How To - Porting a Suzuki/Wetbike motor
Topic: Porting a wetbike motor for more power (torque)
Expertise Required: Anybody can read this article, but I suggest an engine porting professional to do the work
Estimated Time: Three or four hours
- Before you begin, you need to know exactly what changes/modifications you are going to perform. That is, you need to know exactly what each port's timing, shape, and condition is before you begin
- Before you begin . . . make sure you haven't bored motor yet. Do all port work PRIOR TO final engine boring
- Perform your port map as described here
- Do all of the heavy port work first. That is, if you are going to do things like "raising" the roof of the boost port window, do that first. You'll have a mountain of STEEL filings and grinding stone material.
- Now use some grinding stones to "radius" the intake edge of the ports. That is, turn block over so that you are looking down through the crankcase and round the edges of the steel liner so that you have a smooth transition into the port - not a ledge the air has to go over.
- Now you flip block over and cleanup the edges of the upper ports. Take care that you don't widen, raise, or reshape these ports unless you know exactly what you are doing
- If you are going to modify these ports - modify the steel part first. Then, you can come back and clean up the aluminum later (with proper bits)
- Now you can put in your aluminum (non ferrous) bits and start the aluminum work. I like to start with the upper ports and get the casting ground back to match the port windows.
- Now flip the block over and work on the support ribs that are in the middle of the port openings. Try to shape them so that they come to a smooth point. Again, the idea is to reduce the air turbulence when the air is entering the ports
- This is also a good time to try to cleanup the port openings. You'll notice lots of boogers and stuff. Try to smooth them out if you can
- Polishing - mirror smooth is NOT a good idea. The surface should have a satin finish - or slightly rough/sanded. Engine experts have found that makes the best power
Once you get your engine back from the machine shop (after it was bored and honed to final size) - you can chamfer the edges of the ports so that the rings won't get hung up. Some shops will do this as part of the bore/hone service. Best to check them yourself and/or dress them up a bit too. Before final assembly, don't forget to thoroughly wash/rinse all of the port passages. When you run a white rag with carburetor cleaner through them, it should come out clean - no exceptions.
- Do not raise the roof of the exhaust port - it raises the rpm of the power band. You'll see that a lot in reference to other 2-stroke motors. However, we don't have a tuned pipe, nor do we have an ignition system that goes higher than 5500 rpm.
- Do not change the angle of the roof of the boost ports. They should be around 45 degrees - by design
- Do not hog out bottom port windows to smooth them out unless you have a scheme to decrease crankcase volume. These motors make power by generating good pressure when the flywheel comes around. If you hog out the ports, then you've increased the crankcase volume (giving up some power) and reducing the amount of charge that can run up the ports into the cylinder. Some type of crankcase stuffer is in order if you do this. Note: Don't go wild on this idea or you might blow the center seal.
- If you are gonna hog out the bottom end, don't go too deep or you'll need to find a welder to plug a hole.
Copyright 2011 Capt'n Obveeus