Best cam

OP must’ve ran off.

400Rogue said:

I hear what you are saying, but I'm not going to be trying to maximize torque at idle. I care about the torque range where the engine is operating for a given application. Bigger cam is relative and says nothing about the actual lobe profiles or overlap. And if we are timing our valve events correctly to the pressure wave frequencies, a little lope is fine. Especially if we have a healthy compression ratio our vacuum at idle will be sufficient. If you want to improve torque, we generally want less exhaust duration for a NA application. But that means we may need a tighter separation angle to get to our ideal overlap, thus resulting in some lope.

A lot of aftermarket camshafts have more exhaust duration than intake duration. Even truck cams. But just for fun, what do you suppose would happen if we take the exhaust lobe and make the duration the same as the intake?

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You get more low-midrange torque at the slight expense of high RPM power. I have cammed engines with both single pattern and dual pattern grinds. I am actually changing a 218/228 on a 108 lsa out for a 219/219 on a 112 lsa in my 11:1 383. The 218/228 was the flat out wrong choice and to think it was actually spec'd and ground for a 9.6:1 350. Comp cam insisted it needed the long exhaust duration and tighter LSA. The 2nd cam is an Erson and both Lloyd Elliot and I had input on the specs.

L31MaxExpress said:

You get more low-midrange torque at the slight expense of high RPM power. I have cammed engines with both single pattern and dual pattern grinds. I am actually changing a 218/228 on a 108 lsa out for a 219/219 on a 112 lsa in my 11:1 383. The 218/228 was the flat out wrong choice and to think it was actually spec'd and ground for a 9.6:1 350. Comp cam insisted it needed the long exhaust duration and tighter LSA. The 2nd cam is an Erson and both Lloyd Elliot and I had input on the specs.

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For sure. I'm not saying we always need a tight LSA. It is going to vary a lot per engine and application. I believe we are saying much the same thing just in different ways. I'm just saying that we want to find the balance between lsa and duration to reach our overlap needs and sometimes we may want a tighter lsa, but not always. I like your second cam choice. I think that those same ex. and in. lobes with that lsa will be nice. What is your .006 duration and what ICL are you intending to install that on?

"Lope" in any vehicle with a catalytic converter or two, is going to be really hard on the converter. Leads to catalyst failure.

"Lope" in any vehicle that has a computer sensing misfire, is likely to set codes.

400Rogue said:

For sure. I'm not saying we always need a tight LSA. It is going to vary a lot per engine and application. I believe we are saying much the same thing just in different ways. I'm just saying that we want to find the balance between lsa and duration to reach our overlap needs and sometimes we may want a tighter lsa, but not always. I like your second cam choice. I think that those same ex. and in. lobes with that lsa will be nice. What is your .006 duration and what ICL are you intending to install that on?

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I will be running it with 1.6 rockers and I am planning to put it in on a 108 ICL although straight up would make a bit more HP.

400Rogue said:

A lot of aftermarket camshafts have more exhaust duration than intake duration. Even truck cams. But just for fun, what do you suppose would happen if we take the exhaust lobe and make the duration the same as the intake?

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I’m been listening, I wouldn’t mind knowing if you care to explain.

caminonut said:

I’m been listening, I wouldn’t mind knowing if you care to explain.

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Sure!

A couple terms to remember.

ICL - Intake Centerline. It is specified in crank degrees from TDC.
LSA - Lobe Separation Angle. This is the difference in degrees between the intake and exhaust lobe centerlines. It is the average of the two. Ex. 110 ICL + 110 ECL / 2 = 110 LSA.

IVO - Intake Valve Opening
IVC - Intake Valve Closing
EVO - Exhaust Valve Opening
EVC - Exhaust Valve Closing

These are the 4 valve timing events in every 4 cycle internal combustion motor. The camshaft duration and intake and exhaust centerlines determine when these occur.

When we are discussing overlap, this is time that IVO happens slightly before EVC. It is specified in degrees. It's critical we time this correctly in relation to the pressure waves in the intake and exhaust. This is commonly referred to as scavenging. If we don't get it right we are either closing the exhaust valve too late and sending fresh air out of the exhaust, or closing it too early and still have exhaust gases in the combustion chamber for our combustion stroke. We will never get a perfect overlap for every RPM. Although variable valve timing aims to do that.

Our lobe separation angle ultimately tells us overlap when looking at camshaft specs. The thing to focus on in a given rpm is the valve timing events and try to get the overlap to work with this. A lot of people fixate on valve lift and duration, but what we really should be paying attention to is the valve timing events, dial in the overlap and this will dictate our durations.

Long tube headers, and longer intake manifold runners promotes lower end torque in a naturally aspirated motor. This gets pretty far into the weeds of intake and exhaust pressure wave tuning so I won't spend a lot of time here. But in it's basic form, air does not stop moving when we close a valve. Inside the runners we have an oscilating pressure wave. We want to open the intake valve as the intake pressure wave becomes higher than the exhaust pressure. The higher pressure intake will help push the lower pressure exhaust out of the cylinder, then we want to close the exhaust valve before any more escapes.

What happens when we reduce the exhaust duration and bring it closer to the duration of the intake lobe, provided we don't change the LSA, is it moves the EVC event closer to top dead center. This in many cases helps to increase torque. But we need to be careful not to reduce it too much or our torque will start to suffer.

On the opposite end of the spectrum, let's say you have a lowered truck, you take it to autocross sometimes or other track days and you want more high end power. In that case we may want to sacrifice some low end torque because we need our engine sustaining a higher RPM. So we generally want more duration and you'll see a lot of camshafts with longer exhaust durations than intake. The exact level of duration will depend on the valve timing events, valve to piston clearance, etc. but in that scenario you are likely to want shorter headers and shorter intake runners and time the IVO and EVC around the pressure waves at those higher RPM's. This generally equates to longer durations and overlap.

Take a look at the picture L31MaxExpress posted. The top section is the exhaust lobe and the bottom section is intake lobe. Look at the exhaust close event at 23.07 degrees after TDC. and the intake opens at 17.81 degrees before TDC. That is the IVO and EVC valve events and overlap.

Thank you so much for taking the time to post this, it will take me some time to take all this in. I know I will have to reread this several times to get all this information to soak in.
I really appreciate all this information.

caminonut said:

Thank you so much for taking the time to post this, it will take me some time to take all this in. I know I will have to reread this several times to get all this information to soak in.
I really appreciate all this information.

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Sure thing. If you want to deep dive into camshaft design, I'd suggest this book here. It should give a pretty solid foundation.
High-performance Cams & Valvetrains: Theory, Technology, and Selection

This was written by a former engineering manager for Comp Cams.