Alright, I'm hearing that for each type of cam the duration can differ....i.e. I just recently learned a mechanical cam with a 238 duration @ .050 is about the same range as a hydraulic at 230 @ .050....

Now I'd like to know does this same theory apply when selecting a roller versus flat tappet? Does it matter if it's hydraulic or solid?

I'm no expert, but I would have said the 230 cam, if mechanical, would have had similar power capability to the hydraulic with 238. They are able to have the valves open more quickly with mechanical and even more so with a roller. End result is you can have a "smaller" cam build the same or more horsepower as you change types. To say it different - at a given rpm range, the mech is able to be more aggressive, making more power than the hyd and the roller more than the mech.

I believe the confusion comes from picking out one spot on the lift curve and assigning a number to it. The curves can differ broadly, but can have the same lift at point 'x'. You can beat your brains out trying to understand that stuff, or call the cam grinder and ask for advice. In my experience, I have found making a phone call the easiest of the two choices. They know their product better than you ever will.

In simple turns, a hyd cam will need about 6-8* less than a solid cam to get comparable seat - seat durations. But the solid ramps are always more aggressive.

Solid flat tappets and solid rollers are similar, and Hydraulic flat tappets and Hydraulic rollers are similar. Another thing that can get a guy confused real quick is regarding the advertised duration. Does the cam have X degrees at .004, .006, .016, or .020 tappet lift. I.E at what lift is the published number being advertised at?

Looking at duration at .050 numbers between two cams is sort of like shopping for houses and only looking at the kitchen. Just as Kirk stated, picking out one spot in the lift curve. This will tell you absolutely nothing about ramp speed or "peak Rate", etc.

If you compare Duration of two cams at .020 Tappet lift(a common advertising point for Solid and Solid Rollers), and you also compare them at .050, and something like .200, you get a much better idea about which one would be better. It also matters what the application is, the port size, and allthough some believe that rod to stroke ratio is a huge non issue and irrelevant, that too plays a role in decisions about "what ramp is best suited." I've seen on more occasions than I can count(especially in circle track cars) when a customer buys a cam and is very happy with it who will turn around and install longer rods. Then he will call and say the longer rods really hurt acceleration off the corner and swears nothing else was changed anywhere. I can sell him something with a few degrees less duration and often a different LSA, and he's happy again.

Engines with big ports and really good rod ratios(1.8-2.0) can't tolerate as aggressive Peak Rate as something with a ratio of 1.4-1.6 and small ports can. Installing a cam with a slower peak rate in an engine having 2.0 rod ratios as opposed to an identical advertised duration cam having a considerably faster one has gained power in many cases. It can get to a point where the engine will have a difficulty in building air velocity in the port.


The Peak Rate also plays a role in the valve train RPM stability.

Different rate ramps are happiest in different applications. It is all a matter of what the Owners goal is, and what price he is willing to pay to acheive it.

Solid flat tappets and solid rollers are similar, and Hydraulic flat tappets and Hydraulic rollers are similar. Another thing that can get a guy confused real quick is regarding the advertised duration. Does the cam have X degrees at .004, .006, .016, or .020 tappet lift. I.E at what lift is the published number being advertised at?

Looking at duration at .050 numbers between two cams is sort of like shopping for houses and only looking at the kitchen. Just as Kirk stated, picking out one spot in the lift curve. This will tell you absolutely nothing about ramp speed or "peak Rate", etc.

If you compare Duration of two cams at .020 Tappet lift(a common advertising point for Solid and Solid Rollers), and you also compare them at .050, and something like .200, you get a much better idea about which one would be better. It also matters what the application is, the port size, and allthough some believe that rod to stroke ratio is a huge non issue and irrelevant, that too plays a role in decisions about "what ramp is best suited." I've seen on more occasions than I can count(especially in circle track cars) when a customer buys a cam and is very happy with it who will turn around and install longer rods. Then he will call and say the longer rods really hurt acceleration off the corner and swears nothing else was changed anywhere. I can sell him something with a few degrees less duration and often a different LSA, and he's happy again.

Engines with big ports and really good rod ratios(1.8-2.0) can't tolerate as aggressive Peak Rate as something with a ratio of 1.4-1.6 and small ports can. Installing a cam with a slower peak rate in an engine having 2.0 rod ratios as opposed to an identical advertised duration cam having a considerably faster one has gained power in many cases. It can get to a point where the engine will have a difficulty in building air velocity in the port.


