Horsepower by the numbers
Somebody somewhere started a list of incremental steps pertaining to building a better-than-stock motorcycle motor. This age-old list has served many well, but it seems to confuse many people lately due to the large abundance of new aftermarket performance parts and kits available for American V-twin powerplants. While these upgrades cannot really be clearly defined in a numerical way of gaining horsepower, we have amassed a list of stages to better explain the path to getting the amount of power you deem fit for you and your ride.
Stage Zero
This stage is all about modifying what is currently on your bike, such as drilling out your airbox/intake or removing it altogether for better breathing or also unplugging, eliminating, or bypassing your exhaust’s stuffed-up emissions systems and therefore eliminating the backpressure within it. This won’t get you big horsepower numbers, but some should be felt on the butt dyno.
Stage 1
Photo: Hot Bike Staff
Stage One
Stage One upgrades usually require no internal motor modifications due to the fact that all you are doing is broadening the means of getting a better air/fuel ratio into the motor with a high-flow air filter or intake system and the engine’s spent gases out of the motor with new free-flowing muffler(s) or a complete aftermarket exhaust system. Many manufactures also tout Stage One kits as being larger-displacement offerings with new cylinders and pistons. And some folks go as far as doing some small ignition modifications and adding a simple electronic tuner to the bike as well to make up for the changes to the stock air/fuel ratio setting.
Stage 2
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Stage Two
Stage Two is mainly about mating new cams to your Stage One mods. Since you have already mastered Stage One you have what you need to draw air and fuel into the motor and get the gasses out more freely than the stock bike possessed. The cam upgrade is going to be a better way to draw fuel in the motor. The cam acts like a door letting fuel through to the combustion area. And a different cam’s lift and duration decide how wide the door is open and for how long. There is nothing particularly ingenious about how a cam works since all it does is handle rotary movement from the crank and transfers that motion to open the valves. But it’s the way a specific cam does this job that makes all the difference in the world. There are so many different theories on which performance cam and what amount of horsepower they make, but that is another story for another time. This is also the time for a plug-in power tuner, which can adjust a multitude of aspects of how your engine can be adjusted for the aforementioned upgrades. And dyno tuning of your bike with a trusted professional should also come in with this stage.
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Stage 3
Photo: Hot Bike Staff
Stage Three
This upgrade generally is all about the heads and valves. It is a pretty large monetary investment with a ton of questions and options that need to be tackled. Harley combustion chambers have benefited from better gas flow since the first one was built, but as we know The MoCo makes machines for the masses. This means for us hot rodders bigger and better things need to be done in the Stage Three realm. Sure, you can get ported heads off the shelf from many manufacturers, but what is the intended usage? What is your flavor of riding? Do you want torque or horsepower? Want your engine to come alive on higher or lower revs? Do you care about fuel efficiency, or do you want a two-wheeled dragster? Like the Stage Two cam selection, this is where we tell you to investigate what modified or performance heads best suit your motor setup and your riding style. This is also another time when bigger cylinders and pistons come into play for some folks. Also, adding larger injectors or a bigger carburetor to the induction system usually accompanies this stage if you are so inclined. And don’t forget to dyno tune!
Stage 4
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Stage Four
This stage is all about the bottom end of the motor: upgrades like welding, lightening, blueprinting, and balancing. If the engine’s reciprocating assembly is not balanced correctly with all of the other high-performance mods you have done to the engine bad things could happen. Big-horsepower motors need the crank strengthened by welding it where weak spots are or replacing the crank altogether. Balancing smooths out the complete powerplant by making sure the bottom end is spinning perfectly straight. Blueprinting of the engine makes sure that all of the parts in the bottom end are working the best they possibly can in unison. The smoother the engine runs, the less these negatives have an effect. Any way to limit this friction will offer good gains in all the three stages you have done before it.
This is usually where spending some serious coin comes in since you are really getting into the guts of the engine. But, remember, by having your bottom end re-worked and making it stronger, lighter, and truer, it makes for a better-performing engine all around. As with any upgrade, make sure that bike gets on a dyno before any road miles get underway.
Stage 5
Photo: Hot Bike Staff
Stage Five
Stage Five is the addition of forced induction, such as superchargers and turbos. This is a big-money investment, but for you go-big-or-go-home kind of riders, shelling out the duckets to add almost double the horsepower of your engine, the $5,000-plus price tag is no issue. For many using a turbo or supercharger kit it skips most of the aforementioned stages. Yes, you can just buy a forced induction system, bolt it to your stock motor, and get all the ponies you could ever dream of. And yes, with any forced induction kit a ton of dyno tuning needs to be done by somebody who is a pro on tuning blown or turbo’d bikes to get it working right.
We hope this list of upgrade stages helps you better understand what is available in the marketplace for hopping up your engine and that it aids you in finding a clearer path to getting more horsepower (and therefore more happiness) out of your motorcycle’s motor.
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