Selecting the camshaft. . .

[Taylorman]

General rule of thumb is you prop a boat around 1000 rpm over max torque to run max rpm. This doesn't torque load the drive. So we went from a max rpm of 5500 to 4500. All we did is match cam duration at .050" for what we needed by using the formula.
Do you understand?
Chris
I got all that. What i dont understand is why you picked 224 duration on the intake. By using 224, we get 263 cfm's on the intake. By looking at the flow chart for the Canefields, they flow 263 at .400 lift. What i dont understand is how you decided that 263 cfms was the optimum airflow. Why wouldnt you change the duration till you get the desired airflow at the same lift that you picked for the lift (.500).
Now duration.
(502/2) * 4500/1728= 653.64
653.4 / 8 = 81.67
224/720 =.31
81.67/.31= 263.45
So we need our duration at.050" around 224 on the intake.
As I stated this math will get you very close. It is not black and white but it will sure get you closer to the target cam you need then guessing at lobes in a book. How do I know it works? I personally have never one a championship like Bigkat or any of you. What I do have are close working relationships with engine builders across the states that build championship caliber engines that I work with on camshafts. So not only do I know this stuff works on the dyno, I know it works in the application.
How good is this math. Just this past fall I had partners in a engine business have a friendly competition amoung each other. 4 engines 2 a piece. One chose me, the other used another cam grinder nationally known. My customer had a 421 and a 406. His partner had a 434 and 421. These were IMCA's going to the Super Nats. Long story short my customers stuff with lesser heads bested both engines. He supplied me with flow numbers and the particulars of the combinations, his partner was asked CID, gear, rpm range. You cant' cam what you don't know.
Okay, next exhaust lobe.
Chris
Questions?

[Norseman]

bump

[cstraub]

Okay, I will complete this this weekend. Sorry work is crazy. Seems everyone wants go fast parts.
Chris

[Havasu47]

Bumb

[Norseman]

Chris;
We will wait for you, this is great stuff!!!!

[cstraub]

Sorry, between quoting customers, doing camshafts, and getting some projects done around the house before my Bristol company comes I have been busy.
Okay, how to determine the amount of exhaust duration:
It has been my experience that if you use the following for a general rule of thumb it will get you pretty damn close.
The amount of duration needed for the exhaust is determined by 3 factors; I/E ratio %, CID, and rpm. Again you must have the flow numbers on the heads to do this.
When the Exh. flow is 75% of the intake flow your engine will require a single pattern camshaft.
For every 2% below the 75% range you need to add a point more duration to the exhaust side.
For every 2% above the 75% range you need to deduct a point of duration from the exhaust side.
Now CID and rpm will vary this to a degree, but for the most part with our 500 to 580CID engines in these boats turning 5500 and 6K rpm these rules hold true.
Okay, lift next but it will have to be later.
Chris

[Norseman]

bump :supp:

[Havasu47]

Bump

[Norseman]

Chris;
Your leaving us hanging here!!

[cstraub]

Sorry, between company for the Bristol Race, being out of town, and work. . .business is crazy right now I just haven't had time. I have to leave to go to FL to pick up my dad's new boat this afternoon. I will continue next week when I get back. I need this fishing trip!!!!!
Chris