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What mods are required to fit RB25 gearbox to NA?

I wonder where you got THAT idea. Haha.

You would need an adaptor plate made of 20mm aluminium. And then a custom clutch. And a custom tailshaft. And a custom powerplant frame.

Dann

mazdatenfive wrote:What mods are required to fit RB25 gearbox to NA?

Chat with CT, he has one in his SP race Car.

NitroDann wrote:I wonder where you got THAT idea. Haha.

Im sure he already knows, that was the implication above.

Dann

It is not as easy as people have indicated in my high jacked thread.
• The front of the RB25 Bell housing is cut and MX5 front bell housing is welded using a gig to ensure it all lines up.
• The RB box needs to be pulled apart so the main shaft can be machined to the correct length.
• A new mounting point is made for the clutch slave cylinder and clutch line.
• New Nissan clutch plate
• Rear mount for the gearbox is to be made.
• New Tail shaft
• New mount for the power frame
• New hole for the gear shift which will need some of the centre console being removed
• New exhaust as the RB box is much bigger than the standard box and the dump pipe will need to be moved.
• You will potentially need to change the diff ration as the RB rations are very different from standard MX5
• I also now also run solid engine mounts
All up I have spent close to $5K including the cost of the new box which are now getting harder to find.
I have no idea what your engine/car is to need the above box but I run an SP race car in QLD for the past 2 years have spent thousands on gearboxes including a 5 speed Quaife gear set that lasted 1 race meeting and cost me thousands to land in Australia. The simple fact is MX5 gearboxes along with the power frame are not designed to have that much power put through them. The main reason we keep blowing them up is the flex in the gearbox from the load the engine is trying to push through the slicks causing the box to twist/flex that damages the gears and eventually strips every tooth of 3rd or 4th gear.
If you are serious about the above I can put you in touch with the guy that helped most of the QLD guys and also CT how is now running the above.
Neil

Thank you Neil for the info.

Anyone just tried TIGing more braces to the box/bellhousing?

Dann

NitroDann wrote:Anyone just tried TIGing more braces to the box/bellhousing?

Dann

I think that is what Daniel has tried?

My gearbox only had the SE gears installed.

Neil

Dont know..... The SE gears are said to be stronger but Ive never heard of anyone kill 5 regular 6 speeds, and then fixig it with an se gearbox or gearset.

Dann

The SE are just Hardened gears so should last longer than the standard set.

But it all cames down to the gearbox flex.

Thats my understanding also.

Why did you do RB25 swap not FC?

Dann

Whats FC?

NitroDann wrote:Thats my understanding also.

Why did you do RB25 swap not FC?

Dann

Neil d wrote:
Whats FC?

Thats probably why...?

Dann

neil d wrote:But it all cames down to the gearbox flex.

I assume from that oil/oil temperature was not an issue?

The FC/FD box is not known as being super strong....albeit still stronger than the stock mx5 6 speed but probably not a big enough amount. The RB25 box is the same in the 300ZX TT's, R32 and R33 skylines and is considered pretty bullet proof. It's what the high powered Silvia's usually get modified to so it's a pretty well-proven solution.