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Z31 Camshaft Specs

Nissan VG30/33 camshaft information.


Understanding cam specs and their affects will help you select the best cam for your specific engine. The four important camshaft specs to understand are duration, centerline, separation and lift.

DURATION

Duration refers to how long a valve is opened in relation to crankshaft rotation. This open valve time period is expressed in degrees of crankshaft rotation. So, a cam specification of 220 degrees duration simply means the cam holds the valve open for 220 degrees of crankshaft rotation.

As strange as this may sounds, more duration can be helpful in high RPM engines but not low RPM engines. The extra degrees of open valve time in high RPM engines gives the air flow a little more time to get into (or out of) the cylinder in spite of the piston's stroke. However, at lower RPMs, more duration can cause less power because the valves will be open at the wrong time in relation to the piston's stroke up or down in the cylinder.

In order to measure a camshaft's duration, you must use a degree wheel in conjunction with a predetermined lift point. The most common duration references are advertised duration measured at 0.050-inch lift. While the advertised numbers are supposed to be measured at 0.020-inch lift, some cam grinders measure farther down the lobe to make their camshaft look more radical than it really is. Because of this confusion, most engine builders use the 0.050-inch duration figure,

CENTERLINE

The cam's centerline specification is used to tie the valve timing to the crankshaft's rotation. This spec is expressed as the number of degrees the crankshaft must rotate from top dead center until the cam has rotated to the peak (or centerline) of the lobe.

The centerline spec and the duration spec can be used to calculate when the valves open and close in relation to the crankshaft's rotation. When the valves open (or close) relative to the crankshaft's rotation is known as valve events or valve timing. Some cam manufacturers will provide valve event information and others only provide duration and centerline information.

Understanding the effects of valve events or valve timing is the real secret to understanding engine performance. For the engine to run at its peak performance, the valves must open and close at the correct time in relation to the piston's position and the crankshaft's speed.

FINDING INTAKE LOBE CENTER

Remove ALL lash. With your dial indicator on the retainer or follower, rotate the engine in the direction it would normally turn, and come up to .050 inches of lift. Write down that figure from the degree wheel. This is your opening figure. This is when the intake opens BEFORE Top Dead Center. Example would be 10 degrees on the degree wheel BTDC.

Now go over the top on the lobe until your indicator is .050 inches off the Base Circle. Now you should be where the intake closes AFTER Bottom Dead Center. Keep in mind to continue turning the engine in the same direction it runs and DO NOT BACK UP. Example would be 39 degrees on the degree wheel ABDC.

You can now calculate your duration. The valve opens at 10 degrees, plus it closes 39 degrees, plus 180 degrees (the distance in degrees between TDC and BDC). Your duration at .050 inches of lift would be 229 degrees.

+10° Opening Before Top Dead Center (BTDC)

+39° Closing After Bottom Dead Center (ABDC)

+180° Distance from Top Dead Center (TDC) to Bottom Dead Center (BDC)

= 229° Total duration @ .050 inches of lift


You can now calculate your lobe centerline. Divide your total duration by 2 and subtract your intake-opening figure. This would normally be the smaller number of the two figures.

229° / 2 = 114.5°

114.5° - 10° = 104.5°

104.5° would be your lobe centerline.

Please Note: If you have a low overlap cam, the intake opening may be AFTER TDC, if so, you will have to SUBTRACT that figure from the closing number and add 180. This will be the duration at .050 inches of lift.

-10° Opening After Top Dead Center (ATDC)

+39° Closing After Bottom Dead Center (ABDC)

+ 180° Distance from Top Dead Center (TDC) to Bottom Dead Center (BDC)

= 209° Total duration @ .050 inches of lift

You can now calculate your lobe centerline. Divide your total duration by 2 and add your intake opening figure. This would normally be the smaller number of the two figures.

209° / 2 = 104.5°

104.5° + 10° = 114.5°

114.5° would be your lobe centerline.

FINDING EXHAUST LOBE CENTER

Once again remove ALL lash. With your dial indicator on the retainer or follower, rotate the engine in the direction it would normally turn, and come up to .050 inches of lift. Write down that figure from the degree wheel. This is your opening figure. This is when the exhaust opens BEFORE Bottom Dead Center. Example would be 44 degrees on the degree wheel BBDC.

Now go over the top on the lobe until your indicator is .050 inches off the Base Circle. Now you should be where the exhaust closes AFTER Top Dead Center. Keep in mind to continue turning the engine in the same direction it runs and DO NOT BACK UP. Example would be 8 degrees on the degree wheel ATDC.

