Supercharger

The best layout for making serious power is a mid-engine location.

Mid-Engine benefits:

Eliminates prop-shaft.
Result: lower weight and cost

Shorter exhaust and lower exhaust back pressure.
Result: more power; lower weight

Room for a raised induction system and straighter intake path.
Result: more power

Room for bolt-on performance parts (eg supercharger)
Result: more power

Lower yaw moment of inertia.
Result: improve cornering response

Let's hope that Mazda builds a mid-engine RX-7.:D

wakeech

actually, (here's my favourite phrase) it depends... there are always advantages and disadvantages in every solution...

first off, the RX-8, and RX-7's of the past have been truly mid-engined, just in the front...



well the elimination of the prop shaft does help a little in the reduction of driveline mass, generating less parasitic loss: in reality though, this helps only when a 0.2% gain in performance is considered big. the arguement that it reduces cost is overly simplistic, but not wrong... you have to remember that in the instance of just the drivetrain, it may be cheaper to eliminate the prop shaft as a component, but it might be more expensive to design and produce a rear-end of a car which incorperates the tranny, engine, suspension, diff, etc etc etc... not to mention all the bracing that's needed to support all that stuff (see the back of the Lambo drop-top concept??), which may end you up with a heavier car... also, balance could be comprimized because of the concentration of all those heavy bits in the back of the car.



it's true that a shorter length exhaust will work more efficiently at a high rpm than a longer one, but length and diameter don't have a very big impact on back pressure, unless it's grossly undersized for the application, and there's a huge boundary layer killing your flow... anyways, yeah, shorter translates into higher rpm efficiency, but i submit for your approval the exhaust of any MR2 ever made: think that has less backpressure than a Y-pipe RX-7 with comparable components?? not with those 3 (or whatever) 180 degree bends...




i don't know what a "raised induction system" would benefit you, but a straighter intake path can easily be designed into a front engined car (ram-induction), and again having the engine in the back won't necessarily guarantee you a straighter intake path, it depends on how the engine is packaged.



room in the engine bay is completely independant of whether or not it's front or rear engined, and is compeletely dependant upon how much room the engineer left around the engine for whatever purpose... ever look in the back of a Mark I MR2?? yeah, not much room... well, okay, enough for the twincharger, but still, not much



this isn't a given... it all depends on how close together you can package everything within the wheelbase... given the properties of the rotary engine (mega small size), one could feasibly design a front mid-engined car with comparable inertial qualities to a rear-engined one...

and a final note, why i don't think an RX-7 should ever be rear-engined: it's freakin' ugly. the RX-7's long hood and sleek, round, muscular, sexy *** should never be stretched, fattened, or otherwise violated... that is all.

BryanH

Try one 180 and two 90s. At least on the MKIs it's that way.

One also has to remember that mid-engined cars require not only the typical front firewall but a rear firewall as well, and perhaps even a third firewall (between engine bay and trunk, as in the MKI MR2). This is great for structural rigidity but it adds weight. My '87 MR2 weighs more or less the same as my front-engined '85 Corolla GT-S (same engine, similar length vehicle as the MR2). The MR2 has a much stiffer chassis though, and fewer drivetrain losses (no need for power steering, no driveshaft).

With a front-midship engine layout you can achieve a fairly low polar moment of inertia, but it will never feel the same as a rear midship layout. The light front end takes very little time/effort to change direction, and the feel of pure, non-assisted rack and pinion steering is wonderful.

Supercharger

Mazda can keep the cost of a mid-engine RX-7 down by sharing major parts with other Mazda cars.

Manual and Auto gearbox: Mazda 6

The Renesis is mounted sideways across the chassis, with the intake/exhaust facing rearward.

Brakes: RX-8

Re-tune the bias.

Front Suspension: RX-8

Steering: RX-8

No trunk. No spare tire.

You can compensate for the altered weight distribution by using smaller front tires and bigger rear tires. The Porsche Boxster is an example.

A mid-engine car can look great - Ferrari 360.

wakeech

i think an even better way to share components would be to base the RX-7 on the RX-8 chassis, considering it's level of capability and the amount of money they put into developping it...

and put the motor in SIDEWAYS??? NEVER!! :p ahahahaa... jk...
the RENESIS is seriously so small you wouldn't need to do that no matter what, and usually the trunk and spare can go up front, under the hood, shielded from the radiator... and the best way to deal with the altered weight distribution is to alter the wheelbase, but again you'd basically be making a new chassis and redesigning the suspension...

i'm a purist, and when i think RX-7, i think long hood, not broken nose... who would buy a mid-engined "E-Type", or 250-series Ferrari?? not i sir, not i.
for comparison's sake, i'll see if i can find two cars which really illustrate this point well...

submitted for your approval, two 1964 250 series Ferrari racecars:

the ugly, rear engined 1964 Ferrari 250 GTO LM

the beautacious, front engined 1964 Ferrari 250 GTO Berlinetta as designed by Pininfarina (that's the one in the foreground)...

and an extra for good measure, the 1964 Ferrari 275 GTB (which is really similar to a GTO, but plush, with a stroked 250 series engine)

of course, this is in my very unhumble opinion, but i'm one for big hoods, and cable-less shifters. give it to me rotary style, baby... front mid-engined all the way.

BryanH

I don't know of any transversely mounted rotary engine application. It's been tried, too. Something to do with the output shaft location and there being no transaxle the right size/shape to deal with that.

The only mid-engined rotaries I know of all have the traditional north-south engine position.

http://community.webshots.com/photo/...5139HeFGUuZWGb
http://community.webshots.com/photo/...5234kHbtulvhGU

Sputnik

Well, it's not going to be as easy as putting a Camry V6 in an MR2, but it's not hard for a car company to design those parts.

I like the idea of a mid-engined RX7, personally. But having to design a separate chassis (as opposed to using the RX8 chassis) would be an expensive hurdle.

---jps

wakeech

i keep sayin', the RX-8 chassis DOES have the RENESIS mounted in the middle, just the front middle

Sputnik

You know what I mean.

---jps

Supercharger

Mid-Engine Rotary Race Car