RX-8 on LPG, the math.
02-14-2017, 07:51 AM
#1
RX-8 on LPG, the math.
Hi guys, so January 2016 I have converted my RX-8 to LPG. Frowned upon by many, but given the fact that the Renesis is guaranteed to crap out on me before 200.000 on whatever fuel it runs, I went with the cheaper alternative of LPG vs Gasoline.
I'm from Europe, and where benzin/gasoline costs roughly 1,50 euro, LPG just 0,55 euro, which is roughly a saving of 1 euro per liter. My current mileage is at an average of 15 liter per 100km. The installation cost me 1200 euro in the Czech Republic, whereas I currently live in Germany. I have the LPG installation since 95.000km, I'm not at 103.000km, which makes the installation just 8.000km old. I can drive 6,66km or every liter, so dividing 8000 by 6,66 makes 1201,21 euro. In just 1 year and 8.000km, the entire LPG installation has been paid off, and from now on, I run the car for roughly 15 euro per 100km cheaper. I bought the car for 2700 1,5 years ago, with all the maintenance I'd say a total of 3600 until now. 3600 euro multiplied by 6,66km for every liter is 24.000km to save those 3600 euro that the car has costed me ever since I bought it. Before I reach 103+24=127.000km, other maintenance costs will occur, but you get the idea. I doubt it will cost me another 1000 euro until 127.000, so it's safe to assume that by 135.000km, running on LPG has returned the cost of the LPG installation, and I saved enough money to buy myself another engine or easier, another RX-8 if the engine dies.
The advantages of LPG are for example, that the fuel is injected as a gas, versus gasoline as a liquid. So it's pretty impossible to flood an engine on LPG, nor does it wash away the oil film on the rotor housing, nor is the oil contaminated. Carbon deposits are less and the combustion temperature is colder to that of gasoline. Many people argue that LPG burns hotter, which is not true. In normal engines, the valves would overheat because they are not cooled by the injected gasoline, versus to LPG that is basically a "dry" fuel. So flash lube is added to lubricate and cool the valves. My exhaust gas temperatures even dropped by 20 degrees celsius when I drive my car on the highway (it's the only reliable measure).
There is a slight powerloss on LPG, but you can program the LPG ECU so that it switches to 100% gasoline when your press your Accelerator Pedal over 80%, it's really up to you. So you can have the best of both worlds, by injecting 100% gasoline when you require power, and 100% LPG when you require economy during cruising.
If you want to know what installation I'm using, there is currently only 1 on the market that has the "Wankel Mode", so it's easy to find if you are curious. Overall, it's more economical and even healthier for the engine to run on LPG. Yes, I currently have starting issues as you might read my threads, which is related to a dead coil. Mixture isn't ignited and the engine floods itself during starts, and almost instantly starts when I cut off fuel supply. I still have 80k miles old original coils, so it's no wonder. I will order new ones from Hitachi or NGK.
I didn't really make this thread to show off or preach how LPG is superior to gasoline, but to look at the facts. I am willing to admit that I'm wrong based on facts, and I don't expect anything more than a decent discussion about gasoline vs LPG aka "Cooking gas" and how it affects the engine, and so on.
I'm from Europe, and where benzin/gasoline costs roughly 1,50 euro, LPG just 0,55 euro, which is roughly a saving of 1 euro per liter. My current mileage is at an average of 15 liter per 100km. The installation cost me 1200 euro in the Czech Republic, whereas I currently live in Germany. I have the LPG installation since 95.000km, I'm not at 103.000km, which makes the installation just 8.000km old. I can drive 6,66km or every liter, so dividing 8000 by 6,66 makes 1201,21 euro. In just 1 year and 8.000km, the entire LPG installation has been paid off, and from now on, I run the car for roughly 15 euro per 100km cheaper. I bought the car for 2700 1,5 years ago, with all the maintenance I'd say a total of 3600 until now. 3600 euro multiplied by 6,66km for every liter is 24.000km to save those 3600 euro that the car has costed me ever since I bought it. Before I reach 103+24=127.000km, other maintenance costs will occur, but you get the idea. I doubt it will cost me another 1000 euro until 127.000, so it's safe to assume that by 135.000km, running on LPG has returned the cost of the LPG installation, and I saved enough money to buy myself another engine or easier, another RX-8 if the engine dies.
The advantages of LPG are for example, that the fuel is injected as a gas, versus gasoline as a liquid. So it's pretty impossible to flood an engine on LPG, nor does it wash away the oil film on the rotor housing, nor is the oil contaminated. Carbon deposits are less and the combustion temperature is colder to that of gasoline. Many people argue that LPG burns hotter, which is not true. In normal engines, the valves would overheat because they are not cooled by the injected gasoline, versus to LPG that is basically a "dry" fuel. So flash lube is added to lubricate and cool the valves. My exhaust gas temperatures even dropped by 20 degrees celsius when I drive my car on the highway (it's the only reliable measure).
