Mazda RX8 - What should I know?
Discussion
Have to say mpg is the main reason I've not owned one. I'd want it for a daily driver, not a weekend warrior (have other cars for that). But the mpg is just too low to be a realistic proposition. For those levels of fuel consumption I could run my Camaro daily and still be better off.
RobM77 said:
Slightly off topic, but what are the engineering reasons behind the low mpg?
The inherently crap combustion chamber shape is the primary issue. 1) As others have said it has a large surface area which ensures lots of heat is lost into the rotor and housing and the length of the combustion chamber means it takes longer for combustion to finish, and therefore more time for heat to be absorbed.
2) The trailing edge of the combustion chamber acts a bit like a moving squish band, creating a high speed stream of gas. Unfortunately, because this effect continues after combustion has started, it pushes back the flame front creating a pocket of unburnt fuel/air, hurting economy and emissions.
There are several schemes that have been used to reduce the impact of these flaws, but they are effectively sticking plasters over a problem which is fundamental to the design.
A secondary issue is that even when Apex seals are in good shape they don't seal as well as piston rings, so some leakage of compression and combustion gasses is inevitable.
300bhp/ton said:
Have to say mpg is the main reason I've not owned one. I'd want it for a daily driver, not a weekend warrior (have other cars for that). But the mpg is just too low to be a realistic proposition. For those levels of fuel consumption I could run my Camaro daily and still be better off.
When the owners of large American V8 coupes wont touch one due to the MPG, then the MPG is a problem.Feeling smug with the last tank of Super in my 350Z, 29.5 MPG, a record.
Mr2Mike said:
RobM77 said:
Slightly off topic, but what are the engineering reasons behind the low mpg?
The inherently crap combustion chamber shape is the primary issue. 1) As others have said it has a large surface area which ensures lots of heat is lost into the rotor and housing and the length of the combustion chamber means it takes longer for combustion to finish, and therefore more time for heat to be absorbed.
2) The trailing edge of the combustion chamber acts a bit like a moving squish band, creating a high speed stream of gas. Unfortunately, because this effect continues after combustion has started, it pushes back the flame front creating a pocket of unburnt fuel/air, hurting economy and emissions.
There are several schemes that have been used to reduce the impact of these flaws, but they are effectively sticking plasters over a problem which is fundamental to the design.
A secondary issue is that even when Apex seals are in good shape they don't seal as well as piston rings, so some leakage of compression and combustion gasses is inevitable.
When I posted my question I was thinking of the seals in the rotary engine and wondered why they wouldn't seal as well as piston rings. Is it the direction of curvature compared to direction of motion? i.e. piston rings go straight up and down a surface curved orthogonally to the motion of the ring, whereas in a rotary engine they're following a curve ahead of them the whole time in the same plane as their motion (so, like a hamster in a wheel, the oncoming surface is always 'higher'/'closer' than the surface under the hamster).
stugolf said:
I haven't owned a Skoda for 10 years?
??http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Edited by otolith on Friday 4th September 11:04
otolith said:
Its actually my Mrs car but she isn't a member of the forum
Thought I'd contribute as I've had my RX8 for over a year now. I bought mine knowing it had hot start issues, reached 68k before it needed a rebuild as the previous owners didn't treat it very well sadly.
The main issue that causes wear are the coil packs breaking down (need to be replaced every 30k and use genuine or high quality coils) yet people still driving it hard which causes fuel wash and also destroys the CAT causing overheating issues (it's hard to tell when it's not firing on all in a rotary unlike a piston when it's easy to tell it's not firing on all cylinders) and also oil not being changed regularly enough (oil service intervals in the UK are longer than in other countries).
Apart from apex seal issues caused by the above there's bearing wear as Mazda specced the wrong oil for the RX8 in an attempt to increase efficiency and emissions, they use 5w30 which is too light, one condition for engine rebuild warranties state you need to use 10w40 as that's what previous engines (RX7) use and they have no wear to the bearings and use the same ones (part numbers identical).
The engine not getting up to temperature before being driven hard is also a factor, for some reason the UK version of the RX8 came with two oil coolers where as the Japanese and American ones didn't and so the UK engine is actually over cooled, takes an age to get to temperature and in winter time sometimes never does!
This can be remedied by the "mouse mat" mod which is literally sticking a mousemat over one of the coolers when the weather gets cooler.
Plenty of Americans (I do too as well as most enthusiasts) premix the fuel with 2 stroke when filling up at the pumps (about 100-250ml per tank) to reduce wear and plenty of the cars in America do over 250k on the original engines so if simple precautions are taken then there's no reason why the Renesis engine can't be more reliable than a piston one.
