Nicasil has several advantages including lighter weight and better heat transfer. There was a guy, Steve Hmmond that used to do a ton of TZ350 stuff and offered re-plating through his company MOTRAC. No idea if he/they still exist though.
The easiest and cheapest path to go down is a set of spannies and maybe a slightly higher CR and leave those barrels stock.
If you want more, you are looking at making exhaust ports wider & Taller and making the 4 transfers wider. If you go far enough, you will need the set of 32mm TMX flat slide carbs that I am about to sell off.
Okay......and what bargain price had you in mind, for a poor pensioner, who lives on his own, with just his motorbike and a one eyed cat for company,(cue violins)!
I hadn't seriously thought about price. But the one eyed moggie touched a heart string - or was that just a broken violin string?
Before we even start a serious discussion about price and delivery and jetting, first it would be good for you to think about what size carbs you really want for a mild street bike. 32mm may be a little large for a mild street motor. I'd start off working out what size you can physically fit and then talk to peopel about what carbs they have on their hotted up 550s
I just don't want to sell you something that will not do what you need it to do.
I might not need them right now, but if I've got them and I need them, I don't need to find them. And probably when I need them, and I don't have them, I won't be able to find them! (If that makes any sense).
I follow but when I have them I can't find them because I have so much stuff I can never find anything.
So if you have them you can't find them and if you need them you can't find them either....
As I said earlier I don't know if 32mm is a good fit on a 550 because I have not tried them. I got them for a 750 as a straight drop on replacement that someone else was planning. They came to me with other stuff that I also can't find.....
No kidding, I vote for riding the GT550 as/is and finding a Kaw H1 for a hot-rod. The GT550 is a great ride, and extremely reliable, but it's no speed demon. In the UK you guys have Rick Brett, the world's authority on Kaw triples. He's in Nottingham, get in touch. An H1 (or H2) is what you want for that massive two-stroke speed fix.
Lane
If you stroke it more than twice; you're playing with it.
Too many bikes, too much time, ENOUGH SPACE, FINALLY! Never enough money.........
Tell that to Kevin Hutchison who won the ManCup last year with his modified GT750 drag bike. He beat all the hot rod H2s. Or tell that to Brett deStoop who did over 200MPH on his lightly modified GT750.
GT550 is a sleeper. Stock it only makes about 38hp at the rear wheel. In a race version it should not be too hard to get that up to 80 or more HP and for a steet bike 60 should be fairly easy for a professional porter. I just revisted my notes and MOTA runs and when I changed from 28 to 30 to 32mm carbs, it did not measurably add power except at the very top end and larger carbs cost more down low and midrange than they gained at the top. I didn't spend teh time to work out why that was, but rationally a 200cc RD400 can make 50hp on 28mm carbs and my RZ350 makes around 60rear wheel hp with 26mm carbs.
I suspect that 32mm flats might actually make more power and might have better mid throttle response but if I were building a hot street 550 I would probably start with a set of 28mm flat slides.
For another data point, my GT750 makes around 80HP with very mild tune and stock CV carbs which were flow rated as the same as a 32mm round slide. That suggests that a mild 550 should be able to make around 60hp on stock carbs.
When i measured intake window port area on GT550 at cylinder wall, it wasn't much more than 28mm carbs had to offer it for area. So that is a limit - intake port window area. I think the port windows are too small even for stock 28mm carbs.
The cylinder aluminum inlet track and at the start looks tight and a sharp bend and the divider is long and thick. The oil feed pipe sticks up in between one of the intake tunnel passages disturbing flow.
I have raised the EX port ~2mm and shaved piston skirt ~2mm on separate instances and really no effect, which is not typical. I am suspecting the intake port/passage needs some more area and flow improvements. Yes, the transfer porta are enduro tuned, but usually a little change on these others ports makes a difference to a limit. Or the transfers are an issue? I plan to try intake port work next sticking with the 28 mm.
The engine as is, mid-range does like extra compression. 0.020" off head or gasket and you can feel with your butt dyno and in your arms.
You might be surprised that with a minor increase in intake port width and a lot of cleanup, that stock small intake can support over 75 crank HP - in theory at least. Without much of a change there is enough port time area.
But at that level the pipes are trying to peak 1000 revs below where the ports are trying to peak, so it gets a bit peaky.With a little more optimization bigger carbs and porting closer to a tuned RD400 starts to work much better
Exhaust Ports.
Wider and taller, three people suggested this.
Raise them, three people.
Ream exhaust spigot, one person.
Clean them up, three people.
Inlet
Clean them up, two people.
Thin the divider, two people.
Lower brass oil feed pipe, one person.
Shorten SRIS tubes, one person.
Open Intake, one person.
Standard carbs, 28mm flat slides, 30mm.
Transfers
Widen them, two people.
Sundries
Raise Compression, two people.
Raise cylinders and restore compression, two people. (what does this do?)
Chambers, everybody!
Shave piston skirt, one person.
Chamfer all edges, one person
Cut cylinder heads into three, most people.
Use the Nikosil cylinders, 19" rear rim and ditch the centre stand.
Exhaust Ports.
Wider and taller, three people suggested this. Yes
Raise them, three people. yES
Ream exhaust spigot, one person. No
Clean them up, three people.
Inlet
Clean them up, two people.
Thin the divider, two people.
Lower brass oil feed pipe, one person. not a good idea IMHO
Shorten SRIS tubes, one person. I would not bother
Open Intake, one person. yes with caution. Wider and raise teh roof as much as practical to clear piston skirt
Standard carbs, 28mm flat slides, 30mm. For moderate performance improvement at moderate revs use stock carb. For more top end go with larger carbs
Transfers
Widen them, two people.
Sundries
Raise Compression, two people.
Raise cylinders and restore compression, two people. (what does this do?) when you raise the exhaust port, the effective compression at low to mid revs is lower, so it's usually a good idea to raise CR to compensate fr that loss of performance
Chambers, everybody!
Shave piston skirt, one person. I am not a fan
Chamfer all edges, one person ports should always be chamfered
Cut cylinder heads into three, most people. that's usually a good idea
Use the Nikosil cylinders, 19" rear rim and ditch the centre stand. 18" both ends not 19....
Someday someone will do a port map and port timing in degrees for the GT550. Maybe not
Buy a bunch of spare cylinders, heads, etc and experiment.
I would love to have a set of Plated Cylinders with the extra scavenging ports: awesome. Then I would focus on a set of chambers tuned for what you want. Pipes alone can completely change your engine. I have Bassanis (?) and to me those are matched well for stock engine. Jemco's look similar in cone shape/size but bigger outlet. Not sure about Higgspeeds.
I might clean up first part of intake passage, shorten/delete SRIS tube in transfer passage and lower intake oil injection tube as well. I want to street ride
