Big Bore Vs. the Stock Engine.

The area UNDER the Torque Curve is what really matters!


OK, the ANCIENT debate between Torque and Horsepower is one that never seems to get resolved. I will try and give a VERY general explanation of why you can NOT have one without the other and which one is really putting a smile on your face,,,,

1) Given 2 engines running at the same rpm.. if one engine has more HP, it automatically has more torque.. ALWAYS!! Torque is measured and HP is calculated via mathematical formula using TORQUE as one factor.

2) HP and torque can NOT be separated in terms of what is doing what with respect to how your engine runs (see #1).. They are connected ALWAYS and can not be separated..

3) Stating that torque is what is accelerating you down the track is simply incorrect.. Why? See #1 and #2 above..

Now, here is where the "FUN" begins...and hopefully, I can related to this Big Bore topic..

1st.. a few basics... CVT Equipped Engines should be clutched ALWAYS at peak HP rpm..

ANY good engine will have a peak torque output rpm 200-500 rpm LOWER than the peak HP output rpm. WHY.. Because you clutch for peak HP.. NOT peak Torque..

So, when your engine is heavily loaded and it begins to drop a few hundred rpm.. It will fall into its PEAK Torque realm and have a much easier time at recovering and returning back to peak HP rpm... Hence, the reason for having the engine's peak torque rpm lower than its peak HP rpm.. Without this relationship.. the engine would be VERY hard to clutch in a full load situation. Make sense?

When people talk about engines, they like to quote and cite peak HP numbers..For example.. RK Tek 860R makes 180HP at 8300 rpm. Peak torque is closer to 7900/8000 rpm.. OK, so, those are the peak numbers.. What MANY fail to realize is that the area under the torque curve is what really makes one engine stand out over another.

Different engines build TORQUE at different rates.. Some build torque rather rapidly and then hold the torque across a very wide rpm band.. This is a good engine and one that will accelerate very hard and will be very easy to clutch.. The area under this torque curve would look like a bumpy straight line with very little upward slope.
Some engine builds do not build torque quite as fast but can get to the same torque numbers as another engine.. This engine's torque curve will look like a side of a mountain.. So, while the 2 engines can make roughly the same torque and HP, their torque curve can look completely different. So, the area under the curve really tells you how the engine will "perform" under real-world operation.

In flat land racing, this curve is not so important (note: I did NOT say NOT important. just not as).. because you come out of the gate and immediately hit the desired rpm and stay there for the duration of the race. so, what the curve looks like BELOW the rpm you are running are inconsequential.

Now, boon docking and mountain riding.. Different story.. It is very common to have your engine quickly lose rpm because you are on and off the throttle. So, the flatness of the torque curve becomes a big player..

This is where the Big Bores really shine... I will speak to my BB, because it is , obviously, the one I know the most about...

The 860R builds torque at a very rapid rate when compared to the stock engine. It builds it faster and builds much more of it.. So, you have a very broad and very flat torque curve.. So, when on and off the throttle OR when your sled hits a super "Deep" spot and drops some rpm.. The BB is MUCH less effected and can recover much faster than the stock engine.. WHY?? Much more TORQUE AND HP at ALL rpm.... Simple as that.. Where the stock engine will get overloaded.. the Big Bore will be much less effected by it and continue to pull...

The RKT 860R has massive torque and HP increases in the 6500-8000 rpm band. So, it has a much easier time handling anything "HIGH LOAD" situation it encounters. This becomes very apparent when banging a steep hill with 3ft of fresh and deep powder.. There is no comparison between the Big Bore and the stock engine.

Getting into the mathematics and physics behind the relationship of torque and horsepower was never the intent of this article.. I wanted to keep it very simple and refrain from the physics involved..  However; there are some very good articles on this very subject all over the web.. Just search for "Horsepower vs. Torque" and you will have a grundle of hits that will keep you reading all night...


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