Steve, I am not taking sides either way. And have no reason to doubt your claim. Only thing is I don't believe you can end up with a 1015 motor. Here is why. Cylindrical volume is V=πr2h (the radius r is squared). So in your case it would be bore for a 1015 motor is 69.4 mm (diameter) which is 3.47 cm radius. And the crank on a Z2 is 58 mm which makes the cylinder volume highiet of 5.8 cm. plug everything you get the following displacement
(pi)*(3.47)sq*(5.8) then times 4 (four cylinders) = 877.60 cc
Smaller than your original 903 cc motor. Now, can the rods from your 903 engine have been used in place of the 750 rods (don't know if that is possible, I have no clue)? In that case, it would have made it a 1015 motor. But like say, I have no doubt you that you are using that crank. Don't have to prove anything to anyone man. So don't get rushed into anything.
It does seem to be a little detuned with the stock 1015 pistons. With the cast or billet pistons, the deck height was even. With the stock ones, it was about 2 mm lower thus lowering compression. All i had then was a German made caliper so I didn't measure it. I now have a digital one and will show the depth with the stock pistons and compare with the 10.25/1 Wiseco's. 58-66 is quite a jump and 8 mm would be hard to miss. If the throws on the crank are shorter, wouldn't the rods be also? I was oblivious to this issue until now. I want to know too. I remember a stamp on the counter balance and the rods have markings as well. It would be helpful to know what the Z2 markings are to compare. If I have to go back to a 903 crank to get the ponies this bike deserves, then so be it. There was interest in this crank for a member's turbo build. We'll see.
Just checked eBay for a Z2 crank. Lots of plain bearing KZ 750's and some triple cranks too. No Z2 750 cranks. I don't trust eBay and If I do buy a 903 crank, it will probably be from The Old Kaw Guy. He's always treated me right.
I bought a new throttle cable while there. The one I have is almost two years old.
It seems to me that part of the confusion is that overbore piston kits are typically labeled with the resulting displacement, not the piston diameter. Wiseco sells a 1015, 1045, 1075, etc. So it seems perfectly natural to say that you have a "1015 kit" in your engine even if you were using a short stroke crank. We all understand that you wouldn't actually have 1015cc, but it's a very easy way to communicate which pistons you purchased.
I think the idea of running a short stroke crank seems pretty cool, depending on how far into the red you can safely build the valvetrain to go. Modern bike engines are all way oversquare.
The stroke of the Z2 crank has been established, but no one seems to know if the rod length was altered. It seems possible that Kawasaki used the same deck height for both the Z1 and Z2, and just used longer connecting rods to compensate for the shorter stroke length. If that were the case, then a Z2 crank should drop into a Z1 with no changes at all. Does anyone know the rod length, or relative deck height of a Z2 compared to a Z1?
'78 Z1-R in blue, '78 Z1-R in black, '78 Z1-R in pieces
'95 GPZ1100 (sold)
Tyrell Corp wrote: I think the idea of running a short stroke crank seems pretty cool, depending on how far into the red you can safely build the valvetrain to go. Modern bike engines are all way oversquare.
Yup, also I think just boring out with oversize pistons alone won't make big power gains without more cam and other tuning work. It is more about a motor's breathing than capacity.
Has a 'bored and stroked' under square motor been done before on a zed?
If you could find pistons with the right pin location it would probably be a riot to ride in a light bike.
Still recovering,some days are better than others.
Yes, this is possible, using a short stroke z400J crank with a wiseco "610cc " kit bored out 550 block, same pin size. The rods and forged one piece crank are bulletproof but I think there are factors limiting rpm on any 8 valve ,
Short stroke would lose some bottom end tourque, something the big old kz were good at, the later GPz more power but a lot more 'cammy'.
Good luck on the build Steve, you have most of the bits and the vision for something really nice there.
1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces
PLUMMEN wrote: Its like a 396/427 chevy versus a 454 chevy.The 427 and 454 have the same bore,but the 427 uses the same stroke as 366/396 which makes it a real riot to drive .
Was thinking the same thing ..... the 383 Chevy and the 302 Z28 motor too.
1978 KZ650 b-2
700cc Wiseco kit 10 to 1.
1980 KZ750 cam, ape springs, stock clutch/ Barnett springs.
Vance and Hines Header w/ comp baffle and Ape pods, Dyna S and green coils, copper wires.
29MM smooth bores W/ 17.5 pilots, 0-6s and 117.5 main
16/42 gearing X ring chain and alum rear JT sprocket....
The following user(s) said Thank You: PLUMMEN, SWest
You've got to be kidding. The 4 valve piston was Z1E's fault. Like I said, it set me back two weeks. They didn't have just one piston to send me like now. It will cost me $125 for a new piston, figure in gaskets and we're looking at $200. As it is, I'm burning up rear tires. Makes it tough to save the money and keep up with what the bike needs normally.
I'll do it.