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Automotive Why don't we see more I6s being produced?

  1. May 13, 2012 #1
    It has perfect primary and secondary balance, has a smooth power delivery, and can be very fuel efficient. So why do we see so many V6s?

    Except for BMW and the Cummins diesel, I can't think of another I6 produced today. Back at the dawn of the automotive industry, they were very popular. What changed?
  2. jcsd
  3. May 13, 2012 #2
    Better fuel economy with 4 cylinders.
    Straight 6 takes up lots of room, as you kind of have to mount it longitudinally.

    As the industry trend is to increase cabin space, reduce CO2 and increase fuel economy, smaller capacity and physically smaller engines are being used.

    It's a shame because the BMW Straight 6 is truly mighty engine.
  4. May 13, 2012 #3
    True, but I would think that for 6 cylinder applications, the straight six would be preferred. It would necessitate a slightly (around a foot or less) longer engine bay, but in all other areas, a straight 6 is superior to a V6 (I think, am i wrong?).
  5. May 13, 2012 #4
    It's horses for courses.
    Both have pros and cons, and can be engineered to work for an application.

    As a sweeping statement; it's always wrong to make sweeping statements. Especially regarding cars and engineering, as everything is a compromise. I do love straight 6's though.
  6. May 13, 2012 #5
  7. May 14, 2012 #6

    Ranger Mike

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    As usual Chris x is spot on...fyi..the straight 6 as a power brute but it was HEAVY.
    Chevrolet 230 cid had 140 Hp but weighed 465 pounds Ford's big 240 cid inline 6 made 150 hp but wieghed 449 pounds..we raced a straight line 6 , was VChevy 292 cid from factory..truck engine, made 165 HP and 280 ft pounds torque..stock.. and won many races against the flat head Ford V8s...all were nose heavy but in a truck..who cars..
  8. May 14, 2012 #7
  9. May 16, 2012 #8
    #1- Weight

    #2 Sheer size- it won't work transverse in an aerodynamic car

    #3 Thermal inefficiency- and cost of parts production

    #4 Torque rules, but Horsepower sells cars

    Just look at the I6s of history, Chryco's slant 6, Fords various models ending in the 4.9L 300, GM's 250-6, Jeep's 4.0-----the best thing about these engines is/ was that the only thing that would kill them was running out of oil. To build an engine this bullet proof, it required a lot of weight.

    Unfortunately, they were horrid to make pass emissions and lacked the RPM range to efficiently and cleanly move a vehicle.
  10. Jul 12, 2012 #9
    I think the biggest reason is fit. You have to think of a car in its totality. Most v6 cars are front drive transverse mounted. A i6 is a long motor which would be a tough fit in a engine bay. VW's vr and w engines split the differences of the classic and v design.
  11. Jul 13, 2012 #10
    As above.

    I6's need an engine bay longer than a v8, or I4, and way longer than a V6.

    In times of old, an engine bay wasn't THAT long with an I6, but these days with crumple zones, air con, pedestrian safety and increased aerodynamics, the nose cone in front of the engine must be even longer which makes for a bad car. All that length should be (in the manufacturers eyes, as posted above) taken up with passenger compartment.

    I don't see BMW venturing away from I6 in a hurry, it's their trademark and tradition almost. Most american manufacturers all went to V6 or V8, with the v8 for tradition (who in america wants to own a sports car without a "V8 buddy"?) and the V6 for cost of just chopping the front two cylinders off and dropping the price of the car without redeveloping the whole engine bay and subframe to fit an I6 in it.

    The thing with racing and I6's is that they have a high CoG compared to a V8, or V6, and even slanted over (like BMW, and TVR slant it a LOT) it has a higher and further forward CoG than a slanted I4.

    E46 m3 engines are one of the most advanced N/A I6's in the world and they weigh like 200kg+! Compare that to a turbo'd I4 with more power and you're at a 50kg weight penalty for no reason. Even LS1's are only a few kg more than an S54 engine.
  12. Jul 15, 2012 #11
    I have a related question which has been bugging me for quite awhile. If a inline 6 has perfect primary and secondary balance what is the case for two strokes, i.e., in what configuration does a two stroke have perfect primary and secondary balance? An inline 3?
  13. Jul 19, 2012 #12
    Part of my business is putting them into cars that originally had V6s or 4 cylinders.
  14. Aug 27, 2012 #13


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    I drive an XR6 (Australian car, Ford Falcon variant) which is a 4L straight six. Awesome motor for a naturally aspirated, 270hp and 400Nm, and still gets good fuel economy for a large sedan. You can get turbocharged variants (XR6T/F6)- the F6 makes more than 400 horsepower stock, and monstrous torque.

    The V6 equivalent would be the commodore V6 (SV6) and the XR6 will kill it easily. Roughly the same power but kills it in terms of torque.

    It's a nice feeling motor to drive with too
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