HARLEY-DAVIDSON PERFORMANCE
Harley-Davidson performance has been the subject of many books. Many of these books go into
great detail, right down to the nuts and bolts. Our purpose here is to help you
understand and define what power you need and what is necessary to make that power.
WHAT IS PERFORMANCE
Harley-Davidson performance means different things to different riders. To some, it's
just about getting a little extra power and better sound from their Harley. Some want to make 100 hp or more for those stop light to stop light runs. Or they might want
to enter one of those dyno drags. That’s all good, but when you modify your engine that much, you can create problems with heat, noise, maintenance, reliability and rideability. Most Harley riders need power in the low to mid rpm range.
If your bike is going to make a lot more power, you're probably going to ride it faster and harder. If you ride harder, you might want to think about upgrading your brakes
and suspension.
DEFINING POWER
When you talk about Harley-Davidson performance, do you mean torque, horsepower or both? Torque is twisting
power. It's this low-rmp twisting power that gets you moving. Horsepower is the higher-end
spinning power that keeps you moving.
If you look at the difference between a Harley-Davidson V-Rod and a regular Harley Twin Cam 96, you'll see that the V-Rod with its' 1200cc engine puts out a lot more horsepower than the
Twin Cam 1584cc, but puts out less torgue.
The V-Rod puts out this horsepower buy spinning faster. The V-Rod is able to spin faster because of its' four valves per cylinder and dual overhead cams. Basically it’s because of the V-Rod's overall breathing ability.
The traditional Harley-Davidson Twin Cam and V-Rods have much different engine characteristics which
result in different power characteristics. Most Harley riders will stick with their Big
V-Twins even though the V-Rod makes more horsepower. I've ridden V-Rods and didn't like the
way they handled.
HARLEY-DAVIDSON PEFORMANCE BASICS
An internal combustion engine is basically an air pump. The faster you spin it, the more air
it processes within a given time. The amount of power it produces is governed by the amount
of fuel it burns, which depends on the amount of air it can breathe. More air can mean
more power. Turnning the engine over faster will also increase air and fuel flow and cause it to
make more power.
Compression is also a factor. The more air an engine compresses into the combustion chamber,
the more fuel it can burn in each air/fuel charge. Ignite more fuel, produce more power.
Changing compression ratios can be much more involved than bolting on a few parts.
USING WHAT YOU HAVE
Harley-Davidson performance can be increased by working with what you have. This is usually done by bolting on a set of slip-on mufflers and a high-flow air filter, along with remapping the fuel injection or carburetor re-jetting. The cost will be about $1,000 in parts and labor. The gain is usually around 10 horsepower.
Here's a great article about EFI and some modifications that can be done for better performance
Harley-Davidson EFI
The next step is to replace the stock cams with those that give higher lift and longer duration. By installing cams with more lift (to open valves further) and with more duration (to open valves longer), it's possible to get a big performance increase from your engine. This can be done without removing the heads. Depending on the cams, it might be necessary to replace the valve springs. These changes can take a stock Harley-Davidson from about 65hp to 85hp.
Check out Harley-Davidson Cams for great cam tech tips.
Compression and how it affects performance
Going beyond this point would mean getting into the engine. Now you’re talking about replacing stock cylinders, pistons, heads and other parts that go along with it. You would be adding quite a bit more power, but you’re also looking at some serious money. This serious money will get you to 100hp or more.
IGNITION
A stock Harley-Davidson ignition is designed to prevent engine damage and work with the restrictions set by the government. Preventing engine damage obviouisly protects your investment while limiting warranty claims.
The ignition module does this by limiting engine rpms by sensing detonation. An aftermarket module can be set to retard the spark and provide more push at lower rpms. Some ignition modules are adjustable and have a varity of advance curves. These units are priced from $200 to $500. When you really hop up an engine, an ignition module can help unleash more power.
USABLE POWER
Let's look at where you want to make power. Remember, torque is the twisting/pushing power that occurs at the lower rpm range and horsepower occurs at higher rpm ranges. For most Harley-Davidson riders, it makes little sense to try to increase engine performance to the 4,000 to 6,000 rpm range, when most of your riding occurs between 2,000 to 4,000 rpms, especially when doing so negatively effects torgue. You can get good low to mid-range Harley-Davidson performance without a lot of modifications.
If you're looking for better Harley-Davidson performance, expect to spend money. Depending on the level of performance, it could be very serious money.
For good tips on exhaust, check out
Harley Exhaust
IF YOU'RE LOOKING FOR GREAT DEALS ON PARTS AND ACCESSORIES CHECK OUT J&P CYCLES.
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