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I think the power your looking for is doable. I did my 650 way back in 81 and it was still running great when the bike was totaled in Sept. 03. My 650 had Yosh 716 cc 10 3/4 to 1 pressure cast pistons Yosh road and track cams ported head with 750 valves and 29 smooth bores and Yosh racing header, it made 85 RWHP at 10,500 rpm. I ran this bike hard all those years spinning it to 10 /11 thousand all the time with no problems. I think with 880 cc's and a little more compression you should hit the numbers your after. Good luck.
Mark

Post edited by: Mark Wing, at: 2006/01/06 02:11

So the crank and rods are the same for 650 or a 750?
Also are the forged pistons or hyperutectic better. I hear that the forged are heavy,and have more clearence in the bore. and that the hyper pistons are light weight and good for the street. Is this true?

Post edited by: Snakebyte, at: 2006/01/06 08:11

I would be surprised if top end will hold to 13000rpm. Can you keep a basically 30 year old designed valve and spring to follow a cam profile at that speed?

Steell, The 920 motor is just my Z-1 motor. Limited by rules to 930cc with unlimited carbs. or 1025 with 29mm smoothbores. I stuck with 29's, however. Crank was balanced and blue printed by Falicon, Ported by Star Racing, Pistons were 67mm JE 12:1 custom, Cams are Web hard welded grind 125. Which has 435 lift and 288 duration. Heavy Duty springs and shim under bucket. Carbs are Keihin CR's running velocity stacks. Frame was fully gusseted and has 2003 Kawasaki ZR-7 front end 41mm forks and 17" wheels, with emulators and 1.0 kilo springs. Rear shocks are progressive full adj, ride height 16", rear swingarm is braced and gusseted. Bike shows no sign of frame flex. Hope you build one.

RomSpaceKnight wrote:

...Canadian 1985 750 GSXR's came with a 29mm flatslide, which I have on good authority can be bored to 32mm. Pretty rare carb. I believe most went south years ago to be run on Yank bikes in 86, when the Yanks finally got GSXR's, but with CV carbs...

Unless there were others of which I'm unaware, the 29mm "flatslides" were CV flatslides, like the 36s and 34s that were used on later oil-cooled GSXRs. Kim's KZ650 (basically stock, otherwise) has a set of those on it, and likes them very much, BTW.

Squish, or quench, area makes for a faster burn, which needs less ignition advance and/or octane. This is partly due to the turbulence it creates in the chamber, and partly just because of the smaller, more open chamber (note that engines with smaller bores generally run higher compression, other things being more or less equal). On 900s and 1000s, this is one advantage of the'84-model GpZ 1100 head over the older hemis: more swirl in a smaller chamber, despite bigger valves.

To Old-Skul

I have initiated contact with Arias. I am waiting to hear from them if they have ever made 72mm pistons. I am going to have pistons made. I am going to request 12:1 compression and must send them a stock piston and the cylinder head. It will be a 750 LTD head. I haven't determined whether I am going to use stock rods or ZX-9 rods, difference being 15 or 17mm pin. That shouldn't be a problem changing pin size, though on a second set. Yes, there will be a sizeable compression increase due to the large squish band on the 72mm piston. They can't tell me how much obviously until they see the head and then it will only be approximate. My idea all along is to assemble the best components I can put them together and whatever I get is what I get. Since this is for road racing, I need reliabilty for 25 miles at a time. I will run Web cams grind no. 189. That is .400 lift and 290 degree duration.

When I built my first KZ650 to 680cc with those cams. We went to Mid-Ohio finishing the bike the night before. We actually had the bike done the week before and it was pumping oil up the cylinder head bolt towers and out the head gasket. Motor sounded great. Three different people looked at it. Went to a solid copper head gasket off of KZ700. It was 8 thou thinner than the graphite gasket. Started it, pistons hit the valves, terrible clatter. Put another base gasket on and it still shoved oil up the cylinder stud holes. Thats when a friend of mine stopped by and saw that I had stepped down the breather hose to fit into the over flow bottle. We changed the size of the hose, problem solved at 6pm night before practice.

At the track following morning we set rpm limiter to 9000 rpm, stock setting. I went down straight and got passed by SR500, I almost killed myself. Played with jetting set RPM to 9500. A little better, still get passed by hot SR500. My mechanic callled WEB cam and asked where this motor should hit. The guy at WEB wasn't sure because of our porting but said the valve springs were good for 5000 over stock. He set the limiter to 13,000 and told me to open it up. Well at just over 9500 it felt like I hit nitrous. I have been running it at that RPM ever since. Before I re rung it we actually raced it at 13,500 several times. I had to race it in Heavyweight Superbike at Beaver Run in Pennsylvania since I broke several springs and exhaust guide on my Z-1 at Gratten several weeks before. I dueled both days with 2004 National Champion on a KZ1000 before finding out on Sunday that if I drafted down the back straight I could actually pull up on him. Almost smacked the back of him on the last lap before out braking him and passing him both days for third place behind the CBX and a big bore Moto-Guzzi. There were a lot of people on big Kaws,GS750's and CB750 four valves that were not happy finishing behind the little 650. It was probably the most fun race I ever had.

To Ahrma120,

That's a great story!

The cams in my bike are similiar, they come in earlier about 7000rpm and sign off just past 11,000 but when you hit the power band it does feel like nitrous. It'll lift the front wheel on my bike in first just a hair and can cause a brief waggle in second as well.

Keep us advised on those pistons and how your project progresses. With an additional 215cc, I bet that CBX is squarely in your sites this year. I'll be at Barber rooting for you!

Did the bottom end of your motor last the whole season at 13000 rpm without a rebuild? How much maintenance does it take during a year?

Last if the reciprocating mass of 880cc unit is significantly more, you might want to consider a milder cam grind (something that hits in the 11,000 - 12,000 range) to keep internal forces in the motor down. This might also help build an easier\broader torque curve. Good luck again!

They were not CV type. I have a set at home. I may bore them to 32mm if I can't afford or won't part with money to buy 36mm RS carbs. They come right off a 1985 GSXR 750. Bike unavailable in US till 86. They are true flatslides and look identical to Mikuni RS series carbs. Are a tad better of a carb than the round slide 29mm smoothbore carbs so popular with kz's. Swapped em for a set of 29mm smoothbores in 92. If I decide to go with 36mm RS carbs will make them available (29mm flatslides will trade for naked slavegirl).

Post edited by: RomSpaceKnight, at: 2006/01/06 16:28

To Old-Skul Bottom end has lasted two full seasons plus a top-end rebuild. I have also ran several track days with the bike.

HI Guys,
Any further progress on this? Keen to see if the 100+ hp is reached.

What is the power range on '82 GPZ 750 cams?

I can't give you the power band figure, but the intake cam on the 82 GPz and 82 KZ750E has the same part number. The exhaust cams have different part numbers, but I suspect that is because the 82 GPz 750 has an electronic tach so the exhaust cam does not have the tach drive gear.

The above info is from buykawasaki.com, and it is not always correct.

83-85 GPz750 cams are different, they boost the power in the upper rpm range at the expense of low and midrange power.