TomX8

After roughly 2 months of waiting and some research, today I am handing over my RX8 to the garage that will convert it to Liquid Petrol Gas. This time it's a different garage and a different system.

The first try failed because their ECU couldn't read out the RPM signal and other signals which were vital to make the LPG system running. Another company in Belgium is using the same ECU and they charge around 4000 dollars, but even they are saying it's not recommended since it's not running so well... Well, if you use the wrong system, ofcourse it won't run wel.

The brand will be the polish AC STAG, which have a computer with a "Wankel Mode", which can understand the RX-8's ECU, thus knowing when which ports are open by reading the fuel injector signal and the ability to read out everything else such as the RPM signal etc.

The garage wasn't really enthousiastic about converting a Wankel at first, but after I have provided them some documentation on how to convert and calibrate the LPG system in a Wankel engine (RX-8 specifically), the owner saw potential and decided to go for it. It's mainly thanks to the engineer from AC STAG Headquarters in Poland which provided me with all the explanations and info.

This is the AC STAG system running in an RX-8

I do it because it's cheaper to run (1,60 euro for Benzine vs 0,75 euro for LPG), and already had this idea in mind before buying the car. This brat one time told me that an RX-8 should run on gasoline and not on LPG, but if an RX-8 would run cheaper than some beat up Miata, I'd be pissed too. I expect hate anyway, like in any other LPGRX-8 topic.

I should get the car back on Friday, so I will update certainly afterwards whether they failed or succeeded.

nycgps

iTrader: (1)

can't afford gas and u wanna own a sports car ?

TomX8

If you travel like me around 3000km per month, then it makes a difference whether I burn 480 euro or just less than 200 euro . 280 euro of monthly savings are quite nice, which will pay off the installation in just 5 months and the car itself in another 10 months. You must be stupid not to do it, just because the "The car is supposed to run on Benzin!" nonsense. I'd like to see you pay 5,5 dollars per gallon.

Love_Hounds

Actually ny raises a good point. The Renesis isn't know for longevity, so fuel isn't the only concern when it comes to cost of operation.

Sport cars aren't cheap in the long run.

Also, I'm pretty sure the energy density of LPG is lower then gasoline, so your MPG will likely decrease. Not sure if you included that fact in your calculations.

TomX8

LPG doesn't cause carbon buildup like gasoline does, and since the engine mostly dies because of the carbon buildup in the cat and the rotors, it should only prolong the life of my still healthy engine. Starts hot in 105F/40C weather after a 200km long drive without any problem, reached 235km/h on GPS on a straight highway in Germany so I don't see any problems there.

I know that the MPG will decrease with LPG, but the fact remains that it's still considerably cheaper than gasoline and engine friendlier. It also runs hotter, but certainly not as hot as an RX-8 with a clogged cat.

Love_Hounds

Hate to be a bearer of bad news but eventually side and apex seal wear, all rotaries suffer this. I doubt LPG will slow this process down actually it may make it worse depending on how the oil injected will get spread across the housing without gasoline.

TomX8

For all I care the engine dies after 40.000km, as the LPG installation will have saved me enough to get another RX8 and install another LPG installation.

If it's just the seals that will wear, I would just need to rebuild and replace the seals, which is still cheaper than an entire engine, isn't it?

Love_Hounds

Um what? Why would you need to replace the entire engine? You can clean carbon buildup off. So again, don't see the advantage especially if the seals wear faster, but good luck.

TomX8

There is no certainty that the seals will wear faster, but there will be no carbon buildup, so that's one advantage besides the savings.

Love_Hounds

Um burning motor oil causes carbon deposits. Are you going to use a Sohn adapter and run some sort of synthetic oil, like an ashless two-stroke?

nycgps

iTrader: (1)

Well , right now I drive at LEAST 4K km a month. and just this past December I drove 6K km, yes , 6000 km, That's for my work. and each fill up cost me about 1000 HKD, which is 112 for today's rate. u do the math.

and I'm not crying.

you can do it all you want, hell u can even try to run diesel on it, but for me, if I wanna save gas, I get another car and stop crying.

TomX8

It does, but not nearly as much as gasoline that burns in the cat, because so far I had to refill just 5 liters in 15000km. I just run Valvoline according to the ACEA specifications.

Who says a sportscar cannot be economical? Just accept that I will be paying half the price for fuel for the same car and same performance.

I bought an RX-8 2004 HP for the price of a VW Polo 1.2 2003 and now I will have an RX-8 with the economy of a VW Polo 1.2 2003 . Now Polo's from that year tend to consume around 7 liters/100km and an RX-8 around 13 liters/100km according to the userbase of autoweek.nl. Euro98 = 1,60 euro and LPG 0,75 euro, you do the math.

