If you can do it, more power to you. You might prove the extensive history wrong, and we will eventually get to say: "You can do this cheaply and quickly if you are a prior F1 mechanic".


The more I think about it, the more that would confirm my opinion that it isn't worth doing. If trying to do a swap wasn't exclusive enough, now you have to be an F1 mechanic first to have a decent shot. Am I right?

Or maybe profession doesn't really have anything to do with it except a subset of skills that might be useful.




I don't bother making claims about who I am on the internet. It's pointless. I be who I am and let people make their own conclusions, and I let the resulting reputation speak for itself.

I'm just a plain 'ol Joe. :)

So anything but a rotary or a v8 costing $10k is unacceptable? Practical and affordable is not an option?

KFC - You just can't win can you? lol

kicker, anything is acceptable as long as you have a good supporting reason behind it. The world of car enthusiasts is a world where hairbrained ideas are generally more accepted than rejected. This thread started with a desire for an engine with ...and I quote:
That's what triggered this whole discussion, since his stated goals are met with a quick replacement engine. It devolved from there.

"Practical" and "Affordable" are options, but they exist in other cars. They don't exist in the RX-8 when you start tossing "engine swap" around. Sure, there are some swaps that are more practical than other, and some swaps that are more affordable than others. But even the cheapest most practical swap out there is LESS practical and LESS affordable than just getting another car that is closer to what you want.

That's my core point in all of this. You have already tossed practicality out the window as soon as you start a swap, regardless of the choices and regardless of the outcome.

You certainly have to posess a quality skill set to carry out the work your self and want to do it more for the engineering challenge than simply to desire a specific car and get someone els to do most of the work, that's not fun. If I won the lottery, I would buy nice fast cars but have a workshop kitted out with all the machinery to do another conversion. I do it because I enjoy the challenge.

And THAT is an excellent reason. I can understand that reason completely. I too enjoy challenges simply because they are challenging.

That doesn't change my opinion about the viability of an engine swap in an RX-8 chassis, but good luck tackling the challenge that is going to be bigger than you currently predict :)

Relevant experience is always helpful.

This thread reminds me of the good old days when every week there would be a thread like this pop up .

KFC ... Have you ever heard a NA 4 rotor ?

http://www.streetfire.net/video/mad-mike-tears-up-the-hamilton-v8-supercar-track_2245169.htm
Have a listen

I have yeah, way too impractical for daily use, mine will be on a proven LPG system as well. :-)

:eek: Shields up!

What about this bad boy? YUM!

Are you serious, or just trolling?

Legot, DON'T FEED THE TROLLS!

You have to admit it sounds awesome . I have to say the sounds from a two rotor don't do that much for me either though.

The 4 rotor sounds better than the 6 IMO.

Horrible, sounds wrong.. :banghead:

Of course.
Let me guess.... You've never been in a car on lpg?
Well in this country petrol costs £1.34 per litre, that's $7.60 per US gallon, so we have to look for alternative fuels. I hate diesel and the Italian lpg systems are the best! I have had mine on lpg for over a year and I can honestly say I can't feel a difference! I've towed another car on a "A" frame and did comparison tests on hills to see if the torque drops and it feels the same, I can switch over easily.
LPG costs £0.62 per liter and I do get the same mpg ($3.50 per US gallon), I use the same amount of litres of petrol to lpg. I was amazed because I heard you get 10% drop on both, power and mpg, not so on mine. It is a clever system and the injectors are very fast.

LPG is a good fuel solution. It's even a good fuel for the rotary. No argument from me there.

I think diesel is the best rotary fuel, since it's weaknesses are where the rotary shines, and it's strengths are where the rotary is weak. Plus diesel is an oil, so internal lubrication problems are inherently solved. But a diesel conversion isn't easily obtained :)

There have been a few threads on the subject with most opinion saying the lubrication of the apex and side seals becomes an issue . Your one wore out or ?

Hmm, interesting, I thought that most people would hate the idea? Is diesel still hated in the US?
I know that diesel cars don't really exist in Canada, just VW, here every manufacture build them and as small as 1.4L.
How do you think rotary engine builders could get around the low compression issue to run a diesel?

The Renesis, and all prior versions of the rotary would be hard to adapt to diesel. Mazda already stated publicly that the 16X revision is able to run on any fuel they tested it with, including diesel. How exactly and at what compression ratios, I don't know, but I believe them.

