Extended Swingarm Chain Guide

Schnitz Racing Dry Nitrous Jetting and Recommendation Chart

*For Fuel Injected 4 Cylinder Motorcycles (one injector per cylinder) with Single Nitrous Jet.

Cam Lobe Centers Explained

      One of the least understood topics and regarding engine tuning and building continues to be the concept of cam timing and “lobe centers”. The opening and closing process of an inlet or exhaust valve as controlled by a cam lobe constitutes a complete “event” in the cycle of the engine. Like any event, it has a beginning and an end. Naturally, then it also has a middle or center. The location of this center in relation to the rotational position of the crankshaft is known as the lobe center.

The process of “degreeing” cams allows the engine builder to place the lobe center of a cam in the correct orientation with reference to the crankshaft. The opening and closing points and resultant figures of the cam, although important, are very difficult to reference to set cam timing and are, after all, the result of where the lobe center is placed. Therefore the lobe center is used to reference cam timing. The difficulty in measuring the opening and closing points is the result of the very shallow and gradual starting and stopping of the valve motion. How do you tell just when the valve motion starts and stops? If you pick a specific amount of lift at some height beyond the initial gradual motion and always use that amount as a marker for the beginning and end of the motion, the center will always be halfway between these points. Therefore, the lobe center is computed from a timing number derived at a specific valve lift. Any lift could be used to compute this, but in the Japanese motorcycle industry 1mm or .040” is traditional. U.S. (automotive) cam grinders have used .050”. This “checking height” must be used to minimize the effect of the shallow opening and closing ramps on the cam lobe. Without this, each builder’s subjective notion of when movement starts would be the defining factor of timing. One picture is worth a few thousand of my words so now refer to my crudely drawn diagram for clarification.  
      The diagram graphically shows how these points lie in relation to the degrees of crankshaft rotation. The usable range of lobe center values for just about all commonly used engines is only about 15 degrees wide from about 98 to 112 degrees and for the engines we use, the right spread is even smaller than that. Small changes of one degree can have considerable effect on the power delivery characteristics of an engine.

Very generally speaking, the effect of moving lobe centers is as follows:
Advancing the intake and retarding the exhaust (“closing up the centers”) increases overlap and should move the power up in the RPM range, usually at the sacrifice of bottom end power. The result would be lower numerical values on both intake and exhaust lobe centers.
Retarding the intake and advancing the exhaust (“spreading the centers”) decreases overlap and should result in a wider power band at the sacrifice of some top end power. This condition would be indicated by higher numerical values on both intake and exhaust lobe centers. By moving only one cam the results are less predictable, but usually it is the intake that is moved to change power characteristics since small changes here seem to have a greater effect. With twin cam engines we have the luxury of moving the cams independently.

