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Old 09-17-2010, 09:27 PM   #39 (permalink)
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Join Date: Jul 2010
Location: Melbourne, Australia
Posts: 236

bugler - '91 Mazda 626
90 day: 35.89 mpg (US)
Thanks: 15
Thanked 25 Times in 22 Posts
Shadetree the firing order you mentioned has its benefits for more regular power and therefore should reduce lugging compared to the alternative. It does however have the disadvantage of worse balance as 2 cylinders will be going up and no cylinders will be going down.
There are trade offs for both methods and if i do progress with this mod (after changing to a manumatic) i will have to attempt both methods.
Also the ECU i have is from 1991 or probably designed a bit earlier so it doesn't appear intelligent enough to compensate the idle for the lower power. I can however tune the idle myself, i have been considering overriding the computer idle control as well as im an electronic engineer and i think i can give it a better response than the ECU does after i have made a few changes to reduce the idle level for the car in its current 4 cylinder state.

If i am just deactivating the injectors and opening up the air intake of the deactivated cylinders but leaving the pistons then definately the firing order you mentioned is the best as the unused cylinders will balance out the powered cylinders and the more regular firing order will help lugging.

elhigh your point about weight reduction and drag reduction is definately important. I had only considered this mod after reducing weight and drag (not as much as id like though). The car can accelerate with plenty of power to spare and it can maintain highway speed with power to spare. if i didn't then i wouldn't consider this mod.
I also like the idea of using the cylinders in the middle for localized heating keeping each other warm for good combustion and reduction in shaft whip

solarguy interesting to hear you were driving a 4 cylinder deactivated to a 3 cylinder for a few months must have been a wild ride. I have a friend at work that had the exact same experience of the piston breaking at the shaft only a month or 2 ago. You mention that you would have bad vibration at certain speeds, i assume this was due to vibration at a natural frequency of the engine since the removal of one of the piston heads caused a serious loss of balance rather than the engine lugging at a low RPM like i saw with mine during my very brief test drive.
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