42 mpg in a TJ

[TJ Jim]

Keep drinking the koolaid. It only gets better

 

[srimes]

Keep drinking the koolaid. It only gets better

Guy named Jim handing out koolaid

 

[srimes]

@srimes, I stopped "following the science" long ago.

View attachment 620219

big difference between science and "The Science^TM"

 

[NskLJ]

Alright boys, get out your notepads. I've got some numbers to consider!

Working on the hypothesis that 42 mpg is achievable by better matching the engine's efficiency (wants a relatively high load) to the chassis efficiency (wants to be relatively slow, like 25 mph) via elevation change. We need a road like I've drawn below, where the jeep powers uphill on leg "a" and coasts downhill on leg "b," where "b" is significantly longer and less steep, so you start and end at the same elevation. Ideally the start and end points would be the same, but finding that perfect route would be tough. As long as the start and end elevations are the same I'd consider it a valid test.

View attachment 620206


I took this video going up the mountain, behind a loaded semi going slowly.


Instantaneous mpg reading seems to be running around 15 mpg, but let's round down to 14 for this concept.

For road pitch I used google earth to measure distance and elevation that covers this section of road.
Elevation: 2280 ft to 3990, 1710 ft
Distance: 6.1mi
Pitch: 280 ft/mi

Goal is 42 mpg, uphill climb nets 14 miles for 1 gallon, which means I'd need to coast downhill with the engine off for (42-14=) 28 miles with the same elevation change. Burn 1 gallon going uphill for 14 miles, don't use any gas downhill for 28 miles. 14+28 = 42 miles on 1 gallon of gas.

28/14 = 2, so the downhill slope needs to be half as steep as the uphill slope.

So the question is, will the jeep reliably roll downhill in neutral with the engine off at with a pitch of 140 ft/mi? Pretty sure it will, as it'll coast downhill on this section at about 50 mph.

I don't consider these measurements to be accurate enough to provide "proof," I do think they provide a very strong indication that it is actually physically possible.

Rolling down a mountain in neutral with the engine off will be difficult to test safely. Maybe roll on the shoulder with the flashers on?

Coasting with engine off isn't driving a Jeep, lay off the weed

 

[Steel City 06]

Or using a capacitor that would “discharge slowly” to drive the starter motor and turn the engine “freely with no resistance”. Dude obviously has no knowledge of what happens when you connect a capacitor to a coil of wires, or how much current a starter motor pulls.

I actually added a 62-Farad capacitor (one of the Eaton OEM models) to my battery setup along with one of the overpowered and tall-geared Powermaster high-speed starters.

The starter was definitely faster than OEM without it, but with the capacitor, you can now feel the whole car lean to one side slightly when you first crank it. The instantaneous voltage sag on startup was reduced a good 1.5V or so as well. The spike only needs to last about a quarter second or so.

No real reason why, just wanted a crazy fast start.

 

[Cooper Smith]

Alright boys, get out your notepads. I've got some numbers to consider!

Working on the hypothesis that 42 mpg is achievable by better matching the engine's efficiency (wants a relatively high load) to the chassis efficiency (wants to be relatively slow, like 25 mph) via elevation change. We need a road like I've drawn below, where the jeep powers uphill on leg "a" and coasts downhill on leg "b," where "b" is significantly longer and less steep, so you start and end at the same elevation. Ideally the start and end points would be the same, but finding that perfect route would be tough. As long as the start and end elevations are the same I'd consider it a valid test.

View attachment 620206


I took this video going up the mountain, behind a loaded semi going slowly.


Instantaneous mpg reading seems to be running around 15 mpg, but let's round down to 14 for this concept.

For road pitch I used google earth to measure distance and elevation that covers this section of road.
Elevation: 2280 ft to 3990, 1710 ft
Distance: 6.1mi
Pitch: 280 ft/mi

Goal is 42 mpg, uphill climb nets 14 miles for 1 gallon, which means I'd need to coast downhill with the engine off for (42-14=) 28 miles with the same elevation change. Burn 1 gallon going uphill for 14 miles, don't use any gas downhill for 28 miles. 14+28 = 42 miles on 1 gallon of gas.

28/14 = 2, so the downhill slope needs to be half as steep as the uphill slope.

So the question is, will the jeep reliably roll downhill in neutral with the engine off at with a pitch of 140 ft/mi? Pretty sure it will, as it'll coast downhill on this section at about 50 mph.

I don't consider these measurements to be accurate enough to provide "proof," I do think they provide a very strong indication that it is actually physically possible.

Rolling down a mountain in neutral with the engine off will be difficult to test safely. Maybe roll on the shoulder with the flashers on?

Boss, a marijuana persuaded shitposter is the one making the claim. I wouldn't look too deeply into it lol

 

[Cooper Smith]

I actually added a 62-Farad capacitor (one of the Eaton OEM models) to my battery setup along with one of the overpowered and tall-geared Powermaster high-speed starters.

The starter was definitely faster than OEM without it, but with the capacitor, you can now feel the whole car lean to one side slightly when you first crank it. The instantaneous voltage sag on startup was reduced a good 1.5V or so as well. The spike only needs to last about a quarter second or so.

No real reason why, just wanted a crazy fast start.

You'd have to use a toilet as a dielectric at that point...

 

[Zorba]

I actually added a 62-Farad capacitor (one of the Eaton OEM models) to my battery setup along with one of the overpowered and tall-geared Powermaster high-speed starters.

