My RX8 VAG 20v project.

My RX8 VAG 20v project.

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Discussion

John_S4x4

1,333 posts

227 months

Monday 3rd March 2014
quotequote all
WOW ! Great start. £500 seems a bargain and you're right, the engine does sit waaay back.
I do wonder what would happen in regards to having cut the bulkhead and putting it back on the road (SVA/IVA test ?). Best of luck with the project thumbup

petey1979

Original Poster:

27 posts

96 months

Monday 3rd March 2014
quotequote all
Tbh I've not really looked that far ahead ha
Ha

Would a full sva be needed?

aka_kerrly

12,030 posts

180 months

Monday 3rd March 2014
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This looks promising!! I've also spotted a few stupidly cheap RX8s with dud engines in and surprised there aren't more conversions taking place.

I don't know the ins and outs of a SVA but I've more than one car in the past with an engine conversion which involved cutting the bulkhead and a panel simply screwed in place to make an inspection hole - not good in my opinion!!

rotarymazda

538 posts

135 months

Tuesday 4th March 2014
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e21Mark said:
I like a turbocharged rotary, but isn't it the perception / issues / mpg / reputation (delete as appropriate) that has helped the RX8 values plummet? I think a more usual, normally aspirated engine would open the RX8 up to a whole new market.
mpg, car tax (£450), and engine lifetime (40K-120K) are the issues. Dead ones are now going for £500 as the OP says.

I have a ported RX8 engine in a mk1 mx5, a much better proposition. I get 212rwhp (~240bhp) in a 1000kg car without forced induction.

I run mine with a separate oil supply and a custom metering controller, registered it as a 1.3L. That sorts out tax and reliability.

As for mpg, well......

Forced induction RX8 engines don't seem to last long, the side seals just can't cope with the heat.

Converting to the RX7 engine has been done and then you go as fast as you like.

I would have thought that the MX5 NC engine with a turbo would be a nice fit and good for 300bhp. The gearbox is the same.

The electronics for the RX8 will be difficult to work around, how will the traction/abs be done?

Edited by rotarymazda on Tuesday 4th March 10:01

petey1979

Original Poster:

27 posts

96 months

Tuesday 4th March 2014
quotequote all
Std ecu will be retained for using the rx8 dash (speedo etc) I assumed the abs was controlled by its own ecu anyway?

Will not be using traction control

Fastdruid

7,333 posts

122 months

Tuesday 4th March 2014
quotequote all
The RX-8 is CANBUS, Speedo is driven from the DSC HU/CM (as Mazda call it, aka ABS ECU). Tacho from the PCM (aka engine ECU). Fuel gauge is a simple resistance jobbie.

The HU/CM and PCM are linked and coded to one another, without the PCM the HU/CM will go into ABS only mode and will show the DSC warning light.

As the RX-8 is DBW I'm not sure how the PCM will handle being fed an RPM signal without a pedal (or a throttle body) I'd expect errors. I'd personally be wary even if you fooled it to get the DSC to work of using it on the road as the HU/CM will at times request a torque reduction (or theoretically increase) and without the ability to fulfill that request it could go horribly wrong.

Without the Steering ECU (or without the rack) the Steering fault light will come one.

It is possible to control the cluster on its own without the ECU, pretty easy with an arduino although might be a bit trickier to make it automotive suitable. Doing it that way you can also override some of the errors that'll come from the missing hardware. I've got a cluster that I had a play with and got everything working out of the car. Shout if you want the CANBUS ids.

petey1979

Original Poster:

27 posts

96 months

Tuesday 4th March 2014
quotequote all
Fastdruid said:
The RX-8 is CANBUS, Speedo is driven from the DSC HU/CM (as Mazda call it, aka ABS ECU). Tacho from the PCM (aka engine ECU). Fuel gauge is a simple resistance jobbie.

The HU/CM and PCM are linked and coded to one another, without the PCM the HU/CM will go into ABS only mode and will show the DSC warning light.

As the RX-8 is DBW I'm not sure how the PCM will handle being fed an RPM signal without a pedal (or a throttle body) I'd expect errors. I'd personally be wary even if you fooled it to get the DSC to work of using it on the road as the HU/CM will at times request a torque reduction (or theoretically increase) and without the ability to fulfill that request it could go horribly wrong.