With a single cam engines you must advance or retard the intake and exhaust together, usually using the intake lobe center as the reference and only the cam grinder can spread or close up the centers when the cam is ground.
Basically, here’s how it’s done in the real world. I’m not going to tell you what lobe centers to use, as this varies from engine to engine, just how to determine them.
Many engine builders take lobe center measurements with zero valve lash (clearance) so that all movement can be detected. In fact, the valve lash can actually be slightly negative, that is the valve can be held slightly open by the cam with the valve in the closed position. You may also do the calculation with the running clearance at the valve. The amount of pre-load or clearance on the valve has no effect on the lobe center number but will effect the opening and closing numbers. What IS important is that, for future comparison purposes, you always do it the same way with the same lash value. It is also very important that an accurate top dead center “TDC” reference be used when degreeing cams.
Therefore, this should be checked carefully and the degree wheel and pointer set accordingly. Take a great deal of care when setting up your degree wheel, pointer, method of turning the engine, and dial indicator. A change of one degree can be significant, so accuracy is very important. A dial indicator is used to measure the valve motion in hundredths of a millimeter or thousandths of an inch. Set your dial indicator so that the plunger pushes on the retainer or tappet and moves as nearly parallel to the valve travel as possible. It is not necessary to use any particular valve, use one that allows the easiest indicator set-up and that you can easily see from the same side as the degree wheel.
I recommend that you begin with the intake cam, since the intake is the most likely to be damaged by an insufficient amount of valve to piston clearance or incorrect timing. Always start with the cam sprockets closest to the stock position.  Begin with the valve fully closed and with the dial indicator zeroed.  Double check the plunger movement to see that it moves freely, does not interfere with the cam lobe, rocker, or any other moving parts, and returns to zero when moved and released.  Rotate the engine in the correct direction while watching the dial indicator. Stop when the pointer shows 1mm of movement. Note this number.  On an intake cam, this will be a value before top dead center (BTDC). Continue rotating the engine, watching the dial indicator as the valve opens, then begins closing again. By counting the revolutions of the pointer and watching it return towards zero, you can stop when the valve lift is still 1mm before fully seated, noting the degree wheel value at this point. On the intake cam this will be a value after bottom dead center (ABDC). It is important to stop at the correct point because you should avoid turning the engine backwards as this unloads the cam chain and can result in an erroneous reading.

To compute the lobe center, you:
	A. Add the two opening and closing numbers noted
	B. Add 180 to this sum
	C. Divide this sum by 2
	D. Subtract the smaller number of the two opening and closing numbers from this quotient.

The result is the lobe center. For Example:
Intake opens (at 1mm lift) 38 BTDC
Intake closes (at 1mm lift) 68 ABDC

38+68+180=286, divide by 2 =143, subtract 38 from 143 = 105
The lobe center on this cam is 105 degrees.

The method is the same on the exhaust except the opening number will be a value before bottom dead center (BBDC), the closing value will be after top dead center (ATDC) and again, subtract the smaller number.
For Example:
Exhaust opens (at 1mm lift) 60 BBDC
Exhaust closes (at 1mm lift) 40 ATDC

60+40+180=280, divide by 2=140, subtract 40 from 140 =100
The lobe center on this cam is 100 degrees.

Note that in both cases, it is the smaller of the two numbers that is subtracted.
Also note that the 286 and 280 degree values are similar to what may be the advertised duration of the cam. This number is called the “checking duration” as it is dependent upon the checking height used (in this case 1mm).

Remember, the opening and closing values (and duration) are dependent on the checking clearance and will vary based on this amount. The lobe center number will not. This is why published numbers are not a good way to compare cams. You must always know the checking height that was used to derive those numbers.

To change the lobe center, loosen the sprocket attach bolts and move the crankshaft slightly to alter it’s relationship to the cam. Retighten the bolts and re-check. When the selected value is finally reached, tighten and loctite the bolts, then re-check one more time. With a little experience you will know which way to go to advance or retard a cam to achieve the desired lobe center.

Caution:
Moving lobe centers can drastically alter valve to piston clearance. And remember, the closest point is rarely at TDC. The most critical is the intake and usually occurs somewhere after TDC. Make all adjustments in small increments and NEVER force the engine past any resistance until you know the cause.
Changes to the power output are can be subtle, hard to predict, and frankly, most of this has been explored to death so it’s unlikely you will find some “new power”. But each engine is different and cam timing must be part of any fully prepared engine. Be careful with following “we always did it that way” thinking.
The advent of electronic fuel injection and four valve heads has changed the cam requirements of engines. Increased valve area means less “cam” gives you more flow. On an injected engine you no longer need to create a strong vacuum signal through a carburetor throat for good fuel atomization. The injector is going to get the fuel in there instead of flow across a jet. The only way to optimize cam lobe centers is through extensive and careful dyno or performance testing.

Article originally published in City Bike, a fine San Francisco publication.

