EV 914's Options

[raynekat]

Whether you like 'em or not....they are definitely a wave of the future.
Not sure what I think about the whole idea myself.

Still have the rear luggage boot which is nice.

It's pretty slick the bolt in rear cradle that holds some of the batteries, Tesla motor, cooling, etc.

The "custom" look is pretty bad as to me.

https://www.youtube.com/watch?v=hJTNsH-SIqk

[930cabman]

One of my favorite parts of the 914 is the light weight. Batteries and light weight are not a fit.

The technology is at least a bunch of years away until EV's can compete with our time tested IC engines

[bbrock]

One of my favorite parts of the 914 is the light weight. Batteries and light weight are not a fit.

The technology is at least a bunch of years away until EV's can compete with our time tested IC engines

Hmm, the last 8 Le Mans winners were EV hybrids using Lithium ion batteries. Seems they can compete in at least some respects.

And again, review the examples we are talking about here. Dump part of the front battery pack and move what you can into the fuel tank compartment and you have a lightweight 914 that weighs no more than a stock six with probably a little over 100 miles of range that will smoke most ICE configurations we've stuffed into these chassis.

I'm not an EV fanboy and think they have some improvements to make before an EV will be parked in my garage, but the technology has a lot to offer even today. These two cars in particular check a lot of boxes.

[Superhawk996]

And again, review the examples we are talking about here. Dump part of the front battery pack and move what you can into the fuel tank compartment and you have a lightweight 914 that weighs no more than a stock six with probably a little over 100 miles of range that will smoke most ICE configurations we've stuffed into these chassis.

@bbrock

I think you missed the part where I was super generous with my package assumptions and said let's ASSUME we can package 62L of battery with 100% package efficiency.

I made no allowance for Battery Management System, battery cooling loop plumbing, high voltage wiring, and power electronics.

You will get nowhere near that battery capacity I calculated in the that fuel tank compartment in REALITY

Take a look a the Beetle picture closely. You'd be lucky to fit 2 of those battery modules in the volume available for the fuel tank. So maybe 10 KWh of battery capacity with only 80% of that being usable (IMG:style_emoticons/default/shades.gif) You will get no where 100 miles of range on batteries that only take up the fuel tank compartment on current battery technology . Oh, and take a look at the weight of the Beetle battery pack -- I was also super generous with the weight estimate too (IMG:style_emoticons/default/laugh.gif)

You will not keep the dynamic handling character of a 914 with an EV conversion.

You're reference to LeMans is an apples to oranges comparison. I don't deny that a purpose designed EV racer can do well w.r.t. handling given the batteries will be packaged for low Cg and centralized mass . . . a cobbled 914 EV conversion is another story and the handing WILL be degraded because of the physics and the realities of where we are w.r.t. battery technology.

Seems the boundless optimism is creeping in. (IMG:style_emoticons/default/grouphug.gif)

[bbrock]

I think you missed the part where I was super generous with my package assumptions and said let's ASSUME we can package 62L of battery with 100% package efficiency.

Watch the video again. These cars have 52KWh of batteries. Twenty-six KWh are in the frunk and 26 KWh in the engine bay. The drive train PLUS rear battery pack and cooling is roughly the weight of a six cylinder engine and transmission according to the vid. Just dump the front pack altogether and you are already close to, or exceeding 100 mile range by your calculations. Now let's add whatever batteries to the fuel compartment we can to equal the weight of a full fuel tank. Your calculations indicate you get about 12KWh in 44.6 Kg of batteries that would approximate the weight of a full gas tank. Let's knock that down to 10KWh to allow for the electronics that are already in the fuel compartment. That's an extra 42 miles of range by your calculation. So we would be looking at what, 120-150 miles of range without adding any weight? I could have some fun with that.

It isn't optimism. It's just doing some math on what has already been built.

[Superhawk996]

The drive train PLUS rear battery pack and cooling is roughly the weight of a six cylinder engine and transmission according to the vid.

@bbrock

You know I can't resist a good debate. (IMG:style_emoticons/default/rolleyes.gif)

I think we are all over the map. I'm not debating that you can get 100 miles of range out of a 914 with a 26 KWh battery. That is agreed.