Verbruik Volkswagen Polo 1.4 16V 75pk Comfortline (2004) | Verbruiksmonitor - AutoWeek.nl
Verbruik Mazda RX-8 Renesis Upgrade (2006) | Verbruiksmonitor - AutoWeek.nl

I've give you a visual aid. These 2 cars cost the same, except that the other one runs on cooking gas. Which one do you take?

Love_Hounds

That literally makes no sense. We are concerned with carbon buildup inside the engine, which decreases performance, to the point were the engine can become choked.

The catalytic converters in the 8 get clogged quicker then most due to the exhaust temperature of rotaries and the burned oil. Occasional misfires don't help either, but a healthy engine with healthy components(like ignition) doesn't misfire often.

TomX8

Carbon buildup occurs when it's driven for fuel economy in low RPM, and a redline a day keeps the carbon away, right? Unburnt fuel is one of the main causes of cat failure, which is lead back to the failing coils. When this unburnt fuel is burned in the cat, it overheats the cat and deposits carbon aswell. But you can correct me if I'm wrong.

Love_Hounds

Well you are wrong about burning fuel in the catalytic converter and it's correlation to carbon deposits. The carbon buildup we are talking about takes place inside the engine from the combustion of fuel and burning of oil.

I'm not going to argue that a clogged catalytic converter is a serious problem that can literally burn a car to the ground but, the hypothesis that you'll avoid carbon deposits in the engine from running LPG (you're still burning fuel and you're still burning motor oil in the rotor housings) is not very likely.

Redlining helps remove carbon from inside the engine, at least that is the theory, however unless you plan on racing this car, you'll still see carbon deposits in the engine even if you "redline a day" and otherwise drive normally.

T_Mags

Slight derailment, but wasn't red line a day generally disproved once we had a few 200-300k rotaries come out (Think Elf or something like that was his username)? All the cars that reached that milestone did so with highway miles and with the stock OMP set up.

Love_Hounds

People get lucky and they may not always realize how high they climb in the RPM range before shifting. Also, is there a difference from bringing it up to 8,000 RPMs vs. 8,500 RPMs(the beginning of the "redline" in a series one manual) for a few seconds, not much.

Here's a post from the new owners thread: https://www.rx8club.com/new-member-f...2/#post4533728

TomX8

Whether there is carbon buildup INSIDE the ENGINE or CATALYTIC CONVERTER, the carbon will mess the engine up eventually. And this is either caused by a faulty ignition (causing the mixture to burn in the cat and depositing carbon there, clogging and raising the temperature in the rotors, causing apex seal failure) or depositing carbon in the inside, simply from the engine just runnng.

By the time I burn 1 liter of oil I have burned 300 liters of petrol, and which one of these deposits more carbon? LPG deposits much less / little carbon. The engine oil will actually stay cleaner and will lubricate better on the long run when running on LPG because it's not contaminated by carbon. Adding to the fact that LPG doesn't wash away oil, the lubricated layer on the rotor housing remains intact, improving the lubrication of the engine even further.

It's in fact so clean, I drove on my moped behind busses running on LPG in the winter to warm up.

1. Carbon deposits are reduced to virtually nill : Go LPG - How does my vehicle benefit from using LPG as a fuel?
2. Generally, LPG burns more completely and does not cause carbondeposit: Autogas Italia s.r.l. web site FAQ
3. LPG burns cleaner than petrol. This means less emissions out of the exhaust and less carbon deposits in the engine. : FREQUENTLY ASKED QUESTIONS, LPG TECHNICALITIES & LEGISLATION | WWW.LPG-CARS.CO.UK
4. This also results in much lower carbon deposits and almost no oil contamination: https://books.google.cz/books?id=xUD...eposit&f=false
5. Since there is little carbon deposit in the cylinder head or contamination of oil by carbon, all parts of an LPG engine should run cleaner: https://books.google.cz/books?id=hNg...eposit&f=false
6. LPG does not wash oil away from the cylinder walls, hence the lubricating layer is not washed away, increasing the lifespan of the engine by 50%. Also, does not generate black carbon: https://books.google.cz/books?id=1zm...eposit&f=false

LPG does deposit SOME carbon, but significantly less. LPG contaminates oil significantly less with carbon and doesn't (mix with / wash away) the lubricated layer. The engine itself remains cleaner, better lubricated on the long run and generally should life longer.

It's cheaper, it's cleaner (internally and environmentally), increases the lifespan of your engine. As an added benefit, I can turn off my engine without any worry of flooding as soon as the engine switches to LPG. Which is roughly after 1 mile. Another nice extra is the Octane rating of 110, even increasing the power output if the engine is tuned for LPG: http://www.liquidlpg.com.au/files/ca...51522_f483.png

"The dyno graph below shows the power output of a VF 325kW HSV Clubsport converted to Liquid LPG in our Sydney workshop. The vehicle maintains all its power running on LPG and delivers $ back to the family"
LPG vs Premium 98 Petrol | Orbital Autogas

Based on this, LPG is a better fuel for the RX-8 than petrol.

