Better MPG, lower emissions
02-02-2004, 03:00 PM
#11
Registered User
Join Date: Sep 2002
Location: N
Posts: 871
Likes: 0
Received 0 Likes
on
0 Posts
Two exhaust valves melted, creating holes in two cylinders of my Nissan Sunny beater so I was running on two cylinders for awhile. The vibration and resultant stresses from the engine were terrible. It took a second's worth of hesitation before the car would get moving. It was also a carb so fuel was just getting dumped out the exhaust without burning, causing fuel consumption to double.
Granted, this was not normal operation, but I bet with modern electronics there are still lots to think about. Running only 3 out of 4 cylinders might cause some uneven rotation in the crank or vibration, so you'd be limited to even factors of cylinder count for example.
///Robin
Granted, this was not normal operation, but I bet with modern electronics there are still lots to think about. Running only 3 out of 4 cylinders might cause some uneven rotation in the crank or vibration, so you'd be limited to even factors of cylinder count for example.
///Robin
02-02-2004, 03:18 PM
#12
Registered User
Join Date: Oct 2002
Location: Melbourne
Posts: 167
Likes: 0
Received 0 Likes
on
0 Posts
I remember seeing an advert here a few years ago for a Ford (I think) which could continue to run without coolant in the event of a cooling system failure by progressively shutting down cylinders to keep heat under control. Not the same thing, but interesting nonetheless.
02-02-2004, 03:42 PM
#13
Registered User
Thread Starter
Join Date: Jan 2004
Location: SF, California
Posts: 3,759
Likes: 0
Received 0 Likes
on
0 Posts
Hmm...so some good feedback so far here's more of what I've been thinking. I don't think this should compromise aggressive performance. If you floor it you would get all four cylinders, just wouldn't see much performance benefit. However if you were just cruising on the highway it would only generate the power that you need to maintain speed. No more no less.
One solution to excessive wear issues and also may help balance the engine is to change which cylinders are firing. If I'm running 2 then one cycle may be cylinders 1 and 3 and the next may be cylinder 2 and 4.
Obviously the hardest thing about this would be in the tuning, to get the engine running smoothly and to get the most benefit from the system. THe circuit design, is not that bad just deciding how to control and what inputs. Specifically I'm guessing it would need to be a combination of RPM and throttle measurement.
I've lost two plugs in my old probe and know it's possible to run just curious how much it could hurt the engine. Hmm...for me there was just a huge power loss, not too much vibration, but the probe didn't have enough power to overcome that loss of cylinders.
By nature I'm a scientist, who likes to experiment and tweak(within reason and my knowledge of course
Thanks for feedback and ideas. I've got a couple of projects/ideas in mind. Trying to find a used F20C to experiment on. Don't want to risk my new engine
One solution to excessive wear issues and also may help balance the engine is to change which cylinders are firing. If I'm running 2 then one cycle may be cylinders 1 and 3 and the next may be cylinder 2 and 4.
Obviously the hardest thing about this would be in the tuning, to get the engine running smoothly and to get the most benefit from the system. THe circuit design, is not that bad just deciding how to control and what inputs. Specifically I'm guessing it would need to be a combination of RPM and throttle measurement.
I've lost two plugs in my old probe and know it's possible to run just curious how much it could hurt the engine. Hmm...for me there was just a huge power loss, not too much vibration, but the probe didn't have enough power to overcome that loss of cylinders.
By nature I'm a scientist, who likes to experiment and tweak(within reason and my knowledge of course
Thanks for feedback and ideas. I've got a couple of projects/ideas in mind. Trying to find a used F20C to experiment on. Don't want to risk my new engine
02-02-2004, 04:17 PM
#14
This is REALLY a lost cause for an existing engine that wasn't designed for it. I still doubt the benefits of a 4 cylinder running on 2, even if it was designed for it.
If the active cylinders rotated from 1/3 to 2/4, it would definitely cause odd vibrations. Inline 4 cylinders are difficult to balance as they are, but if you go from 1/3 to 2/4 then you would have a single rotation periodically that had 2 combustions instead of 1.
