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11-01-2023, 06:34 PM | #1 |
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Location: Melbourne, Australia
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Model A camshaft
Howdy, I've been given this camshaft - it's been ground to the specs in the pic. I'm not an expert in these so my question is - is this a standard cam or something else. Any help would be appreciated. Thanks!
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11-01-2023, 07:26 PM | #2 |
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Re: Model A camshaft
Why not ring Clive Cams and ask what grind number 566 is?
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11-01-2023, 09:05 PM | #3 |
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Re: Model A camshaft
Hey thanks for that - just made a call to Clives! The tag that came with it looked a 100 years old - didn't think they'd be in business. cheers.
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11-01-2023, 09:16 PM | #4 |
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Re: Model A camshaft
So what grinds is it?
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11-02-2023, 10:12 AM | #5 |
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Re: Model A camshaft
This might help:
https://www.fordgarage.com/pages/camshaftspecs.htm |
11-02-2023, 11:37 AM | #6 |
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Re: Model A camshaft
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Last edited by Jim Brierley; 11-02-2023 at 11:38 AM. Reason: added info |
11-02-2023, 05:57 PM | #7 |
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Re: Model A camshaft
So, it seems that cam shaft is a B 6250 grind?
Given the EXCELLENT condition of the distributor/oil pump drive, it is an excellent cam shaft. Good pickup, Greg.
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11-03-2023, 06:55 AM | #8 |
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Re: Model A camshaft
What is the significance of intake & exhaust valve overlap? Functionally, they are separated by the compression stroke, so I see no interaction of the overlap. However, I suspect the overlap means something to setup cam grinding.
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11-03-2023, 08:32 AM | #9 | |
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Re: Model A camshaft
Quote:
You're looking at it in the end of the intake stroke / beginning of the compression stroke.
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11-03-2023, 10:35 AM | #10 | |
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Re: Model A camshaft
Quote:
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11-05-2023, 08:29 AM | #11 |
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Re: Model A camshaft
I can imagine at very high engine RPM, the intake & exhaust valves may overlap open because of the time it takes the valves to open and close. However, does that matter in a very low RPM motor such as the Model A's?
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11-05-2023, 12:28 PM | #12 |
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Re: Model A camshaft
During the overlap period intake air is mixed with exhaust, causing the rough idle common in performance engines. At high RPM's inertia of the gases force intake air into the exhaust, and packs more air into the cylinder. More air in the cylinder, almost like lightly supercharging, equals more power. Valves open and close slowly, in comparison to when the lifter is further up the lobes ramps , so the valves are only open a small amount, but enough to cause what is termed a ramming effect. Air has weight, so the extra filling of the cylinder is effective.
Another thing that seems odd is that the exhaust valve starts to open long before BDC of the piston. This is to allow the pressure in the cylinder to bleed down before the piston starts back upward, which would take horsepower away. That's enough to make a guys head hurt! Last edited by Jim Brierley; 11-05-2023 at 12:39 PM. Reason: added info |
11-05-2023, 02:28 PM | #13 | |
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Re: Model A camshaft
Quote:
Bob, This is a complex association, many variables to power and drive ability are determined by these valve timing events. It goes much deeper than what I see in previous postings, to touch on a few, this much I know... As rpm increase, air demand is greater. To supply the additional air and fuel, designers open the intake valve sooner, which allows more time for the intake charge to fill the cylinder. With an early-opening intake valve, at high rpm the exiting exhaust gas also helps draw the intake charge through the combustion chamber and out the exhaust-that's good for purging the cylinder of residual gas, but it also increases fuel consumption by allowing part of the intake charge to escape before combustion and can make for a rough idle. In a perfect world, the optimum intake closing point would occur just as the air stops flowing into the chamber. An early-opening exhaust valve may benefit scavenging on high-rpm engines because most useful cylinder pressure is used up anyway by the time the piston hits 90-degrees before BDC on the power stroke. Later exhaust valve opening helps low rpm performance by keeping pressure on the piston longer. Lift, the magnitude of the valve peak opening (don't forget to factor rocker arm ratios on push rod engines), duration, the value in degrees that the valve has left it seated position. Lobe displacement angle (some refer to this as lobe separation angle), the displacement angle (LDA) between the center lines ground into the cam, are all engineered for the engines intended purpose. Duration, lift, and LDA combine to produce an "overlap triangle." The greater the duration and lift the more overlap area, LDAs remaining equal. Given the same duration, LDA and overlap are inversely proportional: Increased LDA decreases overlap (and vice versa). More overlap decreases low-rpm vacuum and response (why race cams usually employ vacuum pumps for accessory function, and also produce that lopey thumping exhaust note we associate with race engines), but in the midrange overlap improves the signal provided by the fast-moving exhaust to the incoming intake charge. This increased signal typically provides a noticeable engine acceleration improvement. Less overlap increases efficiency by reducing the amount of raw fuel that escapes through the exhaust, while improving low-end response due to less reversion of the exhaust gases back up the intake port; the result is better idle, a stronger vacuum signal, and improved fuel economy. Due to the differences in cylinder head, intake, and exhaust configuration, different engine combos are extremely sensitive to the camshaft's overlap region. Not only is the duration and area of the overlap triangle important but also its overall shape. Much recent progress in cam design has been due to careful tailoring of the shape of the overlap triangle. The most critical engine factors for optimizing overlap include intake system efficiency, exhaust system efficiency, and how well the heads flow from the intake toward the exhaust with both valves slightly open. Like I said very complex issue, but the take away from this would be anyone serious about making power, time spent to understand this would be well spent. No component has more effect on the power an engine makes than its induction system. The cam is the blueprint for this combination....Hope this helps. |
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