# Project "EV7"...88 Mazda RX7 build



## PowerSurge (Jan 24, 2013)

Well I finally found a car for my EV build. It's an 88 RX7 (minus motor).

Goals are 70mph highway speeds, and 70 mile range between charging. Since the motor, controller, other electronics, and lithium batteries will cost upwards of $12k, this will be a pretty long term project and I am going to start with prepping the car for the conversion. Removal of all parts related to the gas engine (ignition, fuel system, etc) will be first. Then clean up the body and replace any needed body/trim parts. 

Here's my parts list, I will update this as I learn more or make changes:

Warp9 Motor
CEV adapter plate, flywheel adapter, and motor mount
Soliton1 (hope to get one, but DAMN they are $$$!)

Anyway, here's some pics. 























































The paint cleans up perfect with some polish compound...will be buffing the whole car out soon...


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## Yabert (Feb 7, 2010)

PowerSurge said:


> I plan to use a Warp9 motor, and possibly a Curtis controller (need to do more research on controllers)


More research yes! The curtis was a logical choice 10 years ago. 
But today, Soliton, Zilla and Warpdrive are the choices.


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## dougingraham (Jul 26, 2011)

I bought an 87 new off the lot and they were nice driving cars. It will make a good EV and there is probably a little more room for batteries than in my 85 RX-7.

Warp9, Soliton, and at least 60 100AH cells will get you close. Finding room for the batteries will be the difficult part. The 70mph is no problem at all. I can do that with only half my batteries. With all the batteries in I should be able to do about 100mph. It would go faster but the gearing is wrong to do that. The 70 mile range will be the issue. With only the 33 cells I have in the car now I can just make 36 miles when the temps are in the 50's or higher. With your slightly heavier car and 60 cells you will probably make your 70 miles on warm days. If you can find room I would put in 70+ cells. I was not willing to increase the weight of my car much so when I get the front battery box in place my car will be about the same as stock (52 cells). With 33 cells and the charger in the back my car is right at 600 lbs on each rear wheel. The front is light now but will also be at 600lbs.

I think you are being optimistic if you think you can do this for $12k. I am at $17k now and not complete although I have all the expensive stuff in the car.


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## PowerSurge (Jan 24, 2013)

dougingraham said:


> I bought an 87 new off the lot and they were nice driving cars. It will make a good EV and there is probably a little more room for batteries than in my 85 RX-7.
> 
> Warp9, Soliton, and at least 60 100AH cells will get you close. Finding room for the batteries will be the difficult part. The 70mph is no problem at all. I can do that with only half my batteries. With all the batteries in I should be able to do about 100mph. It would go faster but the gearing is wrong to do that. The 70 mile range will be the issue. With only the 33 cells I have in the car now I can just make 36 miles when the temps are in the 50's or higher. With your slightly heavier car and 60 cells you will probably make your 70 miles on warm days. If you can find room I would put in 70+ cells. I was not willing to increase the weight of my car much so when I get the front battery box in place my car will be about the same as stock (52 cells). With 33 cells and the charger in the back my car is right at 600 lbs on each rear wheel. The front is light now but will also be at 600lbs.
> 
> I think you are being optimistic if you think you can do this for $12k. I am at $17k now and not complete although I have all the expensive stuff in the car.


Thanks for the info. When you talk about different numbers of cells, does that mean I have to change entire battery setups every time I want to change cells? Don't I need to keep my voltage the same?


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## dougingraham (Jul 26, 2011)

PowerSurge said:


> Thanks for the info. When you talk about different numbers of cells, does that mean I have to change entire battery setups every time I want to change cells? Don't I need to keep my voltage the same?


Motor RPM is proportional to voltage. You will need a certain minimum voltage in order to get to your speed goal. The motor has a maximum allowed voltage. The motor controller can be used to limit the voltage the motor sees. So even if you have say a 170 volt limit for the motor, the battery pack voltage could be up to the limit of the controller 340 or more volts depending on the controller. The controller will prevent the voltage from exceeding the limit you set. With a controller like the Soliton you can run up to a 98 cell pack (or maybe a couple more). Extra voltage is not wasted. The motor controller converts voltage to current so the motor will see more current than the battery in this situation.

You can add more cells to increase the voltage which will also increase your range. With a performance car about the smallest size cell you want to use would be 100AH. Most of the 100AH cells can handle 8 to 10 C rates for a few seconds. This would mean 800 to 1000 amps. At 1000 amps the WarP9 motor will put out about twice the torque of the original rotary engine.

If I hadn't wanted to keep the car's weight about the same I would have put in 98 100AH cells for a high voltage pack that would give a range of about 100 miles at a cost of an additional 300 lbs. I am actually seeing a little bit over 1 mile of range per cell 100AH cell. I am hoping that will go up as I fix some mechanical issues with the car.

Good luck on your build!


