest displacement yet produce 15-20% more Horsepower? I am aware that the first two engines are parallel twins and the Triumph is an inline three, but how does that factor in? What tuning is done to produce such a drastically larger amount of horsepower?

I appreciate any knowledge someone can lay on me!

Compression can play a part in HP, IIRC.

In a word… Efficiency.


Why do you think internal combustion engines can’t get more efficient from old designs?

Computerization, mass flow sensors, variable timing, close tolerances, etc.

Usually the word “tuning” refers to people hot-ridding their cars/computers to deliver more fuel in the air to the engine to generate more horsepower. For example I have a car that is “tuned”; used to make 450 hp, now makes over 550 fiddling with the fuel maps and boosts.

Efficiency of air flow through the intake system, combustion chamber efficiency, compression ratio,rpm operating range and a variety of other things all have an effect.
Simply, the more air and fuel you can get in and out and burn, the more horsepower you can create. That's why a small turbocharged engine that crams air under pressure into the engine, can create a lot more power than one that only used the atmospheric pressure.
Beyond that, it's a complex subject to understand all the science behind this.

The term tuning nowadays mostly refers to changes in the software mapping that controls many functions in a modern engine.

I appreciate the explanations and understand...I guess that leads me to ask why, given the fact that its possible to increase the efficiency of these engines, dont these companies simply do that and increase power? Is it intentionally left less efficient to produce a bit of a weaker engine in order to satisfy a market share?

A better word for tuning is optimizing.

Compression
Reliability
Production numbers

I imagine Yamaha makes a lot more of their 700cc twin than the other 2 combined.

The BMW & Triumph are a more premium brand & probably more of a 2nd bike than a beginner.

Comparatively, the Triumph Trident 660 is a 660cc triple producing 80hp and has been reviewed as being more beginner friendly.

Also, being that a lot of these are globally available & some countries have license restrictions, some may be built to be able to handle reduced power modes. IIRC, the Yamaha 700 may have an A2 version (47hp max)

With more power comes more heat and more
mechanical stress of various bits, not only of engine, but
entire drive train. Braking & suspension are more
stressed in managing production of higher power.

Higher spec components, reliability and necessary
maintenance add to unobvious cost of the extra power
output. What is that "2 seconds faster" to 60mph worth?

quote:

Originally posted by signewt:

What is that "2 seconds faster" to 60mph worth?

Tune - including ECU mapping, race cats in custom exhaust, quick shifter, cryo-treated front discs, new brake fluid annually, racing clutch (x2), rdot tires, etc. etc.


Funny anecdote: I’ve always had to pay more for auto insurance because reportedly my car is a high theft item.

However, recently I realize no one’s ever gonna steal that car… at least not driving.

Even if you knew how to drive a manual, the clutch in there super picky with only a 7 pound fly wheel. lol

An engine is effectively an air pump. More air in and out and the faster can can pump it, the more HP it can create. Compression ratio, throttle body diameter, camshaft lift and duration, cylinder head flow, and operating RPM are just a few of the reasons why two engines of the same nominal displacement can produce wildly different levels of HP and torque.

Or at least with Harley Davidson even with the CVO line it’s an opportunity to sell tuners and parts (Stage 1 and up).

We used to say the bike’s the cheap part, we’re going to get you with accessories.

quote:

What is that "2 seconds faster" to 60mph worth?

Speed costs money, how fast do you want to go?

quote:

Originally posted by dwd1985:
I appreciate the explanations and understand...I guess that leads me to ask why, given the fact that its possible to increase the efficiency of these engines, dont these companies simply do that and increase power? Is it intentionally left less efficient to produce a bit of a weaker engine in order to satisfy a market share?

Cost.

quote:

Originally posted by signewt:
What is that "2 seconds faster" to 60mph worth?

It's not 'how fast can you go?' it's 'how fast can you afford to go?'

Now the OP knows some of the variables in play, here's an example of the why:
Say a drag racer & a grocery getter have the same size engine - 5.7L V8 (~350 cubic inches, commonly called the 'small block chevy').
From a stop, the drag racer can go 1/4 mile in 5 seconds*
The grocery getter can go 1/4 mile in 20 seconds.
Which do you think would be able to get to 100,000 miles first? How many engine rebuilds will it take?