Without the Steering ECU (or without the rack) the Steering fault light will come one.

It is possible to control the cluster on its own without the ECU, pretty easy with an arduino although might be a bit trickier to make it automotive suitable. Doing it that way you can also override some of the errors that'll come from the missing hardware. I've got a cluster that I had a play with and got everything working out of the car. Shout if you want the CANBUS ids.
mate, pretty much everything you just said went waaay over my head haha

I knew the car is canbus, I was hoping to pick up feeds for the tacho from fitting a rx8 crank sensor and wheel I assumed the speedo picked up a signal from the hubs along with the abs

is there a sensor on the throttle pedal? or on the body end? I will be keeping the pedal and adding a cable operated throttle to it.

is there any way of completely disabling the dsc completely?

any info you could send me on this would be great.

pete

other than the dash light what other problem can removing the steering rack cause?


HughG

3,244 posts

211 months

Tuesday 4th March 2014
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I like the idea of one of these, as I think I said in the previous thread, and previously gave it a little thought. Conceptually I was thinking along the lines that Fastdruid mentioned.

Fastdruid said:
It is possible to control the cluster on its own without the ECU, pretty easy with an arduino although might be a bit trickier to make it automotive suitable. Doing it that way you can also override some of the errors that'll come from the missing hardware.
Simple electrics I can deal with and I made the loom for the last kitcar, but electronics I don't have a good handle on. Fastdruid, or anyone else in the know, any thoughts on whether using the instrument cluster alone, or trying to piggy-back the whole car systems would be the easier approach for someone (me) who's good at simple electrics, but hasn't ever had to work on electronics.


s p a c e m a n

9,916 posts

118 months

Tuesday 4th March 2014
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Just pull the cluster out and stick a stack dash or something in there?

petey1979

Original Poster:

27 posts

96 months

Tuesday 4th March 2014
quotequote all
Same here, I built the entire management loom on my 205 including fuse/relay box but programming etc is a little beyond me.

I was also planning on piggybacking the engine management. And keeping everything else apart from the steering rack.

I have to admit if any lights came up on the dash I was going to remove the bulb.......yeeehaw ha

Fastdruid

7,333 posts

122 months

Tuesday 4th March 2014
quotequote all
petey1979 said:
I have to admit if any lights came up on the dash I was going to remove the bulb.......yeeehaw ha
Er, they are LED's smile

Fastdruid

7,333 posts

122 months

Tuesday 4th March 2014
quotequote all
petey1979 said:
mate, pretty much everything you just said went waaay over my head haha

I knew the car is canbus, I was hoping to pick up feeds for the tacho from fitting a rx8 crank sensor and wheel I assumed the speedo picked up a signal from the hubs along with the abs
I doubt it's that easy as the RX-8 doesn't have a simple crank sensor but an eccentric shaft sensor and I'm not sure how that relates to RPM's. You might find you get 3*RPM (or RPM/3).

Speedo is driven from what I presume to be an average of all 4 wheel speeds picked up by the ABS or DSC HU/CM (some RX-8s' only had ABS) from the ABS sensors (built into the hubs on the front, discrete on the back). It's sent to the cluster via CANBUS

petey1979 said:
is there a sensor on the throttle pedal? or on the body end? I will be keeping the pedal and adding a cable operated throttle to it.
There is no physical link between pedal and throttle body, total DBW. There are two sensors in the pedal (for redundancy)

petey1979 said:
is there any way of completely disabling the dsc completely?
Yes, same way as you'd turn it off. If you hold down the DSC off button for >10s it totally disables it as it assumes a fault, if you were to hard wire that link in then it would do the same every time (it resets on power on).

petey1979 said:
other than the dash light what other problem can removing the steering rack cause?
Well if you remove the column as well you'll remove the steering angle sensor but that only really is of use with the DSC working.

I'm also not 100% sure about the airbags, I think the cluster monitors the seat belts and the airbag computer is linked, I didn't do too much on that though.

petey1979

Original Poster:

27 posts

96 months

Wednesday 5th March 2014
quotequote all
Steering column is staying, just changing the rack to 'normal pas'

So is there any reason why the dsc won't work if I keep the correct shaft sensor and pick up wheel? Surely crank speed is crank speed and as long as the correct wheel and sensor are used all should be well?