There is a slight powerloss on LPG, but you can program the LPG ECU so that it switches to 100% gasoline when your press your Accelerator Pedal over 80%, it's really up to you. So you can have the best of both worlds, by injecting 100% gasoline when you require power, and 100% LPG when you require economy during cruising.
If you want to know what installation I'm using, there is currently only 1 on the market that has the "Wankel Mode", so it's easy to find if you are curious. Overall, it's more economical and even healthier for the engine to run on LPG. Yes, I currently have starting issues as you might read my threads, which is related to a dead coil. Mixture isn't ignited and the engine floods itself during starts, and almost instantly starts when I cut off fuel supply. I still have 80k miles old original coils, so it's no wonder. I will order new ones from Hitachi or NGK.
I didn't really make this thread to show off or preach how LPG is superior to gasoline, but to look at the facts. I am willing to admit that I'm wrong based on facts, and I don't expect anything more than a decent discussion about gasoline vs LPG aka "Cooking gas" and how it affects the engine, and so on.
02-14-2017, 11:07 AM
#2
Metatron
iTrader: (1)
Three questions about your conversion....
1 - I don't follow your math - if you are only getting 6.66 kilometers per liter, and I get 30 km on a liter of petrol, how is it cheaper?
30km/6.66 = 4.55 liters of LPG,
so 2.47 euro for 30km, versus 1.5 euro for petrol.
2 - How many liters in your trunk, and how far can you go on that?
If the cylinder only holds 30 liters, that's only a range of 200 km/120 miles.....
3 - If you have a successful LPG conversion, why did you post this, last week?
"My engine seems to flood itself every time I start it. A few times it started right away after I cut off the fuel supply by pressing the accelerator pedal all the way down. LTFT is 7-13% at Idle, 6% during cruise.
Any solutions?"
.
1 - I don't follow your math - if you are only getting 6.66 kilometers per liter, and I get 30 km on a liter of petrol, how is it cheaper?
30km/6.66 = 4.55 liters of LPG,
so 2.47 euro for 30km, versus 1.5 euro for petrol.
2 - How many liters in your trunk, and how far can you go on that?
If the cylinder only holds 30 liters, that's only a range of 200 km/120 miles.....
3 - If you have a successful LPG conversion, why did you post this, last week?
"My engine seems to flood itself every time I start it. A few times it started right away after I cut off the fuel supply by pressing the accelerator pedal all the way down. LTFT is 7-13% at Idle, 6% during cruise.
Any solutions?"
.
02-14-2017, 11:12 AM
#4
FULLY SEMI AUTOMATIC
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02-14-2017, 01:52 PM
#6
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no 9k, anyone who drives any type of fun/sports car what cars about mpg should be banned from life
02-14-2017, 02:07 PM
#7
What am I doing here?
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Three questions about your conversion....
1 - I don't follow your math - if you are only getting 6.66 kilometers per liter, and I get 30 km on a liter of petrol, how is it cheaper?
30km/6.66 = 4.55 liters of LPG,
so 2.47 euro for 30km, versus 1.5 euro for petrol.
2 - How many liters in your trunk, and how far can you go on that?
If the cylinder only holds 30 liters, that's only a range of 200 km/120 miles.....
3 - If you have a successful LPG conversion, why did you post this, last week?
"My engine seems to flood itself every time I start it. A few times it started right away after I cut off the fuel supply by pressing the accelerator pedal all the way down. LTFT is 7-13% at Idle, 6% during cruise.
Any solutions?"
.
1 - I don't follow your math - if you are only getting 6.66 kilometers per liter, and I get 30 km on a liter of petrol, how is it cheaper?
30km/6.66 = 4.55 liters of LPG,
so 2.47 euro for 30km, versus 1.5 euro for petrol.
2 - How many liters in your trunk, and how far can you go on that?
If the cylinder only holds 30 liters, that's only a range of 200 km/120 miles.....
3 - If you have a successful LPG conversion, why did you post this, last week?
"My engine seems to flood itself every time I start it. A few times it started right away after I cut off the fuel supply by pressing the accelerator pedal all the way down. LTFT is 7-13% at Idle, 6% during cruise.
Any solutions?"
.
24 mpg is is around 10 km/L.
30 km/L is close to 70 mpg. How are you doing that in an '8?
6.67 km/L is about 15.7 mpg.
Assuming you could get 10 km/L on petrol (and I doubt it), that would be 800 L for 8,000 km for 1200 Euro (at 1.5 Euro/L). The same distance on LPG (at 6.67 km/L) is about 660 Euro (at 0.55 Euro/L).
If the conversion cost 1200 Euro, Tom is close to half-way towards breaking even.
Also, he addresses the "flooding" issue in his post. Propane doesn't burn well when too far outside of stoich. I can see the combustion chamber having so much propane that it won't ignite (Mythbusters had this problem a bunch of times).