What I want to focus on is the falsehood that the EV conversion doesn't destroy the 914 dynamic handling character. I get people will do conversions - that's fine if they want to spend a whole lot of money to build a less capable 914 (less range than gasoline, degraded handling vs. a stock 914, and shitty range as compared to purpose designed EV).

I call (IMG:style_emoticons/default/bs.gif) that the power pack unit in the video is roughly the weight of a six:

From information I can find on-line

Tesla rear motor unit: 290 lbs
26Kwh batteries (let's use the Beetle numbers) -- 280 lbs
Two cooling tanks with lets say 4 gallon of water - 32 lbs
Cradle with sufficient structure to support all the weight - 75 lbs (estimated)
Radiators -- 2 @ 4 lbs each = 8 lbs
Fans --4 @ 1 lb each = 4 lbs
Total = 689 lbs.

I'm a little unclear on where the power electronics are - are they in the front battery module or the rear? How much do they weigh (guessing about 10 lbs based on weight of Tesla SiC MOSFET inverter)? That looks like it may be the inverter DC to DC converter on the side of the rear battery pack?

Now lets talk moments of inertia

Look at this picture - that is A LOT of mass siting up at the TOP of the engine compartment. Not only the coolant but probably also the power electronics (inverter, DC/DC converter, some of the batteries, etc.) that are sitting up high in the engine compartment. This is unlike a boxer engine that puts most of that mass low in the vehicle. That is going to lead to increased propensity for the vehicle body roll as well as fore/aft pitch when braking and accelerating.



Now let's look this one



So the motor is well behind the rear axle. This is a 290 lb mass that is going to seriously degrade the handling by adding moment of inertia to the vehicle. Not only because of the mass and it's rearward placement, but also because it's running (and its gyroscopic rotation) laterially across the car. This is unlike the gas powertrain where the crankshaft, transmission gears, and differential, are centralized and rotating along the central axis of the vehicle.

Then of course we have the radiators stuck out at the farthest end. At least they are relatively light.

My main bitch with all this are the flippant remarks by those that do these conversions and gloss over them with remarks that it's about the same weight (IMG:style_emoticons/default/bs.gif) The burden of proof is not on me to prove that the vehicle has been degraded. It's PHYSICS. Those doing conversions don't get a pass on physics and math just because it's an EV.


I'm not saying my mass numbers or engineering analysis are 100% correct - I'm working with what I can find on-line. However, I am tired of having to be the one to dig out the numbers while those doing the conversions just spin a fairy tale about how good the vehicle is while driving a straight line down the motorway.

If these conversions are so good, then post numbers (mass, range, moments of inertia). Moments of inertia could easily be modeled with some basic CAD work. The onus is not on me . . . they have the components, they can measure where they are packaged, they can determine with a high degree of precision what the degradation is instead of me doing napkin math. Yet they never tell you that information . . . I wonder why?

I propose the following challenge for those that want to do an experiment to see how mass and its placement degrade vehicle handling.

Go to Home Depot, buy some 50 lb bags of pea gravel. They only cost about $4 a bag. Buy 6 bags (300 lbs). This will cost you all of $30 to learn a very important lesson in Physics. Go have a field day -- move that mass around between the Frunk, the passenger compartment, and the Trunk and see how it changes the vehicle handling. Arrange the mass longitudinally vs. laterally and note the change. If by chance you can't tell the difference . . . an EV conversion won't bother you a bit. (IMG:style_emoticons/default/laugh.gif)

[914e]

The drive train PLUS rear battery pack and cooling is roughly the weight of a six cylinder engine and transmission according to the vid.

@bbrock

You know I can't resist a good debate. (IMG:style_emoticons/default/rolleyes.gif)

I think we are all over the map. I'm not debating that you can get 100 miles of range out of a 914 with a 26 KWh battery. That is agreed.

What I want to focus on is the falsehood that the EV conversion doesn't destroy the 914 dynamic handling character. I get people will do conversions - that's fine if they want to spend a whole lot of money to build a less capable 914 (less range than gasoline, degraded handling vs. a stock 914, and shitty range as compared to purpose designed EV).

