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Millionth Cam Question 

 

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 Post subject: Millionth Cam Question
Posted: Sun Apr 04, 2010 11:50 am 
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I often see cam specs listed, but I don't understand how to translate that info. I just want to have a better understanding of what the terminology refers to and how that affects the performance of the car. Does anyone know of a good reference guide or something that puts it in simple terms?

 

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 Post subject: Re: Millionth Cam Question
Posted: Sun Apr 04, 2010 1:12 pm 
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Quote:
ok then. so how about we start with lift.

Lobe lift- is the difference in height between the radius of the base circle and the height of the eccentric (the height of the bumpy bit if you will)

valve lift is is the distance the valve is lifted from its seat. almost all quoted valve lift numbers are as measured with ZERO lash. (valve clearence set to ZERO)
valve lift is the product of lobe lift and the rocker ratio. in the case of the I6ohc engine it will be lobe lift by 2 for pre EL hybrid and by 1.8 for hybrid and AU spec engines.

Duration- is the time IN DEGREES OF CRANKSHAFT ROTATION that the valve is lifted off its seat. crow cams 2222546 has a duration of 290deg on both the intake and exhaust lobes.


Timing- expressed as in35/75 ex75/35 (crow cams 2222546) is the point in crankshaft rotation that the valve is unseated and seated (for lack of a better term) by the cam shaft. in this case the intake valve is unseated 35 BTDC and is seated again at 75 ABDC
and the exhaust valve is unseated at 75 BBDC and seated at 35 ATDC


Found: ford-4l-and-6-cylinder-f1/6cyl-cams-spec-list-t57092.html

Seconds to Find Information: 3

Current Hang Over level: 10/10.

I'm sure it couldn't be that hard to find that info on here?

(I'm in a grumpy mood, just woke up :evil: )

Also quick 4 second google search found:

http://www.hotrod.com/techarticles/113_ ... index.html

Plenty of Info to keep you reading.
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 Post subject: Re: Millionth Cam Question
Posted: Sun Apr 04, 2010 6:50 pm 
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mabye im wrong but he could have been asking what all those things do to performance and so on, like what does lifting the lobe do rather than the lift of the lobe is the bumpy bit

 

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 Post subject: Re: Millionth Cam Question
Posted: Sun Apr 04, 2010 7:53 pm 
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What is meant by Basic RPM?

The camshaft's basic RPM is the RPM range within which the engine will produce its best power. The width of this power band is approximately 3000 to 3500 RPM with standard lifter cams, and 3500 to 4000 RPM with roller lifter cams. It is important that you select the camshaft with the "Basic RPM Range" best suited to your application, vehicle gearing and tire diameter. Why is Cruise RPM at 60 MPH important?

When selecting a new camshaft, you can raise or lower the engine's basic RPM range. It is important to be sure the vehicle's drive train is capable of matching your selection. The cruise RPM at 60 MPH is a way of rating your rear end gearing and tire diameter to determine if these components match the RPM potential you are desiring.

What is Camshaft Duration and why is it important?

Duration is the period of time, measured in degrees of crankshaft rotation, that a valve is open. Duration (at .050" lifter rise) is the deciding factor to what the engine's basic RPM range will be. Lower duration cams produce the power in the lower RPM range. Larger duration cams operate at higher RPM, but you will lose bottom end power to gain top end power as the duration is increased. (For each ten degree change in the duration at .050", the power band moves up or down in RPM range by approximately 500 RPM.)

What is the difference in Advertised Duration and Duration at .050" Lifter Rise (Tappet Lift)?

In order for duration to have any merit as a measurement for comparing camshaft size, the method for determining the duration must be the same. There are two key components for measuring duration-- the degrees of crankshaft rotation and at what point of lifter rise the measurements were taken. Advertised durations are not taken at any consistent point of lifter rise, so these numbers can vary greatly. For this reason, advertised duration figures are not good for comparing cams. Duration values expressed at .050" lifter rise state the exact point the measurement was taken. These are the only duration figures that are consistent and can accurately be used to compare camshafts.

How does Valve Lift affect the operation of an engine?

Lift is the distance the valve actually travels. It is created by the cam lobe lift, which is then increased by the rocker arm ratio. The amount of lift you have and the speed at which the valve moves is a key factor in determining the torque the engine will produce.

What is Camshaft Lobe Separation and how does it affect the engine?

Lobe separation is the distance (in camshaft degrees) that the intake and exhaust lobe centerlines (for a given cylinder) are spread apart. Lobe separation is a physical characteristic of the camshaft and cannot be changed without regrinding the lobes.

This separation determines where peak torque will occur within the engine's power range. Tight lobe separations (such as 106?) cause the peak torque to build early in basic RPM range of the cam. The torque will be concentrated, build quickly and peak out. Broader lobe separations (such as 112?) allow the torque to be spread over a broader portion of the basic RPM range and shows better power through the upper RPM.

What are Intake and Exhaust Centerlines?

The centerline of either the intake or exhaust lobe is the theoretical maximum lift point of the lobe in relationship to Top Dead Center in degrees of crankshaft rotation. (They are shown at the bottom of the camshaft specification card as "MAX LIFT.") The centerline of the cam can be moved by installing the camshaft in the engine to an advanced or a retarded position.

How does Advancing or Retarding the camshaft's position in the engine affect performance?

Advancing the cam will shift the basic RPM range downward. Four degrees of advance (from the original position) will cause the power range to start approximately 200 RPM sooner. Retarding it this same amount will move the power upward approximately 200 RPM. This can be helpful for tuning the power range to match your situation. If the correct cam has been selected for a particular application, installing it in the normal "straight up" position (per the opening and closing events at .050" lifter rise on the spec card) is the best starting point.

Why is it necessary to know the Compression Ratio of an engine in order to choose the correct cam?

The compression ratio of the engine is one of three key factors in determining the engine's cylinder pressure. The other two are the duration of the camshaft (at .050" lifter rise) and the position of the cam in the engine (advanced or retarded). The result of how these three factors interact with one another is the amount of cylinder pressure the engine will generate. (This is usually expressed as the "cranking pressure" that can be measured with a gauge installed in the spark plug hole.)

It is important to be sure that the engine's compression ratio matches the recommended ratio for the cam you are selecting. Too little compression ratio (or too much duration) will cause the cylinder pressure to drop. This will lower the power output of the engine.

With too much compression ratio (or too little duration) the cylinder pressure will be too high, causing pre-ignition and detonation. This condition could severely damage engine components.
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 Post subject: Re: Millionth Cam Question
Posted: Sun Apr 04, 2010 9:05 pm 
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^ Best post ever! Exactly what I needed to know and without all the sarcasm and crap that's so common nowadays. Thank you very much! :D

 

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 Post subject: Re: Millionth Cam Question
Posted: Sun Apr 04, 2010 10:40 pm 
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Sticky??

 

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 Post subject: Re: Millionth Cam Question
Posted: Sun Apr 04, 2010 10:46 pm 
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Well done short and sweet
+1

 

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 Post subject: Re: Millionth Cam Question
Posted: Fri Apr 09, 2010 8:27 pm 
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GeZza200 wrote:
Sticky??


+1 for sure :)

 

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