My Bumblebee Electric, upgrading from DC to AC Options

[palmer_md]

Hello all,

I'm a long time lurker here, and I've posted a few times, but I'm starting this thread to discuss the upgrade I'm doing to my 74 bumblebee LE.

I converted the car to electric drive starting in 1995. I purchased the car in 1994 with the intention of putting in a chevy v8 or something, but after looking at what that would take I opted to put in an electric drive train. The car was sitting in a field with weeds all around and no interior, engine, transmission or anything. It took a few years to just get the car restored before I could put in the electric drive. I got the car on the road as an electric in 1997. It has been a fantastic car for commuting and it is a lot of fun to drive, but with all the lead in the car it was a bit heavy.

I decided last year that I was going to upgrade the car to lithium power which will remove about 700lbs of battery and give me more power and more range at the same time. I purchased a gearbox (BorgWarner 31-03) that is the same as a Tesla Roadster, and I got a Siemens induction motor and inverter that will give me almost as much power as the Roadster. I should end up with a little less weight than the Roadster which should allow me to have similar performance numbers...assuming I can get enough grip from the tires.

In order to fit this motor and gearbox under the hood, I'm going to have to remove the firewall between the trunk and the motor bay. The gearbox sits between the axles (obviously) and the motor will sit above it (hence the space time conflict with the firewall). This is not a problem since I've seen posts with this firewall and trunk floor removed and then triangulating by putting a bar between the strut towers and then two more from the towers down to the rear trans cross bar in the trunk. This part of the build is all pretty clear in my mind. The connection between the strut towers works perfect as an upper mounting point for the motor and gearbox. Existing motor and trans mounting locations work for the lower support.

The area where I have a question is with regard to the gearbox location. In order to put the gearbox and electric motor in the car, it installs like a transverse motor in a FWD vehicle. The gearbox is mounted slightly to the driver side of the vehicle and the motor is to the passenger side. So instead of the existing 901 getting installed exactly in the center between the two wheels, I'll have to mount the eGearDrive about 5" toward the driver side of the car comparatively, and then I'll have to put in an intermediate half shaft on the passenger side to allow for the articulating portion of the axles to both be equal length (about 5" shorter than stock). Anyhow, this is my question, and one that I thought I'd ask for help here first before heading to a drive shaft shop to get opinions. Will the suspension work well with 5" shorter drive axles. It means probably steeper angles as the suspension articulates, but I think it should work. I just don't have any experience in this area and I'm going to have to get some help with this decision before I start cutting the trunk apart to install all of it. If it does not look like it is going to work I'll have to come up with a plan "B".

I'll post some pictures in a later post, but I wanted to get the question about the drive shafts out there since I need that answered.

Thanks,
Michael

[palmer_md]

I'm still looking for some information about suspension travel. My question in post #6 was not answered. How much suspension travel does a 914 have?

My car is sitting without any motor or transmission, and just for the sake of documenting some numbers I found that the distance from the edge of the fender to the center of the wheel is about 14" when sitting like this. When I jack up the car and let the wheel "hang" it extends to 15". When I loaded all my batteries into the car is dropped to 12". I'll have another 250lbs to add with the motor and gearbox, so I assume it will drop another 0.5 inches. to put it at about 11.5 inches. That makes the downward travel about 3.5 inches. How much upward travel can I expect. Is there a suspension wiki somewhere? I have not found anything so far regarding how much travel to expect on the rear suspension (nor the front).

[slivel]

I'm still looking for some information about suspension travel. My question in post #6 was not answered. How much suspension travel does a 914 have?

My car is sitting without any motor or transmission, and just for the sake of documenting some numbers I found that the distance from the edge of the fender to the center of the wheel is about 14" when sitting like this. When I jack up the car and let the wheel "hang" it extends to 15". When I loaded all my batteries into the car is dropped to 12". I'll have another 250lbs to add with the motor and gearbox, so I assume it will drop another 0.5 inches. to put it at about 11.5 inches. That makes the downward travel about 3.5 inches. How much upward travel can I expect. Is there a suspension wiki somewhere? I have not found anything so far regarding how much travel to expect on the rear suspension (nor the front).

I'm not exactly sure that I understand your needs here but I'll give it a shot. It appears that you have a rough idea of the travel from full droop to full compression. Most people would do this measurement without the coil spring installed.

