TOPIC:

Need help. Just smart enough to build it and stupid enough to ride it. I have campaigned a Z-1 in Heavyweight Superbike the last two years and have come in second the same. I have decided that the Z-1 is not the answer. Don't get me wrong the Z-1 as built is awesome. So, I've decided to build a better handling KZ-GPZ. That would be a much more powerful version of my KZ650. The bike must be a twin shocker 82 or earlier under the rule book.

Here are my parameters for my fellow KZ fans to weigh in on. 120 HP minimum, 350lbs or less, 57 inch wheelbase with no more than 24.5 degrees of rake. 17" wheels twin rotor front brakes with rear disc.

The frame is not a problem, I have done two already fully gusseted and braced. Ditto on swingarm. Although this bike will use a ZRX 1200 swingarm. I have three KZ750LTD motors in excellent condition and two 1977 KZ650 motors and one brand new 77 650 crate motor.

I'm planning on using the KZ650 bottom end with the KZ750 top end and retain the roller cam chain. I've been going back and forth on HYVO versus roller. This website has sort of convinced me that roller is the way to go especially to degree the cams perfectly. Plus I know a couple of guys that keep breaking the HYVO's in racing applications, but those have all been Honda's. So maybe its just a Honda supplier problem. But for big cams and springs for high RPM applications, it appears roller is the way to go. Am I right? Is there any problem swiching KZ750 top ends with a KZ650 bottem end, if I switch all of the timing chain guides and rollers and cam sprockets?

The next thing is how to get to 120+ HP. My Z-1 is 130 and weighs 440. My Z-1 is 66x67 bore and stroke. the 650/750's have a 54 stroke. I have read, in the Archives tha Arias has made 72mm bore pistons. They said they didn't have any knowledge of that. So I looked in Kawasaki's parts bin. The last two valve big bore was the ZR1100 92,93 model. I have ordered one of those pistons for the time being. It doesn't fit in the cylinder head without major modifications and has a diameter of 73.5mm. Does anyone know if I can resleeve a KZ750 cylinder to accept a 73.5mm size. I like the idea of using an OEM piston because I can order it from the factory instead of a custom piston. It has a fairly high dome and is coated and has blow by holes drilled for the rings. It is cast also which means it doesn't expand like a forged piston and I believe will seal better and longer. The ZR piston also takes a bigger piston pin than the little KZ's. If I make them fit it will give me displacement of around 920cc. With the same bore and stroke of early ZX-9's (92,93).
I'm also worried about valve clearance. I have some early Andrews cams that have milder profiles than my Web Cams. I've heard that when you go to an oversize piston you cannot install large cams. I guess how large won't be known until you start to assemble unless someone else has done it.
Finally I am thinking of moving to 33mm Keihin CR carbs as opposed to 29mm. I will lose rideability but gain top end or are the KZ750 valves too small to take advantage of the bigger carbs. I ported my KZ650 motor and Star Racing did my Z-1 yet I am only running a couple of sizes different in jetting. Which makes me think I should stick with 29's.

Any help out there on whom I should send the crank to or what I should do on piston size, cam chain etc. would be greatly appreciated.

Getting 120 HP from a 650 is asking a lot. That is double the stock output and I think it cannot be done unless you use a turbo and nitros and even then you will probably blow the bottom end.
Back in the early 80's I turboed my 650 and ended up bending a con rod.
All I can tell you is good luck with that.

IMHO, getting 120 hp from a 750 is doable, but it ain't gonna be streetable. 880cc is the max with the 750 cylinder block, any larger and you bore into the fins, Lorcan has a custom made big block for a 900cc 750, but I think he's a long way from finishing it. There is talk on www.750turbo.com (lorcan's site) of a group buy of LA sleeves and JE pistons, for your application I think the thicker 880 sleeve with the 810 bore would probably be the best idea, otherwise I think you will have problems with liner distortion with the thin liners in racing conditions (ie lots of heat).
100 hp out of an 810 kitted GPz750 is fairly normal, so I think 120 hp out of a all out race motor is possible.
Unless you need the kickstarter on the 650, I don't understand why you don't want to use the 750 bottom end.

Guess you know where to look now

Check out this thread:
kzrider.com/forum/viewthread.php?tid=18320
Steve Darlington basically lays out the recipe.

