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... What makes these cars ripe for a hybrid conversion is the transmission on them has an "output" shaft that goes to a front viscous coupled differential.

The front differential can be removed, making the cars rear-drive only. An electric motor could then be fitted where the differential once was, and power fed into the drive train through the front of the transmission.
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The electric motor would be turning at the speed of the engine, through the rear differential.
The speed statement doesn't make sense. The output to the front final drive is at transmission output speed, not engine speed (which is the speed of the transmission input); as a result, the motor would be turning at the speed of the transmission output (or the input to the differentials), not at the engine speed.
 

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... I'm interested to see where you wind up with your FWD approach.
The proposed approach here is not FWD - it doesn't replace mechanical drive of the front axle with electric drive; instead, it eliminates any drive of the front wheels (making the car just RWD), and converts it to a parallel hybrid. That gives it more peak power, but less drive traction, more total mass, and more weight on the non-driven front tires.
 

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Elephant Racing developed their own hybrid system that fits between the engine and transmission. The installation cost is $75k (you read that right), so I'm interested to see where you wind up with your FWD approach.

https://www.roadandtrack.com/new-ca...erformance-aftermarket-porsche-hybrid-system/
This is apparently the system which inspired this project idea, as noted in strathconaman's earlier post in another thread:
Re: Project AWD KERS Viper

The primary difference is mounting the motor/generator between the engine and transmission input (Vonnen) or using the front transmission output (here).
 

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I love the parallel hybrid idea, you could use the front motor of a Tesla model s, 300hp added to the 911.

Alternatively couldn’t you get a rwd 911 and just switch over the front suspension hardware to the C4 model?
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The charging could be through regen, you could actually have regen on slightly turned on all the time to charge up what you used on your bursts of acceleration.
That's called a "through the road" hybrid, and it's very inefficient.
 

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My question is on the power delivery control, when you press the throttle the gas motor will rev up and the electric motor will rev upas well, how does the electric motors rpm get determined by the road speed? No electronic speed synchronization is needed?
Applying "throttle" doesn't speed anything up; it increases torque output (whether it's an engine or any kind of electric motor in a car). Of course the car will likely speed up, which means that the motor goes faster, but not directly because of the accelerator pedal position. In an automotive application, the motor speed determines the frequency of the power supplied to the motor (plus a slip factor in the case of an induction motor), not the other way around. The only reason for management of the speed of the front and rear axles is for traction control (detecting and limiting wheelspin); synchronization is not needed for operation.
 

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Didn’t Toyota/Lexus use a parallel hybrid technology for the rear electric motor in one of their hybrid suvs?
That is not a "through the road" system.

In all Toyota and Lexus hybrids with a transverse engine and AWD, the rear wheels are powered only by an electric motor, with no mechanical connection to the engine. This includes the hybrid versions of the Highlander, RAV4, RX, NX, UX, and now even the Prius (optionally); Honda and BMW have some models which similarly have an electric-only axle. The difference between this and the system proposed above is that the Toyota system never generates power by running the engine to drive one set of wheels to drive the motor on the other set of wheels as a generator; instead, as Isaac97 mentioned these vehicles are hybrids with motor-generators connected to the engine, so they can generate from engine power without the losses of going through tires. The electric-only axle only generates for braking.

The drive to the rear wheels of these hybrid vehicles with front engines and rear electric-only drive is a series hybrid configuration.
 

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Thank you for the information Brian but I guess I’m just especially dense on this topic. Do I have the below written correctly?

If a rear engine car had an independent electric axle upfront, it would be considered a Parallel hybrid. Because the motors are disconnected from one another and paralleled through the road.

And remain a parallel hybrid when under braking or zero throttle the electric axle regenerates power back into the e-axle driving battery pack.
Yes, it would be a parallel hybrid... although parallel does not mean that the engine and electric motor are disconnected from each other, only that either can drive the vehicle without the other.

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but the minute the regen is activated while the car is being powered by the gasoline rwd engine it becomes an inefficient series hybrid, because you are using rear mounted gas engine to power up the battery of the front e-axle.
No, that's still parallel, although it's an interesting point... in any parallel hybrid the energy flow over a whole cycle of battery charging and discharging does go from engine to electric system to road, like a series hybrid does all of the time. This one is particularly inefficient because of the tire losses.

The other reason that through-the-road systems are bad is that it is inherently undesirable to the dynamics of the vehicle to be braking with one axle while driving the other, particularly with the front braking and the rear driving.

Yes, it would be a parallel hybrid, of the 'through-the-road' type as Brian said (I hadn't seen that term before, thanks for the new word!).
It's not a series hybrid - in a series hybrid, there is a completely separate generator and the engine is not connected to the wheels directly.

As a matter of fact, the front axle is a better spot for regen anyways (front axle braking is preferable). But when charging via regen you're putting extra load on the drivetrain, on the tires and on the original engine -- more wear everywhere, and probably losing at least 10% of the power (plus inefficiencies in the electric motor).
For pure track use, this is probably fine, and does allow you to reduce costs.
All true :)
Although even on a track, braking the front while driving the rear isn't good for stability.

The reduced cost (by not having a generator at the engine) also causes reduced functionality, and even the extremely cost-conscious major auto manufacturers don't cheap out in this way.
 

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For a more efficient drivetrain, how about the Tesla SDU up front and then a smaller generator connected to the transmission's front wheel output shaft? Well that's more weight and more complexity... Hybrids are hard.
That would work. Of course, with an AWD transaxle just using the stock AWD is much lighter and cheaper, and the stock AWD system plus a single motor-generator would provide a temporary power boost and regenerative braking, using all four wheels. Yes, hybrid vehicle design is inherently complex and difficult.

But it would still offer better generation capabilities, although the ideal is connection directly to the flywheel (allows generation while idling/at any speed/in neutral).
At the engine output is a good place for a motor-generator because it turns at a suitable speed without additional gearing, and stays in a suitable shaft speed range even with changes in road speed. On the other hand, generation while not driving isn't typically an important feature. Most hybrid vehicles use the hybrid system to avoid running the engine at all when stationary, in neutral, or driving at very low speed; the rare exception is someone using the vehicle as portable generator set for a work site or emergency power backup.
 

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Isaac97's idea of using the now unused output shaft of the AWD transmission is a good one if a generator can be appropriately sized for the RPM range. I'm not sure on the SW controls the cars have regarding torque split between the rear diff and front diff... i assume some custom ECU work would be required to determine the right amount of torque split to the generator based on the state of charge of the battery.
My understanding is that in the 996 generation of 911 this is not an issue, because the output shaft to the front is the same output as to the rear differential: there is no centre differential. The required speed difference between front and rear axles is accommodated by a viscous coupling between that shaft and the front differential, mounted at the differential end of the shaft. That means that a generator (or motor-generator; see my previous post) can be mounted at either end of this shaft (in front of the transaxle or behind the front unit) and will act like it is on the transmission output. The generator can be controlled to produce whatever power is desired, regardless of the AWD system operation. Both earlier and later 911 AWD systems are different - this is the easiest generation to work with.
Hagerty: Behavior modification: All-wheel drive tames the 911
 
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