DIY Electric Car Forums banner

1 - 11 of 11 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter #1
Hello all,

I've been an occasional lurker on here since 2015, now finally starting to get serious.

I live in Somerset in south west UK, where EV components seem to cost at least 30% more than the rest of the world!

Mechanically I'm pretty proficient. I've been messing with cars (mostly older cars) for 35 years now including several full restorations. Equipment-wise I have MIG welding kit which I know how to use and TIG welding kit which I'm a beginner stage. I have a small lathe and a small mill.

The victim I'm eyeing up at the moment is the 1972 Triumph GT6 I've just restored. This is now a more or less complete running and driving car. I did consider the electric route during the restoration but ended up doing a partial rebuild on the original engine and a full rebuild on the transmission. The engine rebuild doesn't seem to have been entirely successful which is one reason why the EV route is back on the table.

The GT6 is the "big brother" to the Spitfire with a coupe roof and bigger 6 cylinder 2L engine.

In standard trim it weighs about 920kgs, heavily biased to the front. Remove the engine and associated IC stuff is going to loose between 300 and 350kgs (the engine block and head alone are close to 200kgs!). The gearbox and overdrive are about 35kgs.

The original engine has around 100 bhp and 120 lb/ft. This particular car has a 3.63:1 rear end, but 3.27, 3.89 and 4.11 are easy swaps.

I'd like to at least match the original 0 - 60 time of 10 seconds (8 would be better!)

Needs to be able to reach 80 mph and maintain 70 mph.

If I can't get at least 100 miles per charge it won't be worth doing.

I know very little about power electrics except some involvement over the years with industrial 3 phase motors (0.55kW to 45 kW typically and generally 4 pole) and associated inverter drives. These don't seem to get used at all in the EV world so are presumably unsuitable?

I like the idea of direct drive, without gearbox (similar to Duncans Dubious Device) as the Triumph gearbox is a feeble and easily broken thing. Failing that I'll re-purpose something else, but would prefer to save the weight and effort if practical.

I'm a big believer in re-purposing used parts wherever possible and have been exploring the possibilities of using components for OEM EVs. For batteries I don't think there is better way. For motors/gearboxes, the packaging tends to be unhelpful for RWD though I've been wondering about the rear drive package from the Mitsubishi Outlander PHEV - not least because they are really pretty cheap. Otherwise fork lift motor maybe?

Budget? Prefer to stay under £ 10k (sterling) but not sure if this is remotely realistic. Aftermarket EV parts prices seem significantly higher in the UK than many parts of the world. Couple of conversion specialists I've spoken too seem to consider £ 30k to be the minimum! Frankly, at that money I'd be buying a used Tesla!

Look forward to your thoughts....

Thanks

Nick
 

·
Administrator
Joined
·
6,108 Posts
Hi Nick
The problem is the range
You could stick a forklift motor like mine - although it's little brother a 9 inch motor would probably be kinder to the triumph diff - in place of the gearbox - don't worry if you lose some foot room as you also lose the need for a clutch

The problem is fitting enough batteries!
I would expect a GT6 to be smaller in frontal area and considerably more aerodynamic than my device
So you would only need twice as many batteries!

Chevy Volt batteries are great - but they are large for their capacity -
I was very intent on keeping the C of G down low - the result is very very flat cornering

You could probably double stack the batteries under your bonnet - that may give you enough space
 

·
Registered
Joined
·
4,768 Posts
The GT6 is the "big brother" to the Spitfire with a coupe roof and bigger 6 cylinder 2L engine.
I met a guy who had combined the body of a Spitfire and chassis of a GT6, because he wanted a six-cylinder convertible; while there were surprising detail differences, they really are just two variants of the same car, of the same size and design. A good thing about this is that while the GT6 is relatively rare, Spitfires are much more common, even here in Canada, so there's lots of applicable knowledge.

In fact, my wife has a Spitfire, and the possibility of converting that is what brought me to this forum. The conversion turns out to not be viable for me at this time, but it certainly can be done.

I wouldn't expect to find many examples of GT6 conversions, but I was surprised to find how many Spitfire conversions are out there.

I'd like to at least match the original 0 - 60 time of 10 seconds (8 would be better!)

Needs to be able to reach 80 mph and maintain 70 mph.

If I can't get at least 100 miles per charge it won't be worth doing.
That sounds reasonable, except for the range, due to the lack of good space for battery.

I know very little about power electrics except some involvement over the years with industrial 3 phase motors (0.55kW to 45 kW typically and generally 4 pole) and associated inverter drives. These don't seem to get used at all in the EV world so are presumably unsuitable?
Those industrial applications typically use induction motors. Until about a decade ago, technically advanced EVs and conversions typically used 3-phase induction motors, and many were actually adapted from standard industrial designs - typical current practice is still 3-phase AC, but permanent magnet instead of induction. Commonly the adapted motors were wound for lower supply voltage (to match what is reasonable in a vehicle battery) and had better cooling, since they are pushed to much higher power (although not continuously) than the same size of motor used industrially. The HPEVS line of "AC-nn" motors are induction motors. Tesla used only induction motors before the Model 3. Since EV motors are always driven by a variable-frequency inverter (not line power) they can have more poles for smoother operation.

