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Heres how to make RB25DET gearbox work with R31 speedo

Bozz

By Bozz,
in Classic & Vintage (1950's-1980's)

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Bozz Proficient

Bozz

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Posted

If you're a bit electronics inclined, this will save you hundreds of dollars by not getting a pro to do it.

To save a bit of time, I found an electronic square wave frequency doubling circuit on the internet and slightly altered it to suit the way the electronics in the Skyline work. Next I designed a circuit board that would fit all the components and built it. It works and is pretty accurate

Here's the original circuit:

http://users.otenet.gr/~athsam/freq...r_with_4011.htm

I simply added a FET to the output (pin 11) to sink the current from the speedo instead of relying on the CMOS IC to do it.

Parts:

IC1 - CMOS 4011 quad NAND gate

R1 and R2 - 10kohm 1/8 or 1/4 watt resistors

C1 and C2 - 1nF capacitor (Code on cap - 102)

Q1 - Any FET that can handle 50-500mA of Source-Drain current.

The next link is the circuit board diagram I designed to mount all the components on. If you aren't able to, or dont want to etch your own circuit boards, you can simply buy a small amount of veroboard from the local electronics shop.

http://members.optushome.com.au/pisstnbrok...qmultiplier.gif

Hope it helps someone

Bozz Proficient

Bozz

Posted
  • Author
Posted

Yep its finished and I've been driving it all day... Love it

The RB25DET gearbox is so much better than the RB30E gearbox...

Problem I'm finding is that all gearing is a bit taller, with fifth being a lot taller. Acceleration is reduced in first and it gets me to about 75km/h where the RB30E gearbox used to get me to about 65km/h at redline.

Now I can bump up boost and make the engine more powerful since I dont have serious traction issues anymore :D

  • 11 months later...

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