The starter was definitely faster than OEM without it, but with the capacitor, you can now feel the whole car lean to one side slightly when you first crank it. The instantaneous voltage sag on startup was reduced a good 1.5V or so as well. The spike only needs to last about a quarter second or so.

No real reason why, just wanted a crazy fast start.

62 Farad. That still just blows my mind - when I was in high school electronics, it was explained that a 1 Farad capacitor would be room filling. Now look at the tech! "Mr Kuhn" would be as flabberghasted as I am!

 

[John’o]

Thank you! I have enjoyed this post SOOOO much!!! Seriously OP’er. No shade.

 

[Cooper Smith]

62 Farad. That still just blows my mind - when I was in high school electronics, it was explained that a 1 Farad capacitor would be room filling. Now look at the tech! "Mr Kuhn" would be as flabberghasted as I am!

The future is now! A 100 farad capacitor fits under the passenger seat these days. Even did a tire iron delete for extra weight loss while making room for my sick new cap! I haven't had to buy a battery since November of 2002, And I was born in '04!

Jeep TJ electric swap coming soon...

 

[Zorba]

The future is now! A 100 farad capacitor fits under the passenger seat these days. Even did a tire iron delete for extra weight loss while making room for my sick new cap! I haven't had to buy a battery since November of 2002, And I was born in '04!

Jeep TJ electric swap coming soon...

SuperCaps just might solve the EV battery problem - Phillip Jose Farmer predicted this with his "Battacitor" in the "Riverworld" series - charge like a capacitor, discharge like a battery.

 

[John Cooper]

The future is now! A 100 farad capacitor fits under the passenger seat these days. Even did a tire iron delete for extra weight loss while making room for my sick new cap! I haven't had to buy a battery since November of 2002, And I was born in '04!

Jeep TJ electric swap coming soon...

I think @Cooper Smith has been watching way to many of the OP's youtube videos...

 

[Steel City 06]

The future is now! A 100 farad capacitor fits under the passenger seat these days. Even did a tire iron delete for extra weight loss while making room for my sick new cap! I haven't had to buy a battery since November of 2002, And I was born in '04!

Jeep TJ electric swap coming soon...

Much smaller than that...
The 62F Eaton capacitor is only 2x3x11 inches.
https://www.eaton.com/content/dam/e...n-xtm-18-supercapacitor-module-data-sheet.pdf

62 Farad. That still just blows my mind - when I was in high school electronics, it was explained that a 1 Farad capacitor would be room filling. Now look at the tech! "Mr Kuhn" would be as flabberghasted as I am!

https://www.mouser.com/ProductDetail/Eaton-Electronics/XTM-18R0626-R?qs=BJlw7L4Cy79Jn%2BcyMqjlXg==
https://www.digikey.com/en/product-highlight/e/eaton/xtm-18-and-xvm-16-supercapacitors

Charging it up was fun. Couldn't find a good resistor so I burned up a long piece of 22 AWG wire to charge it without blowing up my battery.

 

[Steel City 06]

Eaton also makes a 500-Farad capacitor for automotive use:
https://www.eaton.com/content/dam/eaton/products/electronic-components/resources/data-sheet/eaton-xlr-lv-supercapacitor-module-data-sheet-elx1332-en.pd

That would probably start your car without a battery

 

[Zorba]

Eaton also makes a 500-Farad capacitor for automotive use:
https://www.eaton.com/content/dam/eaton/products/electronic-components/resources/data-sheet/eaton-xlr-lv-supercapacitor-module-data-sheet-elx1332-en.pd

That would probably start your car without a battery

I wonder what the charging considerations would be for such a thing. Its gonna look like a dead short to any source voltage.

 

[KennethS]

Charging it up was fun. Couldn't find a good resistor so I burned up a long piece of 22 AWG wire to charge it without blowing up my battery.

Imagine attempting to drive your Jeep by discharging that into the starter motor as our “friend” proposed.

 

[srimes]

Boss, a marijuana persuaded shitposter is the one making the claim. I wouldn't look too deeply into it lol

Oh I get it, dude was wacko. But there were several responses that it was totally impossible for a TJ to get 42mpg, so I got to thinking about it and I think it actually is possible with an ideal course. I'm just nerding out a little.

I poked around on google earth and I'm a potential spot to try it. The the other side of the mountain pass is about half as steep as this side. I could use GPS to make sure I stop and start at the same elevation. If only I was comfortable rolling down the interstate shoulder with the engine off...

 

[Cooper Smith]

I think @Cooper Smith has been watching way to many of the OP's youtube videos...

I gotta say, they are definitely eye catching.

 

[Cooper Smith]

Much smaller than that...
The 62F Eaton capacitor is only 2x3x11 inches.
https://www.eaton.com/content/dam/e...n-xtm-18-supercapacitor-module-data-sheet.pdf


https://www.mouser.com/ProductDetail/Eaton-Electronics/XTM-18R0626-R?qs=BJlw7L4Cy79Jn%2BcyMqjlXg==
https://www.digikey.com/en/product-highlight/e/eaton/xtm-18-and-xvm-16-supercapacitors

Charging it up was fun. Couldn't find a good resistor so I burned up a long piece of 22 AWG wire to charge it without blowing up my battery.

I wanna know how much those cost.

 

[TJ Jim]

I wanna know how much those cost.

$189.
https://www.digikey.com/en/products/detail/eaton-electronics-division/XTM-18R0626-R/10461229