Love_Hounds

You're making a lot of assumptions, not to mention several of the links you listed(and even you point out) deal with piston engines and "cylinder heads". I'm just trying to argue that there is more to work here then you seem to be aware of.

Also, your attachment to the correlation between a catalytic converter clogging over time and engine failure due to carbon deposits is amazing. It's pretty easy to detect a failed catalytic converter and relatively cheap to replace it or remove it and run a "catless" midpipe and it's relatively cheap and easy to replace your ignition components in a timely manner, it's not that easy or cheap to remove and rebuild an engine.

TomX8

Carbon deposit is chemical, not mechanical. So it's irrelevant if the sources talk about piston or wankel engines.

Easy to replace is one thing, but most actually don't know (when) they have to replace it eventually to prevent engine damage. I don't know if you are being sarcastic or not by calling my correlation amazing, but it's simple physics. Water cooks a hell a lot faster and hotter when you put a lid on the pan, doesn't it?

Love_Hounds

Well, I'm done. You've dismissed the points I've made and you keep changing what you're talking about(cooking water? Maybe implying that a bad catalytic converter is stopping exhaust flow so the engine heats up faster or something).

Again, good luck with this, from your arguments here, it seems you'll need it.

Brettus

iTrader: (2)

Will be very interested to see how this pans out long term . Keep us informed and be sure to update both good and bad news !
I always thought that LPG was a very "dry" fuel and would wash away the oil barrier which is contray to what you are saying . If there is any doubt you might want to consider upping the omp rate.
Good on you for trying something different .

TomX8

Quote:

Originally Posted by Love_Hounds

Well, I'm done. You've dismissed the points I've made and you keep changing what you're talking about(cooking water? Maybe implying that a bad catalytic converter is stopping exhaust flow so the engine heats up faster or something).

Again, good luck with this, from your arguments here, it seems you'll need it.

I don't need luck, just sources with knowledge about the subject. Give me sources to back up your arguments and I will gladly change my view if it proves me wrong.

Quote:

Originally Posted by Brettus

Will be very interested to see how this pans out long term . Keep us informed and be sure to update both good and bad news !
I always thought that LPG was a very "dry" fuel and would wash away the oil barrier which is contray to what you are saying . If there is any doubt you might want to consider upping the omp rate.
Good on you for trying something different .

LPG is a liquid when you fill up the gastank, but as the car is running, it's passing through a "reducer" which vaporizes the Liquid Petrol Gas, into a... gas...

The theory is that once the RX-8 switches over to LPG, you can turn it off without flooding it (my RX-8 switched to LPG within a mile in -15 celsius), because LPG is a vapor and leaves the oil layer intact, while petrol stays in the engine and washes away the oil film. Hence why LPG is called a "dry" fuel.

You may have heard aswell that LPG can burn the valve seatings or valves itself.

The most common misconception you'll hear about LPG is that it makes an engine run hotter than Petrol. This is no more than myth.
LPG has only 85% of the calorific value of the same amount of petrol, so it is impossible for it to create more heat. It can only make 85% as much.
There is one factor missing though - The cooling effect that squirting wet petrol mist into the cylinder has on the valves. The evaporating petrol mist will cool the valves very slightly but that cannot happen when injecting a gas that has already been vaporised before injection. When running on LPG the gas does not have quite as much cooling effect on the valves. As a result of this difference you'd expect to see LPG operation showing slightly higher valve temperatures, but overall that isn't the case. We just established that LPG can only produce around 85% of the heat that petrol can, the lost benefit of petrol mist cooling on the valves is cancelled out by the cooler combusion temperatures of LPG - in short, both fuels end up roughly even when considering valve temperatures during operation.

Source: http://www.go-lpg.co.uk/VSR.html

Basically the RX-8 runs rich make the engine run cooler, but a quick search has revealed that running rich with LPG does not give the same cooling effect as Petrol does. Running rich on vapor fuel doesn't have the benefit of evaporative cooling, because it's already evaporated...

1. Volvo Owners Club Forum - View Single Post - LPG running lean - how will I know?
2. Volvo Owners Club Forum - View Single Post - LPG running lean - how will I know?
3. Go LPG - Will the performance of my vehicle be any different when using LPG?
4. LPG tune/fuel mixtures in turbo application, any suggestions? - Engine & fuel engineering - Eng-Tips

Which should allow me to move from a rich mixture to a stoichiometric one on LPG 15.8:1

Love_Hounds

Care to give your sources more consideration seeing that they contradict themselves?

StealthTL

iTrader: (1)

If he doesn't know the difference between cat blockage and engine carbon, then getting him up to speed on any of the other mythical claims he makes will be difficult (though entertaining).

Cats are never blocked by 'carbon'. They can melt from heat, or be blocked by deposits from 'ashless' oil additives, but carbon is never a problem.

Too much 'warming up behind a bus on his moped' perhaps....