which camshaft edelbrock or crane? 4x4

[oil pan 4]

I was trying to be vague for people that don't know cams that well.
The equation.
Hp=tq/5252Xengine rpm, I know this there for I know hp and torque are proportinal in a liner aspect.
No where can I find a cam calculation that uses the rockers to determin duration. Please explain this to me.
Becasue I like knowing things.
lift gives you torque.
Duration decides where you make the torque.
Lift decides how much torque you will make.
Higher lift will give you more torque at any given rpm. More lift will keep you rpm power band in all most the same place.
More duration will keep you making your toruqe higher in the rpm band.
This is basicly how it works there are many more factors that can come in to play. I will explain a few of them below on a "big cam scenario".
Here is a little some thing I typed up over on the advanced tech forum at camaroz28.com.
If you have ever typed any thing on the advanced forum at camaroz28.com you had better know what you are taking about or they will take you apart.
As for the position of the piston and valve.
On a big cam it start with over lap.
The intake valve opens as much as 15 and some times as much as 20 degrees (20 is more for 14,000rpm motor cycle engines) BTDC.
The exhaust valve closes lets say 8-10 degrees ATDC when the piston is moving down there is still exhaust getting blown out.
At low rpms this is bad. exhaust gets sucked into the intake runner at low rpms while there is vacuum in the intake. To take full advantage of this there must be positive pressure on the intake valve at high rpms when the intake valve starts opening at 15 degrees BTDC There is a slight vacuum in the chamber. because the exhaust valve opened before BDC, letting the exploding gas blowing its self out. but I'm not going to get to far into that.
As the intake valve starts really opening with the piston at 5-8 degrees (I mean open enough to let some air move) BTDC. There is intake air being sucked in and getting forced into the chamber chasing out the exhaust while the piston is moving up in the cylinder.
As both valves are open there most (about 1/16'') at the same time and the piston is at TDC the exhaust is sucking all of its self out and the intake air is starting to force its self and it is taking over.
Once the exhaust valve closes all the way the intake air is trapped and the piston is moving down.
The intake valve is open its most well after 90 ATDC. Its open it's most around 30-50 degrees before BDC depending on if its a big turbo cam or big N/A cam.
And closes as late as 40 degrees ABDC (don't think I have seen any that close later than that), that is when most of the air is sucked into the cylinder (ABDC). Yes there is a lot of air still getting sucked into the chamber because the runner air was accelerated during the time when the piston was between around 90 ATDC and full valve open. So now that the piston is moving up and air is getting into the chamber by means of some unseen force.
At this point the engine is super charging its self. The amount of self super chagrined is determined by a lot of factors, rpm, runners, valve timing (mainly intake open ABDC), spark timing comes into play a lot when you do FI and more.
The self super charging really starts with the exhaust opening well before BDC on the power stroke and the exhaust blows its self out creating a slight vacuumed sucking the piston up the bore and some times contaminating the chamber with oil if you don't have good oil control.
That is how a cam works.

[oil pan 4]

Shop around and you will find a deal.
Call as many places as you can think of that might sell a cam or know some one who does, if they don't deal cams but sell a lot of other car stuff than they might know some one who does.
The more choices you have the better.
When I did this I only got one place over and over again, so that is where I got my cam.

[Cannonball]

confused, which cam do i want the crane 260 or the comp 260h or 252h?

You want the Crane Powermax H-260-2. The Comp Cams 260 is a single pattern cam and you don't want that.
Part # for the Crane H-260 is 253902 this includes the cam, lifters and installation lube.
H-260 specs = 204 intake duration @.050. 216 exh. duration @.050. .427 int. lift and 454 exh lift.

[oil pan 4]

You will have to get new lifters with that cam, you can't reuse the old ones.

[geoffinbc]

Oil pan. By increaseing from a 1.5 to 1.6 rocker you can gain 2 to 4 degrees of duration at the valve. I'll let Crane Cams explain.

How does an increase in Rocker Arm Ratio improve the engine's performance?