Related Products
Cam Degreeing DVD
Cam Degreeing Kit

*Stock spring "ok" if shimmed, GSXR750 springs are better

*GSXR750 Spring "ok" PM Spring/Retainer Kit is better

*PM Spring Kit Required

*Must use PM Spring/Retainer Kit
**Must check valve to piston carefully fly cutting of stock pistons likely or use piston kit.

Nitrous

Jet:

FUEL JET

NOS Pump:

FUEL JET

Hi-output Pump:

HP Gain/

Per cyl.:

HP Gain/

2 cyl.:

HP Gain/

4 cyl.:

14

16

14

6hp

12hp

24hp

16

18

16

9hp

18hp

36hp

18

22

18

12hp

24hp

48hp

20

24

20

15hp

30hp

60hp

22

26

22

17hp

34hp

68hp

24

28

24

20hp

40hp

80hp

26

30

26

25hp

50hp

100hp

28

32

28

30hp

60hp

120hp

30

34

30

34hp

68hp

136hp

32

36

32

38hp

76hp

152hp

34

38

34

40hp

80hp

160hp

36

40

36

45hp

90hp

180hp

40

44

40

50hp

100hp

200hp

42

46

42

60hp

120hp

240hp

This is just a guideline, there are many variables such as – nozzle type and distribution block type

– that will change your particular set-up.  Consult your engine builder for fine-tuning tips.

40

18

HP

N2O

Fuel

15

18

16

25

26

22

35

31

26

50

35

31

75

41

35

HP

N2O Jet

Fuel Jet

60

18

100

26

22

150

31

26

180

33

28

200

35

31

250

41

35

300*

46

46

400*

52

57

Pumps - How they Really Work!!
by Doug Meyer

..First a little about pumps. A pump moves a fluid. It creates a flow with pressure. You can have a lot of flow at a low pressure or a little flow at a high pressure or high flow at a high pressure or low flow at low pressure. Different types of pump designs are best for each of these requirements. Examples- a centrifugal pump like the water pump on your bike creates a lot of flow at a low pressure. A gear pump like the oil pump can create a generous flow at a high pressure. Flow and pressure are generally related in that if you retard the flow, the pressure builds. Allow the flow to increase and the pressure falls. Pumps are spec’ed with a certain flow at a certain pressure. An easy example would be a bucket and a hose. Household water pressure is about 35 psi. Run a hose onto a bucket and you get a fair amount of water in there pretty quickly. Put your thumb over the end and the pressure goes up dramatically, and the flow (amount of water getting into the bucket over a given time) goes down. The “spray” is better, though (remember that). Each type of pump has it’s limitations. Pinch off the flow in a centrifugal pump and it just spins freely with no problem (and no pressure). Restrict the flow in a good gear pump and the non compressibility of the fluid can build pressure until something breaks or blows up. That’s why there are pressure relief valves in oil systems. Pumps have a flow vs. pressure efficiency curve. Turn a pump too slow and flow is very small or zero, ask it to flow too much and pressure begins to drop- it can’t “keep up”, it cavitates or can’t move the fluid fast enough to satisfy the requirement and the pressure drops.

