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| CFM question https://www.slantsix.org/forum/viewtopic.php?t=6820 |
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| Author: | Dennis Weaver [ Sat Sep 13, 2003 12:32 am ] |
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Quote: For example, what is the cfm requirement for a single cylinder, 4-cycle, 225 cube engine, with 90% VE, running at 1 rpm? It's 213 cfm.
How d'ya figure? What kind of blower are you using to get 213 cubic feet of air into a cylinder displacing 225 cubic inches in one revolution in one minute? Enjoyed your post, but need to rethink the math on this one!  I hope the intake valve was hanging open on this theoretical revolution and the piston was not on the power downstroke...  "DW" |
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| Author: | mustangsix [ Sat Sep 13, 2003 12:48 pm ] |
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OOPS.  this is a Mars lander situation.....good catch, Dennis. This is what happens when I ponder aimlessly late at night.Let me try to clarify; I meant one intake stroke. Let's call it 2 rpm so that you have one intake stroke per minute. A 225 cube single cylinder with a 95% VE will suck in 213 cubic inches on every intake stroke. On the other three strokes, the carb does nothing. If you use the usual CFM formula, you assume that the carb is flowing continously. In this hypothetical situation, it does not. It flows as the intake pulses and the CFM requirement is larger because the air has to be ingested in less than a minute. A multi-cylinder engine fed from an intake manifold with a plenum chamber tends to average these pulses out and the flow looks continuous. You won't see your vacuum gauge jumpng with every stroke. But as you start dividing the manifold into split configurations(153-624) or an individual runner, the time component becomes a bigger consideration. |
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| Author: | Dennis Weaver [ Sat Sep 13, 2003 12:58 pm ] |
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I grokked your logic the first go-around, mustangsix, and it seemed valid and informative, even with the erroneous calculation  Glad there are other ponderers out there! "DW" |
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| Author: | Slanted73 [ Sat Sep 13, 2003 6:20 pm ] |
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| I'm so confused!!! |
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| Author: | Dennis Weaver [ Sat Sep 13, 2003 6:49 pm ] |
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Quote: I'm so confused!!! "DW" |
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| Author: | Guest [ Sat Sep 13, 2003 9:02 pm ] |
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Quote: I grokked your logic the first go-around, mustangsix, and it seemed valid and informative, even with the erroneous calculation
I'm old enough to have read "Stranger in a Strange Land"! Glad there are other ponderers out there! "DW" Seems the issue with the cfm-thingy is, you use the cfm calculation to make sure you have ENOUGH carb that can feed the c.i.'s at the rpm's. Having a little more carb than mathematically needed probably isn't a bad thing. Many of us seem to be tinkering with the motors anyway to make more RPM's available or otherwise increasing the Volumetric Efficiency, two factors in the equation. I went with the 8007 390 cfm Holley, but haven't had a chance to test it out, my starter died. |
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| Author: | Slanted73 [ Sun Sep 21, 2003 7:02 pm ] |
| Post subject: | I guess I might be at two choices.... |
Choice one would be 3 1920's on a common plenum. Undecided linkage. Choice two would be with six carbs. However, I'm thinking now that I would have seperate intake mainfolds for 1,2....3,4....5,6. Then I'd run one primary and one secondary carb on each manifold. I'm thinking that by seperating the three sets of carbs that the slant wouldn't be trying to drink from way too much carb at once. Does this one sound more doable? |
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| Author: | Slant Cecil [ Sun Sep 21, 2003 8:39 pm ] |
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Here's how an AMC/Jeep owner increased CFMs without the big$ of Webbers.   The adapters could be made for any downdraft 1 or 2 barrel. The intake is Cliffords 3x2 webber. Cecil |
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| Author: | Slanted73 [ Mon Sep 22, 2003 9:57 am ] |
| Post subject: | CFM on a 2 barrel |
I have an old 2 barrel off my '64 Polara. I had also thought of using three 2 barrels. That's the CFM on these? |
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| Author: | Slanted73 [ Mon Sep 22, 2003 9:58 am ] |
| Post subject: | Slant Cecil |
Thanks for the pic. |
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