It's also worth buying some Bilt Hamber Dynax S50 and spraying it down inside the sills as most Mazda's rust from the inside out, it's a real problem on MX5's but also 8's as well.
BTW, when I got mine rebuilt they put a 5k rev limiter on it for the next 800 miles and I got an average of 26mpg so it's not too bad if you drive gently.
The main issue that causes wear are the coil packs breaking down (need to be replaced every 30k and use genuine or high quality coils) yet people still driving it hard which causes fuel wash and also destroys the CAT causing overheating issues (it's hard to tell when it's not firing on all in a rotary unlike a piston when it's easy to tell it's not firing on all cylinders) and also oil not being changed regularly enough (oil service intervals in the UK are longer than in other countries).
Apart from apex seal issues caused by the above there's bearing wear as Mazda specced the wrong oil for the RX8 in an attempt to increase efficiency and emissions, they use 5w30 which is too light, one condition for engine rebuild warranties state you need to use 10w40 as that's what previous engines (RX7) use and they have no wear to the bearings and use the same ones (part numbers identical).
The engine not getting up to temperature before being driven hard is also a factor, for some reason the UK version of the RX8 came with two oil coolers where as the Japanese and American ones didn't and so the UK engine is actually over cooled, takes an age to get to temperature and in winter time sometimes never does!
This can be remedied by the "mouse mat" mod which is literally sticking a mousemat over one of the coolers when the weather gets cooler.
Plenty of Americans (I do too as well as most enthusiasts) premix the fuel with 2 stroke when filling up at the pumps (about 100-250ml per tank) to reduce wear and plenty of the cars in America do over 250k on the original engines so if simple precautions are taken then there's no reason why the Renesis engine can't be more reliable than a piston one.
It's also worth buying some Bilt Hamber Dynax S50 and spraying it down inside the sills as most Mazda's rust from the inside out, it's a real problem on MX5's but also 8's as well.
BTW, when I got mine rebuilt they put a 5k rev limiter on it for the next 800 miles and I got an average of 26mpg so it's not too bad if you drive gently.
I bought mine from new in December 06. It's just gone through 160,000 miles!
I still love the car as much as the day I bought it. In fact I still find myself happily looking out the window to admire it sitting on the drive and it still brings a smile to my face.
It's on its original motor, clutch and cat / exhaust system. The only major work required to date has been a new rear diff at c. 130k. As it happened my mechanic found one wrecked 30k car and we just swapped the rear axle unit. Other than that a new rear spring was required (It's a PZ version so bit of a bu**er to track one down and get fitted in time for a MOT)
Yes, they take time to get used to - but sensible care and attention is all its ever needed. I change the coil packs, plugs and leads at intervals as part of my preventative maintenance program. The oil usage is not as dramatic as some on here might make out. I just see it as part of the care this car needs. So, if you have an interest in cars then taking care of it is part of the connection you have with the vehicle.
I can never get enough of the 2nd / 3rd gear acceleration - It gets used on some nice B roads as well as the long haul stuff for work. Neither situation feels a compromise. I think you get a lot of car for the money and you're certainly not short of comfort or luxuries in the cabin on a 231 variant.
Fuel has been pretty consistent throughout its time with me - c. 50L = c.300 miles (and I do 'enjoy' the car)
There are a lot of knowledgably and helpful people at specialists and the cold start / stop procedure is just about being mindful and has never been a problem for me. Yes, it can feel a bit of a pain to keep it revved at 4k for 30 seconds if you're just moving it off the drive - but 30 seconds of your life - is it really that big a deal?
I've always loved it for its quirkiness and the fact it's not just another box with wheels. My two year old loves it and shuns my wifes MB in preference to ride in "Dada's car". The stage 1 car seat can be a bit of a fiddle to get the car seatbelt fitted due to the high tunnel running through the car. But if you don't have children that need this type of seat, then 4 seats and funky rear doors are great.
The age old advice of trying one is very sound as they can be marmite - just enjoy the linear sensation of keeping your foot in until the beep starts at 9k until 10k, hopefully through some twisty bits.
Best of luck in your deliberations.
I still love the car as much as the day I bought it. In fact I still find myself happily looking out the window to admire it sitting on the drive and it still brings a smile to my face.
