Drag/street bike bottom end build

I posted a similiar thread a while back, asking for ideas on what i would need to build a bottom end for a kz that would withstand the abuse of a 1200-1300 build that would be driven on the track but occasionally on the street. I am thinking about going with a 1260cc kit. Ape offers this kit with a 13.5:1 comp ratio. Is this too high for the street? This would involve boring the upper cases and installing new sleeves i believe. I know for sure i will have the crank welded. I thought about having the transmission cut. Do you think this is necessary? Also someone mentioned a heavy duty 2nd gear being installed, ape sells hd 2nd gears in an input and output, would i need both? Are these transmission mods over doing it? Also, if i went with a j style head would i have to get a hyvo type crank sprocket installed? Ape also sells heavy duty transmission bearings. Would these be advised?

If you go with a 1260 kit and use a stock cylinder, you will probably run into problems. You will have to use oversize cylinders, which will come with the kit, that requires boring cylinder and upper cases. Using that size cylinders in a stock block won't leave much for cooling. Lots of times, you can even see the cylinder itself because the stock cylinder doesn't have that much meat. It would be ok for a dragbike but marginal on the street. Dragbikes aren't running that long and can get away it. Really depends on how you are going to use it. I wouldn't go bigger than a 1200cc in a stock block. Have heard that a 1260 in a stock block has problems with keeping cylinders round because of lack of support. I wouldn't use the 13.5:1 on the street either. You would have to use some good fuel (read expensive) as that comp. ratio will make a LOT of heat, especially if you try to ride it on the street. There are ways to help that out some by altering cam timing etc. but why go to all that trouble? Have the crank welded and, if you can, indexed, to be sure it is true. A MK11 crank is heavier but stronger because of the 16T center pin but the Z1 crank is lighter and will rev faster. The KZ1000 crank is in between. Best case scenario is to have a 16T center pin put in a Z1 crank for the best of both worlds but that costs some bucks to do. HD case and cylinder studs would be a very good idea. I wouldn't build that motor without them personally. Might be a good idea to use a crank center support plate also. Cutting the transmion would be a very good idea also. If nothing else but for insurance against the abuse you will be putting it through. A HD second gear would help but I have heard different opinions on them. I know a guy who was running a high 8 second bike without one but I'm sure it was marginal. I have bben told a KZ trans is good down to about low nines to high 8's. Much lower and a J model trans. would be a good idea. If you can get a MK11 trans., you can proably get by without the HD second gear. A MK11 trans. second gear is about .030 wider that a regular KZ1000 trans. Going with what you are talking about, I would use the HD 2nd gear for insurance if nothing else. I believe in over-building my motors for the added strength. To use the J head, you will need the cam tower conversion done. Basically, anything you can do to build the motor stronger will help and give you some peace of mind when you are trying to stretch your throttle cables. A HD clutch basket wouldn't be a bad idea also, if you want to go that far. Miy not be necessary but wouldn't hurt.

Wow,Racer...some really good and detailed info,there bud.

I guess your name wasn't just picked at random,eh.:laugh:

sounds like racer is in my basement helping me build mine.
i would for sure do the clutch basket. the z1 motor i have had a tamborine for a basket and a stock 900 did that. imagine what a 1200/1260 would do.
it gets real expensive real quick.
i wish i knew what i was in for when i started this project.
i am depleating my funds real fast.
for sure mill the cap and use the ape support plate.
and the studs, mains and cylinder studs.
do it right the first time.
nothing worst then having a problum and saying " shit, i should've spent the extra $200"
( i over engineered my build also )

now all i need is a set of xc rings and i'm done.
oh well, maybe next paycheck. i mean you can only hide so much from the wife and that fricking e-bay always gets me.

KZ1000 non j models have a steel clutch basket.

Remember if you use a J head you must use J pistons. The pin location in the J piston is in a differenct location than the KZ piston. You'll also need a different cylinder base gasket (thicker).

Be sure an buy a overshift bushing and if you have a spare $10.00 buy the teflon guide that mounts in the main bearing support. This will make installing your cams much easier as the cam chain won't rotate on the crank sprocket.
Good luck,
Buzz

If you use the J head it would be best to use J type pistons to match the head like KruZer mentioned. APE sells a spacer in different thicknesses to bring the cylinder height back up to where it will need to be because of the different pin location in the J type pistons. Some guys use KZ pistons with a J head but you have to be careful that the valves don't touch the pistons because the valve angle is different and the J head has bigger valves and won't fit in the valve relief on the KZ pistons. Best set-up is J pistons with J head and use the right spacer for your set-up. Decide which direction you want to go before you start buying parts. If in doube, give Jay a call at APE and he can tell you what you need. He has probably forgot more then we will ever know!

I would not recommend using a stock cyl’s with anything over 1200cc. As was mentioned by racer54. They are prone to warpage due to lack of wall thickness.
My understanding on the j head is that u can get just as much flow out of a stock head but there is more labor involved in the porting.The j has large valves but u can increase the kz’s valve size as I did. u pay extra to buy a j head and then u need to pay extra for the tower conversion and pistons.U realy need to price it out booth ways first. Personally I have gone the stock route on my 1327cc motor. I went with a kz back cut trany and billet 2nd gear.I also use a mk11 crank witch requires mk11 cam gears.
Check this site out.
www.flowbenchtech.com/porting/CRH/kz-data.htm

Larry did my head .it was ported to 138cfm,then Larry brought it up to 150cfm. he can answer any questions u may have if u call him.

ive been told you can use a 1260 kit in stock kz block if you use suzuki sleeves,but ive never gone over 1197 on a stock blck myself;)

You can use the sleeves that come with the 1260 piston/sleeve kit in a stock block. Problem is that when you bore out the block that big for the sleeves, there isn't much left of the block in some areas to support the sleeve itself and that's where the problem is. I have seen a stock block with 1260 sleeves and you could actually see the sleeve in some areas because it bored through the cylinder itself. That doesn't give the sleeve any support and it can go out of round. Dragbikes can get away with this because they don't run that long and I'm sure there are a few streetbikes getting away with it also, but......I don't think it is condusive to a good motor set-up for the street. Why take the chance...stay at 1200 or smaller in a stock block and be safe.

I just had one built and first pass timing chain broke ...snapped cams and dropped few values....if ya doing all them upgrades pick up a d.i.d. cam chain  
...to save alot you can do 1075cc kit with high comp pistons....still a beast ..save a bunch of money and I don't think you will miss the 90 something cc or whatever 

you know this was posted in 2008 ???