My GT550 build plan
Posted: Thu May 01, 2014 6:45 am
Gents,
I've recently joined this forum and in reading the old threads, I ran across several references to the GT I built a couple years back so to help those that are thinking about juicing their 550's, here's a copy of my original build plan. Whenever you build an engine, I highly recommend that you write a written build sheet. If you don't, I can almost guarantee that you will forget one or more mods that you had thought about doing.
*****************************
The plan, includes a set of expansion chambers by Jemco and after a bunch of careful measurements was to open up the intakes, by reaming out the spigots 3.5mm, taking the intake bridge to a razors edge, rounding that edge and then tapering up to full size as it approaches the cylinder bridge to maintain heat transfer. I also moved the starting point for the bridge way back to just in front of the oil feed and putting a nice concave curve to it enhancing the flow and opening the accompanying intake tracts 2.5 as they travel to the wall of the cylinder. Rather than lowering the intakes, I took 2.4mm from the bottom of the piston intake skirts effectively increasing the intake timing to allow the bigger carbs to do their thing. The tranfers with that stupid "shelf" arrangement where the port size on the crank is so much bigger than the receiving port on the cylinder have been tapered to provide smooth flow from the crankcase to the cylinder. They are plenty big enough, they just need more laminar flow....that why they've been tapered. The exhaust ports were widened .8mm on each side and raising it 1.6mm (I should have taken this up 3.5mm in hindsight) while maintaining the same shape. All the joining surfaces and ports are being machined smooth to enhance flow. This is a big deal on any two stoke and needs to be done on any older model as they were terrible about alignment back then. The head got dropped off to have 20 thou's taken off and since the center cylinder actually runs cooler then the outside ones do(per my research), I'm leaving it as a one piece head for now, I can always cut it later(now cut into 3 separate heads). I bought a nice set of 30mm carbs (from an H2) to finish it off. I don't have any illusion about it ever being a rocket (too heavy for that); I just would like a little bit more safe power, especially in the upper range.
********************************
Now that it's done, there are a couple things I would have done differently as is always the case and also some of the added things that weren't in my original build plan.. First, as my above edit indicates, I should have raised the exhaust higher. Even 3.5 would not have made it too radical nor would I have lost mush from the bottom end. Remember, when you widen the exhaust, you are effectively adding power to the bottom. Another and I can't stress this enough and several of you guys that have written to me over the years have already heard this.....don't waste your time "porting your engine unless you are willing to put the effort into opening up the extremely small intake tracts! If you want a shock, get a H1 barrel and compare the two intake's! I also cut a half-moon into the intake side of the piston to remove stress points caused by sharp corners. Another thing that I did was a very slight re-aiming of the transfers, a little more up and a little more rearward effectively moving the point of intersection to the rear third of the cylinder. This raised the point (rpm) that the power came on and more closely matched the Jemco pipes that Jon built for me. The 30mm carbs were fine but you could go up to 32/34. The H2 carbs that I used were tough to jet but we have to remember that they came jetted for larger cylinders so I was really starting in no-mans land with no starting reference. Sorry but I made so many jetting changes, I don't remember where it ended up. Remember to chamfer EVERY single edge, and don't forget your pistons! I also would suggest that with this new-found power, you address a few things in the frame that will no longer be up to the task. The shocks, forks and swingarm are great places to start along with wider wheels to hold modern tires. At an estimated 75hp or so, you aren't going to need gsxr parts but there are several mods around that will enhance your ride unless like me, you wanted to keep it nearly stock appearing
I've owned a couple of Titans & GT's in the past and one I built as my q-ship back in the 70's....looked like hell but would eat most other bikes for lunch. We raced a buffalo and a H2 and while I don't say this often on the Kaw boards, the Zuks are much better engineered and will last forever if you take care of them. Highly modifying the GT series engines for power takes a bit more work because they were engineered to be comfortable touring bikes but that good engineering pays off because you won't have some of the issues that my Kaws have had.
Now I've got my first buffalo in many years coming soon and I can hardly wait to strip it and build another street ripper.