So I don't know how to answer the last question, because either the 16X can run the higher CR needed, or there is something different Mazda did to assist in the ignition. Plus, keep in mind that Mazda's latest diesels have CRs as low as 14:1, which is an achievable CR on a rotary, assuming you build the engine with the correct dimensions.

And yes, diesel is still a hard sell in the US. But your point about diesel in the EU just really makes another point in it's favor, since a gas version has a harder challenge to meet EU requirements, a diesel might be the ticket there.

Ironicly, diesel is cheaper to make but £0.05 to £0.09 per litre more at the pumps...:rant:

No I've never been in an LPG car, I don't have many friends.

I'm sure it's a fair solution, but I've never looked it up until you posted that, so +1 for you. Can you go into how you're going to implement it? I'm curious as to how a pleb would go about something like this. What types of obstacles do you expect to face in using a low cost solution for it? Is it a simple change of fuel delivery method, or is it more like that plus a different type of ignition control?

In the US at least, it's simply that the costs are in a different place. The cost to make and transport is lower, but the core cost of the source oil is higher. So there is an barrel oil price point at which diesel becomes the same cost at the pump as gasoline (which varied depending on which gasoline grade). Lower cost per barrel and the diesel is cheaper, higher cost per barrel and the diesel is more expensive. For quite a few years, the price of oil has been hovering just above that even price point, so diesel has remained more expensive.

Before I sold my '85 RX7 gas was nearing $2/gal. I made a comment to some friends "If gas goes over $2/gal I'll convert the 7 to propane" and as usual "your never going to run that on propane". The next month gas was $2.09 and of course they called me out on it. Just to make them happy I shoved a hose down the intake and connected it to a propane torch head with the orifice removed. Drove it around the block that way just to make them happy. A little bit hard to drive regulating the fuel with a thumb screw. It was a demand regulator away from a full conversion but I decided to sell the car.

I have it on the word of a Mazda regional service rep that one reason Mazda has yet to bring a diesel car to North America as long planned, is that after extensive testing with the diesel fuels available here, Mazda found such poor quality diesel fuels being sold overall and no diesel fuel consistency from pump to pump, rendering impossible any successful tune for a diesel car that has to work well in all of North America. I guess their tolerances to make their Skyactiv Mazda diesel work here are tighter than other carmakers with diesels in North America.

( A side note: a longtime Mazda racer friend of mine that had switched over to VW after also racing VWs for a while, just dumped his new VW diesel sedan. He drives hundreds of miles every day across many states for his government job (so he is using diesel fuel from many different areas in the US) , and in just the first year his brand new VW diesel engine has had to be repaired more than once, and finally nearly totally rebuilt at a cost of several thousands of dollars by VW. He gave up ,saw the handwriting on the wall with the future of this diesel car, and sold the car as soon as the last engine fix was made, and came back to Mazda, buying a MT 2015 Skyactiv Mazda6, which he loves and says the handling and fun reminds him of driving one of his past RX7's. )

The Mazda guy told me that diesel fuel quality standards are far more consistent in Europe and Asia (please Europe and Asia members chime in here about this if you know it to be so). So until that North American diesel fuel situation dramatically changes, don't expect either a Skyactiv Mazda diesel sedan or diesel rotary to be introduced in North America, even though Mazda would love to be the only Japanese car brand in America with a great diesel car for sale. You will just have to watch and root for the Skyactive diesels in Tudor United Sports Racing, which have been gallant, but have been having a tough development time their first season.

I'm glad you asked because I love the conversion, I've had it running on my car for over a year now. I never intending it to be the tidiest installation as I knew it would be coming off with the engine. The system is AEB. I bought this one but at £625 minus the tank.
LPG gas conversion kit Range Rover Super Charger V8 sequential injection AEB

The only tricky thing about the installation was splicing into the cars loom for the injectors. The lpg ecu is now the master, it tells the cars ecu when to go on petrol. On start up it needs to use petrol until the threshold is met on change over. As in, when the water temp reaches 30 degrees C, the revs are over 1200 rpm, the lpg ecu changes over seamlessly. You can't feel it, well, only a tiny bit but you have to be waiting for it.
At 1200 rpm the engine is so smooth anyway. I'm not sure the time frame but it changes 1 injector at a time but I think its all six over a second or 2.
The engine coolant water runs through the vaporizer as it gets very cold and can freeze if the you were to change the threshold temperature lower than 30C.

