Porsche
11-19-2006, 04:15 PM
#11
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one clear advantage with real mid-engined cars not (not front/mid) is the sound of the engine being right next to you and they are often better balanced...someone else already mentioned less powertrain loss. if you haven't driven a mid engined car (even an mr2) give it a try. i personally like it.
11-20-2006, 02:55 AM
#12
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A bunch of random perspectives:
- On a fast track (with few tight turns) I believe a rear-engined car has an advantage over a mid-engined car, because of the traction on corner exit and the grip under braking and to some extent because of improved stability (because of higher polar moment). Everywhere else it would seem a rear-mid-engine would be your best bet. In either case you'd be surprised how much time you make up when you can brake a car-length later than the Corvettes.
- I agree that front-midships is mostly marketing babble, but it is indicative of a couple of things that are benefits. First, it indicates that the engineers have pushed the motor close to the firewall, which benefits polar moment and weight bias. (For the alternative, think of Audi's engine position.) Second, it indicates they've pushed the front axle forward, which also improves weight bias.
- BMW has somehow convinced the world that 50/50 weight bias is the ideal, but I've never seen any justification for this. I suppose if you only went around corners at steady speed under neutral throttle that would be great, but if you live is a world with braking and acceleration then a rear bias is better. No doubt it's better than a front bias, though.
- All wheel drive confounds a lot of this, as it takes traction out of the picture, but nonetheless rear bias is always going to help braking.
After my experience in the last couple of years, tracking front-, mid-, and rear-engined cars it's clear to me that I'll always have at least one car with the motor in the back.
- On a fast track (with few tight turns) I believe a rear-engined car has an advantage over a mid-engined car, because of the traction on corner exit and the grip under braking and to some extent because of improved stability (because of higher polar moment). Everywhere else it would seem a rear-mid-engine would be your best bet. In either case you'd be surprised how much time you make up when you can brake a car-length later than the Corvettes.
- I agree that front-midships is mostly marketing babble, but it is indicative of a couple of things that are benefits. First, it indicates that the engineers have pushed the motor close to the firewall, which benefits polar moment and weight bias. (For the alternative, think of Audi's engine position.) Second, it indicates they've pushed the front axle forward, which also improves weight bias.
- BMW has somehow convinced the world that 50/50 weight bias is the ideal, but I've never seen any justification for this. I suppose if you only went around corners at steady speed under neutral throttle that would be great, but if you live is a world with braking and acceleration then a rear bias is better. No doubt it's better than a front bias, though.
- All wheel drive confounds a lot of this, as it takes traction out of the picture, but nonetheless rear bias is always going to help braking.
After my experience in the last couple of years, tracking front-, mid-, and rear-engined cars it's clear to me that I'll always have at least one car with the motor in the back.
11-20-2006, 05:25 AM
#13
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Originally Posted by rockville,Nov 19 2006, 10:22 AM
The "front-mid" classification is really more a marketing ploy than anything else. Basically the front-mid design is similar to a traditional front engine design. While it is often a good design practice to get the engine mounted further back in the engine bay/push the wheels further forward, it's not substantially different than a non-front-mid car. Also, some cars could be classed as front-mid depending on engine choice. Both the Jeep Wrangler and older BMW 3 series were offered with I4 and I6 motors. The shorter I4 motors were behind the front axle line. The longer I6 motors were not. So technically they were both mid-fronts when equipped with the base motor.
The reason why I mention this is because a layout where the engine is in front of the passenger compartment is largely similar regardless of whether or not the motor is 1" in front or behind the front axle. The engineers don't make a big fuss about the classification, the marketing people do. Also, historically many/most of the really old "front engined" cars were actually front-mid by the definition above. In all these cases we are basically talking about longitudinally mounted engines.
