Cylinder head flow data is provided for each of the stock heads so you can see for yourself what the performance differences and potential are. Just for example, an 88CFM @ 10" of water head is capable of making 130 HP on an engine as small as 1045cc with the right cams and compression. J Heads, in stock form, are not the big power makers that many people think they are. They require port work to bring out their potential, just like the KZ head does. A late model [83-85] 2V GPZ head is a pretty good head in stock configuration. There would be a noticeable difference in performance using one of those heads on a J or on a KZ bottom end with the right pistons to correct the compression ratio, even without porting it. The stock J Head would not provide the same power level as the stock, late model GPZ head. A stock KZ head is rather restricted when it comes to making Horsepower. The runners have a nasty kink that forms a double apex with the sort side radius. Air is turning down and also bending off to the side in two areas very close in proximity. While velocity in a stock KZ port is good [avg 300 FPS @ 28" of Test Pressure] right down the middle of the runner, the CFM capacity is relatively low. Proper porting will improve the CFM without killing the velocity. Improper porting will kill the velocity without raising the CFM. This is why we measure CFM & Velocity. 
| Here it is.....The information you're not going to find anyplace else that I know of. Accurate flow information for the KZ & J heads plus other helpful information to keep you on track. There are countless forums on the Internet with all kinds of opinions and suggestions. Use that information as you see fit. We give you the actual numbers.
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Rebuild Considerations - KZ Street Engine Components - Big Valves -Porting Tech
|  | Design Specifications - Stock Components | Stock Cylinder Head Flow Data | KZ 900 | 1000 | J 998 | 83-85 GPz11 | | Stock CFM @10" Test Pressure - .500" lift | 68 | 68 | 70 | 83 | | Stock CFM @28" Test Pressure - .500" lift | 113.5 | 113.5 | 116.9 | 138.6 | | Intake Valve Size mm | 36 | 36 | 37 | 38 | | Exhaust Valve Size mm | 30 | 30 | 31 | 32 | | Bore mm | 66 | 70 | 69.4 | 72.5 | | Stroke mm | 66 | 66 | 66 | 66 | | Engine Size CID | 55.089 | 61.994 | 60.919 | 66.481 | | CID per Cylinder | 13.772 | 15.498 | 15.230 | 16.620 | | Bore/Stroke Ratio | 1.000 | 1.061 | 1.052 | 1.099 | | Intake Valve Net Area | 1.518 | 1.518 | 1.606 | 1.696 | | Intake Valve Dia. Area | 1.577 | 1.577 | 1.665 | 1.758 | | Intake Valve Stem Area | 0.059 | 0.059 | .059 | 0.059 | | Exhaust Valve Net Area | 1.036 | 1.036 | 1.110 | 1.185 | | Exhaust Valve Dia. Area | 1.095 | 1.095 | 1.169 | 1.247 | | Exhaust Valve Stem Area | 0.059 | 0.059 | 0.059 | 0.059 | | Int Valve/Bore Ratio | 0.545 | 0.514 | 0.533 | 0.524 | | Exh Valve/Bore Ratio | 0.455 | 0.429 | 0.447 | 0.441 | | Exh/Int Valve Ratio | 0.833 | 0.833 | 0.838 | 0.842 | | Exh/Int Valve Area Ratio | 0.695 | 0.695 | 0.702 | 0.709 | | Intake Valve L/D Ratio | .231 | .231 | .225 | .261 | | Exhaust Valve L/D Ratio . | .251 | .251 | .243 | 345 | | Curtain Area -to- Valve Area Convergence Intake Valve Lift | .354 | .354 | .364 | .374 | | Curtain Area -to- Valve Area Convergence Exhaust Valve Lift inch | .295 | .295 | .305 | .315 |  | 83 - 85
GPz1184-85
LTD 1100 |    Click photos for larger version | 83 - 85
GPz11
Ports & Chamber
[stock] |  | KZ | | Note the combustion chamber shape differences in the photos above | | | | Valve Spring & Retainer Note When selecting valve springs and retainers, note the following regarding Shim On Bottom setups. Not all S.O.B. retainers maintain the same valve spring installed heights. Late GPz11 retainers will yield approximately .100" taller installed height than the APE or PM Titanium retainers we've tested | | | | | | How important is an engine's breathing capability? | | Below is a dyno simulation showing 2 different engine sizes, 1075 and 1327cc. One 1075 and the 1327 both have stock KZ cylinderheads and identical cams. The other 1075 has identical components but with 88CFM @10". That's basically a stock GPz 1100 head with a little clean up or a STAGE 1 KZ Ported Head. Actual HP and Torque numbers are simulations values. As such, torque numbers tend to run on the optimistic side. In any event, the end result is still a good for trend comparison purposes. The trend for the end result shows the comparative differences in the way the power band changes, where the peak power differences occur and what happens after the Peak HP RPM is reached. Effectively, the difference between allowing the smaller engine to breathe with a good cylinderhead vs holding the larger engine back with a stock cylinderhead are very clear in terms of peak HP and RPM. The big bore 1327 with stock head, will deliver a nice increase in available power up to a point, then taper off quickly where as the smaller 1075 engine with good breathing capacity will produce more peak power and hold on longer. | | | 