The fuel pump in a ZX-12 is a kind of hybrid between a centrifugal vane pump and gear pump, called a friction pump. The electric motor (which is cooled by and submerged in the fuel) spins a thin plastic disc rimmed with small “teeth” like a very fine gear. This disc spins in a small plastic housing. The fuel goes to the periphery of the spinning wheel, is “grabbed” by the small teeth, spun around and forced out of the housing. It’s not exactly a positive displacement pump like a gear pump, but it’s not exactly a centrifugal pump either. It’s a little of both. Problem is, it has a pretty small sweet spot of good flow and pressure. But, that shouldn’t be a problem because a stock ZX-12 has a very predicable fuel requirement, and as you point out, the pump always spins the same speed. The pump NEEDS only to provide enough fuel to create no more than about 180 hp at no less than 47 psi. The pump does that just fine, but it does that at the very high end of it’s efficiency curve. Ask it to provide enough fuel to create 200 hp and it can barely keep up. It can do it, but let it get worn or let the fuel get hot lowering the vapor pressure, or let the injectors get “sloppy” or let any number of other factors degrade it’s performance and the flow (and pressure) drops. Less fuel means a leaner mix and soon, detonation and broken parts. How much fuel are we talking about here? The answer lies in something called Brake Specific Fuel Consumption (BSFC), which is expressed in pounds of fuel burned per horsepower per hour. Gasoline contains a pretty much fixed amount of heat energy that when “liberated” through burning is mechanically converted to horsepower. In a modern four stroke that amount is fairly constant at between .42 and .5 pounds of fuel per horsepower per hour. As an example let’s pick .5 ‘cause the math is easy. 180 hp would require .5 pounds of gas for each of 180 the hp or 90 pounds per hour (PPH). A gallon of gas weighs about 6.2 pounds so that’s 14.5 gal per hour or .24 gal. per minute at wide open. I’m told by Kawasaki engineers that the stock ZX-12 pump is a .65 liter per minute pump at 45 psi continuous. That converts to .21 gal per minute, 12.7 gallons per hour or 79 PPH. Ask it for more and you might not get it. Interestingly enough, that fuel delivery is enough for about 160 hp at .5 or at a more realistic .47, 164 hp. Guess what the average stock ZX-12 (2000/01) makes for HP? So, why not put in a different pump, one that is sized to deliver much more fuel at 50 psi. That way you are unlikely to be able to approach the point where it can’t “keep up”, where the pressure might drop a bit. The Muzzy pump flows over 350 PPH at 50 psi., enough for 700 hp. More than you need? Sure. But on a modified ZX-12 the stocker may very well be less than you need. There really isn’t anything in between that fits the physical mounting requirements.

A few words about injectors and pressure may be in order here. An electronic fuel injector is a nothing more than an electromagnetically operated solenoid valve. There are two basic varieties, “high impedance” and “low impedance”. In a high impedance injector, a current is sent to the magnetic coil in the injector which lifts a plunger and holds it open for a set period of time (in thousandths of a second or milliseconds) then cuts off and lets it close. Low impedance injectors are a little more sophisticated. They use a high current to quickly open the injector then a lower current to hold it there until closing. Better, but the “driver” circuitry and injectors are more expensive. The “open time” is expressed as a percentage of 100% (always open) and is called the duty cycle. A duty cycle of about 80% is preferred. Most OEM systems (including the 12) use the low impedance injector design. When you more flow from the pump, the only way to increase the fuel to the engine is to lengthen the injector duty cycle. A drawback to this is that the longer you hold a low impedance injector open, the longer the (high opening) current is flowing through the coils in the injector, creating electrical resistance and heat. This is a bad thing for the injector’s health. Also, the longer you have the injector open the more you put the pump into the high flow, high pressure corner of the pump’s output curve. What might help this? How about more fuel pressure? That would flow more fuel through the injector in a shorter time. That additional pressure will also make a better “spray” (see bucket example above). The pressure flow relationship is not linear. It takes four times the pressure to get two times the flow through a constant orifice. Remember, flow through an orifice is volume over time and the duty cycle controls the time. To increase the fuel flow needed on the ZX-12 when raising the power from 165 to 200, would require an 8% increase in flow through the nozzles. If it were to be done with pressure alone, without changing the duty cycle, that would take an increase in pressure of 36%. On a stock system that would necessitate an increase of fuel pressure up to 61 psi., something the stock pump is clearly not up to. Again, the “bigger” pump will allow for more fuel to be pumped at a given pressure. Increase the duty cycle (orifice size) and the pump can “keep up”.

All this talk about fuel flow and quantities makes me think about how easy it is to determine these numbers now that we have electronic fuel injection. Back in the day, to measure fuel flow mechanically we used “turbine” flow meters that put a signal to a digital indicator. WAY back in the day we actually ran a