On the other hand, there can be significant differences when looking at the rear vs mid-rear configurations. When we are looking at a transverse drive the difference may not be much. The difference between the location of the engine crank and axle centerline might be just a few mm (75mm for the Ford MTX-75 used in that V8 Atom on pdcars.net). However, when we look at longitudinal drive lines such as Porsche's it makes a big difference. One puts the engine in front of the gearbox, the other puts it well behind the gear box. That is why people started talking about the difference between rear and front engined cars. BTW, in most racecars they just refer to it as rear engine even though almost all "rear" engined race cars were "mid" engined based on these definitions.
Keep in mind, while the design philosophies behind each of these layouts is real the devil is always in the details and saying one is better than the other because it's A or B just doesn't mean much.
The reason why I mention this is because a layout where the engine is in front of the passenger compartment is largely similar regardless of whether or not the motor is 1" in front or behind the front axle. The engineers don't make a big fuss about the classification, the marketing people do. Also, historically many/most of the really old "front engined" cars were actually front-mid by the definition above. In all these cases we are basically talking about longitudinally mounted engines.
On the other hand, there can be significant differences when looking at the rear vs mid-rear configurations. When we are looking at a transverse drive the difference may not be much. The difference between the location of the engine crank and axle centerline might be just a few mm (75mm for the Ford MTX-75 used in that V8 Atom on pdcars.net). However, when we look at longitudinal drive lines such as Porsche's it makes a big difference. One puts the engine in front of the gearbox, the other puts it well behind the gear box. That is why people started talking about the difference between rear and front engined cars. BTW, in most racecars they just refer to it as rear engine even though almost all "rear" engined race cars were "mid" engined based on these definitions.
Keep in mind, while the design philosophies behind each of these layouts is real the devil is always in the details and saying one is better than the other because it's A or B just doesn't mean much.
11-20-2006, 06:50 AM
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I think you misinterpreted what I was saying. We both agree that moving the weight towards the center of the car is a good thing. You are right that the engineering design objective that
11-20-2006, 07:12 AM
#15
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To me the big Porsche advantage is in braking. That rear-bias weight lets them brake so much deeper into corners and that is what wins races with otherwise similar-speed cars. Porsche is all about racing so I figure that's a continuing reason for 911 evolution.
I don't know why 50-50 distribution would be worse in street driving than some other number. My finest moments at auto-x racing where when I could command over and under-steer attitudes in mid-corner, when the car felt like it was rolling on four ball-bearings and the slightest command would shift the nose. Seems to me that is most easily done with a nearly even weight distribution?
I don't know why 50-50 distribution would be worse in street driving than some other number. My finest moments at auto-x racing where when I could command over and under-steer attitudes in mid-corner, when the car felt like it was rolling on four ball-bearings and the slightest command would shift the nose. Seems to me that is most easily done with a nearly even weight distribution?
11-20-2006, 09:27 AM
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So, in theory, the best engine-layout/weight-distribution would be mid-engine with a rear-weight bias (such as the Elise/Exige)? I hate that Porsche won't switch over to mid-engine for the 911 (or make a Cayman with 911 power). The 997 GT3 would probably be my favorite car of all time (price considered), if only it were mid-engined.
Something I was curious about but couldn't find was with Formula 1 cars. They're mid-engined, I know, but what is the weight distribution of them?
Something I was curious about but couldn't find was with Formula 1 cars. They're mid-engined, I know, but what is the weight distribution of them?
11-20-2006, 09:31 AM
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Hard to argue with anything rockville wrote. I know this is a discussion centered on handling, but when debating the pros and cons of engine placement, it is also important to think about things like engine size, engine cooling, engine maintenance, transmission layout, etc etc, to say nothing of passenger space, luggage space, and styling.
11-20-2006, 09:32 AM
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Originally Posted by Jakup,Nov 20 2006, 01:27 PM
Something I was curious about but couldn't find was with Formula 1 cars. They're mid-engined, I know, but what is the weight distribution of them?
11-20-2006, 09:45 AM
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F1 cars weight distribution likely changes from weekend to weekend. I know cars like a Formula Ford are around 40-43% front. Judging by the relative size of the F1 car