| | When trying to decide on the components you want to use for a rebuild project, take some time to consider how the components interact and effectively contour the behavior of the engine. Remember the 3 ways to improve performance are: - Make it bigger
- Spin it faster
- Make it more efficient
The actual practice is to consider all 3 methods and from them determine if you will get the result you desire from just performing 1 of the 3 methods. In the case of the big block, performing method 1, yields nice gains down low and in the middle but leaves the motor starving for enough air to fill the cylinders at the upper regions of the power band. This also plays into the budget scenario. It costs far less to put together a 1075 with a good cylinderhead than it does to build a big block motor. On the other hand if you have the budget for everything, the big block can then deliver an exceptional performer all around. | Differences between KZ & J Motors from APE's Website |
There are two different KZ1000 engines. The first is the Z1 type which was built between 1976 and 1980. The second is the 1000J, or "J model" as it is called, and was built from 1981 until present ( currently only available in police motorcycles). These engines are different, but some of the parts can be interchanged, and this has caused much confusion. We hope this makes everything clearer.
The first example is simply a big bore Z1 900. This engine came with a kick starter and electric starter. The cam chain tensioner hole in the cylinder block is a rectangle. The ccs cast on the cylinder is 1015. The later "J model" has no kick starter, and the cam chain tensioner hole in the cylinder block is round. The cc's cast on the cylinder is 998. This engine also became the GPZ1100 in 1981 and '82, and virtually everything between them is the same. (The '83-'84 GPZ1100 was changed). Cylinder blocks and lower engine cases are NOT interchangeable. You can not put a J model cylinder on an older style lower end, and vise versa.
Cylinder blocks.. Not interchangeable. If you have a J model block/GPZ1100 block you must use a J model or GPZ1100 cases.
Crankshafts... Early KZ1000 used a roller type cam chain and the crank has that style center sprocket. J model used Hy-vo style chain. J model cranks can be used in early lower end if the center crank pin is changed to one with a roller chain sprocket. The J model connecting rods are approx 1.2 mm shorter than early style rods.
Cylinder head.. J model head has larger valves and ports. This head can be used on earlier style cylinder and lower end by installing APE #CCIA cam chain sprocket adapter in head . How to tell which head you have.. Early style heads have four factory drilled and tapped 6mm holes in the center to bolt in cam chain idler gear. Z1 900 heads have 6 mm exhaust studs, KZ1000 8 mm. On the J model head, the four cam plugs at the ends of the camshaft areas are bolted in, on the early style head, they just push in and the valve cover holds them in. The J model / '81-'82 GPZ1100 cylinder head has a larger combustion chamber than the early style head. When these heads are used on the early style motor, a compression ratio drop of about 2 full points can be expected.
Pistons... All pistons have 17 mm pin holes, but the J model/ '81-'82 GPZ1100 pistons have the pin hole lower in the piston to make up for the short connecting rod. All J model and early '81-'82 GPZ1100 pistons are the same ( '83-'84 GPZ has 18 mm pins ) Therefore any '81-'82 GPZ piston can be fitted to a J model engine to make a big bore engine. Pistons for the J model / '81-'82 GPZ1100 can not be used in a motor that has an early style long connecting rods unless a spacer plate is used under the cylinder block to compensate. If early style KZ pistons are used in an engine that has the short J model / '81-'82 GPZ1100 connecting rods, a special short cylinder block has to be used.
We have tried to make this as clear as possible. When ordering your parts from APE, let us know which engine you have, or if you are mixing early style and late style parts, let our tech/order department know and we will see to it that you get the correct parts combination.
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