DIY Cylinder Deactivation?
#1
05-03-2008, 12:50 PM
DIY Cylinder Deactivation?
I was considering doing this on the beater. Its a 1987 volvo 760 GLE (so it has the PRV V6), and has been getting the same or worse fuel economy than the 7.
The firing order is 1-6-3-5-2-4, so it alternates banks of the V6 for firing order. What I was thinking of doing was just putting a switch on the 12V wire for the injectors in each bank, so when on the highway I could shut one side off to save fuel. Although I would have to give it more throttle, this should bring the engine closer to it's BSFC "sweet spot", which is typically at higher throttle openings since there are less pumping losses and higher intake velocities.
I can imagine a couple reasons why this wouldn't work or would be harmful, but there are still a bunch of unknowns. First, The car only has 1 AFR sensor after the exhaust from both banks come together, so that would see very lean conditions since the deactivated cylinders would still be pumping air straight through. I don't know the authority that the old LH-Jetronic systems give to the AFR sensor to adjust mixture, but I doubt it'd be more than 10%. Unplugging the AFR sensor may default the mixture to the maps, so that might be a work-around, but I'm not sure on that point either.
There will be thermal differences between the banks, and worst-case-scenario they would be great enough to cause cracking... but I'm pretty positive that the coolant and oil will keep the temperature difference small enough.
The cat. converter will be seeing much leaner mixtures and may not work as effectively. I dont know whether the cat's effectiveness is based on the relative ratio of the species that it is reducing (NO, NO2, HC's, CO), in which case the relative ratios should still be OK since the firing cylinders would be close to stoich, or whether the effectiveness also depends on the amount of fresh O2 there (and an excess would cause a reduction of effectiveness).
Vibrations... the cylinders to be shut off would be evenly spaced, so instead of 6 evenly spaced firing pulses, it would only be 3 evenly spaced firing pulses. However, since its only one bank firing at a time, i dont know what sort of resonances or vibrations this may cause that wouldnt be present otherwise.
Can anyone explain any other reasons why this could be bad for the engine, or just flat out not work?
The firing order is 1-6-3-5-2-4, so it alternates banks of the V6 for firing order. What I was thinking of doing was just putting a switch on the 12V wire for the injectors in each bank, so when on the highway I could shut one side off to save fuel. Although I would have to give it more throttle, this should bring the engine closer to it's BSFC "sweet spot", which is typically at higher throttle openings since there are less pumping losses and higher intake velocities.
I can imagine a couple reasons why this wouldn't work or would be harmful, but there are still a bunch of unknowns. First, The car only has 1 AFR sensor after the exhaust from both banks come together, so that would see very lean conditions since the deactivated cylinders would still be pumping air straight through. I don't know the authority that the old LH-Jetronic systems give to the AFR sensor to adjust mixture, but I doubt it'd be more than 10%. Unplugging the AFR sensor may default the mixture to the maps, so that might be a work-around, but I'm not sure on that point either.
There will be thermal differences between the banks, and worst-case-scenario they would be great enough to cause cracking... but I'm pretty positive that the coolant and oil will keep the temperature difference small enough.
The cat. converter will be seeing much leaner mixtures and may not work as effectively. I dont know whether the cat's effectiveness is based on the relative ratio of the species that it is reducing (NO, NO2, HC's, CO), in which case the relative ratios should still be OK since the firing cylinders would be close to stoich, or whether the effectiveness also depends on the amount of fresh O2 there (and an excess would cause a reduction of effectiveness).
Vibrations... the cylinders to be shut off would be evenly spaced, so instead of 6 evenly spaced firing pulses, it would only be 3 evenly spaced firing pulses. However, since its only one bank firing at a time, i dont know what sort of resonances or vibrations this may cause that wouldnt be present otherwise.
Can anyone explain any other reasons why this could be bad for the engine, or just flat out not work?
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