Building the Perfect Street Engine
The Sprocket Twins at Nightrider get hundreds of requests for engine
configurations. Riders want the simplest engine to build, the highest power than
can get, an engine to beat their friends, an engine to go racing with. In short,
every rider wants the ideal engine. They want big power increases and instant
throttle response. They describe thinly discuised race engine sitting in a
street bike. What many riders don't want to discuss or hear are the issues
associated with these "over the edge" engines such as:.
After spending a lot of time thinking about what most riders really want versus what they think they want, I decided to come up with my own requirements for a strong engine upgrade package for Twin Cams. It had to meet the following requirements:
That would be a good start on our "universal twin cam". While there probably isn't the perfect street engine for your Twin Cam engine powered bike, this comes as close as I have seen to meeting that definition. You'll notice that I never mentioned a specific horsepower figure in our "perfect engine" needs. That's because it is too easy to take a single HP or Torque number and take it out of context. A good street engine has a broad torque curve that gets a bike moving quickly and keeps the acceleration going. A good average power number is more important than the maximum number.
If you went to most shops and gave them this list of "wants" for your updated engine, they would probably tell you that it just isn't possible to build this engine. In most circumstances, I'd have to agree with these shops. Then I saw something that complete changed my opinion on what could be built.
Most riders have been conditioned to believe that for good power, you had to raise the compression ratio to 10.5:1. While most of the lighter Dyna's and Softail's could almost get away with this compression riding around on the street, the heavier Road King's and FLH's tend to have severe detonation issues. While the EFI knock sensors could stop the detonation issue, they also resulted in much lower power than possible with the higher compression. I had never been a big proponent of high compression engines for heavy bikes, especially when I knew that once compression ratio's exceeded 9.5:1 the extra power gained for every point of compression gained was very small. But a high percentage of the HD performance industry insisted on going with these high compression engines in heavy, air cooled bikes. The engineering and physics involved in this never made sense to me.
Enter Wes Brown at CycleRama. Wes' shop in West Central Florida has been building world class engines for all type of bikes for many years. I'm sure Wes got tired of riders asking for big power engines in heavy bikes, then having to "back off the tuning" to handle the way most riders lug their engines around town. While sitting in Wes' shop one day and discussing strong street engines he mentioned a very conservative 100/100+ engine he had recently put together. Knowing that CycleRama always puts together strong engines, I expected to see a nice power curve in the 2800-5500 RPM range. I was completely blown away when he showed me the dyno sheet on this table-top smooth power curve at 100ft.lb. starting at 2400 RPMs to over 5000 RPM. This same engine made over 100HP, all from a TC95 with a 9.5:1 compression ratio.
As you can see for yourself, this engine begins making power right off idle and is still pulling at 6000 RPMs. While this isn't going to win you any dyno shootouts, do not underestimate the ability to move your bike down the road at some very illegal speeds. This engine is a "roll on" king. Whatever gear you choose, at any RPM this engine is going to pull like a freight train when you twist the throttle around. With its lower compression, it isn't going to have much of a detonation issue. It is actually going to make a bike run much faster than the horsepower numbers would have you believe. In short, very close to an ideal street engine for any TC powered bike.
While I am showing some alternative engine components, this is for convenience only. The only way to ensure you get the same power results would be to have CycleRama actually build the bike. You should be able to get similar results by order all major components from them. If you want to use other components other than those listed, you can expect different results.
If you want to build an engine like this, you can contact Wes Brown at CycleRama. His phone number is 727.546.0889. I think you will be very happy with an engine like this.
As a note to those riders who want to save some money, this engine combination can be done without going to the 95CID big bore kit. It is estimated that the TC88 version of this engine would make 2-3HP and 3-4 ft.lb. less power, but with the same broad, flat power curve.
|Copyright 1997-2006 Stephen Mullen, Oldsmar, FL -+-|