Since my 13 year old build thread got wiped out, consider this a continuation of the 30-something page thread that is no longer with us. I'm going to get those that don't know or remember up to speed real quick and then get down to the meat 'n taters of this thread... making more power.
I built this thing from the ground up back in 2013-2014 buying each part on eBay. Yep, I started with a bare frame, not a complete bike. It was an interesting adventure in deep dives into parts diagrams, many eBay listings of various parts to visualize how everything went together, wiring diagrams, and browsing pictures of various bikes to get ideas for the direction I wanted to go. Very, very long story short, I ended up with an ST13 main tank, engine, frame, swing arm, and rear wheel with an '06 GSX-R600 front end and an RC51 tail, plus a whole bunch of little stuff to make it all work together. Since I know you're wondering about the weight, it's about 230 lbs. lighter than an intact ST1300ABS. No, really. Anyway, I did some track days, put about 6000 miles on it, and then stopped riding in 2016. Just this past March (2026), I got back on the bike and fell back in love with it. Way back when I was first riding it, I was blown away with the tractability of the prodigious amount of torque but felt that Honda left a lot on the table with this engine. At the time, initial thoughts were supercharger or turbo. That was about as far as it went, though, as I stopped riding shortly thereafter.
Back to the present and wanting to pick up where I left off, I gave boost a bit more thought and just couldn't come up with a way to cleanly integrate either system in the bike without it looking tacked on, so that was out. Fortunately, Honda blessed the bike with a big, burley engine that, at least in my case, is very easy to work on. To give you an idea, it only takes me about ten minutes of leisurely work to get the airbox open, and more time to get my tools together than it does to get the valve covers off. Oil changes? Pff... an oil change on a lawn mower is harder. It's probably the easiest bike to work on that I've ever had. First step was to find a Bazzaz Z-Fi to support the incoming mods. Sadly, they've been out of print since 2022, but I was able to quickly find one and as they say, it was off to the races. I loaded up a map that Catmandu2 put together that dramatically smoothed out the throttle response and idle, and eliminated this weird dead spot I had at between 3000 and 3500 RPM. The butt dyno says I picked up about 5 HP, too. Yay. He spent a lot of time on it and it shows, and it's so good, it's going to be the base map we build on as the mods happen.
So what mods? First let's talk about the exhaust. As you can see, I don't have slip ons that remotely resemble anything you guys have. The biggest restriction I'm seeing in the factory exhaust is what's behind the collectors. The outlet of the collectors is 2", but the pipe they welded to it is about 1.75" and there's no transition... it's just an abrupt step down. The H pipe is good for what they were after- low end and mid range, but I have other ideas. The plan is to cut the exhaust off behind the merge, then weld on two 2" 90 degree elbows that point inwards, then another two 90's that point upwards and merge into one pipe that goes up through the hole in the swing arm, and then split back into two pipes with the cans tucked tightly against the tail. This will basically give me an X pipe, which is better for top end power than an H pipe. All 2" pipe. I'm hoping to get this done by the end of the riding season.
Porting the heads and having some cams and valve springs made will be next. I may have to enlarge and shorten the primaries, but I'll cross that bridge when I get to it. I feel that 175 crank HP isn't an unreasonable number to hit without raising the redline or losing much of that glorious low end.
Before I start digging in to the engine, I'll be taking the bike apart this winter for paint and powder coat. In the mean time, I've started fooling around with velocity stacks since it's so easy to get into the airboxI've drawn up a few different lengths, but this will give you an idea of what I'm working on to replace the OEM rubber stacks. The first one is currently being printed to verify fitment before the other three are made.
So there ya have it. Phase two of this bike doth commence. I'll be posting back here periodically with updates, findings, musings, and discussion related to the project.
I built this thing from the ground up back in 2013-2014 buying each part on eBay. Yep, I started with a bare frame, not a complete bike. It was an interesting adventure in deep dives into parts diagrams, many eBay listings of various parts to visualize how everything went together, wiring diagrams, and browsing pictures of various bikes to get ideas for the direction I wanted to go. Very, very long story short, I ended up with an ST13 main tank, engine, frame, swing arm, and rear wheel with an '06 GSX-R600 front end and an RC51 tail, plus a whole bunch of little stuff to make it all work together. Since I know you're wondering about the weight, it's about 230 lbs. lighter than an intact ST1300ABS. No, really. Anyway, I did some track days, put about 6000 miles on it, and then stopped riding in 2016. Just this past March (2026), I got back on the bike and fell back in love with it. Way back when I was first riding it, I was blown away with the tractability of the prodigious amount of torque but felt that Honda left a lot on the table with this engine. At the time, initial thoughts were supercharger or turbo. That was about as far as it went, though, as I stopped riding shortly thereafter.
Back to the present and wanting to pick up where I left off, I gave boost a bit more thought and just couldn't come up with a way to cleanly integrate either system in the bike without it looking tacked on, so that was out. Fortunately, Honda blessed the bike with a big, burley engine that, at least in my case, is very easy to work on. To give you an idea, it only takes me about ten minutes of leisurely work to get the airbox open, and more time to get my tools together than it does to get the valve covers off. Oil changes? Pff... an oil change on a lawn mower is harder. It's probably the easiest bike to work on that I've ever had. First step was to find a Bazzaz Z-Fi to support the incoming mods. Sadly, they've been out of print since 2022, but I was able to quickly find one and as they say, it was off to the races. I loaded up a map that Catmandu2 put together that dramatically smoothed out the throttle response and idle, and eliminated this weird dead spot I had at between 3000 and 3500 RPM. The butt dyno says I picked up about 5 HP, too. Yay. He spent a lot of time on it and it shows, and it's so good, it's going to be the base map we build on as the mods happen.
So what mods? First let's talk about the exhaust. As you can see, I don't have slip ons that remotely resemble anything you guys have. The biggest restriction I'm seeing in the factory exhaust is what's behind the collectors. The outlet of the collectors is 2", but the pipe they welded to it is about 1.75" and there's no transition... it's just an abrupt step down. The H pipe is good for what they were after- low end and mid range, but I have other ideas. The plan is to cut the exhaust off behind the merge, then weld on two 2" 90 degree elbows that point inwards, then another two 90's that point upwards and merge into one pipe that goes up through the hole in the swing arm, and then split back into two pipes with the cans tucked tightly against the tail. This will basically give me an X pipe, which is better for top end power than an H pipe. All 2" pipe. I'm hoping to get this done by the end of the riding season.
Porting the heads and having some cams and valve springs made will be next. I may have to enlarge and shorten the primaries, but I'll cross that bridge when I get to it. I feel that 175 crank HP isn't an unreasonable number to hit without raising the redline or losing much of that glorious low end.
Before I start digging in to the engine, I'll be taking the bike apart this winter for paint and powder coat. In the mean time, I've started fooling around with velocity stacks since it's so easy to get into the airboxI've drawn up a few different lengths, but this will give you an idea of what I'm working on to replace the OEM rubber stacks. The first one is currently being printed to verify fitment before the other three are made.
So there ya have it. Phase two of this bike doth commence. I'll be posting back here periodically with updates, findings, musings, and discussion related to the project.
looking forward to more posts on this project!
