MoparDaddy
Damn Right I Carry!
Ok. Here's a question that I didn't reply see posted. When choosing a cam, what info does one need to calculate what cam he/she should run, and what formula should he/she use
Choosing the right cam
- Thread starter MoparDaddy
- Start date
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What is the car going to be used for? Then Head flow and compression ratio?. Then what gears and converter do you what to run?
It depends from person to person. I like to look at everything. Some people don't take certain aspects into consideration, such as overlap for example. A fairly recent thread argues the point. I think it's an important factor, just like all the rest of the info.
Different people do it different ways, so good luck getting a solid answer.
Different people do it different ways, so good luck getting a solid answer.
MoparDaddy
Damn Right I Carry!
I'm asking in general. It's something I've never truly been able to figure out. I always see 258's being suggested, but what I wish to know how they calculate what to run. Well use a stock TBI 360 as an example
OldmanRick
Well-Known Member
Hi Chuck. On a TBI system, i'd look at a minor split duration with the intake in the 210/212 @.050 range and a 114/116 LSA max. Since it's a computer controlled deal, you have to keep things tight for a good vacuum signal.
MoparDaddy
Damn Right I Carry!
How do you come up with those number though? I'm not putting a cam in anything. I'm just trying to get a better understanding of how to choose one in the future.
MoparDaddy
Damn Right I Carry!
Thanks bud! Info like that that is what I'm looking for. I want to know how to factor/figure the aspects required. I don't want to HAVE TO post up an engine build to find out which cam to get. I want to be able to determine the proper cam myself. I hope I'm articulating this correctly.
Thanks bud! Info like that that is what I'm looking for. I want to know how to factor/figure the aspects required. I don't want to HAVE TO post up an engine build to find out which cam to get. I want to be able to determine the proper cam myself. I hope I'm articulating this correctly.
You are. But, like I said, people do it differently, so you'll get a lot of different answers and none of them are necessarily wrong.
IMO, for a 100% street car, pump gas with "reasonable" gears, say 3.23-3.55 I like a cam with no more tan 236* @ .050 ground on a 112 or even a 114 LSA. The smaller duration helps bottom end torque to pull the highway gears. The wider LSA gives good street manners and a strong vacuum signal.
But, as I said, opinions vary. Other people like and deal with a more radical choice for the street. I prefer what I outlined. Unless of course the car in question is not my primary vehicle. Then perhaps things can get more radical.
OldmanRick
Well-Known Member
It's really just from a lot of personal experience with different combo's and research from others with similar setup's.
I make a lot of recommendations just from years of seeing things that work and things that don't.
I've never claimed to be any kind of expert, and I hope most take my thoughts as just from someone that has had a hand in some builds, and just makes suggestions to get people thinking.
Check out the video and watch all three.I only posted part one...
http://www.forabodiesonly.com/mopar/showthread.php?t=222114&highlight=cam+rani
http://www.forabodiesonly.com/mopar/showthread.php?t=222114&highlight=cam+rani
DaveBonds
Garage Trash
In order to determine what camshaft to use, the basics are as follows;
1- Determine the use of the car. Be as honest with yourself as possible. What you see yourself doing with the car, vs. what you'd like to do with the car can sometimes be different scenarios.
2- Determine a goal HP/TQ number range that will achieve #1.
3- Build the drivetrain together. If this means you are leaving parts of the drivetrain the way they are, know what you have, even if it requires a little tear down. The more you know, the better you will be able to tune and build the engine to suit the parts within the drivetrain that will end up in the car.
Once you have those ideas squared away, approach the geometry of the camshaft with understanding it's effect on the valvetrain. Rather than thinking about numbers, think about what each operation of the cam performs.
The engine goes through four cycles.
1- Intake valve opens and chases the piston down, allowing the engine to draw in air
-intake valve closes
2-Piston compresses the gas
-both valves are closed
3-Spark ignites compressed gas and forces the piston down
-exhaust valve opens
4- Exhaust valve is open, piston chases exhaust valve until it is shut
-exhaust and intake valve are both slightly open for a short duration, during exhaust closing and intake opening again.
Effects of each geometry on the running cycle-
Lift is equal to the volume of gas allowed into the chamber, static (static, meaning frozen in time, ie. not taking flow into consideration yet)
Duration is equal to the amount of time that gas is allowed into the chamber, taking static lift and giving it the dimension of time for operation.