*1/4 mile times are completely made up - a 5sec 1/4 has a top speed of >250mph

Grocery getter would need oil change every 3k, tires at ~50k. I chose 20sec 1/4 because thats right about 70mph top speed. Interstate, 8hrs a day = 179 days to go 100k. Add a few days for maintenance.
WAG - a 5sec drag racer would go a mile, maybe 2 between engine overhauls. A decent pit crew could get it back on the road by afternoon - so 4mi/day = 25,000 days to go 100k miles - and 50,000 engine overhauls.

One of the common "big bore" aircraft engines -- the series that was factory standard in my V-Tail Bonanza -- is the Continental IO-520 series.

520 cubic inches, approximately 8.5 liters, rated for 285 hp. Factory quoted TBO (Time Between / Before Overhaul) at 2,000 hours, which at normal cruise speed yields something approaching 400,000 miles.

Relatively low HP rating for the displacement, with great reliability.

Add a turbo-charger to this engine, HP increases and TBO decreases.

With the three motorcycles you mentioned, it’s not a difference in tuning. The answer to your question is torque and engine rpm. That’s it. More displacement (cc in motorocycle engines) equals more torque. For a given amount of torque, the faster you can rev the engine, the more horsepower it will make.

The 675cc Speed Triple makes 106hp at 11,850rpm, but max torque is 50ftlbs at 9,750rpm.

Next up, the slightly larger 689cc MT-07 makes 74hp at 9,000rpm. Amazingly enough, max torque is the same 50ftlbs as the Speed Triple only at a lower rpm of 6,500.

Lastly, the 798cc BMW makes 90hp at 8,000rpm. Being roughly 20% larger than the other two also produces roughly 20% more torque as well. In this case, 63ftlbs at 5,800rpm.

This is all an interesting subject and glad to see your interest.
I think you are having a similar learning situation as mine concerning firearms, where I started from the point of thinking a quick study would make me know a lot more.

What I actually found, once I started learning, was that there were a lot more aspects to the subject that I didn't even realize existed. In other words, I didn't know what I didn't know. So it was hard initially to even know some of the questions to ask because I wasn't aware enough about a lot of things.
Let's start with guns, since it's a subject most of us are more familiar with. As a beginner, it seemed very simple.
Just things like bullet design, weight, charging (pressure) that weren't on my radar until I started studying the subject more. Such a seemingly simple subject, except it isn't. My knowledge started out from what I saw on TV or the movies.

A lot of the explanations for what you're asking require an understanding of things most people have a very limited knowledge of at all. I'd probably start out by recommending watching some youtube videos of the subject, and even that will result in creating a lot more questions as you learn.

quote:

Originally posted by trapper189:
With the three motorcycles you mentioned, it’s not a difference in tuning. The answer to your question is torque and engine rpm. That’s it. More displacement (cc in motorocycle engines) equals more torque. For a given amount of torque, the faster you can rev the engine, the more horsepower it will make.

The 675cc Speed Triple makes 106hp at 11,850rpm, but max torque is 50ftlbs at 9,750rpm.

Next up, the slightly larger 689cc MT-07 makes 74hp at 9,000rpm. Amazingly enough, max torque is the same 50ftlbs as the Speed Triple only at a lower rpm of 6,500.

Lastly, the 798cc BMW makes 90hp at 8,000rpm. Being roughly 20% larger than the other two also produces roughly 20% more torque as well. In this case, 63ftlbs at 5,800rpm.

This almost seemed contradictory to me, but then I think it clicked: making torque at higher RPMs produces more HP than making torque at lower RPMs, correct? This is why the Street Triple making the same torque as the MT-07 but at 1.5x the RPMs is producing 20% more HP? And why the BMW producing 20% more torque but at almost half of the RPMs produces 15% less horsepower?

Torque is what moves the vehicle … It is the actual measurement of work produced.

Torque is the force applied by the engine.

HP is a measurement of the power output of the engine.

Horsepower = Torque x RPM / 5,252