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Big Bore Information
Most modern sportbikes have closely spaced bore centers, this is necessary for a compact engine design but limits the amount of material surrounding each piston. The bore center number minus the bore diameter determines the amount of material between each piston. The amount of material between each piston determines more than anything else how large a bore of any engine design will tolerate. Factors involving cylinder design such as a wet sleeve, heat shrink sleeve, or nikasil type coated cylinders must be taken into consideration.

Zlock Racing uses sleeves of our own material and design in all our big bore conversions. Coated aluminum bores in factory stock condition give excellent service. When used in a big bore application we have seen problems with ring wear, compression loss and smoking. The use of sleeves also allows us to use an exclusive gasket retention system reducing the chance of a head gasket leak. All Zlock Racing cylinders are precision bored and three stepped honed to ensure rapid break-in and excellent ring seal.
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Compression Ratios and Cooling
All things being equal more compression will bring more torque and ultimately more horsepower. The limiting factors on large bore motors are usually detonation and cooling capability. On smaller bore engines 750cc and less the short stroke length and large valve area usually prevents you from getting as much compression as you would like.

Most OEM Japanese cooling systems will handle our big bores with up to 13.1-1 cr. under all but the most severe conditions. Special considerations may have to be made for racing applications. We would be happy to advise on your particular project.
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All About Cams
Horsepower gain from cam replacement is definitely possible but less than you might expect. Typical gains will be toward the top of the rev range often above the stock rev limit. An exception: When a big bore is installed the engine will make more power but at a lower rpm, the addition of a performance intake cam will bring the power peak back up and increase total power output. Japanese sportbike engines are usually over exhausted negating any power increase replacing the exhaust valves.

Adding lift to an intake cam is generally the most reliable method of gaining horsepower through cam modification. Casting new cam blanks and grinding to a higher lift is probably the ideal solution but not cost effective for small numbers of cams. The more usual solution is the hard weld regrind technique where material is welded to the nose of the cam and the profile reground. The advantage is cams can be modified one at a time and all stock valve train components will fit. The disadvantage is the hardwood can be subject to separation, inclusions and pitting, many times causing damage to the cam follower. The cam can also warp from the heat of welding causing excessive journal wear. The newer hollow cams seem more susceptible to warping. Another method is to simply regrind the existing cam to a higher lift. The advantage is no welding complications. The disadvantage is limited lift increase and possible exceeding valve clearance adjustments.

Zlock Racing cams are built by regrinding a stock cam to a different lift and profile. The lift and profile is engineered for Zlock Racing and a new master created for the regrinding process. This process removes material from the base of the cam lobe and may move the valve clearance out of adjustment range. To compensate for this the cam may be provided as part of a cam, valve and valve spring set. Normally a racing cam will require the use of different valve springs and stronger valves anyway so the cost remains much the same.
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Cylinder Heads
Cylinder head designs vary widely and the modifications are endless, so to limit the scope of information I will comment only on the most common type of head we see, the modern multi-valve motorcycle head.

Questions usually center around three basic issues, porting, valve jobs and larger valves. Porting has always been seen as a mysterious business tied in some way to horsepower gain. Most people have the idea that more flow is always better and big cfm (cubic feet per minute) numbers on the flow bench will equal more power at the rear wheel. This is rarely true. Current thinking shows that more attention to velocity and direction of flow will yield better results. Current heads generally have excellent design so major work is unnecessary. A small amount of work in the area from the e valve seat to the guide gives good results and is cost effective.

A good valve job is essential to a performance engine. Any engine with more than a season of racing or 5000 street miles will show some power loss due to valve and seat degradation and carbon buildup. In a factory valve job the seat is cut by machine to a specific size with two or three angles. The valves are installed as is and are allowed to seat by running. This method is cost effective but results can range from poor to excellent. Race valve jobs vary according to the rules. Most production rules allow a maximum of three angles and no blending. The five angle job was a method used to avoid the rules and has been largely outlawed. Fully blended seats are best where no rules apply.

Highly modified engines can sometimes benefit from larger intake valves. An assessment must be made of valve seat thickness, cylinder head support and anticipated results based on engine capabilities and head design.

While Zlock Racing can provide almost any cylinder head modification our most popular and cost effective is our street and competition valve job. This involves decarbonizing the head by walnut shell blasting, fully blending the valve seat to the port, and cutting and lapping valves and seats as necessary.
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Transmissions: For street use most transmissions give good service without modification. They vary in design but most have five or six speeds and operate by rotating a shift drum with cam slots that move shift forks which in turn slide the gears back and forth on the shafts engaging and disengaging the gears. The gears are mounted alternately on the shaft in either a splined or freely rotating condition. Adjacent gears have engaging dogs or slots that lock together when moved into contact with each other. When locked together a pair of gears is then able to transmit power from one shaft to the other at a particular ratio.

A common failure mode for this type of transmission is when the locking dogs fail to stay engaged. Symptoms usually involve jumping out of gear or chattering when power is applied. This will typically occur in only one or two gears initially. If left uncorrected the gears, shift forks, and shift drum may be damaged. A good transmission will have all the engaging dogs undercut on both the upshift and downshift sides and the gears shimmed to avoid thrust loading the shift forks. These modifications provide for positive gear engagement and minimal power loss through the transmission. Many stock transmissions have no undercutting or shimming, some have one or more gears done, almost none have all gears modified.

Zlock Racing has transmission modification services available for selected models. The 98-99 ZX9R is a common example as it had a nasty habit of jumping out of gear. Your particular needs are best addressed as an individual case based on model, performance, intended use, and cost. If you think transmission work is needed we would be happy to discuss the specifics of your engine.
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Clutches: Kawasaki clutches are very strong as are most Japanese sportbikes. Except for the most extreme conditions the only modifications needed are stiffer springs and sometimes aftermarket plates. Most of the time the stock clutch is up to the task even in a modified engine. If clutch slippage becomes a problem most of the time it is because the plates and/or springs have become worn and need replacement. Remember, plates and springs are normal wear items.
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Crankshaft and Rods
Crankshaft and rods: Stock components will usually handle performance gains of 10 to 15 percent with acceptable reliability, provided stock rev limits are maintained. If larger gains are anticipated or more RPM is desired then rod replacement should be considered. Another cost effective and worthwhile modification is to lighten and balance the crankshaft, the engine will accelerate faster and run smoother. Highly modified engines may run billet crankshafts and/or long rods. Hard-weld type long stroke crankshafts are sometimes used to increase displacement.
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Ignition Systems
Coming Soon
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Carburation and Airboxes
Coming Soon
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