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## PowerSurge (Jan 24, 2013)

dougingraham said:


> Motor RPM is proportional to voltage. You will need a certain minimum voltage in order to get to your speed goal. The motor has a maximum allowed voltage. The motor controller can be used to limit the voltage the motor sees. So even if you have say a 170 volt limit for the motor, the battery pack voltage could be up to the limit of the controller 340 or more volts depending on the controller. The controller will prevent the voltage from exceeding the limit you set. With a controller like the Soliton you can run up to a 98 cell pack (or maybe a couple more). Extra voltage is not wasted. The motor controller converts voltage to current so the motor will see more current than the battery in this situation.
> 
> You can add more cells to increase the voltage which will also increase your range. With a performance car about the smallest size cell you want to use would be 100AH. Most of the 100AH cells can handle 8 to 10 C rates for a few seconds. This would mean 800 to 1000 amps. At 1000 amps the WarP9 motor will put out about twice the torque of the original rotary engine.
> 
> ...


Very interesting. So if I understand you right, I can run more battery voltage than I want to supply to the motor, and just limit it with the controller. So if I plan to run 144v, I can start with 12 12v batteries and then add more batteries later for more range and have the controller still run 144v to the motor?


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## dougingraham (Jul 26, 2011)

PowerSurge said:


> Very interesting. So if I understand you right, I can run more battery voltage than I want to supply to the motor, and just limit it with the controller. So if I plan to run 144v, I can start with 12 12v batteries and then add more batteries later for more range and have the controller still run 144v to the motor?


Yes, thats what I mean.

You are talking about 12V batteries which implies Lead Acid. I am sorry but you won't make your range requirement if you try to use Lead Acid batteries. You can probably stuff enough lead in the car to make 30 miles for a little while but the range will drop quickly and the car will be terribly overweight requiring suspension upgrades just to support the weight. It won't be much fun to drive like this.


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## PowerSurge (Jan 24, 2013)

dougingraham said:


> Yes, thats what I mean.
> 
> You are talking about 12V batteries which implies Lead Acid. I am sorry but you won't make your range requirement if you try to use Lead Acid batteries. You can probably stuff enough lead in the car to make 30 miles for a little while but the range will drop quickly and the car will be terribly overweight requiring suspension upgrades just to support the weight. It won't be much fun to drive like this.


I don't plan to use lead batteries, I was just using that as an example to understand I don't need batteries that exactly equal my desired voltage. If I can start with 144 volt worth of batteries, and then add more in as time goes on to improve range, that would be great. I previously thought if you wanted to improve your batteries that I'd need to buy a whole new set to keep it 144 volt.


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## dougingraham (Jul 26, 2011)

PowerSurge said:


> I don't plan to use lead batteries, I was just using that as an example to understand I don't need batteries that exactly equal my desired voltage. If I can start with 144 volt worth of batteries, and then add more in as time goes on to improve range, that would be great. I previously thought if you wanted to improve your batteries that I'd need to buy a whole new set to keep it 144 volt.


You can add more in series up to the limits of the controller and for each cell you will gain a little bit more usable torque band (up to the motor voltage limit) and a little more range. For the Warp 9 I believe this is officially 170 volts and with Helwig brushes some say 192 volts.

You can add more cells in series but you have to do this carefully because the state of charge of the new cells needs to be matched to what is already in the car. A 144v pack would be around 45 cells which would be a reasonable number to start with. If you used 100AH cells that gives you a 14.4kwh pack which if you get 300wh per mile would give an estimated average range of 48 miles to flat. 130AH cells give a pack with a capacity of 18.7kwh for an estimated range of 62 miles to flat. Using 180AH cells would give a pack size of 25.9kwh with an estimated range of 86 miles. The other way to get the 86 miles would be to add more 100ah cells instead of starting out with 180ah cells. 45 cells of 180AH = 25.9kwh and 81 cells of 100AH also equals 25.9kwh. 81 cells is a nominal pack voltage of 259 volts. The cost will be similar but with the 100AH cells it is easier to find places to put them and you gain the advantages of the higher voltage. The downside is there are more cell interconnects when you are building the pack. If you choose to use a BMS there will be higher costs for the same reason. 

Of course the larger cells weigh more and the additional weight hurts the range so the above must be treated as rough estimates. There is a point of diminishing returns on adding more cells. With lithium it appears to me to be around 80 to 100 miles. You can get more range but driveability starts to suffer. With lead acid this appears to be around 15 to 20 miles.

As they say, "Your mileage may vary."


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## PowerSurge (Jan 24, 2013)

dougingraham said:


> You can add more in series up to the limits of the controller and for each cell you will gain a little bit more usable torque band (up to the motor voltage limit) and a little more range. For the Warp 9 I believe this is officially 170 volts and with Helwig brushes some say 192 volts.
> 
> You can add more cells in series but you have to do this carefully because the state of charge of the new cells needs to be matched to what is already in the car. A 144v pack would be around 45 cells which would be a reasonable number to start with. If you used 100AH cells that gives you a 14.4kwh pack which if you get 300wh per mile would give an estimated average range of 48 miles to flat. 130AH cells give a pack with a capacity of 18.7kwh for an estimated range of 62 miles to flat. Using 180AH cells would give a pack size of 25.9kwh with an estimated range of 86 miles. The other way to get the 86 miles would be to add more 100ah cells instead of starting out with 180ah cells. 45 cells of 180AH = 25.9kwh and 81 cells of 100AH also equals 25.9kwh. 81 cells is a nominal pack voltage of 259 volts. The cost will be similar but with the 100AH cells it is easier to find places to put them and you gain the advantages of the higher voltage. The downside is there are more cell interconnects when you are building the pack. If you choose to use a BMS there will be higher costs for the same reason.
> 
> ...