An EV's controller/inverter is fundamentally the same as an industrial VFD, but without the VFD's rectifier front-end, because they run on a DC supply; the supply (battery) voltage is as high as the highest voltage to be supplied to the motor, keeping the inverter straightforward. Of course, compact packaging and light weight are much more important in an EV, and liquid cooling is normal due to the power density.

I like the idea of direct drive, without gearbox (similar to Duncans Dubious Device) as the Triumph gearbox is a feeble and easily broken thing. Failing that I'll re-purpose something else, but would prefer to save the weight and effort if practical.
The consensus among Spitfire converters seems to be that the stock transmission is inadequate. The most popular choice for Spitfires is to change to a different transmission, but it could be eliminated. The challenge is to find a combination of motor and battery voltage with sufficient speed range, which means producing enough torque at low speed and able to turn fast enough for the car's top speed, without changing gear reduction ratio.

To determine the required torque at low speed, consider multiplying the stock engine's peak torque by the second gear ratio (2.16:1) or even the first gear ratio (3.50:1), since that's what the final drive can handle, and that's what the stock car uses to accelerate barely adequately. The top speed can be worked out from the final drive ratio and tire size, or just note what the stock engine turns in 4th (1:1) gear at the target speed.

I'm a big believer in re-purposing used parts wherever possible and have been exploring the possibilities of using components for OEM EVs. For batteries I don't think there is better way. For motors/gearboxes, the packaging tends to be unhelpful for RWD though I've been wondering about the rear drive package from the Mitsubishi Outlander PHEV - not least because they are really pretty cheap. Otherwise fork lift motor maybe?
Although production EV motors are essentially always used with a transverse transaxle - the transaxle containing two-stage reduction gearing and a differential - in most cases the motor can be separated from the transaxle to use it to drive a longitudinal transmission or to directly drive a shaft to a final drive (with suitable mounts and adapters).

In the other Spitfire build or planning threads there has been substantial discussion of what can replace the stock final drive unit (differential). Since the axle half-shafts are the lateral locating arms of the Spitfire suspension, any production EV drive unit is not directly usable: none are intended to take that kind of lateral load, although of course it might work. I think the choices are to keep the stock diff or something very similar, or to completely replace the diff, rear suspension, and rear part of the frame.

Among the drive units (motor plus transaxle), the units for the electric-only axle of a plug-in hybrid (Outlander PHEV, Highlander hybrid, RAV4 hybrid, Acura hybrids, Volvo PHEVs...) are generally low in power to be the only motor for a car, but the Triumph is light and the Outlander has more power than typical (it uses the same motor as the front axle). A common issue with these units is that they are not used continuously, so in stock form they are not adequately cooled for continuous use.
 

·
Registered
Joined
·
4,768 Posts
Last year someone was planning to convert a Spitfire:
New Mexico Spitfire
Although he had some specific components in mind that probably won't match your choices, the discussion should be useful.

In post #10 of that thread, I attached a PDF document with a table listing other Spitfire conversion projects... sorry, no GT6's.
 

·
Administrator
Joined
·
6,108 Posts
One thing I would suggest as you are in the UK

Have you ever heard of the "Hurricane"?
It was a fiberglass kit to replace the body on the Spitfire

IMHO it was a much much better looking car

It may be worth looking and seeing if anybody has one sitting in a shed somewhere
 

Attachments

·
Registered
Joined
·
3 Posts
Discussion Starter #6
Thank you all for your replies. Most helpful. Especially the links to the Spitfire conversions. Some reading to do there.

We've already restored this car.... It was a bit of a mission, but turned out ok - there'll be no more bodywork! Restoration thread is here:
http://sideways-technologies.co.uk/forums/index.php?/topic/7535-nick-chriss-gt6-mk-3/page/14/#comments
(I would post pics but it seems they need to be hosted elsewhere? I deleted my photobucket account in deep disgust some time ago, so can anyone suggest a decent alternative?)

In fact, one of the requirements of the EV conversion would be no significant mods to the structures of the car, so it could go back.

I don't know much about EVs, but I do know far too much about small chassis Triumphs. My first car back in '86 was a Herald 1200, then I built a Vitesse convertible (which has the GT6 running gear in a Herald-shaped body) from a pile of parts and I still have that today. It's been a runner ever since it's resto and has been all over Europe on many occasions. It has home-brewed EFI (megasquirt ECU) and a Toyota W58 5 speed gearbox to cure the "chocolate transmission" problem. My son completely restored a MkIV Spitfire a couple of years back, which is his every day car and also has an EFI conversion.

So, those who say the GT6 is like a Spitfire - yes, absolutely. It is. The chassis is the same bar some bracketry. Most of the body is the same - just that the GT6 has a roof and a bulge in the bonnet to clear the big engine. It also has bigger brakes and this particular version has the rotoflex rear suspension, meaning that the driveshafts are not suspension links, though as the spring is still bolted to the top of the diff, there is still a structural element to be got around if you want to use anything else. People do sometimes fit the Datsun/Subaru R160 in order to get something a bit stronger.

