The topic of cams and witch one to run has been one of the best kept secrets in the Raptor world. Itís not a matter of what cam to run most of the time but whoís.
Were not only extremely limited by grinders of cams but also few grinds to pick from.
What Iíd like to do is help you understand cam terminology , basic science behind it. To help you make a more educated cam decision.
A little back ground on me. I know most of you know me a turbo builder. What most donít know is my back ground. I come from a family of hot rodders , drag racers , & builders. My original goal was to be a cam designer. I studied under the head cam grinder/designer at Erson cam back in the late 80ís. As most life took me another direction. But I never stopped being a gear head. I have been very fortunate to have worked on , built , and driven many different machines. , From 2 stroke and 4 stoke quads and motorcycles to drag racing , Baja and off road buggies, to land speed cars.
One key thing I have learned is there is no one person that knows it all.
First thing to know isÖYou ask 10 different people on the net what cam to run 5 will tell you the cam they run is the best the other 5 will tell you what cam they plan to run based on the first 5.
There is no single best cam. The cam is the heart of your build and the build should be built around the cam you choose. Iím not going to tell you what cam to choose that is up to you to decide.
Step 1 understanding a cam card. Thus understanding the cam itself.
Example of a Web 4 cam card.
Valve lift ..........................................Intake.. ..................Exhaust
.................................................. ........ .500".........................460"
Valve lash..........................................005" ...........................006"
Advertised duration.........................290.............. .............290
Duration @.050............................... 266........................... 265
Lobe center.......................................108.. .........................108
Intake opens 25deg. BTDC..................Exhaust opens 60.5 deg. BBDC
Intake closes 61 ABDC.........................Exhaust closes 24.5 ATDC
Web like most cam grinders in the US measure these specs at zero lash @.050 inches valve lift. This is a standard to help compare different cam types and by mfg.
Yamaha and most all Japanese cams are measured. @.040 (1mm) This includes Hot Cams and Megacycle cams.
Iím not going to get into cam degreeing but it is a must. There are tons of how to books , info on the net , & videos. Most of the cams on the market for a Raptor 700 are not CNC ground. So human error is always a factor. A few degrees off one way or another can affect performance and the power one is looking for.
Lets start with the most important part of any cam grind. The 4 main timing events. This would be the opening and closing events in a cam in relationship to the crank/piston. All information is based on Raptor 700 Natural Aspirated builds.
1. Intake opening . This range can be from 11 to 30 degrees BTDC (Before Top Dead Center) This affects duration , intake centerline , lobe separation , and overlap. The direct relationship to this number plays into the intake closing and how much duration your looking for, overlap , intake center line ,& lobe separation. Try and have the intake closing point and exhaust opening point determined along with the above before making this decision.
2. Intake closing. This can range from 42 to 69 degrees ABDC (After Bottom Dead Center) This affects duration , intake centerline , lobe separation. But also has a direct impact on static compression ratio.
Example of impact on cr. A stock stroke 102mm x stock stroke 84mm build with a 11 to 1 static cr piston is really 10.06 - 1 to 8.49 - 1 cr at sea level and has a corrected compression stroke of 76.2 mm to 62.99mm. All based on intake closing. So in turn the later you close the intake (higher the number) causes low in power loss and top end power gain.
3. Exhaust opening. This can range from 41 to 65 degrees BBDC (Before Bottom Dead Center) This affects duration , exhaust centerline , lobe separation. By opening the exhaust sooner (lower number) with a high duration cam 255 degs + will net you more high end power. This with a will tuned exhaust and intake will produce great top end gain, The trade off is loss in low end efficiency. You can achieve a happy medium by keeping the opening a little delayed.
4. Exhaust closing. This can range from 10 to 28 degrees ATDC ( After Top Dead Center) This affects duration , exhaust centerline , lobe separation , and overlap. The direct relationship to this number plays into the exhaust opening and how much duration your looking for, overlap , exhaust center line ,& lobe separation. Try and have the exhaust opening and intake closing point determined along with the above before making this decision.
Lift is the second most important factor in choosing a camshaft. Too much lift is hard to accomplish. Were really limited by , Piston to valve clearance , valve train , valve springs. For most of us .500 max lift is where itís at. There are racers pushing the envelope with much higher lifts but it requires getting into valve train geometry. Something most are not ready for.
Overlap. Range is 20 to 60 degrees. This is a critical area in determining your useable power band. This is the time that the intake is opening and the exhaust is closing. The valves are partially open at the same time. This reading is in crankshaft degrees. Increasing can be done with more duration and or moving the lobe separation angle. What you get is a scavenging affect as the exhaust valve is on the closing side of the exhaust stroke. The intake valve is opening. The exiting exhaust pressure creates a vacuum in the intake as the intake valve is opening. Thus giving you a better intake charge.
This is what Ed Iskenderian call the 5th cycle in a cam naming a cam in the late 50ís the Isky 5 cycle cam. It was pretty cutting edge at the time.
The higher the number the higher the power band. It is critical to have a intake and especially the exhaust system that properly scavenges. Or you will loose more power then you gain. Over lap is easy to calculate just take the intake opening point and the exhaust closing point and add them up. In the case of the Web4 intake 25 + exhaust 24.5 = 49.5 degrees overlap in the Web 4.
Advertised duration this is seat to seat duration at zero lash. Range is 250 to 300 degrees.
Duration @.050 range is 225-275 degrees . In short is what became the industry standard in measuring camshaft duration. It was originated back in the late 50ís to compare different cam grinders cams and different types of cams. To keep the standard of measuring the same..050" of lift after it opens and .050" before it closes. Itís still a good idea to know what seat to seat duration is.
Japan , Hot cams , & Megacycle use .040 (1mm) the difference is 2-4 degrees on average. Open -v- closed points.
Lobe centers intake and exhaust. Range is 100 to 112 degrees. The angle of the centerline of the intake and exhaust lobes. This is checked in camshaft degrees. The Web4 , Megacycle X4 , and a few others are 108 degrees. Increasing the intake from the 108 and decreasing the exhaust would retard cam timing. Thus moving the power band up. Just the opposite would be advancing cam timing and moving the power band down.
Doing this affects the numbers in the 4 main timing events. We will discuss how to use this to your advantage later.
Lobe separation angle. This can range from 104 to 110 on average for the raptor. Itís the degree of angle between the intake center line and the exhaust center line. Increasing it decreases overlap. Decreasing increases overlap. General rule of thumb is it will widen and flatten the power band by increasing and narrow the power band by decreasing. Great tool to use along with intake and exhaust centerlines angles. The Web 4 , X4 , and a few others are 108.
Now when looking at cam follow these basic steps. Your headÖ.Is it ported , what size valves , and valve springs. ( Iím not going to get into custom valve angles , combustion chambers and such. Best to leave that to the racers)
Itís best to start with the intake side of the cam and then work the exhaust in to fit your needs.
The exhaust should flow between 65-80% of the intake. . As soon as you do a 3 mod with duals you are on the high side to possibly exceeding it.
In the next few weeks we will cover Head porting , Motor size , intake . Exhaust ,Compression ratioís , altitude, ect. And how they all affect cam specs.