I call (IMG:style_emoticons/default/bs.gif) that the power pack unit in the video is roughly the weight of a six:

From information I can find on-line

Tesla rear motor unit: 290 lbs
26Kwh batteries (let's use the Beetle numbers) -- 280 lbs
Two cooling tanks with lets say 4 gallon of water - 32 lbs
Cradle with sufficient structure to support all the weight - 75 lbs (estimated)
Radiators -- 2 @ 4 lbs each = 8 lbs
Fans --4 @ 1 lb each = 4 lbs
Total = 689 lbs.

I'm a little unclear on where the power electronics are - are they in the front battery module or the rear? How much do they weigh (guessing about 10 lbs based on weight of Tesla SiC MOSFET inverter)? That looks like it may be the inverter DC to DC converter on the side of the rear battery pack?

Now lets talk moments of inertia

Look at this picture - that is A LOT of mass siting up at the TOP of the engine compartment. Not only the coolant but probably also the power electronics (inverter, DC/DC converter, some of the batteries, etc.) that are sitting up high in the engine compartment. This is unlike a boxer engine that puts most of that mass low in the vehicle. That is going to lead to increased propensity for the vehicle body roll as well as fore/aft pitch when braking and accelerating.



Now let's look this one



So the motor is well behind the rear axle. This is a 290 lb mass that is going to seriously degrade the handling by adding moment of inertia to the vehicle. Not only because of the mass and it's rearward placement, but also because it's running (and its gyroscopic rotation) laterially across the car. This is unlike the gas powertrain where the crankshaft, transmission gears, and differential, are centralized and rotating along the central axis of the vehicle.

Then of course we have the radiators stuck out at the farthest end. At least they are relatively light.

edited to keep this shorter

@Superhawk996

My goal is to weigh the same as a six. One thing I should point out is those conversions used a small drive unit which is roughly 198 pounds. The battery weight sounds about right. The contactors, relay, BMS and so on are in the high part of the battery box, next to the large coolant tank.

On my car I will start at the front. The front pack weighs 95 pounds, the mount, fuses, BMS around 14 pounds. So roughly the weight and location of a full full tank.

I have a 2.5 pound 12 volt battery where EGR counter was located.

The motor is a Hyper9 125 HP, 170 lbs/ft of torque it weights 120 pounds (with the inverter/controller), The transaxle dictates the motor location, the flywheel is 5.25 pounds, the pressure plate is 13 pounds, the disc is stock. I would love to find a lighter pressure plate and disc.

The two rear packs are also 95 pounds each. They are located 1-3/8" above the floor pan, the case is about 1/4" from the firewall and sit on each side of the motor. All the rear mass is a below the top of the trans axle. My engine/ battery cradle weighs 24.5 pounds, the battery cases are a total of 26.5 pounds. Two chargers at 11.5 pounds each. One at the original battery location one at the relay box location. 23 pounds of copper cabling and 15 pounds of contactors, fuses, relays, and DC to DC convertor.

So I'm a around 428 pounds at the location that from what I can find is around 350 pounds for a four and 450 pounds for a six. I believe the mass is a little lower and closer to the center than a six. From what I have found of people weighing complete engine and ancillary parts that seems to be close.I never had an engine to weigh so I have to go off what documentation I can find.

[Superhawk996]

My goal is to weigh the same as a six.

I think that is an admirable goal. Just be aware (which it seems you are) that weight isn't the only thing. It also matters where the weight is located and how it is oriented.

One thing I should point out is those conversions used a small drive unit which is roughly 198 pounds.

@914e

Whats 90 lbs among friends. (IMG:style_emoticons/default/grouphug.gif)

So we'll call the total 600 lbs for that rear module. Way to heavy and the fact is that motor is still behind the axle and is a serious degradation as far as driving dynamics are concerned. (IMG:style_emoticons/default/headbang.gif)

In all honesty, I'm intrigued by your conversion proposal. You get extra points in my book by retaining a transmission and a clutch pedal as an anti-theft device.

It sounds like you are at least trying to minimize the handling degradation and have a decent chance of achieving something close based on what you've laid out. (IMG:style_emoticons/default/first.gif) A big chunk of your success will depend where that front mass goes. If you can get it inside the fuel tank compartment, that is a huge success to keep mass centralized. As it continues to move forward from the OEM location, you'll be adding to moment of inertia even though the weight might be close to a full fuel tank. Location of the front weight matters a lot.

Do you have a build thread? If not, please start one and let's see how it shapes up.