Can someone explain to me what the numbers mean regarding Cams, and how does this relate to which one you choose for your car. Also, what is the average install price if you supply the cam?

 

Hey, I am not an expert. . .but since noone else responded here you go:

I am seeing prices around $1300 for the parts and installation. If you look around for the cam, springs and everything else that is included in the install you are probably talking about $700 for the installation.

The number 224/224 .500 .500 114

I really don't know what the middle numbers are. But the first number 224 is the duration. . .basically how long the valves will stay open. The last number has something to do with the spacing on the cam. So that the smaller the number the more time 2 valves are open at the same time (creates a more noticeable "lope").

Again, I am not an expert. . .this was explained to me earlier today.

I am considering
220/220 .5x .5x 114
224/224 .6x .6x 114

224/224 .6x .6x 112

The last cam is the most agressive. Will idle a little rougher but will produce more power.

 

The first number indicates how long the intake valve is open, the second indicates how long the exhaust valve is open.

The third number indicates the intake lift with standard rocker arm ratio, while the forth number indicates the same for the exhaust valve.

The final number indicates the distance between the intake "lobe" and the exhaust "lobe". Smaller numbers are more agressive, wheil bigger numbers are more idle friendly.

So lets taks a 220/220 xxx xxx 114 cam and examine the timing.

Any valve has to be open longer than 180 degrees (a single stroke).

Convert camshaft revs to engine revs: 114 * 2 = 228
Subtract 1 stroke -180
= 48

Convert duration into start and end times: 220 - 180 = 40

Subtract excess duration from converted lob angle: 48 - 40 = 8

So this cam would open the exhaust vavle 8 degrees before TDC, and close the exhaust valve 32 degrees after BDC; Open the intake 32 degrees before BDC and close the intake 8 degrees after TDC.

Simple--right! (Europeans would have called this cam a 8/32-32/8 so you can see the timing points directly).

The period of time where both the intake and the exhaust are both open is called the overlap region, and effects two things: emissions and header design. Wider overlap periods allow properly tuned headers to convert more wave energy into engine output power. Wider overlap periods also hurt emissions (and the ability to comply with government crap).

You might be surprised that the exhaust valve opens significantly before the piston reacehes BDC. HOwever, almost all of the work that could have been extracted by the recipricating mechanism has been extracted, and the early opening allows the higher pressure in the cylinder to blow down into the exhaust pipes before the piston starts to move upwards.

Likewise, you might be surprised that the intake valve remains open significantly after the piston begins to rise from BDC. While air is low in weight, it is not weightless. Since it has weight (mass actually) it has momentum. So we can delay closing the intake valve until the rising piston would push out thefresh charge already in the cylinder.

A header tune tires together three of these timing intervals.

At Exhaust opening a pressure wave travels down the header, when it reaches the collector, it reflects as a negitive wave back up the header. You want this reflected negitive pressure wave to reach the exhaust valve while it is still open, and while the intake valve is opening. THis allows the negitive pressure wave to begin to pull fresh charge into the cylinder even before the piston begins its downward journey.

For race cars, there is another timing mark. As the positive pressure wave traverses the collector, sooner or later it hist the end of the collector. At this point is reverses as a positive pressure wave, back up the headers and if it arrives at just the right moment, it can push any fresh charge pulled into the header from the negitive pressure wave back into the cylinder.

The conbination of header tuning and inlet tuning can allow well designer engines to operate above 114% volumetric efficiencies for narrow RPM bands!

 

great explanation, I was curious myself. :cheers:

 

WOW!! This is good stuff. :yesnod:

I can see that 40 - 8 = 32, can you add a line explaining where the 32 comes from? :confused:

I understand what you're saying but, shouldn't TDC and BDC be switched? would open the exhaust vavle 8 degrees before TDC, and close the exhaust valve 32 degrees after BDC;


If this was the case, the exhaust valve would be open during a "Down" stroke or intake stroke and vice versa in your next "Intake" example?

I think you can probably just switch the words intake and exhaust in your examples and everything will work properly.


:cheers:


[Modified by scool93535, 3:23 PM 12/6/2002]

 

There is a great tutorial on camshafts on our web site under tech. If you have any more questions, feel free to ask. I am happy to help.
Thanks,

 

Mitch Alsup...great explanation. Just the other day I was asking what these numbers meant and nobody could come up with the 112/114 meaning. Thanks. :cheers:

 

Thanks, I'll check it out.

:cheers: