A brief guide to electric conversions for classic cars
EV powertrain conversions can breathe new life into cars built before 1996.arstechnica.com
Great article. A lot of this vision will depend on how big the retro market becomes.
The electric GMC fully imagined -
- Thread starter hertfordnc
- Start date
Great article. A lot of this vision will depend on how big the retro market becomes.
New FedEx ev vans...
https://www.caranddriver.com/news/a38573183/fedex-electric-vans-general-motors/
Uses two less cells than the Hummer EV and drove from NYC to Washington D.C. on a single charge for it's first public voyage.
https://www.caranddriver.com/news/a38573183/fedex-electric-vans-general-motors/
Uses two less cells than the Hummer EV and drove from NYC to Washington D.C. on a single charge for it's first public voyage.
Considering what new electric vehicles cost and what newer vehicles cost to repair it wouldn't surprise me to see more activity in the retro market. The drivers power seat in my wife's 2013 Mustang stopped working. Repair estimate $1300. Luckily the diagnosis was faulty and I got it working no cost. Enough said as most of us have BTDT. Retro electric sounds pretty good to me.
Also an interesting article on the GM FedEx vans. A GMC motorhome looks like a good candidate for electric retrofit.
I was on the technical program at Patterson to talk about converting a GMC MH to all-electric. That all went up in a cloud of COVID aerosols.
In short, the project is building an all-electric vehicle inside a GMC motorhome. All the accessories that the 455 motor powered now have to be electric. It doesn't have to be developed, just copied. All EV cars have all-electric accessories.
Indeed, the aerodynamic drag is proportional the cross-sectional area x Cd (drag coefficient). Technically those two items are independent, however large trucks and buses tend to be rolling bricks with both high Area and Cd. The GMC MH is an idea candidate for EV conversion. Its X-sectional area is only 53 sf. But the Cd is way above 0.31 for the following reasons:
The 0.31 Cd was obtained on a 16-in wooden model. That's really the lower limit we could expect. And it's not just the roof ACs. Why?
Lowering drag is all about minimizing air turbulence as a vehicle pushes through air. All the following contribute to turbulence: Open grille. Large rearview mirrors. Protruding rear bumper that acts as a wind catcher. Even the headlight cavities are wind pockets. Then there's the undercarriage. All the wind has to twist and turn around the frame, mufflers, and gas tanks. Undercarriage turbulence can add 20%. Last but not least is the hurricane of swirling air inside the wheel wells. I estimate the actual Cd is 0.6-0.8.
All these things can be addressed to reduce the Cd back to 0.31. Then the value of A x Cd for a GMC would be 16.4. whereas a Tesla Model Y is 6.4. The comparison is tangerines and grapefruits. Size matters.
Besides aero-drag, there is also rolling resistance. That's a measure of how much the tires deform on pavement and also pavement roughness. By-in-large, Rolling Resistance goes up linear with speed when aero-drag is speed squared. It is important to note that required hp increased with the cube of speed for aerodynamic drag and the rolling resistance is squared with speed.
Two important vehicle energy consumptions have little to do with Aero+Rolling. And that's acceleration and hill climbing. Those energies are all about vehicle weight. Just like an ICE vehicle, the faster one does those items, the more energy it takes.
Re-generative Energy: Coasting to a stop and going downhill will put electricity back in the battery. But not all of it. The Aero+Rolling energy is lost. And so is running the accessories with AC or heater the most.
Now for why EVs are so great. The EPA issues MPGe ratings for EVs. GPGe is converting an EVs electric use to an equivalent gasoline energy MPG. The Tesla Model Y and 3 have the highest MPGe at 125! Even if an eGMC were to get mere 50 MPGe, that's a far cry from 8 MPG. Why are ICE so poor? Because ICE are mostly waste heat generators with tank-to-wheel energy of only 19%.
The economics get even better since electricity is much cheaper than gasoline.
A growing market has developed for ~12,000 to 14,000 lb day-use delivery vans. One manufacturer is Lightning eMotors in Colorado. They take Ford Transits models 150 and 350, replace the motor with electric and add bunches of batteries. Lots of stop and go. So mileage is only about 100 mileage. Winnebago has introduced a Class B "day-use' MH with a 125 mile range made by Lighting.
I comment about 23-ft vs 26-ft for conversion. Although, a 23-ft unit is 12% shorter, its weight difference is much less than that. The downside of a 23-ft is one loses three feet frame rails for batteries.
In closing, my target range is 300 miles. That's a big enough dream. Not 400. I've done a bottom up weight calc and, yes, the interior will be Spartan to not exceed 12,000 lbs. Also prefer the safer Iron Phosphate batteries.
--- Craig
In short, the project is building an all-electric vehicle inside a GMC motorhome. All the accessories that the 455 motor powered now have to be electric. It doesn't have to be developed, just copied. All EV cars have all-electric accessories.
Indeed, the aerodynamic drag is proportional the cross-sectional area x Cd (drag coefficient). Technically those two items are independent, however large trucks and buses tend to be rolling bricks with both high Area and Cd. The GMC MH is an idea candidate for EV conversion. Its X-sectional area is only 53 sf. But the Cd is way above 0.31 for the following reasons:
The 0.31 Cd was obtained on a 16-in wooden model. That's really the lower limit we could expect. And it's not just the roof ACs. Why?
Lowering drag is all about minimizing air turbulence as a vehicle pushes through air. All the following contribute to turbulence: Open grille. Large rearview mirrors. Protruding rear bumper that acts as a wind catcher. Even the headlight cavities are wind pockets. Then there's the undercarriage. All the wind has to twist and turn around the frame, mufflers, and gas tanks. Undercarriage turbulence can add 20%. Last but not least is the hurricane of swirling air inside the wheel wells. I estimate the actual Cd is 0.6-0.8.
All these things can be addressed to reduce the Cd back to 0.31. Then the value of A x Cd for a GMC would be 16.4. whereas a Tesla Model Y is 6.4. The comparison is tangerines and grapefruits. Size matters.
Besides aero-drag, there is also rolling resistance. That's a measure of how much the tires deform on pavement and also pavement roughness. By-in-large, Rolling Resistance goes up linear with speed when aero-drag is speed squared. It is important to note that required hp increased with the cube of speed for aerodynamic drag and the rolling resistance is squared with speed.
Two important vehicle energy consumptions have little to do with Aero+Rolling. And that's acceleration and hill climbing. Those energies are all about vehicle weight. Just like an ICE vehicle, the faster one does those items, the more energy it takes.
Re-generative Energy: Coasting to a stop and going downhill will put electricity back in the battery. But not all of it. The Aero+Rolling energy is lost. And so is running the accessories with AC or heater the most.
Now for why EVs are so great. The EPA issues MPGe ratings for EVs. GPGe is converting an EVs electric use to an equivalent gasoline energy MPG. The Tesla Model Y and 3 have the highest MPGe at 125! Even if an eGMC were to get mere 50 MPGe, that's a far cry from 8 MPG. Why are ICE so poor? Because ICE are mostly waste heat generators with tank-to-wheel energy of only 19%.
The economics get even better since electricity is much cheaper than gasoline.
A growing market has developed for ~12,000 to 14,000 lb day-use delivery vans. One manufacturer is Lightning eMotors in Colorado. They take Ford Transits models 150 and 350, replace the motor with electric and add bunches of batteries. Lots of stop and go. So mileage is only about 100 mileage. Winnebago has introduced a Class B "day-use' MH with a 125 mile range made by Lighting.
I comment about 23-ft vs 26-ft for conversion. Although, a 23-ft unit is 12% shorter, its weight difference is much less than that. The downside of a 23-ft is one loses three feet frame rails for batteries.
In closing, my target range is 300 miles. That's a big enough dream. Not 400. I've done a bottom up weight calc and, yes, the interior will be Spartan to not exceed 12,000 lbs. Also prefer the safer Iron Phosphate batteries.
--- Craig
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I'm highly suspicious of the 0.3 Cd value.
If you compare the frontal area of the GMC (small) getting 9mpg to a regular Class A (big) getting 7mpg, the difference in mpg isn't big enough. The bricks have a Cd of about 1.0.
If the Cd of the GMC is actually 0.3 the GMC should be getting many more mpg, like 12-14mpg.
If you compare the frontal area of the GMC (small) getting 9mpg to a regular Class A (big) getting 7mpg, the difference in mpg isn't big enough. The bricks have a Cd of about 1.0.
If the Cd of the GMC is actually 0.3 the GMC should be getting many more mpg, like 12-14mpg.
According to Jim Bounds, the wind tunnel test was done with a clean roof, and maybe without mirrors.
And no rear bumper scooping out a good 6 inches from the body
Either the Cd is much higher than 0.3, or the Olds 403/455 is really inefficient
It's a mystery to me. According to random internet source the Toronado also got 8-10 MPG. But 0-60 in sec. and a top speed of 130.
And the car had a much smaller area, this makes me wonder if the Olds motor is just really inefficient.
Todd, M
The problem is that you don't know about automotive testing and the real environment that they exist in.
Passcar versions of spark ignition engines are not very efficient all in the name of reduced cost and convenience. If we had a turbo-diesel drive train engineered for the TZE, they would most likely be turning in fuel rates of 15~18 MPG.
There is a big built in loss in every SI engine out there, think about how you control it?? Your "gas peddle" is attached to a THROTTLE PLATE. The purpose of that is to restrict the amount of air that the engine can breath.
