I was discussing Cams with my roomie and he said that cams can be made to produce either HP or torque. I've only seen the cams that make hp at like 9000rpms. I'll pass on that. But torque on the other hand is something that us civic people DO need. Is this really possible and what effects would it have on the rest of the engine's power band?

 

they product both torque and hp.

redline usually goes higher because the cam lobe lift/duration is not maximized yet with proper tuning.

the primary and secondary cam lobe is what makes your torque mostly and those are a little more agressive with different cams.

what makes big time gains is the vtec lobe on aftermarket cams.

 

They produce more power, and the only way to do that is to increase torque. Simply raising the revs doesn't work because the torque is already falling off before the stock redline on pretty much any engine I've seen.

Cams will raise the torque, usually at high rpms, and will result in more power. However, if you want big power gains you'd probably end up increasing the high end torque and ruining the low end torque, especially with no VTEC. So, even if you're making huge torque numbers at 10000rpms, you won't necessarily be impressing any V8 dudes....

Cams can definately be made to increase low end torque, but that will on the other hand result in crappy overall power. If you're really interested in sacrificing 50hp for that 2 extra ft lbs of low end torque, well, most domestics seem to be tuned like that...


[Modified by Lsos, 8:15 AM 9/24/2002]

 

This is something I wrote on another forum a while back, I figured this would help a little here? I know not all of the following applies to you, but maybe you'll be able to see how different cam (gears) will affect your engine output.

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First of all, read this: http://www.compcams.com/Information/...s/valvtim2.asp

Right now, I can only assume that you have the basic understanding of how a 4 stroke internal combustion engine works? You know of all the major components, and what they do, how they move... For now, we will focus on just the valve train and the 2 out of 4 strokes of the engine cycles: exhaust & intake.

So we know what opens and closes the valves, and how the components move; we know why those valves exist, and we know when they should be opening and closing. Or do we? Right now all we know is that we should open the intake valve and let the piston travel down while pulling fresh air in, then the intake valve should close to create a sealed chamber for the combustion stroke. We know that the exhaust valve should open as the piston travels upward to push the exhaust gas out, and close when the intake valve opens so the fresh air doesn't get sucked out of the chamber. Now, what's this overlap all about?

Imagine your engine idling at 800RPM. That is about 400 complete cycles per minute, or almost 7 cycles per seconds. Just how long is your intake valve opened for, to allow fresh air to be pulled in? Not a whole lot, actually. Not to mention, the air in your intake (manifold) travels in pulses (as your valves keep opening and closing) so it's not a constant "flow" of air. One of the biggest reasons for overlapping, is to use the exhaust flow (and temperature/pressure difference of the two sides) to help PULL more cold, fresh air into the chamber. As the piston is travelling upward during the exhaust stroke, an exhaust "flow" is created and that flow will continue to travel down the exhaust pipe into the atmosphere. Also, your exhaust temperature could be as high as 1700 degrees F (vs 90 degrees F in your intake side), now if you combine these factors (velocity, pressure, temperature) it is not hard to see how exhaust/intake overlapping can help your engine suck in cold air better.

But just how much overlapping is "good"? Now here comes the tricky business... Remember that we were only talking about 800RPM. Now, imagine a race engine screaming at 16000RPM (like an F1 motor). That is 20 times faster than our last example! The engine goes through over 130 complete cycles per seconds and you can imagine just how little time your engine has to breath in fresh air. Now, your overlapping becomes so much more important, or else your engine will simply run out of breath. From this, we can conclude that the need for overlapping is not constant throughout your RPM range and the more is not always better.

What happens when you have too much overlapping? At low RPM your intake valve will open too early, while the exhaust flow isn't fast enough to pull the intake side. End result? Cam reversion. As both intake and exhaust valves are opened while the piston is travelling upward to push out the exhaust gas, the air flow in your intake manifold will actually get pushed back! Another nasty effect is oil and other stuff getting pushed in there as well... That's why street cars with aftermarket (aggressive) cams usually run into EGR problems. Because oil gets shoved back so far it causes EGR sensor failures.

As you can see, there is no true optimal settings. If you are looking for all out top end performance and you don't ever drive below 6000rpm, then sure, by all means retard your exhaust timing and advance your intake timing. And even then, for street use you're not looking at more than just a few degrees in either direction.

There's a whole science in cam tuning... The previous article gave us some very good idea of how cam phasing affects engine performance. And I will quickly do a quote from that article:

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.

I hope what I wrote here today will give you a better understand why you want intake/exhaust overlapping, and why you do (not) want excessive overlapping depending on your other engine modifications and driving style. Remember: cam and cam gear settings is not even half of what you need to do to get a high rev, high power motor. Valve springs, retainers, fuel, cooling, rods, crank... Then there's the whole bore x stroke ratio, rod x stroke ratio... But to quickly wrap this up... Unless you are doing some MAJOR work to your motor, your cam gear settings will not affect your engine output by much. An extra horse or two will not get you anywhere. Instead of spending the money on those unnecessary parts, you should invest the money in an auto program at your local college, or a performance driving school at your local race track. You will be amazed what you can learn from those places.

Ok, I've obviously talked too much here. Have a good day all.

 

While on the cam topic. With a Stage 1, 2, or 3 cams: how will this change the engine tone. Is it easy to tell someone has aftermarket cams? Or, is it only noticable on a stage 3 and not on a 2? We're trying to figure out if a guy we race with has cams, and I'm trying to figure out the best way to tell w/o going into the engine. Any ideas?
SEAN