Lobe separation angle is the measurement between centerlines on intake and exhaust lobes for the same cylinder. This has a direct effect on the overlap within the cycle that RatRod was talking about. The further each line/ wider V angle between centerlines, the less overlap there will be and less time within the cycle spent with both the intake and exhaust valves open.
Total camshaft advance degree adjusts when the valves are opening and closing against the piston cycle. The valve cycle most importantly effected by advancing the cam degree is the intake valve shut cycle. Allowing the intake valve to shut sooner in the piston cycle, before the piston goes from BDC on it's way up, allows the piston to compress the gas during more of it's up stroke.
Once you've broken down the anatomy of a camshaft, you can begin to understand how the geometry effects how the engine produces power and when it will, in RPM range.
There are a lot of other factors, like how an engine scavenges unburnt fuel from the exhaust (aided by the use of headers, especially equal length, long runners) and how overlap has an adverse effect on it. As you can imagine, when the piston chamber has exposed it's pressure to both the intake and exhaust momentarily, it adversely effects flow, inherently effecting vacuum.
V8 engines have a sister cylinder, meaning there is always a second cylinder drawing the exact opposite stroke in the same position on the other bank. This is why the runners on dual plane intakes are laid out the way they are and why scavenging works. It is also why exhaust balancing is important.
IMO, there are a lot of factors that are just as important as camshaft choice, when buying parts that are commonly overlooked, like piston, head and gasket choice and RPM range for engine balancing.
1- Determine the use of the car. Be as honest with yourself as possible. What you see yourself doing with the car, vs. what you'd like to do with the car can sometimes be different scenarios.
2- Determine a goal HP/TQ number range that will achieve #1.
3- Build the drivetrain together. If this means you are leaving parts of the drivetrain the way they are, know what you have, even if it requires a little tear down. The more you know, the better you will be able to tune and build the engine to suit the parts within the drivetrain that will end up in the car.
Once you have those ideas squared away, approach the geometry of the camshaft with understanding it's effect on the valvetrain. Rather than thinking about numbers, think about what each operation of the cam performs.
The engine goes through four cycles.
1- Intake valve opens and chases the piston down, allowing the engine to draw in air
-intake valve closes
2-Piston compresses the gas
-both valves are closed
3-Spark ignites compressed gas and forces the piston down
-exhaust valve opens
4- Exhaust valve is open, piston chases exhaust valve until it is shut
-exhaust and intake valve are both slightly open for a short duration, during exhaust closing and intake opening again.
Effects of each geometry on the running cycle-
Lift is equal to the volume of gas allowed into the chamber, static (static, meaning frozen in time, ie. not taking flow into consideration yet)
Duration is equal to the amount of time that gas is allowed into the chamber, taking static lift and giving it the dimension of time for operation.
Lobe separation angle is the measurement between centerlines on intake and exhaust lobes for the same cylinder. This has a direct effect on the overlap within the cycle that RatRod was talking about. The further each line/ wider V angle between centerlines, the less overlap there will be and less time within the cycle spent with both the intake and exhaust valves open.
Total camshaft advance degree adjusts when the valves are opening and closing against the piston cycle. The valve cycle most importantly effected by advancing the cam degree is the intake valve shut cycle. Allowing the intake valve to shut sooner in the piston cycle, before the piston goes from BDC on it's way up, allows the piston to compress the gas during more of it's up stroke.
Once you've broken down the anatomy of a camshaft, you can begin to understand how the geometry effects how the engine produces power and when it will, in RPM range.
There are a lot of other factors, like how an engine scavenges unburnt fuel from the exhaust (aided by the use of headers, especially equal length, long runners) and how overlap has an adverse effect on it. As you can imagine, when the piston chamber has exposed it's pressure to both the intake and exhaust momentarily, it adversely effects flow, inherently effecting vacuum.
V8 engines have a sister cylinder, meaning there is always a second cylinder drawing the exact opposite stroke in the same position on the other bank. This is why the runners on dual plane intakes are laid out the way they are and why scavenging works. It is also why exhaust balancing is important.
IMO, there are a lot of factors that are just as important as camshaft choice, when buying parts that are commonly overlooked, like piston, head and gasket choice and RPM range for engine balancing.
txstang84
Well-Known Member
Here's a decent article to start with along with all the aforementioned commentary...
http://www.hotrod.com/techarticles/proper_camshaft_selection/
http://www.hotrod.com/techarticles/proper_camshaft_selection/
I like the Bond's post. Kind of detailed,and a flow chart..
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