Selecting the camshaft. . .

[steelcomp]

could you please write a little slower. :notam: :coffeycup

[Blown 472]

Okay, I do need to back up a little and give some credit. This "camshaft" math is what we named Ghetto Math coined by a fellow by the name of Erik K. Sharp guy and it comes from a thread that I was apart of on another board.
Alright. . .now we can proceed. You now need 2 things. A camshaft book for reference and flow numbers off your heads. . . perferablly numbers from your heads but "printed" numbers will work.
We will use a stand lobe that is 230 @.050"
We will use the Canfield 310 head with the following flow numbers:
Lift Int Exh
.300 204 176
.400 266 205
.500 318 237
.600 347 260
Okay we have the following:
(502/2)*5500/1728 = 798.88
798.88/8 cylinders = 99.86 cfm per cylinder
Now lets pick an intake lobe to try. Use the duration @ .50" I will use a cam lobe with 230 @ .050. By dividing the cam duration by the the total degrees of crank rotation of the 4 cycles we get the % of time we have to pack the cylinder for 100% VE
230/720 = .31 (= percent of time to get the air per revolution)
We now use the % of time we have calculated and divide the cylinder CFM requirement by it to come up with the intake port CFM flow that is required to fill our 502 at Max RPM
99.86/.31 = 322 cfm (needed air flow divided by percent of time to get the air in per rev is cfm needed)
So we need 322 cfm and the head at .500" cam lift is 318 CFM. Hey we are right there, but the question is do we run the boat at 5500 rpm all the time?
Okay, I'll stop here for today. Any questions? Please post. Is this helpful? Let me know. No question is to stupid and I will answer to the best of my ability. Blown since you have been good I will give you the equation to convert boost to Barometric pressure: (PSI x 2.035789617) + 29.92
Chris
Where does piston speed come into play?

[Carnivalride]

First off thanks for the info! However as usual more info always leaves me with more questions. :idea: :idea:
Like someone else mentioned where does piston speed come into play?
What about overlap and lobe seperation?
And does it hurt to have a little more head than you really need? Kind of like the larger carb or tunnel ram and 2 4bbls on an engine that only turns 7000rpm if it's a occasional lake mostly race peice?
Still trying to learn as much as I can,
Thanks,
Loren

[steelcomp]

Don't jump the gun, guys. He's going to get to that stuff. This is just the basic beginning req's. There's really an infinite amount of info that CAN go into cam design, but you got to start with the basics, and I think this is what Chris is trying to share with us.
I was looking at Don Terrill's book on building a winston cup (Nextel) motor, and he listed over 100 different Comp Cams lobes as his favorites. That's just lobe designs. One builder. One cam mfgr. Just trying tto illustrate just how many variables can be taken into consideration for a cam. :coffeycup
And does it hurt to have a little more head than you really need? Kind of like the larger carb or tunnel ram and 2 4bbls on an engine that only turns 7000rpm if it's a occasional lake mostly race peice?
The bigger the port in a head, TYPICALLY, the lower the port velocity. On a NA carb'd motor, port velocity is what gets good carb signal. Low velocity, low signal, and vice versa. To have a bigger port than you KNOW you'll need, is unnecessary, adn IMO, will hurt performance. That's why Chris chose the Canfield head. Small port that thinks it's a big port. I've been tought to try and use the smallest port you can get away with, to keep the velocity as high as possible. There's a lot more to it than just that, but I don't want to hijack Chris' thread.

[Fiat48]

Hang on guys. He wants questions about what he stated. The filling the cylinder, cfm and air flow.
"So we need 322 cfm and the head at .500" cam lift is 318 CFM. Hey we are right there, but the question is do we run the boat at 5500 rpm all the time?
Okay, I'll stop here for today."
Quite sure he will continue and get on with the rest of the variables of selection. Lot of meat here and plenty to digest.

[Norseman]

Okay, I'll stop here for today. Any questions? Please post. Is this helpful? Let me know. No question is to stupid and I will answer to the best of my ability. Blown since you have been good I will give you the equation to convert boost to Barometric pressure: (PSI x 2.035789617) + 29.92
Chris
Chris;
This is a great thread, thanks for taking the time to go thru all this!!!
Bob

[Norseman]

Mike;
I think this thread needs to be moved to the " How TO Section"!!
Bob

[cruser]

But how long is the valve at .500 off the seat? It flows 322 cubic feet per minute but is only there a very short time. That must have some influence in the picking the cam exercise.

[cstraub]

Where does piston speed come into play?
Good looks like we are getting some enjoyment out of this. Piston Velocity has to do with the RAM effect. I will touch on that later. As I said this thread will get "joe engine guy" within the "bases" instead of within the "park".
Over lap and lobe sep, we need to think of them as by products. Valve events are what matters timing the charge in, capturing the most we can, shutting the valve to keep it, then opening to release the unused gas and then shutting it so we can start over. Think Valve Events.
I will be busy today, so I will touch on this maybe later or this weekend.
Chris

[cstraub]

Okay,
I am behind, sorry I had a trim project I had to get started. Need to finish before the 500. I will start up again Monday.
Chris