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ok thanx
the magnum seens to have long duration and i meen alot. i have one and i scompared to stock and lots more duration
I see a lot of discussion about the HC stage 2 vs. the HC stage 1 for a stock compression engine. I've done some calculations to define how much the stage 2 might hurt bottom end performance. If you read the entire first post then you know that the issue is the loss of compression from the intake valves staying open a long(er) time. Compression is a dominating factor for producing low end torque. Here's the difference:
Taking into account the valve specifications:
Stock cam cranking compression at 1000ft = 8.2:1
HC stage 1 cranking compression at 1000ft = 7.8:1
HC stage 2 cranking compression at 1000ft = 7.6:1
If you go to a 11.0:1 piston (instead of the stock 9.1:1 piston) then the numbers change to:
stock cam: 9.9:1
HC stg 1: 9.5:1
HC stg 2: 9.2:1
(figures may not be absolute but the comparison is accurate)
Does anyone know where to get the white bros. all around cam for a good price? I live in Mesa, AZ and I would assume that local dealers 1) would be expensive and 2) would have to order it. So I'm willing to go mail order.
Any help is appreciated.
Does anyone use this cam? What are your thoughts?
While extremely informative, I'm sure some people are a bit confused on what the numbers MEAN, and also what the numbers DON'T tell you.
As GPRacer said in the third post, higher lift generally means more power. The valve is actually open more, so the engine breathes better. But it's not always possible to increase lift without increasing duration.
As a general rule, more duration will have more top-end power in higher revs, but less low-end power.
Now let's talk about what the specs DON'T tell you.
What is duration? It's a measurement of how long (in crankshaft degrees) the valves are open. But an important aspect is the definition of "open". If the valve is lifted .001 inches (about half the thickness of a piece of paper), it's not really "open" because you don't get any meaningful amount of airflow through such a small opening. So cam manufacturers define "open" when the valve is lifted at either 1mm (about 0.040"), or 0.050". Both are standard, it just depends whether you're using a metric system or not, but they don't always tell you which one they measure to. YOU need to be aware of the issue because that difference of 0.010" can change your specs by a degree or two. You may wish to talk to the manufacturers to get all the information.
The specs also don't say anything about overlap, and it can be extremely important. Overlap is the amount of time (in crankshaft degrees) that both intake and exhaust valves are open.
Overlap is critical because air has mass, and therefore has inertia. It doesn't move instantly, and it doesn't stop instantly. Both are important.
When the exhaust valves open, the exhaust gasses go rushing out, and the piston begins it's upstroke. The piston gets near finishing the exhaust stroke, and the intake valves open before the exhaust valves close. Why?
You have exhaust gasses moving OUT, and they have their own inertia. Meanwhile, the air sitting in the intake also has inertia sitting still, and it takes energy and time to get that air moving. Wouldn't it be great to use the inertia of the exhaust going out to help kick-start the intake process? This is exactly what overlap does. Because both intake and exhaust are open during overlap, it takes advantage of the inertia of the exhaust gasses to pull a vacuum inside the cylinder, and that vacuum will help get the air moving inside the intake. This means that you can actually begin the filling process BEFORE the piston begins it's downstroke. This is called scavenging.
On a related note, the intake duration actually extends past BDC, because of the inertia of the incoming air. The air is already moving, and doesn't stop instantly. That can be used to stuff the cylinder even after the piston begins it's upstroke, like a super-charging effect.
Now, this stuff happens at high RPM, when air is moving the fastest and thus has the greatest momentum. But what happens if that momentum didn't exist? When the piston begins it's downward stroke, it would pull in air from both the intake AND exhaust, because the exhaust wouldn't have that outgoing momentum and would be free to reverse. Obviously the exhaust won't burn a second time, so any space it takes up is lost power. Likewise, if the intake valves are open after the piston begins it's compression stroke, you certainly wouldn't super-charge the cylinder, you would force a little bit of air OUT, back into the intake. This not only results in lost power, but it would pass through the carb again, and get mixed with more fuel and result in a double-rich mixture.
This is exactly what happens at low RPMs. Without that velocity, the air doesn't have momentum. This is why camshafts designed for high-rev have very poor performance at low RPMs and rough idle. The exact same things that are beneficial at high rpms will cause problems at low rpms.
This is also related to head porting. This is why bigger isn't always better, because the key is VELOCITY, not AMOUNT. Although a larger port might be able to flow a larger AMOUNT, it may have a lower VELOCITY, and that velocity is very important to your scavenging and supercharging effects.
Some info from a recent thread that I thought belonged here too:
Regarding the various Hotcams cams, there are four different cams.
A few years ago 1043-2 replaced 1008-2 as the stg 2 and the "Stroker" cam was released. Hotcams has since dropped the "Stroker" label and now calls that cam Stg 3. But sometimes the old stg 2 (1008-2) is called a stg 3. :confused: Some of the Hotcams "stage" labels are ambiguous. It's better to use the HC part numbers to possitively identify.
1007-1: Stage 1, always has been.
1008-2: The original stage 2. Sometimes called "old stg 2" and sometimes called stg 3. No longer being manufactured.
1043-2: The current stg 2. Replaced the 1008-2.
1051-3: The current stg 3. Use to be called the "Stroker" cam by Hotcams.
Got it? Good. ;)
cam: Intake lift; Exhaust lift; Intake duration; Exhaust duration
1007-1... .354, .354, 246, 246------Intake centerline 106, Exhaust centerline 107
1043-2... .354, .350, 254, 248.5----Intake centerline 106, Exhaust centerline 104.25
1008-2... .348, .349, 254, 254------Intake centerline 106, Exhaust centerline 107
1051-3... .358, .354, 262, 257------Intake centerline 110.5, Exhaust centerline 104.5
Those are the 4 Hotcams cams for the 400EX. It's no wonder some manufactures just stick with numbered names instead of "stages".
I have the 1043-2 and with my mods im wondering if i should get the old stage 2 or a stage 1. Will this work well for my 440 11:1, i already have just have not installed it yet.
Bump.
(Just because I had not seen it up for a while).