Why do they do this? (apart from old habits)
Because they use a spark to start the fire that makes it go and with that fuel and those conditions, that spark will only work over a small fuel/air ratio. So, the amount of fuel/air mix that is let in determines the power output available. They sacrifice efficiency by creating massive pumping looses with the air throttle to make control cheap and easy.
Diesel (compression ignition) engines have to have heavier parts to put the squeeze on the air charge to get the heat to light the fuel, that makes them cost more.
Matt
The problem is that you don't know about automotive testing and the real environment that they exist in.
Passcar versions of spark ignition engines are not very efficient all in the name of reduced cost and convenience. If we had a turbo-diesel drive train engineered for the TZE, they would most likely be turning in fuel rates of 15~18 MPG.
There is a big built in loss in every SI engine out there, think about how you control it?? Your "gas peddle" is attached to a THROTTLE PLATE. The purpose of that is to restrict the amount of air that the engine can breath.
Why do they do this? (apart from old habits)
Because they use a spark to start the fire that makes it go and with that fuel and those conditions, that spark will only work over a small fuel/air ratio. So, the amount of fuel/air mix that is let in determines the power output available. They sacrifice efficiency by creating massive pumping looses with the air throttle to make control cheap and easy.
Diesel (compression ignition) engines have to have heavier parts to put the squeeze on the air charge to get the heat to light the fuel, that makes them cost more.
Matt
This is the wooden model that the 0.31 was derived from. Alex Birch's grandson was at last fall's Wisconsin meetup and brought the model. Supposedly, it was held in a wind tunnel with a post in the bottom. and the bottom was open.... not sure. Nevertheless many missing real-world features. (coffee cup for scale)
Here's a good description from Caterpillar on RV power requirements.
RV Performance Guide
It's for Diesels, of course, but the science is the same. It uses an RV Cd of 0.60.
A 1965 Aero-drag textbook lists a shape-corner rolling box as Cd = 0.86.... Round the leading and trailing edges, the Cd drops a lot .... it depends on how rounded. Cd of 0.6 quite possible. (These, too were wind tunnel models.)
RV Performance Guide
It's for Diesels, of course, but the science is the same. It uses an RV Cd of 0.60.
A 1965 Aero-drag textbook lists a shape-corner rolling box as Cd = 0.86.... Round the leading and trailing edges, the Cd drops a lot .... it depends on how rounded. Cd of 0.6 quite possible. (These, too were wind tunnel models.)
There's a photo out there of the model actually used in the wind tunnel and it's clean, no bumpers.
A slide I had prepared for the Patterson meeting. This slide shows what I described in my lengthy post #24 from last Sunday.
A special shout-out to Mike Sadlon and his fiberglass business.
While at the Wisconsin Meetup, he told me he made a fiberglass rear bumper that was narrower thereby eliminating the rear bumper protrusion. And his new bumper closed the gap between the body and the bumper also eliminating turbulence from under-barrage air. He claimed it helped with noise and improved the gas mileage.
Also in Wisconsin, a GMC coach had rear wheel fender inserts that closed up the square openings. Not sure if Mike made those; I'd be surprised if he hadn't. Those would reduce the turbulence behind the tires.
While at the Wisconsin Meetup, he told me he made a fiberglass rear bumper that was narrower thereby eliminating the rear bumper protrusion. And his new bumper closed the gap between the body and the bumper also eliminating turbulence from under-barrage air. He claimed it helped with noise and improved the gas mileage.
Also in Wisconsin, a GMC coach had rear wheel fender inserts that closed up the square openings. Not sure if Mike made those; I'd be surprised if he hadn't. Those would reduce the turbulence behind the tires.
Early on in my ownership I was trying to figure out where those rear "rounded" t-skirts came from (mine came with a set). Judging by the responses from other owners, I believe they were an aftermarket offering in the 70's. I don't know if Sadlon has made a mold, but they definitely pre-date his operation.
Jeepers creepers, who the heck is driving a 52,000 lb coach ? Can you imagine?
The heaviest Class A is a 2020 Newell at 63,600 lbs. Save up your dough. They are over $1,000,000. Most likely used by NASCAR drivers and the last John Madden.... then there are the others with more money than sense. Neverthelesss, a business expense.
A friend bought an old (2006) big Class A because it was cheap.... the he found out many spare parts were non-existent.. We GMCers at least still have those.. or workarounds.
Houston has a large consignment lot for used campers and MHs. My granddaughter loves going there to play in the "house on wheels"
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No thanks! I wouldn't want one even if money were no object. I love the GMC and a lot of that love has to do with its small size and light weight. It's really not much longer or heavier than my daily driver Suburban.
