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Thread: Cam shaft Q's

  1. #1

    Question Cam shaft Q's

    I am looking at getting a pair of cams for my 3sgte project. I found this on webcamsshafts.com VALVE LIFT- .356, DURATION IN DEGREES - 242, DURATION @.050 IN DEGREES - 218, Grind number 763, hard weld 45-221. What does all this mean? There are some cams on ATS that i was looking at, but hace NO :lolhittin idea of what all the numbers mean. Could one of you knowledgable guys clue me in? Thanx in advance

  2. #2

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    Lift is the max amount the cam will open the valve.
    For our engines [S/A series] that is all you need.
    For most engines [ones that have rockers] you have to adjust for rocker ratio.

    duration is how many degrees [out of 360*] the cam will be pushing on the valve. @ .050 means the duration is measured at .050 inches of lift [gives you a more accurate idea of duration, because you know where the starting point is]

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  3. #3

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    so what si good to use on the 3sgte.. more lift.. or more duration or both? or less? I don't know the specs on the stock cam... Typically more is better.. however that is for an NA motor really... not used to these weird turbo motors!

  4. #4
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    Quote Originally Posted by Summitracing.com
    Camshaft 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 lose bottom end powe
    Quote Originally Posted by Summitracing.com
    Valve lift is the distance the valve actually travels. It is created by the camshaft 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 how much torque the engine will produce.
    And now the big one with all the bulk of info.