So, in a stock scenario, the GT6 diff has to handle 120 lb/ft x 2.65 = 318 lb/ft (427 Nm). In fact they can survive more than this if treated with a degree of respect. My Vitesse makes more like 150 lb/ft and W58 first gear is 3.28:1 giving 492 lb/ft (667Nm). I don't do many drag starts, but if I do it tends to just smoke the tyres. The current diff has survived 50k miles though it is crying a bit now. I do accept that the torque delivery is somewhat different from an electric motor, but for now I'm going to say that the OE diff is adequate. I wouldn't say that about the gearbox though. It's right on the edge at 120lb/ft.

RPM wise, direct drive with the current 3.63:1 rear,
30mph (50kph) - 1,500rpm,
50mph (80kph) - 2,600rpm
70mph (110kph) - 3,800rpm
85mph (130kph - 4,300rpm

Possible battery locations include

- Under the bonnet. Quite a bit of room here, especially in direct drive configuration and the original design expects alot of weight here (bit less would help the handling). Everything here has to be very weather-proof.
- Behind the seats there is a shelf. Some cars had "occasional rear seats" here. Suitable for a medium size dog, children under 10 or a small adult double amputee.... But also some batteries... maybe.
- In the boot area that currently houses the fuel tank and spare wheel.

I haven't yet managed to get a feel for how much battery I need (KWh) and what that might translate to in size and weight..... much more reading needed.

Thanks again

Nick
 

·
Registered
Joined
·
4,768 Posts
(I would post pics but it seems they need to be hosted elsewhere? I deleted my photobucket account in deep disgust some time ago, so can anyone suggest a decent alternative?)
External hosting can be a pain, and this forum does support directly posting images - use the "manage attachments" feature, instead of "insert image".
 

·
Registered
Joined
·
4,768 Posts
... this particular version has the rotoflex rear suspension, meaning that the driveshafts are not suspension links, though as the spring is still bolted to the top of the diff, there is still a structural element to be got around if you want to use anything else.
Interesting! I didn't know that was a factory option. I saw a photo online of this setup, and didn't realize that it was available from the factory.

It somewhat enlarges the range of possible conversions, but it is still unlikely that a salvaged production EV drive unit could go in place of the final drive without body or structure modifications, so you're still likely looking at a motor in the engine or transmission location.
 

·
Registered
Joined
·
4,768 Posts
Possible battery locations include

- Under the bonnet. Quite a bit of room here, especially in direct drive configuration and the original design expects alot of weight here (bit less would help the handling). Everything here has to be very weather-proof.
- Behind the seats there is a shelf. Some cars had "occasional rear seats" here. Suitable for a medium size dog, children under 10 or a small adult double amputee.... But also some batteries... maybe.
- In the boot area that currently houses the fuel tank and spare wheel.
As far as I have seen, battery pack location choices in Spitfire conversions are about what I would expect:
  • everyone uses the fuel tank location, which is over the rear axle
  • everyone uses the engine space (typically sharing it with the motor), and places some modules very far forward, causing an undesirable front-heavy mass distribution like (or worse than) the GT6
  • occasionally someone puts some in the trunk space.
The shelf behind the seats in a Spitfire is substantially compromised by the convertible top stowing there; of course this would not be a concern in the GT6.
 

·
Registered
Joined
·
4,768 Posts
So, in a stock scenario, the GT6 diff has to handle 120 lb/ft x 2.65 = 318 lb/ft (427 Nm). In fact they can survive more than this if treated with a degree of respect. My Vitesse makes more like 150 lb/ft and W58 first gear is 3.28:1 giving 492 lb/ft (667Nm). I don't do many drag starts, but if I do it tends to just smoke the tyres. The current diff has survived 50k miles though it is crying a bit now. I do accept that the torque delivery is somewhat different from an electric motor, but for now I'm going to say that the OE diff is adequate. I wouldn't say that about the gearbox though. It's right on the edge at 120lb/ft.

RPM wise, direct drive with the current 3.63:1 rear,
30mph (50kph) - 1,500rpm,
50mph (80kph) - 2,600rpm
70mph (110kph) - 3,800rpm
85mph (130kph - 4,300rpm
I think the characteristics of the Chevrolet Spark EV motor would be a great match; it is designed for an overall reduction ratio from motor to wheels comparable to a typical final drive ratio. It would match first-gear torque, and provide more power than the gas engine for most of the driving speed range. Unfortunately, I doubt that it would fit between the frame rails in the transmission tunnel. Most production EV motors are intended for much more gear reduction.
 

·
Registered
Joined
·
3 Posts
Discussion Starter #11
External hosting can be a pain, and this forum does support directly posting images - use the "manage attachments" feature, instead of "insert image".
Ah, thanks for that....

This should be a pic of the car on it's first outing under it's own power since 1991..... albeit petrol power......

IMG_2985cs.jpg

Nick
 
1 - 11 of 11 Posts
Top