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Old 01-24-2015, 01:53 AM   #1 (permalink)
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"ADDING" a rear engine to a FWD car to run at the same time.

Hi. I'm new here, so I hope I picked the best sub forum for it.

I have been researching this stuff for days, but the only posts that I can find date back to 2011 and earlier, which is very old in the world of electronics. With the takeoff of Tesla motors, I got an idea that I want to run by some people who know wayy more about this than I do.

There is a TL;DR at the bottom.

Background: I am an Electrical/Computer Engineering major and really like fast cars. I managed, barely, to convince my parents to get me a 2006 Chevy Impala SS, which is a pretty fast car, as my first car. I managed it because, although it is fast, it looks pretty docile, actually isn't too bad on the fuel economy, isn't too high in miles, is moderately cheap, well reviewed, FWD, safe, and the exhaust is pretty quiet. So basically, I managed to follow all of the "rules" for a young male's first car, while also getting a 5.3L V8 rated at 303 HP and 327lb.ft torque. The car gets EPA 19 City and 29 HWY. I actually get more like 16 city and 32 Hwy. It has Displacement on Demand(now known as "Active Fuel Management) which shuts off 4 of the cylinders while cruising, which is why there is such a huge gap between city and highway mileage.
My dream car, however, it the Tesla Model S P-85D. All electric, but insanely fast. Too bad I will probably never be able to afford that one. Either way, I would love to own a Tesla one day. I am in the process of convincing my mom to get a Volt as her next car, but it doesn't look too hopeful.

So anyway, I have an idea, but I wont be able to act on it for several years. I need to know now if it is practical, because, if something happens to this car, I need to know if I should bother keeping it or selling/scrapping it for a different car. It is perfect for the idea that I have. Funny thing is, the reason it is perfect for this idea is also the big "issue" with the car in the first place- the fact that it is a big V8 in a FWD car. When you gas it hard, weight goes to the back tires, leaving the front tires without good traction. I'm sure you guys all know about that. Either way, it is a very fast car... once it gets going.

On to the idea.

Idea: I want to add an electric engine to back of the car which will work at the same time as the front engine. This works out perfectly in my head, because the torque curves of the electric and gas engine crossfade almost perfectly. The car will be AWD, but the back wheels will do most of the work until the gas engine gets in to the torque band.
At the very least, I want to have the car become a straight-line beast, but I am waaaay more hopeful that I can actually really get into this to make a true, daily-driven hybrid. Based off the way the Tesla Model S looks, the rear engine doesn't seem to take up much space. At most, it looks like I'll lose my extra wheel space. I am going in to electrical engineering, but I am not shy when it comes to welding, fabricating, and coding. So I don't care if i have to do any of that to bring it all together. This will probably be a weekend hobby for months or years if I go for it. I obviously wont start until I have a different car to drive in the meantime.
The full plan goes like this: By the time I'm ready to do it, I hope to be able to actually take a 400HP electric motor out of a wrecked Tesla Model S, as they will hopefully be more popular in a few years. If I do manage to find a wrecked model S with the back in tact, I may just take the whole thing and see if I can use the entire rear drive train assembly. Then set it up in the car, most likely with completely custom rear axles and what not. I want it to be fully functional with regenerative braking for the back wheels and everything. I would probably start with a small battery. If it can do 10 miles, it would be perfect. I would set it up to charge off of the gas engine, which will always be on. The reason, I assume, that the gas engine would always be on is because it would be even more work to get the car to work properly without the engine on, but I'm not sure yet. I think this is a good idea anyway, because I can maybe find a way to get the Active Fuel Management(AFM) to stay on all the time. The gas engine on 4 cylinders, combined with the electric engine, should be powerful enough to accelerate the car with hardly any effort. The gas engine would also constantly charge the battery, which would make that low 10 mile range into maybe 20-30. Once the battery is totally done, I just turn the electric engine off for a while, turn AFM off, and the V8 takes on all the work like it normally would.
If i can get it to work out like this, then the next step would be to get the biggest, reasonably-sized battery and get the car to work fully electric.
I guess the car would be kind of like a Prius, but still probably less efficient, 5 times the horsepower, and with an extra 1500 Pounds to lug around.

The goal is to be a complete sleeper. Amazing fuel economy, luxurious ride(which is kinda already has... kinda), and then, when the time comes, a ridiculous amount of horsepower from all 4 wheels.

TL;DR. I am majoring in electrical engineering. I am not a professional engineer yet, but I am about mid-way, so don't be afraid to talk to me with fancy terms relating to the motor. I have a FWD Impala SS with a 300HP V8 engine in the front. In the future, I want to add a 400HP Tesla motor(or some other powerful electric motor) to the back and set the car up to run like a true hybrid for amazing efficiency, but also be able to run both engines at once for insane power. I don't want to have a massive battery, because I like my trunk space, so the V8 stays. This is one of few cars that have such a powerful engine while only being FWD, so that is why I want to try it. I'm down to make custom shafts, axles, and other various fabrication.
My main question is whether or not this idea is plausible. I will not be able to act on it for a few years, but I need to know if I should keep the car around or not.


Last edited by ciano22; 01-24-2015 at 02:09 AM..
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