I'd say start with one of those LTD750 motors, put in an 810 kit, port the head, drop in some '83 or '84 GPz750 cams, some Mikuni BS34 carbs. A GPz fork with some Progressive springs and a fork brace will help, as will a nice swingarm with some nice shocks (KYB, Marzocchi, Ohlins, etc).

You might try a set of wheels from a police bike, I understand they have 18" front and rear.

120hp might be asking a bit much...

Here's my 2cents worth on your project....I think you are really gonna be on the knife edge of reliability with trying to squeeze 120 horse (at the wheel?) out of the 650/750 design. You didn't mention an oil cooler or pipe choices so I'll assume an oil cooler will be necessary and the pipe will run wide open on the track.

I am just beginning my winter 810 upgrade (already have the 700 Wiseco kit in the '77Kz650 Custom) with my goal being 100 streetable ponies measured at the crank. I am looking for a strong degree of reliability and longevity instead of wide open track performance.

In all of my engine upgrade research I haven't come across your suggested cylinder sizing or piston choice but degreeing the 750 cams is mentioned everywhere to properly set the valves after decking the head by 30 thou. This head trimming will also raise up the compression ratio slightly but you have to be careful not to bump the compression up too much unless you are going to be running some serious high octane racing gas.

I have read that the 650 ported head is a choice worth considering because of the increased velocity through the smaller intake runners. The bigger 750 valves should fit. Also look at the 750 Turbo springs and head gasket as they are more durable than stock 650/750 offerings. On the carb side I defer to KZr's resident expert wiredgeorge who has recommended Mikuni34's for my project.

If you stay with factory parts for availability the choice generally seems to lean towards the GPz750 cams as they are a little hotter from the factory, but on the exhaust side they run an electronic tach instead of a gear driven one that came on the Kz650/750. The crankcase cylinder openings will also have to be opened up to accept the 750 jugs.

To get to the magic 350 lb. mark you are going to have to swap wheels, go with an aluminum swingarm with double shocks, strip off every unnecessary wire, bolt and run helium in the frame (just joking.) Let us know what your weight reduction plans are as I have a buddy who drag races a '78 and his ride comes in around 375 lbs stripped down and he can't find any more lb.'s to trim off.

There are some extremely smart folks on this site (including fellow Canadian Steve Darlington) that have gone at least part way down the road you are looking to travel, but I don't think there have been too many that were successful at hitting the magic 120 mark in a 650 frame. I don't doubt the middleweight can take it if you can make it.

In the archives there are numerous threads on the big bore 650 platform including a link to the GPz site plus several members who thrash their tweaked 650's in vintage races.

Cheers-Colin Firth-Ontario Canada

Post edited by: reborn650, at: 2005/12/30 00:44

members.tripod.com/gpz_rider/technical/FAQ2000.htm

gpzrider.lagemann.org/technical/FAQ2000.htm

Two GPz750 FAQs, some duplication between the two.

I assumed you were talking about crankshaft hp, if you want 120 RWHp, you will have to turn some really high rpm, probably 14k+.

Hp = torque x rpm /5252

Aren't the 650 and 750 cranks the same as far as strength goes. Kawasaki lists a different part number but as far as I can tell the only difference from visualization and mic is the roller chain. I'm planning on using the 750 block. Somebody previously said ARIAS has made 72mm pistons for a KZ750. Has anyone actually talked to someone who has seen that motor. With 72mm pistons the motor should make 110 or more. And yes I have a huge oil cooler, actually two one is off a Concour and the one I'm toying with is a early GSXR oil cooled motor cooler. I'm getting ready to send a cylinder out to Millenium to see how big they can sleeve it. A fellow racer took a CB 550 four out to 670cc, the major problem he ran into was excessive crankcase pressure blowing out the base gasket because there wasn't enough surface area left at the case. Thanks guys.

I presume you are not allowed to drop a GPz750 turbo engine in? With a little wiring mod they make 130hp all day.

The billet block I had made takes 73mm pistons for 904cc. As Steel says, you can bore the stock cylinder to 72mm, 880cc, quite easily. You will need to bore the cases for larger sleeves and find some suitable high comp pistons (or have some made). Rods from the 750 turbo are very strong and have a 16mm pin (stock 750 is 15mm), most KZ pistons are 17mm so you may want to consider rod and piston availability together.

