The Cobra has always been my favorite muscle car. It looks like it's going fast just sitting still ;-) I am disappointed to see the low coef of drag too. It turns out that Shelby created the Daytona Cobra for this exact reason. It is far more aerodynamic, which is especially important at very high speeds in racing.
The goals of building this car were 1) maximum fun, 2) enough electric performance so I won't be embarrassed at a drag strip
3) the super energy efficiency that electric brings. Goal 1 is already met. Goal 2 is getting there, and will be reached when all of the batteries are built & installed. Goal 3 is why I'm here!
The 2 speed powerglide is the choice of my friend Jeff, who is also building the same car as me. Another choice is a Gear Vendors 2 speed. Jeff will road race his at Laguna Seca, and should do well with that massive torque.
I am not yet monitoring the exact temp of the motor, but do have 120F sensor watching for that mark. It will speed up the blower that is forcing additional air through the motor. The motor has an internal fan, which might be enough using a transmission, but my lower rpms necessitate additional coooling.
The driving that I will be doing is almost all 50 mph roads. Very little in-town 25 mph stuff. I live out in the sticks and everything is a fair distance. So motor cooling, and the higher current draw for getting up to speed is less of a concern. goal 2 is more important that goal 3 :-(
As for video footage, it's already out there. Nothing much of actual driving just yet, but a lot of short videos of the build process. Starting with a bare frame and working up from there. Search for ev99saturn on youtube to find them. (my first EV build was a 1999 Saturn)
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Originally Posted by allen_dodge
ahh, I cant wait to build my own e-monster, and I always loved the looks of the cobra, though I was surprised to hear the drag coefficient was so high. Just a few things if I may...
Electric motors draw current directly proportional to load which is mostly determined by overall rolling resistance, but gear ratio also has a big effect so having multiple gears to choose from makes it much better for slow speed, stop and go type stuff even if you do lose a little power at the wheels due to drivetrain losses. However, for drag racing the direct drive is not only faster, it's also more durable, so it really depends on whether it's mainly gonna be a road car, or a strip car.
I've never seen anyone use an automatic in an EV conversion, probably for good reason, but you might be able to use a 2-speed powerglide and remove the torque converter, replacing it with a short driveshaft, basically the same way they sometimes delete the clutch in EV conversions. I'm sure it would require some fabrication and it might be more trouble than it's worth, but I know the basic principle is possible because I have seen it done on dirt track cars. I think it would be driveable on the road with no torque converter for the same reason you can drive an EV with no clutch, and even 2 gears is probably more than you need in that thing, but it would help with city mileage, since electric motors are happy running freely at a relatively high rpm to a gas motor.
While it is true that electric motors are more efficient at higher rpm, there is of course a sweet spot. The reasons for this are fairly simple, and it's been a while since I brushed up on it, but from what I remember the iron core of each pole on the rotor retains its magnetic alignment, and has some resistance to flipping its alignment each time the commutator advances. This creates heat in the iron core, but at low rpms its negligible. At higher rpms the iron core is having to realign its poles more often, and the extra heat generated in the core of the rotor is transferred to the copper windings which increases resistance. This is your enemy, both in terms of performance and efficiency. More resistance not only increases amp draw, but reduces power and torque at the same time. In extreme cases the increased amp draw creates so much heat that it creates a vicious cycle that can lead to thermal runaway which will melt your brushes and/or windings like a bus fuse, basically turning your motor into plasma. I'm not saying this is what's going to happen, but it would still be a good idea to get a motor temp gauge if you don't already have one just as a way to monitor efficiency. Long story short, monitor the motor temp in combination with amp draw to get an idea of how much load it's under, any excess heat is a sign that it's exceeded it's efficiency range or has just been run too hard for too long 
also, drafting semis is a great way to reduce your wind resistance, combined with the front grill block, belly pan and windshield rake listed above should give significant improvement. I have the same problem in my vw rabbit (COD .44 i think, even though it's a brick on wheels it is somehow more streamlined than a cobra) and it won't affect the looks as long as you have good brakes  Do you have a video camera? Would love to see some footage of it in action if you can, keep up the good work! |