You can now calculate your duration. The valve opens at 44 degrees, plus it closes 8 degrees, plus 180 degrees (the distance in degrees between TDC and BDC). Your duration at .050 inches of lift would be 232 degrees.

+ 44° Opening Before Bottom Dead Center (BBDC)

+ 8° Closing After Top Dead Center (ATDC)

+ 180° Distance from Top Dead Center (TDC) to Bottom Dead Center (BDC)

= 232° Total duration @ .050 inches of lift

You can now calculate your lobe centerline. Divide your total duration by 2 and subtract your exhaust closing figure. This would normally be the smaller number of the two figures.

232° / 2 = 116°

116° - 8° = 108°

108° would be your lobe centerline.

Please Note: If you have a low overlap cam, the exhaust closing may be BEFORE TDC, if so, you will have to SUBTRACT that figure from the closing number and add 180. This will be the duration at .050 inches of lift.

+ 26° Opening Before Bottom Dead Center (BBDC)

- 10° Closing Before Bottom Dead Center (BTDC)

+ 180° Distance from Top Dead Center (TDC) to Bottom Dead Center (BDC)

= 196° Total duration @ .050 inches of lift

You can now calculate your lobe centerline. Divide your total duration by 2 and add your exhaust closing figure. This would normally be the smaller number of the two figures.

196° / 2 = 98°

98° + 10° = 108°

108° would be your lobe centerline.


SEPARATION

Separation refers to the spacing between the intake lobe and exhaust lobe on the cam shaft. This spacing (or separation) is expressed in degrees on the cam, not on the crankshaft. So, a 108 lobe separation means the intake and exhaust lobes are 108 degrees apart from each other on the cam shaft.

This spec by itself really doesn't mean anything. If you hear someone else is using a cam with 108 separation, don't think that you should use cams that only have 108 separation!

Separation, just like centerline, is another way to tie the duration to the crankshaft rotation and end up with valve events. This spec is a little more complicated though, because it is in cam shaft degrees and the crankshaft rotates two degrees for each one degree of cam rotation. Also, if the cam has been installed either advanced or retarded, the valve events will be different.

LIFT

The final cam spec to understand is lift. While duration refers to how long the valve is opened, cam lift is used to determine how wide the valve is opened.

If the valves are not opened wide enough, they will cause a restriction for the air trying to enter or exit the cylinder. However, opening the valve past a certain point will not increase the flow to (or from) the cylinder. A good way to demonstrate this is with the garden hose in your back yard. When you first start to turn the water on, the flow increases but after a turn or so, opening the valve more has no effect on how fast the water comes out of the hose.

Specs

Manufacturer, type, duration (Int/Exh), cam lift (in inches), other info.

    OE cams:

    Manufacturer Duration Intake Duration Exhaust
    Cam lift Intake Lobe Inches
    Cam lift Exhaust Lobe Inches
    Intake Centerline Exhaust Centerline
    Stock "early" US 7/83 to 7/87 Z31 252 or 193 @ 0.050 252 or 193 @ 0.050 .393" .393" 106 116
    Stock "late" US Z31 08/87+ 248 or 189 @ 0.050 248 or 192 @ 0.050 .393" .393" 114 114
    J-spec Z31 cams 252 or 193 @ 50 thousands 252or 193 @ 0.050 .393" .393"
    European Z31 Cams 264 262 .393" .393"
    NISMO Z31 Cams 264 262 .393" .393"
    USDM VG30 "Truck" cams (D21, WD21 and J30) 248 or 189 @ 0.050 248 or 192 @ 0.050 .393" .393"
    USDM VG33 Cams (all) 240 244 .366" .366"

    Colt Cams:

    Manufacturer Duration Intake Duration Exhaust
    Cam lift Intake Lobe Inches
    Cam lift Exhaust Lobe Inches
    Colt Cam Na/turbo Grind (Stage 1) 256 or 202 @ 0.050 256 or 202 @ 0.050 .420" .420"
    Colt Cam Na (Stage 2) 262 or 210 @ 0.050 262 or 210 @ 0.050 .428" .428"
    Colt Cam Turbo (Stage 2) 262 or 210 @ 0.050 256 or 202 @ 0.050 .428" .420"

      Schneider Racing Cams:


