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Planning performance 1993 Mazda RX-7 Conversion, details within

1K views 3 replies 4 participants last post by  polygonfla 
#1 ·
Hi, if you are curious as to who I am feel free to check out my intro thread http://www.diyelectriccar.com/forums/showthread.php?p=66965#post66965

Now on to my dilemma. Here's the thing: I found this site and started to read about stuff having to do with an EV conversion. The fact of the matter is, I can't wade through all that math. Kilowatt-hours and amps and voltage. It's all supremely thick. I feel like the only way for me to learn all this is to take classes on it, and even then, I hate math and am really not good at it.

There is good news though. 1.) Though I may be bad with math and some science theories, I am not an idiot by any means, and 2.) I am an absolute wiz with cars. I have performed lots of engine swaps, engine conversions, custom work, etc. I am fully 100% confident in my ability to do whatever mechanical work is required in the conversion.

On to what I actually want to do. I have always been in love with the RX7 FD3S, which is the curvy 1993-1995 model. The problem? While rotaries are cool, and once you actually understand them they are even cooler, they are neither super reliable nor efficient. So I have long thought, what do I want to do about this? Do I want to do like a lot of rotary enthusiasts and cling to the idea of the rotary even though in all reality there are better engine options out there? Do I want to spend the money to swap a better rotary like the Cosmo 3-rotor in? Or do I want to give up and swap a Chevy LS V8 in?

None of these options satisfied me, because with gas prices getting so high, I already feel like an indentured servant to fuel companies. My 04 GTO is bad enough, and I haven't even done any sort of tuning to make the fuel milage any worse. I can't stand to have both my cars be gas-guzzlers any longer, but I also don't want to lose the beauty of the 3rd gen RX7.

Dad told me about some of the performance cars that have all-electric powertrains and I was completely sold. My goal, regardless of how long it takes or how much money it costs, is to turn my RX7 FD into a full-electric car with performance better than the factory setup has. I would like it to have screaming performance like that car I have heard about from Tesla, but I will be satisfied with performance characteristics similar to a stock RX7 FD as long as that keeps me capable of driving some fairly long distances. I would also like to, if possible, keep the RX7's legendary 50-50 weight distribution. This shouldn't be very hard.

My main issue is this. I am not really into math or physics or science. I don't know much about advanced electricity. But if I know what I need, I can buy and install it. If somebody could just explain some of this stuff in layman's terms to me, or better yet if someone could say "this is what you need for what you are expecting" and give me basically a parts list, then I would be in perfect shape. I am aware that there are parts lists on some of the wikis and faqs, but most of those parts lists say something to the tune of "Once you figure up your kwh usage, etc. etc. etc., then you divide this drag coefficient by the sum of the totals and multiply by the root of all evil, and you have the parts you need," and I simply can't do those kinds of calculations. If the end result is that I need to take classes to learn how to do this conversion, then that's fine and I will do that. But help on the matter would be largely appreciated.

Thanks for reading.
-Ben
 
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#2 ·
It sounds like you're focusing too much on the math rather than the basic concepts.

So your goals are:
RX-7, 1993-1995
Equal to or better than ICE performance
50-50 weight distribution
Range?
Max Cost?

As the EV converters around here say:
You can have speed, range, and low-cost. Pick 2.

Others may disagree, but I think one of the first decisions is selecting your voltage. Voltage is a good indication of your top speed (as well as overall performance). 72V DC won't be hitting the highway, 120V-144V DC will. Sounds like you'll want at least 144V DC system. If you've got oodles of money you can go to a high voltage AC system.

Batteries are another big decision. Ah rating & DOD (Depth of Discharge) will determine range. If your budget is sub $10k, then you'll be looking at Lead Acids. If you're budget is $20k, then you can look at Lithiums.

If you haven't already, check out www.evalbum.com
This guy went all out... http://www.evalbum.com/260.html
Slightly less expensive... http://www.evalbum.com/120

And also check out the wiki on this site - it has some great info.
 
#3 ·
I too am a car guy and a Mechanical engineer so I know what you mean about all the electrical stuff.

It seems a lot of the cars are built by electrical experts and the detail calculations can get messy. It also appears that predicting battery performance and range is a black art. Also trying to compare battery ratings and each other when they both don't give the same information:confused: Oh and then there is the terrain factor. How much to I add for the hills in my area:confused:

I think I'm just going to copy a battery/motor/controler set up that I've seen others with similar sized cars with performance that is about what I want. Seems like as good a chance as any of getting the performance I want.
 
#4 ·
I think the previous posts are right on the money. You don’t need to be a math wiz, but do need to understand the economics of the project. I think anyone planning a conversion has to start with the budget. There is a reason all the world class performance cars cost as much as they do. You mentioned the Tesla Roadster, the battery pack alone is over $60K wholesale.

For distance you need Amp Hours. Cheap AH’s are lead, and lead weighs a lot. Performance cars try to be as light as possible. Expensive AH’s are the various lithium chemistries, but they are very new and the formulas are changing daily. Look at the problems GM is having with the batteries for the Chevy Volt. They have had to push the release date back a year because the batteries aren’t ready.

I totally want to encourage you with this. Spend some time combing through EValbum.com to get a feel for what works, and understand you will become your own R&D department for developing your own totally custom super car. I would even consider doing a small motorcycle first to get your feet wet. It is in fact what I am doing. I just got the donor bike and am pulling the engine out now.
 
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