But for practical planning of a fully built car, realize that you can control the travel by factors such as spring rate, spring length, adjustable spring perch, and probably several others that I haven't thought of. For example my race car has 350 lb/in springs and has a real world working travel of about 1 1/2 inches. This would not be comfortable on the street but I believe that 3 inch travel could be livable. My car would go into coil bind at about 3 inches compression from static weight on wheels. You definitely don't want to go to the bump stop or to coil bind as this would effectively set your spring rate to infinity and would not be good for you or car. Perhaps others with street driven cars can add to this discussion. Good luck with your project.
Steve

[palmer_md]

I'm not exactly sure that I understand your needs here but I'll give it a shot. It appears that you have a rough idea of the travel from full droop to full compression. Most people would do this measurement without the coil spring installed.
Steve

Well, not quite. I have full droop to car sitting static. I'm missing the full compression and that is my question. How much will it compress. I suppose it does depend on the springs, but I thought I could find some information on the full travel on a stock car. I guess I could remove the springs and measure the full travel distance, but I thought asking the question here would get me a quick answer.

Are there bump stops? I guess my car did not have them when I purchased and if I had them, I guess I could easily measure it. Measuring distance to coil bind may be a bit more difficult. Perhaps I could just purchase the bump stops and then I'd know the answer to my question.

[slivel]

I'm not exactly sure that I understand your needs here but I'll give it a shot. It appears that you have a rough idea of the travel from full droop to full compression. Most people would do this measurement without the coil spring installed.
Steve

Well, not quite. I have full droop to car sitting static. I'm missing the full compression and that is my question. How much will it compress. I suppose it does depend on the springs, but I thought I could find some information on the full travel on a stock car. I guess I could remove the springs and measure the full travel distance, but I thought asking the question here would get me a quick answer.

Are there bump stops? I guess my car did not have them when I purchased and if I had them, I guess I could easily measure it. Measuring distance to coil bind may be a bit more difficult. Perhaps I could just purchase the bump stops and then I'd know the answer to my question.

Yes there are bump stops and they are located in the shock. They are hard rubber-like things slotted and installed on the shock rod and are typically removable and replaceable. On a Koni shock you remove the bump stop and then fully compress and rotate the shock to change the setting from stiff to soft or vice versa. Bump stops are the last bit of protection for the shock when undergoing a hard full compression and are intended to prevent metal on metal contact.
If you look with a flashlight up in the top of your rear shocks you should see the bump stop. I use a bent over coat hanger to retrieve the bump stop from mine when I need to remove or replace them.

Some cars have bump stops mounted to the body or frame and suspension members but to my knowledge the 914 does not use this design on any of the model years.

You can get a rough idea of the distance to coil bind by simply measuring the distance between two coils and multiplying by the number of coil gaps. Normally your suspension will get to the bump stop prior to coil bind as this is a safer transition than directly to coil bind.

In your case it may be best to build the car to completion and with the car on its wheels measure the amount of distance that you have until coil bind and try to get the distance to the bump stop. Measure this with a stiff piece of wire that runs from the bottom of the exposed shock rod to the bottom of the bump stop. If either is inadequate, go to a higher spring rate and/or longer spring. You may have to convert to a shock with an adjustable bottom spring perch. If you are expecting a large amount of suspension travel, then the post about CV joint deflection is important and you must take steps to keep the CV's within their design deflection limits. Cars are systems and one change often leads to a cascade of impacts.

[palmer_md]

Yes there are bump stops and they are located in the shock.

Ok, I forgot about that and you cant see them once installed. I installed them almost 20 years ago, and since then it has just been driven...not any work except battery watering and replacement since then.

And now I have my answer...at least close enough to an answer. I was able to take a coat hanger and with the car wheels hanging at full droop again, I got an estimate by pushing the coat hanger end against the bump stop and then marking the other end at the top of the shock. It was 6.75 inches (+/- 0.25 or so). Assuming this number is good, with a total travel length of 6.75 and the car sitting 3.5 inches up from there, that means I have another 3 inches of compression before hitting the stops. This means I'm sitting about right in the middle and I'm also not worried about drive angles with my shortened shafts. Things are looking good. Not much other progress on the car since I got sick right after Christmas. So much for taking a week off of work to work on the car. Back to weekends and evenings in the new year.