      Inknown Number @ 0.050 Advertised @ 0.006
    • Non-turbo grind 256/256 .420"/.420" CLSA 110
    • Non-turbo grind 262/262 .420"/.420" CLSA 110
    • Non-turbo grind 270/270 .440"/.440" CLSA 110
    • Non-turbo grind 280/280 .450"/.450" CLSA 110
    • Turbo grind 262/256 .420"/.420" CLSA 114
    • Turbo grind 270/262 .440"/.420" CLSA 114
    • Turbo grind 280/270 .450"/.440" CLSA 114
    • Turbo "race only" grind 284/274 .450"/.440" CLSA 114


      Motorsport Auto:


      Inknown Number @ 0.050 Advertised @ 0.006
    • Stage 1 Turbo 262/256 .420"/.420" $169.95 Exchange only
    • Stage 2 Turbo 270/262 .420"/.420" $169.95 Exchange only
    • Stage 1 Non-Turbo 260/260 .420"/.420" $169.95 Exchange only
    • Stage 2 Non-Turbo 270/270 .427"/.427" $169.95 Exchange only
    • Stage 3 Non-Turbo 280/280 .435"/.435" $169.95 Exchange only


      Iskendarian Cams:


      Inknown Number @ 0.050
    • Turbo and non 262/258 .450"/.450" About $200 Exchange only


      PAECO:


      Inknown Number @ 0.050
    • DSV-5800 Street 280/280 Turbo .328"/.328" $230 Each - $250/Core
    • DSV-6200 Strt/Strp 288/288 Turbo and non .360"/.360" $230 Each - $250/Core
    • DSV-6800 RACE 302/302 Turbo and non .373"/.373" $230 Each - $250/Core


      Jim Wolf Technology:


      Inknown Number @ 0.050
    • Stage 1 Turbo (S1) 260/260 .440" About $450
    • Stage 2 Turbo (S2) 266/266 .473" About $450


      Other Custom grinds used by Z31 owners:


      Inknown Number @ 0.050
      Tempestas custom turbo grind 270/270 .480"/.480"

    Valve Springs

    Valve springs are one of the most critical and most overlooked components in your engine. Proper selection of the valve spring begins with identifying the application and selecting all of the valve train components to achieve the engine builders’ goals.

    The spring is selected to complement the system and must be matched with the entire valve train in order for the engine to reach its full potential. It does absolutely no good to install a cam that will rpm to 8000 if you do not have the correct springs. Improper selection of the wrong valve spring is one of the most common causes of engine failure. Other common causes are the incorrect installation and improper handling of the valve springs.

    Selecting a Spring

    1. Use only the valve springs that will give the correct spring pressure with the valve both on the seat and at maximum lift.
    2. The outside diameter of the recommended valve spring may require that the spring pocket of the head be machined to a bigger size.
    3. One of the easiest and sometimes most costly mistakes made in racing engines is not positively locating the spring. A valve spring that “dances” around on the cylinder head or retainer causes harmful harmonics and excessive wear. A spring that is forced onto a retainer is likely to fail at that coil. A spring that is contained properly at the retainer and the cylinder head will offer the longest possible service life.

    Proper Spring Handling

    • Handle springs with care. Never place in a vise, grab with pliers or hit them with a hammer. This will damage the surface of the spring, which will cause a spring to fail.
    • When separating double or triple springs, use only a durable plastic object that cannot harm the shot-peened surface of the spring. Never use a tool or hard metal object like a screwdriver.
    • Valve springs are shipped with a rust preventative coating that should remain on the spring throughout engine assembly. Do not clean springs with acidic or evaporative cleaners. This causes rapid drying and promotes the formation of rust on the surface, which can cause catastrophic failures. Even a slight amount of corrosion can grow to be a problem.
    • When installing springs, use Assembly lube to ease assembly and improve the life of the spring.

    Part Numbers

    Nissan
    1983-1985 Outter spring
    Nissan # 13203-V5000
    1985-1989 Outter spring
    Nissan # 13203-42L03
    1983-1985 Inner spring
    Nissan # 13204-W7000
    1985-1989 Inner spring
    Nissan # 13204-42L00
    Schneider
     
    Outside Diameter
    Inside Diameter
    Installed Height
    Seat Pressure
    Pressure @ .60
    Coil Bind
    Part Number
    Spring Set (includes 12 inner and outter Springs)
    1.380"
    0.810"
    1.600"
    110 lbs
    240 lbs
    0.910
    68022


    Sources used on this page: