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Engine Placement Question...

Discussion in 'Technical Q&A' started by 134282, Mar 8, 2004.

  1. 134282

    134282 Four Time F1 World Champ
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    Carbon McCoy
    i feel really weird coming in this forum, so i try not to; i know NOTHING about "technical" stuff, so i try to steer clear of this place... Please bear with me, though, i have a serious question (at least, it's serious to me)...

    How come some cars are called "mid-engined" when the engine is actually in the back...?

    For instance, a TR's engine is in the back; you know it just as well as i do; find a TR, go to the back, lift up the thingie and there it is, right in front of you... So why is it called a "mid-engined" car and not a rear-engined car...? A 550's engine is in the front; it's a front-engined car... That makes sense to me... The other stuff doesn't... Anyone care to help me formulate a clearer understanding of this...?

    i'm very technically UNinclined and don't usually ponder things such as this, but some questions refuse to leave my head and so i had to ask... i'd really appreciate any response(s) that could help me understand this; thanks in advance, everyone...
     
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  3. dm_n_stuff

    dm_n_stuff Global Moderator
    Global Moderator Lifetime Rossa Owner

    Dec 10, 2003
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    Carb.

    The engine is located in the center of the chassis directly behind the passenger compartment (normally these are only 2-seater vehicles) but ahead of the center line of the rear wheels, making it Mid-engined. Porsche 911 and old style VW bug are rear engined, as the engine sits past the center line of the rear wheels.

    It's a fine line to be sure. But my 911 engine sits very far back in the rear of the car, gas tank in front, my Dino, a true mid engine, sits ahead of the rear wheels but behind the driver, in what I guess is the classic mid engine configuration, much like the Porsche 914.

    I have not looked har under the rear of the latest mid engined Ferraris, but I'm guessing the engine sits ahead of the center point of the rear wheels on those, too.

    Help any???

    Dave
     
  4. Brian C. Stradale

    Brian C. Stradale F1 Rookie
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    Mar 17, 2002
    3,603
    Dallas, TX, USA
    Dave's answer is right on... "mid-engine" means that its between the front and rear axles. Note that the new 612 is called "front mid-engine"... meaning the engine is in front of the driver, but still between the axles... many of the early Ferrari racecars were similarly front mid-engined.

    In that sense, the 360 and its predecessors are "rear mid-engine" (behind the driver but in front of the rear axle). But the default assumption of "mid-engine" is that its "rear mid-engine", so typically "rear" is dropped.

    The 911, as Dave notes, is "rear engine", meaning the engine sits over and behind the rear axle. And of course, most cars are front-engine, with engine over and often partially in front of the front axle. To be "mid engine", it needs to be completely within the axles.
     
  5. ChrisfromRI

    ChrisfromRI Karting

    Jan 28, 2003
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    Chris F
    My 308 GTB is a rear "mid-engine" configuration, and my S2000 is a front "mid-engine" configuration. They both have about the same horsepower, weigh about the same, take the exact same size OEM tires, and both are shod in identical sets of Potenza S02s (streets).

    They drive reasonably similar, although you can get on the power a little sooner in the corners with the 308 GTB, and brake a little later in the corners with the S2000.

    Both seem to have about the same spin potential in a trailing throttle oversteer situation.

    They countersteer a little different since the steering ratio is faster with S2000.

    Kind Regards, Chris
     
  6. PSk

    PSk F1 World Champ

    Nov 20, 2002
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    Technically speaking the Boxer and Testarossa are border line (rear) mid-engined cars as (ALL) the engine is NOT infront of the rear axle line.

    Porsche sell the complete range:

    944/928 - front engined.
    Boxter - (rear) mid engined.
    911 - rear engined.

    Ideally all weight should be between the wheel base of a car. This improves its polar movement (I think that is what it is called) and thus enables the car to change direction quicker ... a very useful thing on a race car.

    I think Bugati was one of the first designs to try and do this with the 'tank' car with the transverse straight 8 just infront of the rear wheels. This was unsuccessful and really way to way ahead of its time. Note this car had a for the time short wheelbase to track ratio.

    Also ofcourse were the Auto Unions (earlier in the late '30s) which had a reputation of been very hairy to drive ... one though must discuss the fact that Auto Union only had part of the solution as they still had a very long wheelbase to track ratio, and thus the car would not react as quickly as we would like nowadays.

    The next real attempt of this (and also a short wheelbase, to make real use of this) was the Lancia D50 F1 car of 1955 (I think the year is right) design by my hero Jano. He went to great lengths to put ALL the weight between the wheels and even mounted the fuel tanks in pannier tanks between the wheels too. The added bonus of this was to improve aero dynamics. Also the engine was semi stressed in that it was used as part of the chassis. Thus many firsts with this fantastic car. Interestingly the drivers did not like the car as it felt nervous to them .. one must remember they were used to 'slower' handling cars that were more controllable.

    Thus it was upto the mid-engined F1 revolution to get the weight between the wheels again but this included other huge advantages:
    - Less weight, ie. no long heavy driveshaft anymore.
    - Driver could be seated lower and thus lower the CofG of the car, and CD.

    But my this stage the mid-engined cars started to win ... and thus all drivers had to come on board.

    If Lancia had continued serious development of the D50 it would have beaten the all conquering Mercedes and slaughtered the pathetic Ferraris of the time, and it would have moved front engined cars to the limit of that design ... instead Lancia ran out of money and gave the cars to Ferrari. Ferrari butched the design (through lack of understanding?) and created the Supersqualo which was not the most successful car ever (although I think Fangio won a WC in '56 in one ... but all Ferrari had to do was keep the car moving forward for Fangio and he would have won anyway ... ie. weak competition).

