Volumetric Efficiency front/rear
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Cruiser
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From: Earth
Volumetric Efficiency front/rear
I asked this in the Power Vision sticky without any response.
What's the typical difference, if any, in volumetric efficiency between front and rear cylinders, assuming a normal stage 1 and properly tuned?
What's the typical difference, if any, in volumetric efficiency between front and rear cylinders, assuming a normal stage 1 and properly tuned?
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Joined: Sep 2010
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From: Phoenix '53, '88, '09 Big Twins
the rear cylinder typically runs hotter.
in the old days , this would require an over-rich mixture for the front cylinder to keep the rear from misfiring- as ignitions got better ( Crane/ Dyna) rear cylinder timing offset was possible- retarding the rear 3ş or so.
we now have more precise controls and better machining.
the front and rear should be equal is terms of compression and displacement as tolerances are closer.
but the challenge is always cooling to the rear ( again the rear may be at a disadvantage, being shorter. some try to add length by adding curves etc. HD on the 09+ changed header design in a good way)
assume ( and I hope for more detailed info) that the rear cylinder may be richer ( longer injector pulse) than the front and the timing retarded to get the best available power from the rear.
The diff front/rear determined by ion sense and o2 voltage to the ecm, then compared to programmed parameters
the above also assumes equal header length etc.
where we get fancy is using scavenging and exhaust pulses to create a more than 100% cylinder fill- this requires cam timing/lift/duration and tuned intake and exhaust tracts to get a gain within a specific rpm range ( that's why 2 into 1's typically get better low rpm power).
The intake charge can be drawn in at high velocity so that when the valves close there may be 10% more air in there than would be at normal atmospheric pressure...add 10% more fuel and get 10% more power
Mike
in the old days , this would require an over-rich mixture for the front cylinder to keep the rear from misfiring- as ignitions got better ( Crane/ Dyna) rear cylinder timing offset was possible- retarding the rear 3ş or so.
we now have more precise controls and better machining.
the front and rear should be equal is terms of compression and displacement as tolerances are closer.
but the challenge is always cooling to the rear ( again the rear may be at a disadvantage, being shorter. some try to add length by adding curves etc. HD on the 09+ changed header design in a good way)
assume ( and I hope for more detailed info) that the rear cylinder may be richer ( longer injector pulse) than the front and the timing retarded to get the best available power from the rear.
The diff front/rear determined by ion sense and o2 voltage to the ecm, then compared to programmed parameters
the above also assumes equal header length etc.
where we get fancy is using scavenging and exhaust pulses to create a more than 100% cylinder fill- this requires cam timing/lift/duration and tuned intake and exhaust tracts to get a gain within a specific rpm range ( that's why 2 into 1's typically get better low rpm power).
The intake charge can be drawn in at high velocity so that when the valves close there may be 10% more air in there than would be at normal atmospheric pressure...add 10% more fuel and get 10% more power
Mike
Last edited by mkguitar; May 7, 2014 at 07:48 PM.
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I has been my experience that most like-for-like cells (rpm/kPa) are generally within 5% to 8% - more then that and I'll try to find out why.
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