If the throttle is the trigger to engage the other HALF of the engine, then you would have a point in throttle that would cause a 2X amount of power. This would not be smooth at all. If you are trying to just compensate for a head wind, or a rate of climb, then you would need to reduce throttle again, which would cut the cylinders back off.
Give it up.
If the active cylinders rotated from 1/3 to 2/4, it would definitely cause odd vibrations. Inline 4 cylinders are difficult to balance as they are, but if you go from 1/3 to 2/4 then you would have a single rotation periodically that had 2 combustions instead of 1.
If the throttle is the trigger to engage the other HALF of the engine, then you would have a point in throttle that would cause a 2X amount of power. This would not be smooth at all. If you are trying to just compensate for a head wind, or a rate of climb, then you would need to reduce throttle again, which would cut the cylinders back off.
Give it up.
02-02-2004, 04:41 PM
#15
Registered User
Gernby is right - this is far more practical on a V-8, due to the angles of the reciprocating parts and the flexibility in firing order. The Cadillac 8-6-4 was a bust because it was executed poorly, not because it was a bad idea.
There are cars today that have cylinder shut down modes when the ECM detects a fatal problem, like overheating. This is part of the limp home mode, which can also include ignition timing changes. Alternating the cylinders (number and sequence) actually helps cool it, as the air pulled through the non firing cylinders will draw off heat, and of course halving the number of cylinders producing heat by combustion lowers the total load on the cooling system. There is no added wear on the non-firing cylinders, since they are still getting adequate lubrication.
I doubt there is much to be gained from this approach for the S2000, since it only has adequate power for normal commuting use, and if you drop two cylinders, they would be working extra hard just to keep up with traffic - you'dikely be flat out in VTEC all the time.
There are cars today that have cylinder shut down modes when the ECM detects a fatal problem, like overheating. This is part of the limp home mode, which can also include ignition timing changes. Alternating the cylinders (number and sequence) actually helps cool it, as the air pulled through the non firing cylinders will draw off heat, and of course halving the number of cylinders producing heat by combustion lowers the total load on the cooling system. There is no added wear on the non-firing cylinders, since they are still getting adequate lubrication.
I doubt there is much to be gained from this approach for the S2000, since it only has adequate power for normal commuting use, and if you drop two cylinders, they would be working extra hard just to keep up with traffic - you'dikely be flat out in VTEC all the time.
02-02-2004, 05:18 PM
#16
Registered User
Join Date: Nov 2003
Location: Richmond
Posts: 71
Likes: 0
Received 0 Likes
on
0 Posts
A couple of points:
1) This is not new, as others have pointed out. Cadillac's "Northstar System" has included cylinder rest modes for some years, though as others have stated this was more for heat management and so forth, not performance.
2) No one said that the ECU would have to keep the SAME cylinder(s) idle all the time, so maybe that would help with the balance problem? Our cars have the pistons in 1 & 3, 2 & 4 in the same position, but 180 deg. out of phase on the valvetrain correct?
Still though, might not be enough cylinders to allow for rest...
Matt
1) This is not new, as others have pointed out. Cadillac's "Northstar System" has included cylinder rest modes for some years, though as others have stated this was more for heat management and so forth, not performance.
2) No one said that the ECU would have to keep the SAME cylinder(s) idle all the time, so maybe that would help with the balance problem? Our cars have the pistons in 1 & 3, 2 & 4 in the same position, but 180 deg. out of phase on the valvetrain correct?
Still though, might not be enough cylinders to allow for rest...
Matt
02-03-2004, 12:36 PM
#17
Registered User
Join Date: Aug 2002
Location: Come see me after class.
Posts: 20,840
Likes: 0
Received 0 Likes
on
0 Posts
For better mpg and lower emissions, all you need is SFI (or maybe direct injection) and an O2 sensor and knock sensor for each cylinder. Then, let the computer run it as lean as possible.
02-03-2004, 12:49 PM
#18
Running a hot air intake during the winter might also improve economy and emissions. Maybe even warming the fuel before the injectors, since atomization would be improved. This would reduce power, but the fuel would be burned more completely.