I think it may well be a case of getting it all running then go from there, figure it out then.




Fastdruid

7,333 posts

122 months

Wednesday 5th March 2014
quotequote all
But crank speed isn't that simple on a rotary.

The 'RPM' on a RX-8 is the output shaft speed which is 3* rotor speed (so 9000RPM Output = 3000RPM Rotor).
If the eccentric sensor measures the rotor position then by using it you will get 3* RPM.

WRT the DSC as I said before part of the way the DSC interacts with the PCM is to request less (or more) torque to prevent wheelspin/oversteer. Without the ability to reduce torque I don't know what the DSC will do if it thinks you are oversteering so personally I'd turn it off as it could make things worse.

petey1979

Original Poster:

27 posts

96 months

Wednesday 5th March 2014
quotequote all
Ah yeah I see what you mean, you not sure what it reads?

Let's hope it's crank speed not rotor speed then.

How does the dsc work on an rx8 then? Via brakes, diff or engine?

petey1979

Original Poster:

27 posts

96 months

Wednesday 5th March 2014
quotequote all
It's ok just had a read.

Brakes and also throttle if it gets too out of hand.

So yeah I'll just disable it.

vrod

949 posts

160 months

Wednesday 5th March 2014
quotequote all
Good luck with the project, I had the 231 RX8 in winning blue that had every extra on it for just over 3 years and loved it. In the end it became a pig to start when hot. Changed the coil packs as that is the usual problem, it sorted it out but I never re gained confidence and the mpg was the final killer.

I always thought if it had a flat four engine it would be perfect. Maybe the subaru or toyota GT engines. The emissions would also mean they could now make them again!
I love the styling and the handling, you'll end up with a nice motor at the end of it.

madaxgt

6 posts

163 months

Monday 31st March 2014
quotequote all
Fastdruid said:
The RX-8 is CANBUS, Speedo is driven from the DSC HU/CM (as Mazda call it, aka ABS ECU). Tacho from the PCM (aka engine ECU). Fuel gauge is a simple resistance jobbie.

The HU/CM and PCM are linked and coded to one another, without the PCM the HU/CM will go into ABS only mode and will show the DSC warning light.

As the RX-8 is DBW I'm not sure how the PCM will handle being fed an RPM signal without a pedal (or a throttle body) I'd expect errors. I'd personally be wary even if you fooled it to get the DSC to work of using it on the road as the HU/CM will at times request a torque reduction (or theoretically increase) and without the ability to fulfill that request it could go horribly wrong.

Without the Steering ECU (or without the rack) the Steering fault light will come one.

It is possible to control the cluster on its own without the ECU, pretty easy with an arduino although might be a bit trickier to make it automotive suitable. Doing it that way you can also override some of the errors that'll come from the missing hardware. I've got a cluster that I had a play with and got everything working out of the car. Shout if you want the CANBUS ids.
Awesome project and very similar to mine I just finished except I put in a GM 1.6 turbo out of a corsa vxr. I thought it was going to fit without trimming the bulkhead but not quite so I did a smallish cut (not quite as big as yours). The dash is all in with the a/c/heater (modified to clear the new bulkhead) and have the ecu working with the power steering, rev counter gauges etc but apart from one.

It is up and running and ready to be mapped and I have ALMOST got mine MOT'd but failed as I have an ABS light up. We have a fault code of no can bus communication from the abs module but we think we are sending it the correct messages, obviously not! The speedo doesnt work either but the sensors are all fine.

Fastdruid if you could send me your list of the CANid's that would be a massive help as we dont know what is what module.

madaxgt

6 posts

163 months

Monday 31st March 2014
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Petey if you want to get the car all to work properly which I should do soon hopefully contact me and I can tell you what ecu I am using. I also managed to get my engine behind the front strut towers and I think (pinch of salt required!) the engine may be lighter than the rotary, even with an iron block.

Dont want to start my own thread or ruin yours but i can post some pics so you can see what I did if it helps. Its taken me over 12mths as I had so many hiccups, predicted it would take 6mths working on it in my spare time.

Escy

3,086 posts

119 months

Tuesday 1st April 2014
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Put a build thread up for it, i'd like to see it. What gearbox did you use?