12-24-2006, 04:11 PM
So as I said I would on my last thread, I'm going to do a thread on cams, cam degreeing, rocker arms, Valve to Piston clearances, and basically the whole valvetrain on a typical pushrod V-8. Hopefully this will help everyone interested out, and we won't have any more accidents like I had. I'm going to start off with the VERY basics, so that anyone who isn't familiar with how cams work, and what they do, won't be lost before they get started. That and right now I don't have an engine to use for degree a cam etc.
First off, What is a Cam, and what are its duties?
- Cams simply open valves at the correct time to allow the incoming Air/Fuel Charge in, and exhaust out.
- Cams, in many ways, are the brain of the engine.
- In many applications, cams have the fuel pump eccentric built on to power the fuel pump
- Cams have lobes that the lifters ride on. As the cam turns, the lifter is moved, which transmits that upward movement to the pushrods and rocker arms, which turns the upward movement of the pushrod into a downward movement of the valve.
-Cams also contain the distributer drive gear which drivesthe distributer shaft and oil pump.
What are the parts of a cam, and why are they important?
-Journals: Where the camshaft rides inside the bearings in the block or heads.
-Base circle: Basically the backside (heel) of the cam lobe, and the theoretical circle that would be created if the lobe was not present.
-Opening and closing ramps: Area between the Opening and Closing Flanks. The Opening and Losing ramps deal with how fast the valve will start to open.
-Opening and closing Flanks: Area between the nose and the ramps of the lobe. Also deal with how fast the valve will open, and what kind of lifters can be used with the Cam
-Nose: Peak of the Cam Lobe.
So, what am I looking at when I read Cam Specs?
- Lobe lift is how high the lifter will be lifted off of the base circle.
- Duration is how long the Valve will be open, measured in degrees of Crankshaft Revolution.
- Valve overlap is how long both the intake valve and the exhaust valve are open simultaneously at TDC of the exhaust stroke.
OK, Wow. What advantage does all this give me in my engine?
- A cam with longer duration and a high lift typically has a higher powerband than an engine with an opposite cam, considering that the engine is tuned to flow the correct amount of air for such a powerband.
-A cam with a high lift and a short duration will typicall accept boost better, as there will usually be less overlap, and the boost will not be lost out the exhaust valve while both valves are open.
I hear about degreeing cams all the time, but I have no idea what it means.
- Checking the grind. While you are degreeing a cam, you can make sure the valves open at the correct time according to the manufacturer of the cam. You can also check lobe lift while degreeing a cam.
- You can tune your powerband a little bit by advancing or retarding a cam. So say your Cam has a powerband of 2500 to 5000 RPMs. You can lower or raise the point your engine will make maximum power, but only withing the specs of your cam. (in this example, between 2500 and 5000 rpms.
WTF? You lost me with Advancing and Retarding a Cam
- Advancing a cam simply means changing where the cam is indexed on the cam gear. When you advance a cam, you allow the valves to open a few degrees earlier than if the cam was installed straight up. This lowers your powerband by allowing more cylinder pressure to build during the comppression stroke.
- Retarding a Cam does the opposite. It raises the powerband by allowing the engine to breathe better at higher RPMs.
All right, So what is this Piston to Valve Clearance you speak of?
- As the piston moves up in the bore on the exhaust stroke, bother valves are open. The intake valve is moving down toward the piston, and the piston is basically Chasing the exhaust valve closed. The most typical Piston-Valve contact is the piston hitting the exhaust valve somewhere around 10 degrees before top dead center. The second most common is the Intake Valve hitting the piston at around 10 degrees after TDC.
You check to make sure there is enough clearance that when the rods stretch under tremendous force at higher RPMS, the pistons do not come into contact with either of the valves.
-The larger your cam, the most chance there is that a piston could hit a valve, due to less piston-valve clearance. The centerline of the lobes also affect your piston-valve clearance.