I guess, as an engineering exercise, it's interesting (I do like the benefits of a non-liquid fuel). But I can't imagine that the propane tank in the trunk is doing anything good for handling.
Last edited by NotAPreppie; 02-14-2017 at 02:12 PM.
02-15-2017, 11:17 AM
#9
Three questions about your conversion....
1 - I don't follow your math - if you are only getting 6.66 kilometers per liter, and I get 30 km on a liter of petrol, how is it cheaper?
30km/6.66 = 4.55 liters of LPG,
so 2.47 euro for 30km, versus 1.5 euro for petrol.
2 - How many liters in your trunk, and how far can you go on that?
If the cylinder only holds 30 liters, that's only a range of 200 km/120 miles.....
3 - If you have a successful LPG conversion, why did you post this, last week?
"My engine seems to flood itself every time I start it. A few times it started right away after I cut off the fuel supply by pressing the accelerator pedal all the way down. LTFT is 7-13% at Idle, 6% during cruise.
Any solutions?"
.
1 - I don't follow your math - if you are only getting 6.66 kilometers per liter, and I get 30 km on a liter of petrol, how is it cheaper?
30km/6.66 = 4.55 liters of LPG,
so 2.47 euro for 30km, versus 1.5 euro for petrol.
2 - How many liters in your trunk, and how far can you go on that?
If the cylinder only holds 30 liters, that's only a range of 200 km/120 miles.....
3 - If you have a successful LPG conversion, why did you post this, last week?
"My engine seems to flood itself every time I start it. A few times it started right away after I cut off the fuel supply by pressing the accelerator pedal all the way down. LTFT is 7-13% at Idle, 6% during cruise.
Any solutions?"
.
2. 45 liters in my trunk, 40 usable. I can drive 260km on a tank. If I run out on LPG, I can still run on petrol, and drive to the closest fuel station that offers LPG (pretty much most).
3. The engine ran fine for the entire year, and from one start to another I got these starting issues. As said, dead coil(s).
Mazda RX-8 MPG - Actual MPG from 631 Mazda RX-8 owners
Austin Gas Prices - Find Cheap Gas Prices in Texas
https://www.google.de/webhp?sourceid...euro+per+liter
You are running your RX-8's in the US cheaper than a ******* Toyota Aygo in Europe. Try it, find a car that takes less than 4,32 liters per 100km, running on Petrol, on Fuelly.com. You won't. Or find me a car that runs just as expensive in the US as an RX-8 in Europe. That's 42liters to 100km, or rather, a truck: 2007 Freightliner Columbia MPG - Actual MPG from 6 2007 Freightliner Columbia owners
Running this thing in America is as expensive as running an RX-8 in Europe, if you only look at the fuel costs. A Freightliner Columbia 2007, probably including a trailer.
Ban me.
I'm not sure about yours or Tom's maths...
24 mpg is is around 10 km/L.
30 km/L is close to 70 mpg. How are you doing that in an '8?
6.67 km/L is about 15.7 mpg.
Assuming you could get 10 km/L on petrol (and I doubt it), that would be 800 L for 8,000 km for 1200 Euro (at 1.5 Euro/L). The same distance on LPG (at 6.67 km/L) is about 660 Euro (at 0.55 Euro/L).
If the conversion cost 1200 Euro, Tom is close to half-way towards breaking even.
Also, he addresses the "flooding" issue in his post. Propane doesn't burn well when too far outside of stoich. I can see the combustion chamber having so much propane that it won't ignite (Mythbusters had this problem a bunch of times).
I guess, as an engineering exercise, it's interesting (I do like the benefits of a non-liquid fuel). But I can't imagine that the propane tank in the trunk is doing anything good for handling.
24 mpg is is around 10 km/L.
30 km/L is close to 70 mpg. How are you doing that in an '8?
6.67 km/L is about 15.7 mpg.
Assuming you could get 10 km/L on petrol (and I doubt it), that would be 800 L for 8,000 km for 1200 Euro (at 1.5 Euro/L). The same distance on LPG (at 6.67 km/L) is about 660 Euro (at 0.55 Euro/L).
If the conversion cost 1200 Euro, Tom is close to half-way towards breaking even.
Also, he addresses the "flooding" issue in his post. Propane doesn't burn well when too far outside of stoich. I can see the combustion chamber having so much propane that it won't ignite (Mythbusters had this problem a bunch of times).
I guess, as an engineering exercise, it's interesting (I do like the benefits of a non-liquid fuel). But I can't imagine that the propane tank in the trunk is doing anything good for handling.
The car always starts on petrol to warm up the vaporizer which evaporates the LPG into just "PG". So it always floods itself in Petrol. I have never ever flooded my RX-8 with LPG, simply because it's impossible.
You might be right about the handling, but how often do you push an RX-8 to such limits where 60kg extra on the rear axle become noticable? Maybe on the track, but I strongly doubt it on a public road.
Last edited by TomX8; 02-15-2017 at 11:24 AM.
02-15-2017, 12:10 PM
#11
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