The lobe lift of the cam is increased by the ratio of the rocker arm to produce the final amount of valve lift. A cam with a .320" lobe lift using a 1.50:1 ratio rocker arm will have a .480" valve lift (.320" x 1.50 = .480"). If you install rocker arms with an increased ratio of 1.60:1, with the same cam, the lift would increase to .512" (.320" x 1.60 = .512"). The engine reacts to the movement of the valve. It doesn't know how the increased lift was generated. It responds the same way it would as if a slightly larger lift cam had been installed. In fact, since the speed of the valve is increased with the higher rocker arm ratio, the engine thinks it has also gained 2° to 4° of camshaft duration.

The end result is an easy and quick way to improve the performance of the existing cam without having to install a new one. See the Buyers Guide section for availability of increased ratio rocker arms. Remember, whenever you increase the valve lift, with either a bigger cam or larger rocker arm ratio, you must check for valve spring coil bind and for other mechanical interference. Please review the previous sections concerning these matters.

So basically the increase ratio makes the valve open to an effective lift earlier than with a lower ratio. Thus increasing duration.

[614streets]

Ive had a 2030 , its not a bad cam, it has looser lsa which is really good for a unblown engine. I cant say I didnt enjoy the 2030.

The 272 is better suited for a more modified engine.

To be honest a solid flat tappet from schneider cams are worth taking a look at. Also dont forget LAZER cams custom grinds.

[614streets]

A 1.6 rocker will open faster than a 1.5 ratio and the duration is not changed but you would actually see different flow numbers during the lift duration cycle

[dbtk2]

In reality the duration is changed...Let me quote what was already said above:

So basically the increase ratio makes the valve open to an effective lift earlier than with a lower ratio. Thus increasing duration.

Rockers can't change when the cam opens and closes the valve, but by multiplying the speed at which the cam opens the valve, you can open the valve a lot quicker at the beginning and end of the cam lobe, so when it first starts opening the valve the valve is opening faster than before, allowing a lot more air to come in during that time, whereas before the valve may have not even been open enough to let much air in at all.

So, technically you aren't getting more duration with higher ratio rockers, but in reality you are, if that makes any sense to you.

Shawn

[614streets]

The cheapest place to buy a crane 260 might be paw. I belive about 100 bucks, just add paw lifters and its still under 150 bucks

If you buy a 260 from paw and grab lifters off ebay you'll save some dough as well.

A solid cam will make more power
Again dont overlook schneider or lazer cams.

[614streets]

In reality the duration is changed...Let me quote what was already said above:

So basically the increase ratio makes the valve open to an effective lift earlier than with a lower ratio. Thus increasing duration.

So, technically you aren't getting more duration with higher ratio rockers, but in reality you are, if that makes any sense to you.

Shawn

Exactly.

[geoffinbc]

Yea no change in the cam. But there is a change at the valve. Like Crane Cams said. The engine doesn't know, it just reacts to it. So get that valve above .050 lift sooner and you have made more "effective" duration. Advertised camshaft duration will never be changed.

[oil pan 4]

The crane cams thing:
"the engine thinks it has also gained 2° to 4° of camshaft duration."
That is the answer I knew I would hear.
You get the duration by adding the BTDC opening degrees with the ABDC closing degree and adding 180.
BTDC opening + ABDC closing +180=advertised duration

Crane Cams wrote:

How does an increase in Rocker Arm Ratio improve the engine's performance?

"The lobe lift of the cam is increased by the ratio of the rocker arm to produce the final amount of valve lift. A cam with a .320" lobe lift using a 1.50:1 ratio rocker arm will have a .480" valve lift (.320" x 1.50 = .480"). If you install rocker arms with an increased ratio of 1.60:1, with the same cam, the lift would increase to .512" (.320" x 1.60 = .512"). The engine reacts to the movement of the valve. It doesn't know how the increased lift was generated. It responds the same way it would as if a slightly larger lift cam had been installed. In fact, since the speed of the valve is increased with the higher rocker arm ratio, the engine thinks it has also gained 2° to 4° of camshaft duration.

The end result is an easy and quick way to improve the performance of the existing cam without having to install a new one. See the Buyers Guide section for availability of increased ratio rocker arms. Remember, whenever you increase the valve lift, with either a bigger cam or larger rocker arm ratio, you must check for valve spring coil bind and for other mechanical interference. Please review the previous sections concerning these matters. "

This does not tell me what my duration is after a different rocker install. Other than it is unchanged.
It tells me that I have more lift and that the valves open faster.
It looks like most of us knew that.