In the summer (25c to 30c) in changes over nearly instantly or a 1/4 of a mile. In the winter (15c to 0c) it can take up to 3 miles so it's not to bad. I've thought about putting in block heaters to plug in for an hour just to see if it changes over a lot quicker.

The tank sits in where my spare tire goes. In the 24 years of driving, I've only ever had 2 flat tires, I carry a tire repair can if I get a flat.
the whole installation took me 4 days so I expect it to be a bit quicker putting it on the 8 as I know what I'm doing with it. Oh, I recently put a flash lube kit on it, meant to give added protection to for the valves but it's not needed on this engine, I just thought it would be good to have it as it's cheap.
I hope this helps.

I bought mine as a project but I stripped the engine. The damage evidence to the parts suggest that the owner let the oil level run low and starved the bearings and injection. The front bearing was so far worn that it crumbled apart. Housings are not usable nor the eccentric shaft, virtually nothing was usable. People in the UK abuse the rotary and don't understand that it needs certain run times and shut down. You can abuse a piston engine and still get the long mileage.

Have you measured the difference in where the output shaft ends up being placed? The Renesis exits from the center, a V6 exits from the bottom. Same dimensions of the total block means you have a much lower transmission mounting location, or the entire engine has to sit higher, potentially creating different problems.

The centres don't change, anywhay, the engine is in, I'll take photos later to show the mock up engine in with the cut outs to the bulkhead.


The RX-8's ECU will not be able to run a V6. Different injector behavior, different spark count, different spark sequence, etc... You will need to use another ECU, which will mean that all the existing RX-8 electronics will need to be removed or completely re-written with custom firmware.

I'm running megasquirt to run the ignition and injection.

They did, it's called a Mazda6. "RX" means Rotary Experimental, so anything else in the chassis is called something else other than "RX".

The Mazda6 never had a V6 in this country, I've seen it was released in north america but it's that a front wheel drive? Looks ugly anyway.

That's very interesting. I've heard of it, but never really looked into it, so I admit I'm ignorant of all the pros & cons of it.
It's one thing to read about it, but another to see it used in normal everyday circumstances.
How does the LPG meet the octane requirements of the Renesis?

Our premium gas is currently on a price decline, but it's only a matter of time before it goes back up.
That is something i will definitely be reading up on over the winter.
Thanks for the link.

I don't know the octane of the LPG, it burns hotter and cleaner so no deposits in the combustion chamber. Our petrol is 95 and 98 so perhaps it would be near equal.
I know that the renesis would use 2 lpg ecu's as it has 4 injectors running full time and the other 2 making a total of 6, they come on about 3k rpm ish. That means it's difficult to get a good set up, that's another reason why I didn't pursue the renesis route.

BigC, octane matters for preignition from the heat of compression. Think about what happens when a substance reverts to a gas from a liquid (ie, liquid propane gas)... :)

Posted From RX8Club.com Android App

There are YouTube clips of RX8 LPG conversions. They work, sertainly can't shorten the life of the engine for the amount of years you plan on having the car for?

I'd bet LPG would, on average, increase the lifespan of a Renesis by 50-100%. Gasoline as a fuel, and it's attributes, are significant factors in almost every critical reliability problem the engine has. Virtually any other fuel would be better, with alcohols and lpg better for cooling reasons, diesel better for lubrication and performance reasons.

Edit: and hydrogen for emission reasons

Propane does burn hot with no lubricating properties so modern engines can suffer, that's why there's flash lube available. I've heard the rotary responds very well with high octane and turbos.

Thanks, I'm not at all knowledgeable about this.
I am intrigued, and will definitely start reading up on it over the Winter as my workload eases up.

Propane RON = 112 according to Wiki. No idea what it's "Observed Road Octane Number" is.

Engine might last longer without gasoline washing off the oil.

...and no carvon to deal with.