    Quote Originally Posted by Summitracing
    In an effort to simplify what actually happens inside an engine, Competition Cams invites you to "take a walk" inside a typical engine, just like the one you might have in your car. We will discuss valve events, piston position, overlap and centerlines. Although we can not explain cam design in such a small space, we might be able to clear up some of the most misunderstood terms and make clearer what actually happens as the engine goes through its four-stroke cycle. We will graphically illustrate the relationship between all parts of the engine and try to help you understand how the camshaft affects the power of the engine. Put on your walking shoes, open your eyes and get ready for a good look inside this engine. We begin with the piston all the way at the top with both valves closed. Just a few degrees ago the spark plug fired and the explosion and the expansion of the gasses is forcing the piston towards the bottom of the cylinder. This is the event that actually pushes the crankshaft around to create the power and is referred to as the "power stroke" (figure 1). Each "stroke" lasts one half crankshaft revolution or 180 crankshaft degrees. Since the camshaft turns at half of the speed of the crank, the power stroke only sees one fourth of a turn of the cam, or 90 camshaft degrees. As we move closer to the bottom of the cylinder, a little before the piston reaches the bottom, the exhaust valve begins to open. By this time most of the charge has been burned and the cylinder pressure will begin to push this burnt mixture out into the exhaust port. After the piston passes the true bottom or Bottom Dead Center, it begins to rise back to the top. Now we have begun the exhaust stroke, another 180° in the cycle (figure 2). This forces the remainder of the mixture out of the chamber to make room for a fresh, clean charge of air-fuel mixture. While the piston is moving toward the top of the cylinder, the exhaust valve quickly opens, goes through maximum lift and begins to close. Now something quite unique begins to take place. Just before the piston reaches the top, the intake valve begins to open and the exhaust valve is not yet fully closed. This doesn't sound right, does it? Let's try to figure out what is happening. The exhaust stroke of the piston has pushed out just about all of the spent charge and as the piston approaches the top and the intake valve begins to open slowly, there begins a siphon or "scavenge" effect in the chamber. The rush of the gases out into the exhaust port will draw in the start of the intake charge. This is how the engine flushes out all of the used charge. Even some of the new gases escape into the exhaust. Once the piston passes through Top Dead Center and starts back down, the intake charge is being pulled in quickly so the exhaust valve must close at precisely the right point after the top to keep any burnt gas from reentering. This area around Top Dead Center with both valves open is referred to as "overlap". This is one of the most critical moments in the running cycle, and all points must be positioned correctly with the Top Dead Center of the piston. We'll look at this much more closely later. We have now passed through overlap. The exhaust valve has closed just after the piston started down and the intake valve is opening very quickly. This is called the intake stroke (figure 3), where the engine "breathes" and fills itself with another charge of fresh air/fuel mixture. The intake valve reaches its maximum lift at some defined point (usually about 106 degrees) after top dead center. This is called the intake centerline, which refers to where the cam has been installed in the engine in relation to the crankshaft. This is commonly called "degreeing". We will talk about this later also. The piston again goes all the way to the bottom and as it starts up, the intake valve is rushing towards the seat. The closing point of the intake valve will determine where the cylinder actually begins to build pressure, as we are now into the compression stroke (figure 4). When the mixture has all been taken in and the valves are both closed, the piston begins to compress the mixture. This is where the engine can really build some power. Then, just prior to the top, the spark plug fires and we are ready to start all over again. The engine cycle we have just observed is typical of all four- stroke engines. There are several things we have not discussed, such as lift, duration, opening and closing points, overlap, intake centerline and lobe separation angle. If you will refer to the valve timing diagram when we discuss these terms it might make things a lot easier to understand. Timing Image Most cams are rated by duration at some defined lift point. As slow as the valve opens and closes at the very beginning and end of its cycle, it would be impossible to find exactly where it begins to move. In the case illustrated, the rated duration is at .006" tappet lift. In our plot, we use valve lift so we must multiply by the rocker arm ratio to find this lift. For example, .006" x 1.5 =.009". Instead of the original .006" tappet lift, we now use .009" valve lift. These opening and closing points are circled so that you can see them. If you count the number of degrees between these points you will arrive at the advertised duration, in this case 270 degrees of crank- shaft rotation. In this illustration this is the same for both the intake and the exhaust lobes, thus making this a single pattern cam. Some cam manufacturers rate their cams at .050" lift. If we again multiply this by the rocker arm ratio, we get .075". we can mark the diagram and read the duration at .050" lift. This cam shows around 224 degrees, standard for this 270H cam. The lift is very simple to determine. You can simply read it from the axis going up. This is the lift at the valve as we said earlier. Sometimes you will hear lift referred to as "lobe lift". This means the lift at the lobe or the valve lift divided by the rocker arm ratio. In this case, it would be .470" divided by 1.5 or .313" lobe lift. The lift is simply a straightforward measurement of the rise of the valve or lifter. We touched on opening and closing points a little earlier, but now we want to consider them even further. We talked about when these points occur, and how they are measured. As you can see in figure 1, the valve begins to move very slowly then picks up speed as it approaches the top. It does the same closing, coming down quickly then slowing to a gentle stop. It's kind of like driving your car. If you were to go from 0 to 60 mph in a fraction of a second and stop instantly, you can imagine what that would do to the car, not to mention the driver. It would be much too severe for any valve train to endure. You would bend pushrods, wear out cams, break springs and rockers, and lose all dynamic design. The cam would not run to the desired RPM level as you would have all these parts running into each other. As the valve approaches the seat, you also have to slow it down to keep the valve train from making any loud noises. If you slam the valve down onto the seat, you can expect some severe noise and a lot of worn and broken parts. So it is easy to see that you can only accelerate the valve a certain amount before you get into trouble. This is some- thing Competition Cams has learned over the years-how far you can safely push this point. Looking a bit further at the timing points, the first one we see on the diagram is the exhaust opening point. We have all noticed the different sounds of performance cams, with the distinct lopes or rough idle. This occurs when the exhaust valve opens earlier and lets the sound of combustion go out into the exhaust pipes. It may actually still be burning a little when it passes out of the engine, so this can be a very pronounced sound. The next point on the graph is the intake opening. This begins the overlap phase, which is very critical to vacuum, throttle response, emissions and especially, gas mileage. The amount of overlap, or the area between the intake opening and the exhaust closing, and where it occurs, is one of the most critical points in the engine cycle. If the intake valve opens too early, it will push the new charge into the intake manifold. If it occurs too late, it will lean out the cylinder and greatly hinder the performance of the engine. If the exhaust valve closes too early it will trap some of the spent gases in the combustion chamber, and if it closes too late it will over-scavenge the chamber; taking out too much of the charge, again creating an artificially lean condition. If the overlap phase occurs too early, it will create an overly rich condition in the exhaust port, severely hurting the gas mileage. So, as you can see, everything about overlap is critical to the performance of the engine. The last point in the cycle is the intake closing. This occurs slightly after Bottom Dead Center, and the quicker it closes, the more cylinder pressure the engine will develop. You have to be very careful, however, to make sure that you hold the valve open long enough to properly fill the chamber, but close it soon enough to yield maxi mum cylinder pressure. This is a very tricky point in the cycle of the camshaft. The last thing we will discuss is the difference between intake centerline and lobe separation angle. These two terms are often confused. Even though they have very similar names, they are very different and control different events in the engine. Lobe separation angle is simply what it says. It is the number of degrees separating the peak lift point of the exhaust lobe and the peak point of the intake lobe. This is sometimes referred to as the "lobe center" of the cam, but we prefer to call it the lobe separation angle. This can only be changed when the cam is ground. It makes no difference how you degree the cam in the engine, the lobe separation angle is ground into the cam. The intake centerline, on the other hand, is the position of the centerline, or peak lift point, of the intake lobe in relation to top dead center of the piston. This can be changed by "degreeing" the cam into the engine. Figure 1 shows a normal 270 degree cam. It has a lobe separation of 110°. We show it installed in the engine 4° advanced, or at 106° intake centerline. The light grey curves show the same camshaft installed an additional four degrees advanced, or at 102 degrees intake centerline. You can see how much earlier overlap is taking place and how the intake valve is open a great deal before the piston starts down. This is usually considered as a way to increase bottom end power, but as you can see there is much of the charge pushed out the exhaust, making a less efficient engine. There is a recommended intake centerline installation point on each cam card, and it is important to install the cam at this point. As far as the mechanics of cam degreeing, Competition Cams has produced a simple, comprehensive video (part #190) that will take you step by step through the process. On these pages we have discussed theory, but the video will show you how to actually get the job done. Competition Cams has put a great deal of effort into the design and engineering of our camshafts. All of these points were considered for each cam we build. What we intend to do here is show that camshaft design is not some "black art", but rather a series of decisions and compromises based on the exact application of the cam. Only our many years of experience can say whether a certain combination of lobes will work, so you should trust the judgement of those who have engineered these combinations. If you have any other questions, the Competition Cams Technical Staff can be reached at 1-800-999-0853 and will be glad to answer them for you, or you may also contact Summit's technical staff at 1(330)630-0240.
    This was the easiest way I could think of to explain it without confusing you and myself.

