bigger bike, modern bike, or sup up my 550?

Those are the options I'm considering. I love my zr550 to death, but I've done just about every mod I can think of and I'm addicting to improving/learning/tinkering/shopping for parts/dreaming..and of course riding and enjoying the results. The only thing left to do on my 550 is a overbore/cam upgrade. I'm trying to decide if I want to do that, or level up to a bigger and/or modern bike. I'm actually leaning toward getting a bigger old school Z and doing an overbore with porting, cams, ignition, tuning etc. along with full resto-mod along the lines of Bulldock or Sanctuary builds. I'm ready and willing to drop serious cash into the project. Just need to decide which way to go...

It really all depends on you. if you want to go Fast I would look at a big KZ or more modern bike. A small displacement bike will never have the torque of a larger bike and torque is what you feel on the street. I have a few bikes, a couple of KZ's and while I love the KZs they cannot compare to my Aprilia. Its light, fast, handles great, reliable, gets good mileage. super predictable, and yet that is kind of what makes it boring to me. I have a fully built KZ1000 that every time I throw a leg over my heart starts beating faster.
that being said I'm in the process of building a hot engine for a "slow" kz750 twin, mostly because I can't leave anything stock alone but also because very few people are hot-rodding these engines. There is very little aftermarket support, and that has a certain appeal to me. I see very few ZR550s and even less with a crazy engine, so the cool factor is high.

DoctoRot wrote: It really all depends on you. if you want to go Fast I would look at a big KZ or more modern bike. A small displacement bike will never have the torque of a larger bike and torque is what you feel on the street. I have a few bikes, a couple of KZ's and while I love the KZs they cannot compare to my Aprilia. Its light, fast, handles great, reliable, gets good mileage. super predictable, and yet that is kind of what makes it boring to me. I have a fully built KZ1000 that every time I throw a leg over my heart starts beating faster.
that being said I'm in the process of building a hot engine for a "slow" kz750 twin, mostly because I can't leave anything stock alone but also because very few people are hot-rodding these engines. There is very little aftermarket support, and that has a certain appeal to me. I see very few ZR550s and even less with a crazy engine, so the cool factor is high.

Curious, what are you doing to soup up your KZ750. I have a 77 twin and want it to go faster. Ive topped out around 105mph.

650Dude wrote: Curious, what are you doing to soup up your KZ750. I have a 77 twin and want it to go faster. Ive topped out around 105mph.

Crank balanced by Falicon
Forged high-comp Venolia pistons (stock bore)
Port and polish
Took .050” off the head so static compression is 10.6/1
Custom cam regrind by Web Cams
Free flowing pipe by yours truely.
C5 optical ignition
At first I will run the stock BS38s but I have a rack of RS36 carbs where one carb body is ruined so I’m going to build a rack and linkage for this application using what’s there.
Right now I’m planning on running stock gearing but I may go up a tooth or two on the big sprocket so I doubt it will go over 105 before it’s redlining but it will get there in a hurry.

Vic, what are you planning for the KZ 750? I have one, and love it dearly . I also have a couple of parts bikes and a ton of parts. I am thinking about building a rat bike out of the extras and would like to give it some more power. I am thinking about boring the cylinders, putting a 2 into 1 exhaust on it, rejetting the carbs, and maybe experimenting with different sprockets. Any other ideas?

Vic, just saw the above post after I made my post. Question : what is the C5 ignition?

C5 Performance is the only company (as far as I know) making ignitions for the KZ750 twin . www.c5ignitions.com/
After digging into the 750 twin engine I have come to the conclusion it is engineered really tamely for reliability. lots of potential for more power. some guys are getting 85 to the wheel out of these engines.

If you have any more questions about modding a 750 twin engine DM me or ask me in my project thread so we don't clutter up Z-addicts thread.

Would you keep the 550?
I would like to see a properly modded ZXR1100 which would more than satisfy your power craving. First mod would be a round headlight, please.