That's some great info. I am still learning the electronic aspects of all this. 

Since you did an RX7, do you know if there is a premade motor plate I can buy? And did you keep your clutch or go clutchless?


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## dougingraham (Jul 26, 2011)

PowerSurge said:


> Since you did an RX7, do you know if there is a premade motor plate I can buy? And did you keep your clutch or go clutchless?


I kept the clutch. You can shift a lot faster with a clutch and if you are used to driving a manual it is a pretty painless transition. You can just sit down and drive it.

The RX-7 as a conversion has one gotcha and that is the flywheel. You can't use the stock flywheel because it has a counterweight except for the Turbo II. What I ended up doing was buying a 12 lb racing flywheel and from Mazdatrix. The motor coupler and adaptor plates I got from Electro Automotive. I recommend against buying from them because they take your money and don't deliver when they say they will. Canadian EV seems to have a kit but I don't know anything about it other than that it exists. I can't tell from the pictures how it is set up. Here is the link to my build photo album.

Picassa Photo album of RX-7 EV conversion

I have descriptions on most of the photos. Since you didn't get the motor with your car, the photos of some of that might be of interest.

I will watch this thread with interest and if you have any questions please ask, or PM me. I am still working on the car but I got a little burned out last summer with about 60 hours one week right before EVCcon 2012 to get the car ready to take. Fortunately I got it done enough that I have been driving it at least 5 or 6 days a week since then.


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## PowerSurge (Jan 24, 2013)

dougingraham said:


> I kept the clutch. You can shift a lot faster with a clutch and if you are used to driving a manual it is a pretty painless transition. You can just sit down and drive it.
> 
> The RX-7 as a conversion has one gotcha and that is the flywheel. You can't use the stock flywheel because it has a counterweight except for the Turbo II. What I ended up doing was buying a 12 lb racing flywheel and from Mazdatrix. The motor coupler and adaptor plates I got from Electro Automotive. I recommend against buying from them because they take your money and don't deliver when they say they will. Canadian EV seems to have a kit but I don't know anything about it other than that it exists. I can't tell from the pictures how it is set up. Here is the link to my build photo album.
> 
> ...


I appreciate you input (and everyones!) and look forward to your advice. I had my own performance shop for 15 years, so fabrication and building 1000hp cars is no problem, but I have a lot to learn about this electric stuff


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## PowerSurge (Jan 24, 2013)

Ok, some more progress. Pulled the gas tank, filler neck, exhaust, all exhaust hangers and hardware, and all under car heat shielding. Also pulled all the rear interior out, and removed all sound deadening and any parts back there not needed for this build. 




















Also started wheeling the car out. Paint is looking great!


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## dougingraham (Jul 26, 2011)

Whats the deal with the hood? Is that a fiberglass hood where the paint is shot or can I just not see it well enough?


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## PowerSurge (Jan 24, 2013)

dougingraham said:


> Whats the deal with the hood? Is that a fiberglass hood where the paint is shot or can I just not see it well enough?


That's a really rusty steel hood that is now in the trash. I have an alloy non turbo hood coming for it.


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## PowerSurge (Jan 24, 2013)

I machined up the flywheel today. Since I don't need a ring gear, I knocked it off and then machined the inch of material that was behind it down so that it was even with the end of the pressure plate area. Then I machined the huge counterweight portion off the back. The next step is give it to a flywheel shop to zero balance it and resurface the disc area. Also saved a little more weight as the machining removed almost 5 lbs off it.


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## dougingraham (Jul 26, 2011)

Nice job with the flywheel. I think you could machine off a lot more material and be fine.


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## PowerSurge (Jan 24, 2013)

I'm sure I could, but I did all that machine work on the brake lathe at work and it took 3 hours just for that much lol.


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## PowerSurge (Jan 24, 2013)

Nothing too crazy progress wise. I replaced the non-working power window regulators with some weight saving manual setups, and I finally got my hood! This is off a convertible RX7 which comes factory with an aluminum hood.


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## PowerSurge (Jan 24, 2013)

Little more progress on the RX7....

The entire interior is out except for the seats. Dash is pulled out. I got a chance to compound out the entire car and she's looking great now! 

I also bought my Warp9 motor, just gotta figure out how to ship it here from PA to FL.


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## Thaniel (May 25, 2008)

Looking good. I've always liked that style of rx7. Seeing yours makes me miss mine.


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## PowerSurge (Jan 24, 2013)

Got the motor


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## onegreenev (May 18, 2012)

Whats the cross wire? A test wire for 12 volt testing of the motor?


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## PowerSurge (Jan 24, 2013)

onegreenev said:


> Whats the cross wire? A test wire for 12 volt testing of the motor?


No idea, that's how it was delivered, lol.


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## Thaniel (May 25, 2008)

Great stuff. Is that a 9" or 11" or?


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