Good luck guys,
jeff
I've recently joined this forum and in reading the old threads, I ran across several references to the GT I built a couple years back so to help those that are thinking about juicing their 550's, here's a copy of my original build plan. Whenever you build an engine, I highly recommend that you write a written build sheet. If you don't, I can almost guarantee that you will forget one or more mods that you had thought about doing.
*****************************
The plan, includes a set of expansion chambers by Jemco and after a bunch of careful measurements was to open up the intakes, by reaming out the spigots 3.5mm, taking the intake bridge to a razors edge, rounding that edge and then tapering up to full size as it approaches the cylinder bridge to maintain heat transfer. I also moved the starting point for the bridge way back to just in front of the oil feed and putting a nice concave curve to it enhancing the flow and opening the accompanying intake tracts 2.5 as they travel to the wall of the cylinder. Rather than lowering the intakes, I took 2.4mm from the bottom of the piston intake skirts effectively increasing the intake timing to allow the bigger carbs to do their thing. The tranfers with that stupid "shelf" arrangement where the port size on the crank is so much bigger than the receiving port on the cylinder have been tapered to provide smooth flow from the crankcase to the cylinder. They are plenty big enough, they just need more laminar flow....that why they've been tapered. The exhaust ports were widened .8mm on each side and raising it 1.6mm (I should have taken this up 3.5mm in hindsight) while maintaining the same shape. All the joining surfaces and ports are being machined smooth to enhance flow. This is a big deal on any two stoke and needs to be done on any older model as they were terrible about alignment back then. The head got dropped off to have 20 thou's taken off and since the center cylinder actually runs cooler then the outside ones do(per my research), I'm leaving it as a one piece head for now, I can always cut it later(now cut into 3 separate heads). I bought a nice set of 30mm carbs (from an H2) to finish it off. I don't have any illusion about it ever being a rocket (too heavy for that); I just would like a little bit more safe power, especially in the upper range.
********************************
Now that it's done, there are a couple things I would have done differently as is always the case and also some of the added things that weren't in my original build plan.. First, as my above edit indicates, I should have raised the exhaust higher. Even 3.5 would not have made it too radical nor would I have lost mush from the bottom end. Remember, when you widen the exhaust, you are effectively adding power to the bottom. Another and I can't stress this enough and several of you guys that have written to me over the years have already heard this.....don't waste your time "porting your engine unless you are willing to put the effort into opening up the extremely small intake tracts! If you want a shock, get a H1 barrel and compare the two intake's! I also cut a half-moon into the intake side of the piston to remove stress points caused by sharp corners. Another thing that I did was a very slight re-aiming of the transfers, a little more up and a little more rearward effectively moving the point of intersection to the rear third of the cylinder. This raised the point (rpm) that the power came on and more closely matched the Jemco pipes that Jon built for me. The 30mm carbs were fine but you could go up to 32/34. The H2 carbs that I used were tough to jet but we have to remember that they came jetted for larger cylinders so I was really starting in no-mans land with no starting reference. Sorry but I made so many jetting changes, I don't remember where it ended up. Remember to chamfer EVERY single edge, and don't forget your pistons! I also would suggest that with this new-found power, you address a few things in the frame that will no longer be up to the task. The shocks, forks and swingarm are great places to start along with wider wheels to hold modern tires. At an estimated 75hp or so, you aren't going to need gsxr parts but there are several mods around that will enhance your ride unless like me, you wanted to keep it nearly stock appearing
I've owned a couple of Titans & GT's in the past and one I built as my q-ship back in the 70's....looked like hell but would eat most other bikes for lunch. We raced a buffalo and a H2 and while I don't say this often on the Kaw boards, the Zuks are much better engineered and will last forever if you take care of them. Highly modifying the GT series engines for power takes a bit more work because they were engineered to be comfortable touring bikes but that good engineering pays off because you won't have some of the issues that my Kaws have had.
Now I've got my first buffalo in many years coming soon and I can hardly wait to strip it and build another street ripper.
Good luck guys,
jeff
or maybe i could have given them a break and pulled out the 86 1100 slabbie 