You might try this site for engine calculations as to wether or not 120hp is possible. Programs can do engine cfm calcs and more

www.dansmc.com/mc_software.htm

O.K Here is my 2 cents;
Chassis, I would stick with 18 wheels as the motor is wide by modern standards and you need the road clearance. I run 1984 GPZ 550 wheels on a 1983-4 Kz 750 L front end.If you want even lighter and wider wheels I would go with 1985-7 GSXR 750 wheels. The front discs are too wide and possible the discs may be rerivetted on the other side of the carriers.I would not change the rake as it works well as is.You could run a GS 1100 swingarm which is light. It is also about 3 inches longer.I havent personally raced with one but a friend has and says he liked the lenght.The seat pan is steal and if you could replace it with a 83-4 KZ 750(plastic) or something else that would save some weight. My bike weighs 400lbs so I think it will be hard to get it down to 350lbs. I would be content with 375lbsAnother choice for front forks would be 83 GPZ 750 (37mm) all you have to do is bore out the stock triple 1mm. If you use the same front wheel the spacer will also need to be shortened as the 83 GPZ 750 is 5mm wider than the 650 triples.
Engine, I think you should seriously think of 100hp as a reasonable rear wheel limit.There no one way to acheive that.Heres is what has been done by a friend who does alot of my work. KZ 650 motor with a wiseco 810 kit(cases need boring),head ported and reworked using 750 intakes and stiffer springs. CAms will have to be 83-85 gpz 750 or better.Carbs 29mm smoothbores.Now this motor produced 100 RWHP but the real surprise was the compression and the off corner power/response. The smaller ports really drive the fuel/air mixture into the combustion chamber.
Personally I would not bore out the motor over 810 as you may run into heat issues.The motor can aslo be built with the 750 head and you may get more overall HP but perhaps not the same drive out of the corners.If you want to through alot of money at the project I would recomend dual plugging the head.
I would stick with 29mm smoothbores or perhaps 31mm CRs but no bigger than that.

More to think about;
Running the 650 bottom end is a ggod idea to reduce friction loss from the HYVO chain. You will need the KZ750(E model) or ltd 750 head which you have. The head will need to be drilled and tapped for the idler gear.The 650 head has a small combustion chamber and will raise compression over the 750 head by about 20 psi.Before you shave the ehad assemble the motor with modelling clay in the chamber and figure out your piston to valve clearance . then shave the head or head and block to get to about .060" clearance no less.
I am slowly putting together this combination which should yeild 90 RWHP;kz 650 bottom end,gpz 750 pistons,kz 750 head,1984 gpz 750 cams,kz 550 6 speed trani.The head has had the following work ;ported,shaved .015",KZ 1000 intake valves which were reduced in diameter to .5mm over stock,heavier springs(used drag springs,intake outer ,exhaust inner ,others were stock)The spring rate needs to be strong but not too strong.The carbs are likely going to be reworked gpz 34mm mikunis without the dynajet kit and still using a modified airbox. This combination has worked well for me in the past.I have a set of 29mm smoothbores that I also may try.
As a street project I recently tried the 650 head on a Kz 750 motor and was pleasantly surprised.The motor had no machining and the compression is 180 psi on all four.The Keihin 34mm carbs needs only an increase on the primary jet up three sizes. Still using stock airbox/filter.This bike is really responsive through the midrange.
If you need experienced motor work done I have a shop in Iowa ,US and another in Milton ,ontario.
Also I have A turbo 750 bottom end assemble if you want to source out 16mm pistons.Steve 905-864-4759.

Post edited by: darlington, at: 2005/12/31 09:22

What about adding a turbo setup to the 810 kit, that would make the 120 hp and then some wouldn't it? Using the wiseco p809b (8:1 compression ratio) instead of the wiseco k810 (10.25:1 compression). Is there a way to turbo this setup? I see kits for the KZ900/1000 on the mrturbo.com site, would this work on the KZ650/750 bored to 810? possibly with some slight mods, or as a bolt on? I'm hoping to do something like this in the spring if its possible. Any thoughts?