FEH 12.3 to compression ratio
#21
11-10-2008, 09:50 PM
Re: FEH 12.3 to compression ratio
Not "conveniently" forgeting anything.
At low engine RPM, say 1000RPM, and WOT (Wide Open Throttle) then there is virtually NOTHING preventing a FULL A/F mixture charge from entering each cylinder. The rise in HP/torque as RPM rises is the result of more "firings" per second until a point is reached wherein there is not enough intake valve opening time for a full charge to enter and then the HP/Torque numbers begin to decline.
Now, on the other hand, if you hold the throttle partially closed thereby artificially restricting volumetric efficiency, limiting an engine under load to say, 1000RPM, then your statement would be correct.
At low engine RPM, say 1000RPM, and WOT (Wide Open Throttle) then there is virtually NOTHING preventing a FULL A/F mixture charge from entering each cylinder. The rise in HP/torque as RPM rises is the result of more "firings" per second until a point is reached wherein there is not enough intake valve opening time for a full charge to enter and then the HP/Torque numbers begin to decline.
Now, on the other hand, if you hold the throttle partially closed thereby artificially restricting volumetric efficiency, limiting an engine under load to say, 1000RPM, then your statement would be correct.
#22
11-11-2008, 09:13 AM
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Re: FEH 12.3 to compression ratio
Okay, you educate me.
Note: I have NEVER said nor indicated that VE will be anywhere close to 100% at any RPM.
Okay, Let's say the throttle is wide open and the dyno braking is restraining the RPM.
In this circumstance what would keep the cylinder from being fully filled with the A/F mixture...??
And you may also take note that a 4 cylinder engine always has a cylinder on the intake cycle simultaneous with the need to EXHAUST some of the charge of the cylinder in a compression cycle back into the intake manifold.
That's the reason the Atkinson cycle will not work in a 6 cylinder engine absent a positive displacement SC to prevent reverse intake flow.
Note: I have NEVER said nor indicated that VE will be anywhere close to 100% at any RPM.
Okay, Let's say the throttle is wide open and the dyno braking is restraining the RPM.
In this circumstance what would keep the cylinder from being fully filled with the A/F mixture...??
And you may also take note that a 4 cylinder engine always has a cylinder on the intake cycle simultaneous with the need to EXHAUST some of the charge of the cylinder in a compression cycle back into the intake manifold.
That's the reason the Atkinson cycle will not work in a 6 cylinder engine absent a positive displacement SC to prevent reverse intake flow.
#23
11-11-2008, 10:10 AM
Re: FEH 12.3 to compression ratio
Okay, you educate me.
Note: I have NEVER said nor indicated that VE will be anywhere close to 100% at any RPM.
Okay, Let's say the throttle is wide open and the dyno braking is restraining the RPM.
In this circumstance what would keep the cylinder from being fully filled with the A/F mixture...??
Intake manifold/runner length and shape, port shape, path, surface finish. Combustion chamber shape, flow, swirl characteristics. Intake valve lift, profile. Charge velocity/kinetic energy. Look at the torque curves for the 2.3L Atkinison vs. Otto that Ford published. They have basically identical max torque at high RPM, but the Atkinson version has far less torque at low RPMs. Atkinsonizing (sorry, Webster) reduces the pumping loss, which improves efficiency. But, it significantly reduces the VE, which means it gets comparatively less charge at a given (low) RPM and thus produces much less torque, but does so more thermodynamically efficiently despite the lower VE.
And you may also take note that a 4 cylinder engine always has a cylinder on the intake cycle simultaneous with the need to EXHAUST some of the charge of the cylinder in a compression cycle back into the intake manifold.
That's the reason the Atkinson cycle will not work in a 6 cylinder engine absent a positive displacement SC to prevent reverse intake flow.
Note: I have NEVER said nor indicated that VE will be anywhere close to 100% at any RPM.
Okay, Let's say the throttle is wide open and the dyno braking is restraining the RPM.
In this circumstance what would keep the cylinder from being fully filled with the A/F mixture...??
Intake manifold/runner length and shape, port shape, path, surface finish. Combustion chamber shape, flow, swirl characteristics. Intake valve lift, profile. Charge velocity/kinetic energy. Look at the torque curves for the 2.3L Atkinison vs. Otto that Ford published. They have basically identical max torque at high RPM, but the Atkinson version has far less torque at low RPMs. Atkinsonizing (sorry, Webster) reduces the pumping loss, which improves efficiency. But, it significantly reduces the VE, which means it gets comparatively less charge at a given (low) RPM and thus produces much less torque, but does so more thermodynamically efficiently despite the lower VE.
And you may also take note that a 4 cylinder engine always has a cylinder on the intake cycle simultaneous with the need to EXHAUST some of the charge of the cylinder in a compression cycle back into the intake manifold.
That's the reason the Atkinson cycle will not work in a 6 cylinder engine absent a positive displacement SC to prevent reverse intake flow.
Last edited by DesertDog; 11-11-2008 at 04:04 PM. Reason: spelling
#24
11-11-2008, 03:31 PM
Re: FEH 12.3 to compression ratio
What are a few specific models running 12:1 or more on pump gas?
#25
11-11-2008, 05:42 PM
Re: FEH 12.3 to compression ratio
Some of the early 1963 406 CI Fairlanes came with 3-2 BBL and 12.1:1 compression and of course some had 427 CI engines with 2-4 BBL and 12:1...
Some of the Plymouth '63-'65 426 Hemi's came with as much as 13.5:1 compression also.
My '67 427 2-4 BBL GT500 I modified had 13.5:1 compression and I had to add octane boost and it still would dieseled when I turned it off. I had to stall the engine at shutdown by putting it in gear and at the same time turn it off and let out the clutch to stop dieseling.
I gave up on pump gas and high compression engines in 1980 when I sold my Shelby. The new owner had to buy one of my 428 CI long blocks with 10.5:1 compression because of pump gas.
GaryG
#28
11-12-2008, 06:57 PM
Re: FEH 12.3 to compression ratio
GaryG
#29
11-12-2008, 07:07 PM
Ridiculously Active Enthusiast
Join Date: Sep 2006
Location: Beautiful Pacific NW
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Re: FEH 12.3 to compression ratio
The Lexus GS350 V6 for about 2 years now and now the new Porsche 911/997.
#30
11-13-2008, 07:01 AM
Re: FEH 12.3 to compression ratio
GS350 Base Sedan Performance Specs
- 3,456 cc 3.5 liters V 6 front engine with 94.0 mm bore, 83.0 mm stroke, 11.5 compression ratio, double overhead cam, variable valve timing/camshaft and four valves per cylinder 2GR-FSE
- Premium unleaded fuel 91
- Gasoline direct injection fuel system
- 3,456 cc 3.5 liters V 6 front engine with 94.0 mm bore, 83.0 mm stroke, 11.5 compression ratio, double overhead cam, variable valve timing/camshaft and four valves per cylinder 2GR-FSE
- Premium unleaded fuel 91
- Gasoline direct injection fuel system
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