It's on its original motor, clutch and cat / exhaust system. The only major work required to date has been a new rear diff at c. 130k. As it happened my mechanic found one wrecked 30k car and we just swapped the rear axle unit. Other than that a new rear spring was required (It's a PZ version so bit of a bu**er to track one down and get fitted in time for a MOT)
Yes, they take time to get used to - but sensible care and attention is all its ever needed. I change the coil packs, plugs and leads at intervals as part of my preventative maintenance program. The oil usage is not as dramatic as some on here might make out. I just see it as part of the care this car needs. So, if you have an interest in cars then taking care of it is part of the connection you have with the vehicle.
I can never get enough of the 2nd / 3rd gear acceleration - It gets used on some nice B roads as well as the long haul stuff for work. Neither situation feels a compromise. I think you get a lot of car for the money and you're certainly not short of comfort or luxuries in the cabin on a 231 variant.
Fuel has been pretty consistent throughout its time with me - c. 50L = c.300 miles (and I do 'enjoy' the car)
There are a lot of knowledgably and helpful people at specialists and the cold start / stop procedure is just about being mindful and has never been a problem for me. Yes, it can feel a bit of a pain to keep it revved at 4k for 30 seconds if you're just moving it off the drive - but 30 seconds of your life - is it really that big a deal?
I've always loved it for its quirkiness and the fact it's not just another box with wheels. My two year old loves it and shuns my wifes MB in preference to ride in "Dada's car". The stage 1 car seat can be a bit of a fiddle to get the car seatbelt fitted due to the high tunnel running through the car. But if you don't have children that need this type of seat, then 4 seats and funky rear doors are great.
The age old advice of trying one is very sound as they can be marmite - just enjoy the linear sensation of keeping your foot in until the beep starts at 9k until 10k, hopefully through some twisty bits.
Best of luck in your deliberations.
None of the cars people are saying have better mpg will handle anything like as well.
Just saying.
I had the option of buying a Monaro VXR or Evo VIII FQ320 MR when I bought my PZ instead. I never regretted the decision. Not once. Rotaries are very special cars. Not for everyone, but if you get hooked, you get hooked bad!
I'm not sure why stugolf is trying to persuade a bunch of rotary enthusiasts why they shouldn't like them. He seems to be a VAG fan, which is fair enough. But to me, that's like saying your favourite colour is magnolia, your favourite flavour is vanilla, your favourite food is bread and your favourite drink is water. A conformist choice requiring no imagination.
Just saying.
I had the option of buying a Monaro VXR or Evo VIII FQ320 MR when I bought my PZ instead. I never regretted the decision. Not once. Rotaries are very special cars. Not for everyone, but if you get hooked, you get hooked bad!
I'm not sure why stugolf is trying to persuade a bunch of rotary enthusiasts why they shouldn't like them. He seems to be a VAG fan, which is fair enough. But to me, that's like saying your favourite colour is magnolia, your favourite flavour is vanilla, your favourite food is bread and your favourite drink is water. A conformist choice requiring no imagination.
Edited by Ali_T on Friday 4th September 12:26
Ali_T said:
None of the cars people are saying have better mpg will handle anything like as well.
Just saying.
I had the option of buying a Monaro VXR or Evo VIII FQ320 MR when I bought my PZ instead. I never regretted the decision. Not once. Rotaries are very special cars. Not for everyone, but if you get hooked, you get hooked bad!
I'm not sure why stugolf is trying to persuade a bunch of rotary enthusiasts why they shouldn't like them. He seems to be a VAG fan, which is fair enough. But to me, that's like saying your favourite colour is magnolia, your favourite flavour is vanilla, your favourite food is bread and your favourite drink is water. A conformist choice requiring no imagination.
I am voicing MY opinion, the OP asked for opinions that is mine, he didn't say "all rotary enthusiasts give me your opinion" and if you do a search on PH you will find hundreds of RX8 threads with similar contentJust saying.
I had the option of buying a Monaro VXR or Evo VIII FQ320 MR when I bought my PZ instead. I never regretted the decision. Not once. Rotaries are very special cars. Not for everyone, but if you get hooked, you get hooked bad!
I'm not sure why stugolf is trying to persuade a bunch of rotary enthusiasts why they shouldn't like them. He seems to be a VAG fan, which is fair enough. But to me, that's like saying your favourite colour is magnolia, your favourite flavour is vanilla, your favourite food is bread and your favourite drink is water. A conformist choice requiring no imagination.
Edited by Ali_T on Friday 4th September 12:26
I've been a member a long time and the username stugolf stuck over 15 years ago, I like VAG cars but have had many other cars as well
I haven't owned an RX8 granted, I'm just going off people I know who've owned them and the hundreds of threads I've read being a bit different and not conforming is one thing but buying a 2k money pit is quite another
Gassing Station | General Gassing | Top of Page | What's New | My Stuff