    Most stock cams are small and made more for low end power, FI cams notwithstanding. For a street car, you want low RPM power. If you are gonna go for a FI cam with top end, you want more Duration and Lift, it shoves more air in and lets that air out.

    Stock cams are normally around 200*/200* duration with around a .400/.400 lift @.050". This is not to be taken as fact, just guidline!!

    If you go too large like say 250*/250* with a .520/.550 you will make lots of power at top end, with a big huffer forcing the air in, but you will have to make it to the very very high RPMs to see that.

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  5. #5
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    Those cams would be a very modest upgrade over the stock ones. Probably not worth spending much on, but if they are cheap, go for it. Consider the most common cam upgrade for the 3SGTE has 264 degrees duration. More similar to the stock 205 cams.

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  6. #6

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    chris...would you recomend the 264 intake and exhaust hks cams with gears then? i might be looking into cams this summer. i want something that will perform well, but not mess up the idle of the car.
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    I wouldn't recommend HKS cam gears, fyi.

    As for the cams...well, 264's in and of themselves aren't too bad. I have a good friend with them, on his Autronic tuned 185, and it runs as smooth as my car. You couldn't tell the difference to be honest.

    I have no idea how this might be affected on a stock-ECU car though. I know many people have them, I just don't have experience with anyone's cars running that way.

    264's are a very good upgrade imho. They offer very good performance without much compromise in the low end. I would think that idle would be okay...I'm just not sure. If you had something like an SMT6, emanage, PFC, or some other EMS, you could advance the timing at idle if needed and make it run smooth as ever.

    So I'd say, go for it if you can!

    FWIW, I'm in the process of installing ST205 cams on my car. Mostly because I just dont have the money to spend on better stuff.
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  8. #8
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    264 Cams on a mostly stock internal head is a good upgrade. I will be doing this shortly as well.

    I also don't suggest the HKS cam gears, they have been known to strips the screws and in turn jump timing. I would suggest a set of ATS cam gears.

  9. #9

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    I have fitted HKS 264 cams on my ST205 and it won't idle properly as they won't produce enough vacuum at idle to run on the stock ECU. I've had to alter the TPS and timing as a stop gap until I install an Apexi FC ECU.
    Gary

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    Quote Originally Posted by GT4WRC
    I have fitted HKS 264 cams on my ST205 and it won't idle properly as they won't produce enough vacuum at idle to run on the stock ECU. I've had to alter the TPS and timing as a stop gap until I install an Apexi FC ECU.
    Gary
    It is typical to have to raise the idle to around 1000rpms. Though, on a gen 2 engine results have been good. Unaware of the results of a gen 3 ST205 engine with stock ECU, but I guess that answers it.

  11. #11

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    Where on summit is that posted?

  12. #12

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    Thanx for the answers!

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