Gears/diff Speed Ratio Issues

[fattox33]

Hi all,

I had a mate of mine SMS me today saying he was going down to test drive an R32 with an RB25 and R33 box swap, then text me 5 minutes later asking what engine speed mine did at 100km/h in 5th gear, I said around what it should be which is the 2500-2600 mark, and his reply was that the R32 was doing 4000!! rpm in 5th @ 100km/h.

Now I'm a 3rd year mechanical engineer, and have done the research, and according to what I can work out, if the box is standard ratio, the LSD ratio is something like 6.2:1, which doesn't sound quite right for an R32 diff.... So in all your experiences, what could be causing this? There is a possibility that the wrong series of R33 computer was used, but I can't see how this would cause an issue... from memory the motor is a series 1 r33, as is the box, but the ECU and AFM are from a series 2.. I didn't think this would cause problems, but apparently so..

So if you're lazy, basically why would an R32 with an RB25DET and r33 box be doing 4k rpm in 5th gear @ 100km/h? Speedo verified against a GPS.

Cheers

[SargeRX8]

Gps is no way to verify. Check the thread under this called quick question. Similar issue. Get an consult cable o that and read direct rpm from the engine. Does it sound like it's revving at 4krpm or is that just the read out? The difference between 2600 and 4000rpm in sound is very obvious.

[blind_elk]

GPS is an ideal way to verify speed.

I'm not aware of the R32 tacho being switchable, but the difference in revs sounds like a tacho switch to monitor a 4-cyl engine, but getting the signal from a 6.

[SargeRX8]

Even though gps technology tells you it has x +/- tolerance. My mates car and gps are always about 4 to 8 k apart.

[luvpsi]

isnt the speedo drive on a r32 mechanical and the r33 electrical if so id say it has been wired wrong and may need a tacho box (i think thats what they are called)