**I am only comparing vintage bikes in this reply as you can easily buy a modern bike that has huge power and is lighter than most mountain bikes. Zaddict referenced building a restomod from a vintage bike, so that is the only thing I am comparing. The zrx is an amazing motorcycle and is always the correct answer to what big bike should I buy, but it is what I consider a modern bike for the purposes of this thread**

As an owner of a slightly modified zr550 and a very heavily modified kz750, I can only say it is not a very tough choice. Going for a larger displacement bike is the only real solution as you can only make your 550 so fast.
As I am sure you remember, I have put higher compression pistons and cams from the zx550 in my Zephyr and it was a sizable upgrade in power from stock, but even if I was to bore it out to 615 it still wouldn't give me the sensation of being pushed back that the torque of my 750 provides. That is not to say my zr550 is slow....and I would wager if I raced my two bikes against each other, that the 550 could very possibly keep up with the 750. Also note, that my zr550 is geared for lower rpm's at highway speeds, so it is technically slower than if it had stock sprockets.
I have touched on this in my build thread, but one day I went and rode my 750 and 550 back-to-back and the difference in weight and power delivery is enormous!
The zr550 is so much lighter than my kz750 ( and over 50% of my kz750 is made from a zr550!) The 550 felt so light it felt like riding a bicycle in comparison. The 550 engine so effortlessly revs to redline and just gives me a sensation of bike that can't wait to take off down the road. Kind of like an eager dog pulling against the leash because it wants to play.
The 750 is a sensation of torque that propels me forward from a stand still, but once in the higher rev's it doesn't feel all that different...except it isn't as eager to scream to the redline as the 550 is.
The 750 is very easy to maneuver and does not feel lumbering in comparison to the 550 at all. But you can instantly feel the massive weight difference between the two bikes.
I have read of many instances of folks on gpz550's holding their own against the larger displacement vintage bikes. The weight differences is what equalizes the sometime huge gaps in power output.
I honestly don't know the weight difference between the 550 and 750 engines, but it is significant. I have both a spare 550 and 750 engine sitting on rolling platforms in my garage and just pushing them around you can tell the difference in heft. I lifted my completely assembled 550 motor in to the frame once but with my 750, I could only lift the bare assembled engine cases into the frame and had to install the clutch, covers, cylinder block and head while it was in the frame. I simply can't lift an assembled 750 motor off the floor. The kz900/1000/1100 motors are even bigger in size which is reflected in the sizable difference in curb weights from the 750's.
So all that gibberish was to only illustrate, that while you can easily find a larger displacement (vintage) motorcycle that will provide years of fun, you may lose a lot of the nimbleness and "happy puppy dog" feeling the 550 provides.
That why you should keep the 550 and build a really cool 650/750/900/1000/1100 restomod.

Now that my 750 project is almost done, ( just need to finish welding up the Bassani exhaust) I am now planning to remodel my zr550 with some powder coated wheels and a different exhaust. I have to keep myself busy until I can collect all the necessary parts to start the kz650 restomod I want to do.

**Totally of subject, but I need to return to your past thread about installing zx550 cams in your Zephyr. While researching the mystery Yoshimura cams I put in my 750, I instantly realized a massive chunk of mis-information I wrote in one of my replies regarding valve overlap. Needless to say is that I'm an idiot and posted some highly erroneous information that needs to be removed.**

I follow this whole heartedly. I had a 2011 1100 hypermotard Ducati and loved it but the kz650 is just more fun.
If I can cast another vote build your kz650! I have. I don’t really like punching out the ccs on a bike for some reason it seems dishonest. Some people can build the 650 out to over 800 but it just seems like it would remove the soul of the bike.
BUT high compression and hot cams, in my opinion, simply amplify the soul!
My new vote is hot rod kz650! Attached image is my bike

DoctoRot wrote: It really all depends on you. if you want to go Fast I would look at a big KZ or more modern bike. A small displacement bike will never have the torque of a larger bike and torque is what you feel on the street. I have a few bikes, a couple of KZ's and while I love the KZs they cannot compare to my Aprilia. Its light, fast, handles great, reliable, gets good mileage. super predictable, and yet that is kind of what makes it boring to me. I have a fully built KZ1000 that every time I throw a leg over my heart starts beating faster.
that being said I'm in the process of building a hot engine for a "slow" kz750 twin, mostly because I can't leave anything stock alone but also because very few people are hot-rodding these engines. There is very little aftermarket support, and that has a certain appeal to me. I see very few ZR550s and even less with a crazy engine, so the cool factor is high.

Good advice, thank you. I love this line: "every time I throw my leg over [my kz1000] my heart starts beating faster.' I had a brand new Audi at one point that was never as exciting to drive as the much older model I had before, though I could never figure out why. I think you're right - the modern car was just too easy/predictable!

waktaylor wrote: Would you keep the 550?

Definitely. I'd hope to be shot out to space riding it when I die.