Straight six has good primary balance. Most straight six engines are quite smooth.
Smoothest idle?
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1970`s Toro mower with 3.5 horse Tecumseh motor. and Kohler K engines..
I guess my 2012 buick Verano 2.4L idles smooth. You can't tell if the engine is running unless you look at the tach.
Originally Posted By: HemiHawk
Honestly? My Jeep's 4.0 is buttery smooth (at idle). I don't know how much of that has to do with engine design and maintenance, vs it being a straight 6 setup. Maybe straight 6 BMWs are very smooth also.
All straight-sixes are very well balanced, but IME the Jeep 4.0 has some mild random shuddering at idle more related to uneven combustion events compared to some other inline sixes. Kinda like a big-cammed v8 can be perfectly balanced, but still really rough at idle just due to the cam profile causing poor cylinder scavenging at low speed. I don't know what it is about the Jeep that makes it do that, but I have noticed it. Just a hair off idle, though, and the two I've owned were extremely smooth.
Honestly? My Jeep's 4.0 is buttery smooth (at idle). I don't know how much of that has to do with engine design and maintenance, vs it being a straight 6 setup. Maybe straight 6 BMWs are very smooth also.
All straight-sixes are very well balanced, but IME the Jeep 4.0 has some mild random shuddering at idle more related to uneven combustion events compared to some other inline sixes. Kinda like a big-cammed v8 can be perfectly balanced, but still really rough at idle just due to the cam profile causing poor cylinder scavenging at low speed. I don't know what it is about the Jeep that makes it do that, but I have noticed it. Just a hair off idle, though, and the two I've owned were extremely smooth.
1990 Lexus LS400
Smoothest in order:
1) Mercedes M272 3.0 V6 - Can't even tell its idling and sounds like a turbine when I wind the tach out.
2) VW 2.5 - 5 banger. Had the weird 5 cylinder growl on romp but smooth as butter at idle.
3) Mazda 2.5 MZR and Skyactiv 2.5
4) VW 1.9 TDI
5) VW 2.slow
6) Dodge Neon 2.0
Definitely less refined the fewer cylinders. Had an ex or two with the Toyota 1AZ-FE (2.4) and to this day i still don't know why it was praised so highly, guessing it was just because the Toyota badge. That thing was no better than any 2.4-2.5 that came out around the same time.
1) Mercedes M272 3.0 V6 - Can't even tell its idling and sounds like a turbine when I wind the tach out.
2) VW 2.5 - 5 banger. Had the weird 5 cylinder growl on romp but smooth as butter at idle.
3) Mazda 2.5 MZR and Skyactiv 2.5
4) VW 1.9 TDI
5) VW 2.slow
6) Dodge Neon 2.0
Definitely less refined the fewer cylinders. Had an ex or two with the Toyota 1AZ-FE (2.4) and to this day i still don't know why it was praised so highly, guessing it was just because the Toyota badge. That thing was no better than any 2.4-2.5 that came out around the same time.
Originally Posted By: 440Magnum
Originally Posted By: HemiHawk
Honestly? My Jeep's 4.0 is buttery smooth (at idle). I don't know how much of that has to do with engine design and maintenance, vs it being a straight 6 setup. Maybe straight 6 BMWs are very smooth also.
All straight-sixes are very well balanced, but IME the Jeep 4.0 has some mild random shuddering at idle more related to uneven combustion events compared to some other inline sixes. Kinda like a big-cammed v8 can be perfectly balanced, but still really rough at idle just due to the cam profile causing poor cylinder scavenging at low speed. I don't know what it is about the Jeep that makes it do that, but I have noticed it. Just a hair off idle, though, and the two I've owned were extremely smooth.
Some inline 6 engines have less than ideal fuel/air mixture distribution, and that may be a cause.
This may be why Nissan used 6 throttle bodies in the RB26DETT.
Originally Posted By: HemiHawk
Honestly? My Jeep's 4.0 is buttery smooth (at idle). I don't know how much of that has to do with engine design and maintenance, vs it being a straight 6 setup. Maybe straight 6 BMWs are very smooth also.
All straight-sixes are very well balanced, but IME the Jeep 4.0 has some mild random shuddering at idle more related to uneven combustion events compared to some other inline sixes. Kinda like a big-cammed v8 can be perfectly balanced, but still really rough at idle just due to the cam profile causing poor cylinder scavenging at low speed. I don't know what it is about the Jeep that makes it do that, but I have noticed it. Just a hair off idle, though, and the two I've owned were extremely smooth.
Some inline 6 engines have less than ideal fuel/air mixture distribution, and that may be a cause.
This may be why Nissan used 6 throttle bodies in the RB26DETT.
1974 Dodge /6. Idling with the hood up, the only sound was the swishing of the V-belts on the pulleys.
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