These past couple of months have been very interesting concerning the life of my shovelhead and the introduction of said motorcycle to the world of forced induction, more specifically turbocharging. This also happens to be the first time I have ever turbocharged anything, car bike, anything. It has definitley been a learning experience.
Origionally I was going to use this turbo on an ironhead, but I couldn't shake the visions of grenading the transmission and having it lock up on me at some ridiculous speed. Besides that, when you push the extremes of a motor to get more and more power out of it it is only natural that as you get more and more radical with it the potenital for the failure of that motor becomes more and more possible. Now, if you're running a mild motor at low RPM's and you do have a problem with it odds are that it will not be too big a deal, definitley nothing catastrophic. But on the other hand if somthing fails in your big-bored, stroked, high performance screamer when it is wound up tight at full tilt boogie odds are that it ain't gonna be pretty. The other big reason I chose to turbo the shovelhead was simple, If I totally lunch it, like rods through the cases or a blown up cylinder, I can simply order new parts and rebuild. You can't exactly go down to the harley dealership and order brand new engine cases for your ironhead, so if you fuck them up beyond repair you are simply shit out of luck.
A turbo will let a motor produce virtually unlimited power, the biggest factor becomes the acutal suructural integrity of the motor. As boost pressure rises, power output will go up as well, but eventually something will let loose. That's just the way it goes, push it too far, get a little too generous with the boost and ka-boom!!
I'm not trying to say that turbocharged bikes are unreliable, in fact just the opposite is true.
With a naturally aspirated (non-turbo) motor if you are trying to get more power out of it you'll modify the ports in the heads increase to increase airflow. Increase the compression ratio which will let you install higher lift, longer duration cams and still make great torque. But now you'll really be able to breathe at higher rpm's, which is where you'll really shine if you're looking for big time power output. The faster you spin the more air you pump the more fuel you can burn and the more power you will make.
With a turbo motor you can run it low compression with a stock or very mild cam in it and it will be a total pussycat crusing around, it will vibrate less, it will put less of a load on the pistons and bottom end, and will generally last longer than the high compression motor because it is only really going to work hard when you roll on the throttle and the boost comes on. It's performance on demand, and you don't need to beat the hell out of your valvetrain with a radical cam to achieve it.
You will only run into problems if you get too wild with the boost and really test the limits.
I'm going to leave you with a few pictures of what happens when you push it too far. I'll explain how my motor ended up looking like this soon enough, but I'm all typed out for tonight.