    Unfortunately Jano committed suicide not long after this as he felt that he was a worn out machine ... and got in to his head that he had cancer, which was proved after his death was not true. What a shame, how awesome it would have been to have him turn up at historic racing meetings and watch what he created ... with Alfa Romeo, Ferrari and Lancia ... just a legend!

    Owe well ...

    Pete
     
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  8. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,082
    The whole architecture is a continum from the engine hanging so far in front of the front axle that the car is extremely nose heavy to the engine sitting so far behind the rear axle that the car is tail heavy.

    With the engine to the extreme front or rear there is additional room for interior space (e.g. passengers).

    With the engine in the extreme center there is lower rotational inertia at the expense of passenger space.

    When the engine (I mean the CoG of the engine) sits farther forward than the front axle and the car is cornering, the weight beyond the axle takes load off of the rear tires and transfers it to the front (already overloaded) tires. This generates understeer. In addition the weight is a considerable distance from the CoG and therefore adds greatly to the rotational inertia of the car.

    When the CoG of the engine sits behind the rear tires and the car is cornering, the weight behind the axle takes load off of the front tires and put it on the already overloaded rear tires. This generates oversteer. In addition, the weight is a considerable distance from the CoG adn therefore adds greatly to the rotational inertia of teh car.

    When the engine is between the axles there is no levering effect and load is transfered efficiently and without overloading (carefully sized) tires. Since the engine weight is nearly coincident with the CoG, there is little rotational inertia. This makes the car respond quickly to steering inputs.

    Rotational inertia is the property by which an object resists accelerating in yaw. Big inertia cars have to develop big forces to accelerate the car into a turn, take your 1968 Impala lead sled. Little inertia cars don't have as much trouble accelerating in yaw into turns, and feel crisper and more direct. However, the car can be faster than the driver and become unstable (all by themselves or under driver control). There is a balance point where the car feel directly coupled to the road but remains progressivly neutral as the limits are reached. Mid engined race cars can bite a driver faster than you can blink and eye. Mid engined road cars have been progressively refined since the Mangusta to the modern incarnations to draw that fine line between "that feels good" and "I just stuffed my car".

    There are rear mid engined cars {308,...360} and there are front mid engined cars {Panoz, S2000,...} In both cases the engine weight sits between the axles. A Vette is not considered a front mid engine car because some of the block and ancilaries extends beyond the front axle.
     
  9. 134282

    134282 Four Time F1 World Champ
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    Whoa... Ok, i had to read this a few times to get a good grasp, but i think i got it; thanks, everyone... i appreciate it.
     
  10. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
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    Interesting about the 'Vette. I just looked at a new Z06, and, yes, the front edge of the block is right on the axle centerline. Water pump, alternator, etc. are in front.

    What made me wonder is that I distinctly remember my old '72 Vette had the engine set well back. Seems over the last 30 years they've moved it forward just a bit. Also, the Vettes of that era had the engine offset to the right - supposedly to balance the driver's weight (assuming no passenger). It was very obvious looking up from under the car.
     
  11. Wasco

    Wasco Formula Junior

    Dec 9, 2003
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    Randy
    I like keep it simple. It is simply best to have a 50/50 weight distribution on your vehicle for better handling in the corners.

    the true mid engines ( a 914 comes to mind ) is as close to 50/50 as you can get. Note how you jack at one location to lift both front and rear tires off the ground to change a tire. Simularly with 308. And older vette on the other hand can be as bad as 75/25 ( big blocks ) very nose heavy. How you would not have rear tire traction problems in a sharp corner is beyond me.
     
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  13. Spasso

    Spasso F1 World Champ
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    Don't forget, the transmission on the later Vettes is now a transaxle which allows forward placement of the engine and creating more interior space.

    The explanation I got for offset engines was to provide enough room for the driver, controls and other ancillary systems that are not important to the passenger. 70's Chrysler products had a very pronounced offset in their cars also.

    DJ
     
  14. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,082
    But you can have 50/50 weight distribution by having 50% of the weight in front of the front axle and the other 50% in back of the real axle (ignoring that the chassis has to weigh something). However, this leads to large polar moment, and a car that will not turn in and one that does not like to stop turning after you get it turned in. You want things in the 50/50 "RANGE" but exactly 50/50 is not required.

    In addition, 50/50 is not ideal in that you can always simply put bigger tires on the rear (today). What is ideal is that the tire sizes front and read have a footprint equal to the weight carried at each end of the car. So with a 40/60 weight distribution, fronts of 205/35ZR18 and rears of 305/35ZR18 would be just perfect.

     
  15. mk e

    mk e F1 World Champ

    Oct 31, 2003
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    If I recall, the big blocks vettes were more like 51/49, maybe 55/45 but I don't think so. The small blocks were 50/50 for many years. ...I think they still are. A pickup or a small front drive car would be about 75/25. 308s are 35/65, better for braking and acceleration, if not optimal for cornering. I think the low polar moment pretty much makes up for the light front.
     
  16. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
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    You're right about the 'Vettes. I've weighed many of them over the years. Usually around 51%-53% front. Also, check magazine archives.

    Oh, and to pick nits: The C5 Vette has the block at/behind wheel centerline, but the accessories in front. Not mid-engine? But the 308 has most of a cylinder head behind the rear axle, yet it is considered mid-engined. Double standard?
     

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