here is some more informative cam references
A. Beginner's Understanding of Basic Camshaft Terms:
1. Before We Start - 2 Goals You Must Know: 1. What is the PEAK WHP you are trying to achieve? AND 2. Where Do You Want The Power Gain To Be Along the RPMs (POWERBAND LOCATION) ?
HOW DO THE CAM'S SPECS (LIFT, DURATION, OVERLAP or LOBE SEPARATION ANGLE, FLANK STEEPNESS) CHANGE THE POWERBAND OR TORQUE CURVE?
Before you start selecting cams, you may want to first decide where you want your powerband to be. Do you want to gain power in the upper rpm range ( ie. from 5500 to 7200 rpm in a B18A/B and from 6000-8100 rpm in a B18C) or do you want the gain to be more in the midrange from 3500-6000 rpm? Remember that low rod ratio engines, like in our stock Integras, already make more power in the low to mid rpms compared to the higher rpms simply determined by the engine's piston geometry.
This section is based on some lectures from Crane Cams and can help clear up some ideas about selecting cam specs for your engine package. Do you want more duration? Do you want more lift? Do you want a smaller LSA (more
overlap)? How much of each? and Why?
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Legend for Figures Below: The red lines are comparing hp vs rpm. The green
lines are comparing torque vs rpm.
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2. Increase Cam Duration (i.e. How Long the Valve is Open):
Moves or shifts the peak torque and peak hp location to a higher rpm. The absolute peak torque and peak hp number also increases.
Cam duration comparison: the aftermarket cam with 20 degrees more duration has lines with no dots. Lift and LSA are identical. Twenty degrees more duration moves the torque peak up in the rpm range by 1000 rpm (i.e. peak torque occurs later) . With 20 degrees less duration, both peak horsepower and peak torque drop.
3. Increase Cam Lift (i.e. How Much the Valve Lifts Off or Opens From Its Seat):
Higher lift gives a higher absolute peak torque and peak hp number.
Cam lift comparison: the cam with 0.200" (5 mm) more lift has lines with no dots. The duration and LSA are identical. Notice how the torque starts out equal at lower rpm, but the overall torque and horsepower are hurt by less lift, a sure sign of an engine that isn't getting enough mixture at higher rpm.
The ideal amount of lift for the desired powerband location is also affected by the size of the intake/IM runner, size and number of the intake valves, and the amount the intake valves are "deshrouded" from the combustion chamber's wall. Lift can be further increased proportionally by changing the rocker arm ratio without having to change the cam's lift spec.
4. Tighten Lobe Separation Angle (Increase Cam Overlap):
Gives more peak hp but less low end torque.
4 a) Lobe Separation Angle (LSA) Definition:
This is the angle between the intake and exhaust camshaft lobe peaks described in camshaft degrees. This angle dictates two important events: the valve overlap around TDC and how much intake or exhaust valve closure delay there is (see Engine Package I Article for more details on LSA).
Tightening the lobe separation angle (making the LSA value smaller)produces more overlap around TDC. Widening the lobe separation angle (making the LSA value bigger) results in less overlap.
4 b) Overlap Definition:
The amount of time, expressed in crankshaft degrees, that describes the window of time between the the Intake Cam's opening point BTDC and the Exhaust Cam's closing point ATDC (i.e. the brief time when both intake & exhaust valves are partially open simultaneously).
Increasing the degrees of overlap tends to move the powerband up the RPM range. Increasing the overlap can increase peak power, but only if the exhaust system is properly designed and sized to scavenge the cylinder. Decreasing the overlap tends to improve lower rpm range performance.
Overlap can be increased in 2 ways independently:
- Increasing the Duration of the Cam (without changing the LSA)
- Reducing or Tightening the LSA (without changing the Duration)
Affects of Changing LSA: Compare the cam with a bigger 116 degrees lobe separation (lines with no dots) with one having a 106-degree separation (with dots). The smaller LSA cam produces more peak horsepower but with a loss of low-end torque. Smaller or tighter LSA is better for a drag engine than a street machine, due to an increase in valve overlap. LSA can also be slightly increased or decreased by changing the aftermarket adjustable cam gears settings, when you dyno tune.
5. Tailoring the Cam Specs for the Powerband Location You Want: Changing the Duration Spec and LSA's :
(from
http://www.newcovenant.com/speedcraf...camshaft/3.htm )
- Short duration with a wide lobe separation angle might be best for towing, producing a strong, smooth low-end torque curve.