Do you mean carbon?
I've heard the European LPG kits tend to be the best but the polish ones are crap, cheap and nasty. For serviceability and postage reasons, it would be best for you to buy a good kit in the US. I don't know what they are like and what reputation but the bottom line is, injectors 5 and 6 come on for more power and turn off again about 3k rpm, quite complicated in the ecu. That's what I've been told by the person who certified mine after I fit it. I had to do about 8500 miles for it to pay for it self, it's probably double that for someone to fit it. The renesis engine would have to come out because of the nature of the inlet manifold. There is one massive long bolt holding the inlet on that makes it impossible to remove, it will hit the chassis. Even if you were to try and get a drill down there, near impossible. Can't risk ally swarf getting in. You need to drill and tap 6mm holes down as close to the ports or irons as possible, the same goes to a piston engine, as close to the valves as possible but they are easier. Companies probably wouldn't do it as they would have to charge so much to do a renesis compared to a V8 truck. Let me know what you find as I do like all this stuff. :-)

Seeing as carbon is the most common renesis killer, u are correct. My last 2 engines had major carbon issues, and another I had after 50k km from rebuild still had more carbon caked on my rotors than is right & and I thrash the thing 7-9k rpm every gear change nearly every time.
I'm going lpg on my 20b conversion, but not dual fuel. (Dual is rubbish)
U run straight lpg, u tune the car for optimum performance (including different plugs) on said lpg, and because it's straight lpg it runs way more efficient, in fact almost the same bang as 98 per Lt and for those out there who disagree with that then I say ur not doin it right. And of course, higher octane=more boost, easier tune-ability, and at half the price of 98.!!
U buy an aluminium tank which is 50% lighter than conventional lpg tank. U remove the factory tank to cut down weight. Mount the new tank in the boot as forward as possible- mines gonna be 60lt usable Lt.
I will adapt/modify the omp for 2stroke and my lube is sorted.

Sht did I just high jack the thread??! Soz. Saw an opening to preach lpg.

O.P. was discussing LPG, I don't think it's hijacking.
I'm interested fwiw.:)

I thought a lot of the carbon build up was caused by the oil injection? I know why carbon build up happens but isn't the oil a contributor?
How are you going to stop the vaporizer from freezing up if you run it only on lpg from cold? It does happen. When mine is on lpg, it's either on or off, unlike some systems inject petrol 10% of the time while lpg, crap.
Also, where do you find the ally tanks? Are they still certifiable?

No, it's a misconception that oil is the source of the carbon. If you look at pics of rotors that have come out of dead engines, you can see that the rotor is cleaner where the oil injection was hitting it. Virtually all of the carbon buildup in a rotary, or any other gasoline engine, is from the gas alone.

We want to encourage people to switch to 2-stroke oils simply because they show even cleaner rotors where the oil hits them, and the carbon that is there is a bit 'softer'.

Agreed- I didn't fully explain the reasons.
It's obvious it's a better option simply because ur pumping in clean oil instead of dirty oil that's 5-7k kms old. U wouldn't go down the creek n drink dirty water if there's a keg of purified water sitting there hey.
Anyway, from what I've read of others opinions on the subject of hard data blah blah blah, it's just plain obvious that clean 2stroke oil is better than dirty sump oil. Der lol

vapour inj system doesn't have this problem.

Sinfidelity, I was replying to KFC on my last reply, not you :)

Your understanding of the carbon issues is correct

Perhaps you should start an LPG discussion thread.

K. Will do once it's all up n running.

Yeh soz, I kinda realized afterwards reading back a bit further.

Good for you. :rollingla
I love clever engineering and I can see the appeal with the rotaries but they have a fundamental weakness, the corner seals... A massive stress raiser..
Every single designed engine or highly stressed moving part has has a curved or round surface. It's a shame because it would be used more.

For me it's far too expensive to run on a daily basis, 25mpg at the best and just doesn't sound right. The cars heart is the engine, if it doesn't sound cool then it's a let down. How many films use cars with great sounding engines?? Can't say they use the RX7 or RX8?

Cars must be very expensive in the US if someone actually spent $25000 on a conversion?? I bought mine with a dead engine for $600. Everything else I spend money on, I should be able to get most of it back if this fails, ebay is a good friend to me, ha ha.

I've had the bumper removed for a while, much easier to work on while I'm using the mock up eengine. Oh, the real engine I'm putting in is coming out of my 18 yr old MX6 as a cheap test, if it's good and works well after 6 months then I'll rebuild my spare and do a swap over a weekend.

Yes, your dreams are reasonable!

amazed how well the v6 sits in there. Makes me wish I'd used a vr35De rather than Sr20.
It seems everyone in the uk is doing it now. Just about to take the plasma cutter to my friends rxs firewall for a turbo V8 conversion.

Will be watching for updates.