Well, as bored as I am right now, I'm going to have to call it quits for now. Feel free to correct me on anything I may have gotten incorrect, as I did this on the fly.
Later on I will add how to Degree a cam and how to check piston-valve clearance (both with pictures)
First off, What is a Cam, and what are its duties?
- Cams simply open valves at the correct time to allow the incoming Air/Fuel Charge in, and exhaust out.
- Cams, in many ways, are the brain of the engine.
- In many applications, cams have the fuel pump eccentric built on to power the fuel pump
- Cams have lobes that the lifters ride on. As the cam turns, the lifter is moved, which transmits that upward movement to the pushrods and rocker arms, which turns the upward movement of the pushrod into a downward movement of the valve.
-Cams also contain the distributer drive gear which drivesthe distributer shaft and oil pump.
What are the parts of a cam, and why are they important?
-Journals: Where the camshaft rides inside the bearings in the block or heads.
-Base circle: Basically the backside (heel) of the cam lobe, and the theoretical circle that would be created if the lobe was not present.
-Opening and closing ramps: Area between the Opening and Closing Flanks. The Opening and Losing ramps deal with how fast the valve will start to open.
-Opening and closing Flanks: Area between the nose and the ramps of the lobe. Also deal with how fast the valve will open, and what kind of lifters can be used with the Cam
-Nose: Peak of the Cam Lobe.
So, what am I looking at when I read Cam Specs?
- Lobe lift is how high the lifter will be lifted off of the base circle.
- Duration is how long the Valve will be open, measured in degrees of Crankshaft Revolution.
- Valve overlap is how long both the intake valve and the exhaust valve are open simultaneously at TDC of the exhaust stroke.
OK, Wow. What advantage does all this give me in my engine?
- A cam with longer duration and a high lift typically has a higher powerband than an engine with an opposite cam, considering that the engine is tuned to flow the correct amount of air for such a powerband.
-A cam with a high lift and a short duration will typicall accept boost better, as there will usually be less overlap, and the boost will not be lost out the exhaust valve while both valves are open.
I hear about degreeing cams all the time, but I have no idea what it means.
- Checking the grind. While you are degreeing a cam, you can make sure the valves open at the correct time according to the manufacturer of the cam. You can also check lobe lift while degreeing a cam.
- You can tune your powerband a little bit by advancing or retarding a cam. So say your Cam has a powerband of 2500 to 5000 RPMs. You can lower or raise the point your engine will make maximum power, but only withing the specs of your cam. (in this example, between 2500 and 5000 rpms.
WTF? You lost me with Advancing and Retarding a Cam
- Advancing a cam simply means changing where the cam is indexed on the cam gear. When you advance a cam, you allow the valves to open a few degrees earlier than if the cam was installed straight up. This lowers your powerband by allowing more cylinder pressure to build during the comppression stroke.
- Retarding a Cam does the opposite. It raises the powerband by allowing the engine to breathe better at higher RPMs.
All right, So what is this Piston to Valve Clearance you speak of?
- As the piston moves up in the bore on the exhaust stroke, bother valves are open. The intake valve is moving down toward the piston, and the piston is basically Chasing the exhaust valve closed. The most typical Piston-Valve contact is the piston hitting the exhaust valve somewhere around 10 degrees before top dead center. The second most common is the Intake Valve hitting the piston at around 10 degrees after TDC.
You check to make sure there is enough clearance that when the rods stretch under tremendous force at higher RPMS, the pistons do not come into contact with either of the valves.
-The larger your cam, the most chance there is that a piston could hit a valve, due to less piston-valve clearance. The centerline of the lobes also affect your piston-valve clearance.
Well, as bored as I am right now, I'm going to have to call it quits for now. Feel free to correct me on anything I may have gotten incorrect, as I did this on the fly.
Later on I will add how to Degree a cam and how to check piston-valve clearance (both with pictures)
2014 Tacoma TRD Sport Double cab
2017 Toyota iA/Mazda 2
2017 Toyota iA/Mazda 2