- Long duration with a short separation angle might be suited for high-rpm drag racing, with a high-end, sharp torque peak.
- Moderate duration with wide separation angle might be best suited for an all-around street performance engine, producing a longer, smoother torque band that can still breathe well at higher RPM.
Remember, there's always a compromise made when you select your cam specs in N/A engines. You gain hp/torque at one end of the rpms but lose it at the oppsite end.
6. Why Duration and Lift Doesn't Tell Everything About the Cam's Performance Potential ?
Lift & duration don't tell the whole picture. Here's 2 cams (red line and dotted line) with the exact same lift & duration. This is the effect of cam ramp angle that can be measured with a cam doctor (blue shaded in area):
it's the area under the valve lift curve (AUC) that's the major factor overall. AUC combines the effects of lift, duration, and ramp. This what makes some cams with lower specs perform better. The intake valve slams open faster to give a better AUC than a longer duration/lift cam and doesn't sacrifice ABDC and the need for static CR changes to compensate for the reversion loss.
7. When Do I Want To Switch To Roller Cams With Roller Rockers Instead of Standard Honda Cams and Rockers?:
Consider using a Roller Cam and Roller Rockers.....
- when engine stress levels are high.
- when competition requires valve opening and closing velocities faster than a standard rocker can provide, especially with higher
redlines > 9,500 rpms.
- when you simply must have that extra level of performance, but can't sacrifice emissions or low-end drivability.
The N/A Integras like high lift, long duration, big overlap (tight LSA) cams. The forced-induced Integras like high lift, short duration, short overlap (wide LSA) cams. In contrast, the B16A VTEC Civics like high lift, short duration, short overlap cams, due to the B16A's differences in cylinder filling characteristics compared to the Integras which is associated with the B16A's higher rod ratio.
B. Anytime you upgrade cams you should do 4 things:
1. change to the valvesprings that were proven not to coil bind at the cam's max. lift on a Spintron test but not go overly stiff to create excessively high valve seat pressures (stock 40 lb., Toda valvesprings 50 lb., max. acceptable range is 70-90 lb. at 33.66 mm installed valvespring height) causing wear.
if you don't upgrade the valvesprings, even though the company says it's ok to use the stock ones, you still will see mild valve float. Mild valve float is not catastrophic compared to severe valve float or coil binding. But you know what valve float is right? The spring has fatigued at high rpm and loses it's ability to control the rate at which the valve closes against the seat. The valveface slams shut against the seat and transfers this shock or load up the valve stem to the rocker arm and then to the camshaft lobe-rocker arm interface. You get extra wear-related damage and possibly structural fatigue at the valve seat, valveface, rocker arm lobe, valvespring retainer, and cam lobe. Valve float can be identified on a chassis dynosheet as a sudden very sharp or steep drop in hp (in the order of 5% [7-10 whp] or more) at the last 500-600 rpm before the redline.
2. ensure that valvespring installed height is stock (1.320-1.325 in. or 33.53-33.66 mm) and check that the lost motion devices (for VTEC cams) are all present.
3. use assembly lube on the cams during install and do the proper oil change maintenance schedule.
4. Ensure the install is at TDC throughout including the timing belt install. Use a new timing belt or a stronger aftermarket belt, if the mileage (every 40-60,000 miles) or camshaft/application (Toda Spec B,C,D, Killer, or Jun Type 3, or race engine) warrants it. If you can, have the cams degreed. Ensure that the valve lash was set to the camshaft manufacturer's specs, the cam gears & cam journals were oriented and torqued down correctly using Honda's or the manufacturer's specs, and the timing belt is tensioned correctly (no flapping).
C. What's with the different Duration Specs?:
1. "Advertised duration" is the duration @ 0.015 in., 0.020 in., or 0.030 in. valve lift (i.e. whatever the cam manufacturer wants to quote for duration at the lowest readable valve lift on the camshaft degree wheel when they degree the cams on install).
The Society of Automotive Engineers (SAE) chose this as their standard reference for when to measure duration . It is easier to read the dial indicator and cam degree wheel (when you degree your cams) at 0.015-0.030 in. than at the very start of when the valve starts to lift. So the engineers chose the lowest valve lift point to take a cam reading that was also the easiest to read.
Other Standardized Valve Lift Points to Read Duration Spec from:
2. Domestic V8 cam manufacturers reported their cam duration @ 0.050 in. valve lift. This has been their standard.
3. Japanese cam manufacturers report their cam duration @ 0.04 in. (or @1mm).
The lower the lift from which the duration is taken, the bigger the number for duration.