The Peak Rate also plays a role in the valve train RPM stability.

Different rate ramps are happiest in different applications. It is all a matter of what the Owners goal is, and what price he is willing to pay to acheive it.
=
While I will not disagree with most of what you are saying in theory, you are going to have to explain a couple of things to me because I am just a curious kinda guy,, :D

Why is a "good" rod ratio 1.8-2.0?
If this is a "good ratio, what is a "bad one"?
Who decides this?
Does it hold true in all applications?

Tell me how your customer changed the rod ratio enough to "really hurt" off the corner acceleration in the same engine?
How did he not change anything else when he changed rods?

Take a common 358 circle track engine
4.125 x 3.4 or there abouts
Or 4.03 x 3.5, whichever you prefer
Now change the rod from 5.7 to say 6.125
We are talking 1.68 vs 1.80 in one case,
1.63 vs 1.75 in the other.

Now, I have been doing this a long time & I have just never seen this fantastic gain or loss in torque between a "worst case" 1.63, ''best case" 1.8 difference,,, except on the internet of course :D

But I am all ears,, or eyes as the case may be,,, ;)

Solid flat tappets and solid rollers are similar, and Hydraulic flat tappets and Hydraulic rollers are similar. Another thing that can get a guy confused real quick is regarding the advertised duration. Does the cam have X degrees at .004, .006, .016, or .020 tappet lift. I.E at what lift is the published number being advertised at?

Looking at duration at .050 numbers between two cams is sort of like shopping for houses and only looking at the kitchen. Just as Kirk stated, picking out one spot in the lift curve. This will tell you absolutely nothing about ramp speed or "peak Rate", etc.

If you compare Duration of two cams at .020 Tappet lift(a common advertising point for Solid and Solid Rollers), and you also compare them at .050, and something like .200, you get a much better idea about which one would be better. It also matters what the application is, the port size, and allthough some believe that rod to stroke ratio is a huge non issue and irrelevant, that too plays a role in decisions about "what ramp is best suited." I've seen on more occasions than I can count(especially in circle track cars) when a customer buys a cam and is very happy with it who will turn around and install longer rods. Then he will call and say the longer rods really hurt acceleration off the corner and swears nothing else was changed anywhere. I can sell him something with a few degrees less duration and often a different LSA, and he's happy again.

Engines with big ports and really good rod ratios(1.8-2.0) can't tolerate as aggressive Peak Rate as something with a ratio of 1.4-1.6 and small ports can. Installing a cam with a slower peak rate in an engine having 2.0 rod ratios as opposed to an identical advertised duration cam having a considerably faster one has gained power in many cases. It can get to a point where the engine will have a difficulty in building air velocity in the port.


The Peak Rate also plays a role in the valve train RPM stability.

Different rate ramps are happiest in different applications. It is all a matter of what the Owners goal is, and what price he is willing to pay to acheive it.

Interesting....I've been informed by an old timer to go with the largest lift flow my heads can handle yet keep the duration down.

While I'm somewhat familiar with what hydraulic flat tappet cam to run in my engine I was beginning to be curious about the solids...the other day someone had a similar combo to mine and someone advised running a 238 solid....when I inquited about it being too much cam I was to "no it's perfect"....yet I've heard the whole time "no more than 230....no more than 230...."......this being a hyd. flat tappet.

On the average, a solid cam acts kinda like a hydraulic with 8* more at .050. However, that is kinda, not exactly. Hydraulic lifter cams come off the seat at a much lower velocity than solid lifter cams do, and this makes the hydyraulics have much larger seat durations, more overlap, more reversion, and less snap and bottom-end torque. Solid lifter intake cams of 235-243 at .050 make very good street performers, just like hydraulics of 225-235 at .050 do.
You always want as much lift as you can get on the intake. Be careful on how pointy-looking the cam is, though. The more pointy-looking a cam is, the less high lift area it has, and the less air it can flow. Engines never see max-valve lift as a controlling factor, but they do see high-lift area. You generally want as much .200 duration as you can get, within the .050 duration numbers you want.
The best thing to do is to talk to your cam company of choice.

UDHarold

Harold, Is this what area under the curve means? How does my voodoo 268 fare at the .200 lift point?

According to Comp's catalog, their BBC 268 is 134* at .200, and .515" valve lift. The VooDoo 268 for the BBC is 140* at .200, and .542" valve lift.
Now you know.

UDHarold

PS---This is not a snappy answer. Some words are left out, and are better left out.