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All information needed to spec a cam

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Powertrip
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All information needed to spec a cam

Post by Powertrip » Tue Feb 04, 2020 3:07 am

After looking at Mike Jones Cam Recommendation form, I am wondering if there is additional information that could be provided to a cam designer to help with specifying the best cam for my application?

Intake: Full flow curve from .050" to port turbulence and beyond? Flow with radius entry, or with manifold and carburetor attached? Reverse flow numbers?

Exhaust: Full flow curve? Flow without pipe, with pipe, or even header attached? Reverse flow?

Does the amount of information needed vary between a highly competitive class application and say, a weekend bracket racer?

Anything else I'm forgetting? Or am I overthinking things as usual?
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CamKing
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Re: All information needed to spec a cam

Post by CamKing » Tue Feb 04, 2020 9:58 am

If I was designing the actual lobe profiles, then more information would be helpful. My recommendation forms are set up for me to choose the best lobe designs, from my existing profiles.

MCA is a good number to have, but I can calculate the "effective MCA" from the flow numbers.

For flowing the intake, I prefer the radiused entry. I believe that when you flow one port, with the manifold and carb on it, the lack of having the other 7 cylinder's pulses effecting the plenum pressure, will give you a false idea of how the manifold is actually effecting the port flow.

as for flowing the exhaust, I believe that flowing with a pipe extension is more accurate, because on many heads, the exhaust port is still turning at the flange, and you need a pile extension to let the flow straighten out, like it would with headers.
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skinny z
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Re: All information needed to spec a cam

Post by skinny z » Tue Feb 04, 2020 1:42 pm

[quote=CamKing post_id=847087 time=1580828283 user_id=5117]
MCA is a good number to have, but I can calculate the "effective MCA" from the flow numbers.
[/quote]

Is this a formula based calculation or one that comes from examining hundreds (thousands?) of cylinder heads?
While I have flow bench data what I don't have is the MCA. This would be useful in determining the viability of the heads in question. As the current engine is assembled (and I'd like to keep it that way for as long as possible) I've no way to measure that particular value.
Thanks in advance.

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Re: All information needed to spec a cam

Post by CamKing » Tue Feb 04, 2020 2:38 pm

skinny z wrote:
Tue Feb 04, 2020 1:42 pm
CamKing wrote:
Tue Feb 04, 2020 9:58 am
MCA is a good number to have, but I can calculate the "effective MCA" from the flow numbers.
Is this a formula based calculation or one that comes from examining hundreds (thousands?) of cylinder heads?
While I have flow bench data what I don't have is the MCA. This would be useful in determining the viability of the heads in question. As the current engine is assembled (and I'd like to keep it that way for as long as possible) I've no way to measure that particular value.
Thanks in advance.
It's a formula.
We know how much a 1 sqin hole can flow, at a given pressure drop. Using the port flow, you can calculate what cross sectional area would flow those numbers, at that given pressure drop. That's the effective MCA.
Mike Jones
Jones Cam Designs

Denver, NC
jonescams@bellsouth.net
http://www.jonescams.com
Jones Cam Designs' HotPass Vendors Forum: viewforum.php?f=44
(704)489-2449

Powertrip
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Re: All information needed to spec a cam

Post by Powertrip » Wed Feb 05, 2020 12:30 am

This is the 3rd time I'm trying to post this reply...

Mike, it makes sense that you would need more specific information when designing new lobes, but would it not also ensure you are picking the best existing lobes?

Maybe the better question is how much are we leaving on the table using existing profiles vs. custom, in a flat tappet bracket racer application?
I'm guessing not enough to pay the freight! :D
The price of progress is trouble.

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Re: All information needed to spec a cam

Post by CamKing » Wed Feb 05, 2020 10:10 am

Powertrip wrote:
Wed Feb 05, 2020 12:30 am
This is the 3rd time I'm trying to post this reply...

Mike, it makes sense that you would need more specific information when designing new lobes, but would it not also ensure you are picking the best existing lobes?

Maybe the better question is how much are we leaving on the table using existing profiles vs. custom, in a flat tappet bracket racer application?
I'm guessing not enough to pay the freight! :D
When I think more data will help with calculating which existing lobes to you, I will ask for more info.

For a flat tappet bracket race application, having lobes designed would be a huge waist of money, 99% of the time.
Mike Jones
Jones Cam Designs

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jonescams@bellsouth.net
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Jones Cam Designs' HotPass Vendors Forum: viewforum.php?f=44
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Powertrip
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Re: All information needed to spec a cam

Post by Powertrip » Wed Feb 05, 2020 3:17 pm

Why does this forum keep kicking me out?!?!
for the fourth try:

Understood, thanks for the clarification!
The price of progress is trouble.

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