Gearbox options for replacing 240z autobox with RX8 6 speed??

Peter loveday

Club Member
I’m halfway through the conversion myself ( the hard bit in cad is done)
A few things to consider

Shifter position- it depends on which car you have, my series 1 shifter hole is too far back but should be about right for a later car, I will be just shifting the engine back around 20mm or so

Input shaft- the Rx input shaft is not that long, about flush with the bell housing. My solution was to design a bespoke spigot bearing.

Clutch- Rx box uses a ford spline, a hybrid clutch will be needed.

Starter position- bell housing will need adjusting, the Rx box mounts the starter facing in opposite direction down near our exhaust manifold

On a positive note. The box fits, is light, has good ratios and excellent shift quality. The clutch slave is also in a great position

I’ll be doing a 3D scan of the box at some point which I’d be willing to share, my current cad is very basic
 

jonbills

Membership Secretary
Site Administrator
I’m halfway through the conversion myself ( the hard bit in cad is done)
A few things to consider

Shifter position- it depends on which car you have, my series 1 shifter hole is too far back but should be about right for a later car, I will be just shifting the engine back around 20mm or so

Input shaft- the Rx input shaft is not that long, about flush with the bell housing. My solution was to design a bespoke spigot bearing.

Clutch- Rx box uses a ford spline, a hybrid clutch will be needed.

Starter position- bell housing will need adjusting, the Rx box mounts the starter facing in opposite direction down near our exhaust manifold

On a positive note. The box fits, is light, has good ratios and excellent shift quality. The clutch slave is also in a great position

I’ll be doing a 3D scan of the box at some point which I’d be willing to share, my current cad is very basic
That doesn't sound trivial then, even with an adapter plate. Will you publish details and pics as you solve the problems for anyone that might follow?
 

Peter loveday

Club Member
Absolutely, I still feel this is the best gearbox option for the 240 in terms of value and performance. A few technical challenges to overcome but nothing too serious.



I also forgot to mention that there is no speedo drive, you would have to look to the Nissan s15 variant for that.
 

jonbills

Membership Secretary
Site Administrator
Absolutely, I still feel this is the best gearbox option for the 240 in terms of value and performance. A few technical challenges to overcome but nothing too serious.



I also forgot to mention that there is no speedo drive, you would have to look to the Nissan s15 variant for that.
Thanks. Actually I'm pretty sure the s15 nissan box doesnt have a speedo drive either. S14a was the last with the mechanical drive I think.
I don't think it's a huge problem, speed hut and others make gps speedos that look quite similar.
 

8658kv

Club Member
I’m halfway through the conversion myself ( the hard bit in cad is done)
A few things to consider

Shifter position- it depends on which car you have, my series 1 shifter hole is too far back but should be about right for a later car, I will be just shifting the engine back around 20mm or so

Input shaft- the Rx input shaft is not that long, about flush with the bell housing. My solution was to design a bespoke spigot bearing.

Clutch- Rx box uses a ford spline, a hybrid clutch will be needed.

Starter position- bell housing will need adjusting, the Rx box mounts the starter facing in opposite direction down near our exhaust manifold

On a positive note. The box fits, is light, has good ratios and excellent shift quality. The clutch slave is also in a great position

I’ll be doing a 3D scan of the box at some point which I’d be willing to share, my current cad is very basic

Hi Pete,

Hopefully I will be doing this later in the year.

Not using an adapter plate though, I will cut the front of a z bellhousing and fit to a RX8 box.
Plan to machine the spigot shaft to accommodate z thrust bearing. ( this has been done before to a four cylinder Datsun engine, can't find the link )

Will you be using the carbon fibre RX8 prop shaft?

And for a speedo, I did think about fitting a new style , with speed displaying on the windscreen.

I'm a little concerned about the ratio's though. If when done the box is any good, I plan to have some bellhousing's cast, with mounting, and propshaft as a kit.

Steve
 

SeanDezart

Well-Known Forum User
Interested for a future swap although I've noted these ratios for each gearbox type and series :
 

Attachments

  • Gearbox ratios.docx
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hallie

Club Member
Great information everyone thanks

I will dig the rx8 engine and box that I have out and have a measure.

What are the dimensions of a manual 240z box from the engine to the gear lever? (I only have an auto)

I have the carbon propshaft from a RX8 and hope to get a prop made using the RX8 universal joint at one end and a subaru one at the other

I hadnt thought about the speedo issue!
 
Last edited:
Great information everyone thanks

I will dig the rx8 engine and box that I have out and have a measure.

What are the dimensions of a manual box from the engine to the gear lever? (I only have an auto)

I have the carbon propshaft from a RX8 and hope to get a prop made using the RX8 universal joint at one end and a subaru one at the other

I hadnt thought about the speedo issue!

If you can place it on a flat surface measure;

from the bell housing face to gear lever

distance to where the bell housing ends

Diameter of the bell housing

Diameter of the gear housing

I'll do the same for an a type 4 speed and C type box.
 

hallie

Club Member
Have been to look at a 5 speed z box

From the engine block face to the centre off the gear shift is 740mm

Have arranged to borrow the necessary parts to have this adaptor made
 

8658kv

Club Member
Have been to look at a 5 speed z box

From the engine block face to the centre off the gear shift is 740mm

Have arranged to borrow the necessary parts to have this adaptor made

Before having the adaptor plate made, would it not be worth checking starter to tunnel clearance also where the exhaust will run, the solenoid on the RX8 starter sticks out a lot.

As said above the starter fits from the back on the RX8, on the opposite side to the L series.

Access to the starter once fitted looks a challenge.

Steve
 

hallie

Club Member
Thanks Steve

Yes I will be having a close inspection of everything before I get anything made.

I need to get the box out of storage and the autobox out of the car so I can offer the RX8 box in the tunnel to see if its possible or not
 

jonbills

Membership Secretary
Site Administrator
Has anyone made any progress on the rx8 gearbox? I was just looking at ebay - they do seem plentiful and cheap.
 

johnymd

Club Member
I’ve got one in the workshop now.
Shifter is set back 4mm compared to a zed box. A friend of mine is having the bellhousing modified on his so it mates up with a Yamaha r1 v8. I wait till it comes back and see what it looks like. From what I’ve read there are a few similar boxes: Toyota j160, Nissan s15, ect. Toyota one looked a good option but it’s long.
 
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