Getting Tacho To Work In Rb20det Silvia?

[heyhey!]

hye ive finished my rb20det conversion...just wondering if any one knows how to get the ca18 silvia dash tacho to work???

i have both the r32 and silvia dash infrotn of me

anything i can take from one and put in the other??

thanks for any help

much appreciated

[rb20inside]

i too have this problem with a rb20 in a 180sx.

i just change by ear, but to have a working tacho would be nice.

[DRIFTERB25]

hey i guys i just finished my rb25 into the 180 conversion too and i got my silvia tacho to work but its not accurate because it was for a four cylinder ill have a look at the colour of the wire that comes out of the ecu for the tacho and get back to yas,but i wanted to know what tacho is an easy replacement for the 180 one?

[rb20inside]

that's what i mean. mine works (as in moves) it just isnt accurate at all.

when i'm up it the needle will fly round and hit the pin at the end and its still pulling and no limiter.

also i sit on the highway at 100km/h doin 4600rpm.

[BH_SLO32]

Gents,

You have raised my curiosity and I'm keen to find an answer. Given your tachos are actually working I suspect all you need to do is either find an appropriate frequency divider which you connect between the ECU tacho signal output and the tacho itself or install the tacho from an R32.

Given the previous motors were 4 cylinders it stands to reason that you need 2/3rd of the current frequency output by the RB ECU ie divide the 6 cylinder freq by 1.5 (6/4) (eg. 4600rpm = 3066rpm). If I had the diagnostics for the any of the 4 cylinder motors I could confirm.

I did a bit of a search on the net last night and found plenty of very flash (and expensive) frequency dividers but was looking for something a little more basic. Jaycar sell a digital speedo corrector kit ($45) which allows you to adjust the square waveform of a digital speedo signal (freq only I think) which will probably be suitable for adjusting the tacho signal (also square wave output).

If I get the time on the weekend I pop into Jaycar and have a look at the kit. If I think it is suitable I'll purchase the kit and do some testing on my R32 and let you know how it goes. If I get it working I'd be happy to install one in any of cars owned by members in the Brisbane area.

Hope this helps.

PS Anyone searched the NissanSilvia forum or contacted Tokyo Toys (they specialise in RB conversions for Silvias)?

Cheers,

[rb20inside]

cheers, let us know how it goes. possibly keen if gives good results as live in brisbane area.

although it doesnt seem to be as linear as 2/3 of the revs, so we'll see.

yer have searched NS.com, they are pretty much all ricers over there. not much useful thought out information.

Edited February 22, 2006 by rb20inside

[BH_SLO32]

Good news, I believe I found a solution. I purchased a Jaycar “Speedo Corrector” kit and “Digital Tachometer” kit and did some testing in my R32 with RB25. The information provided with the digital Tacho confirmed my suspicions about the required tacho drive signal. The digital tacho can be manually calibrated for 1-12 cyclinder 4 stroke engines.

Traditionally the tacho has been driven off the switched side of the ignition coil (primary side) with a pulse generated when any cylinder fires which on a 4 cyl 4 stroke engine is 2 pulses/rev and for a 6 cylinder 4 stroke engine is 3 pulses.

Newer cars equipped with an ECU may drive the tacho with a low voltage signal as is the case with most skylines. The number of pulses per revolution has obviously not changed confirming my earlier suspicions that the Silvia tacho is looking for a different frequency signal (to suit a 4 cylinder engine – 2 pulses per rev not 3).

I tied into the ECU tacho drive wire and connected the digital tacho which when set for a 6 cylinder engine gave the same reading as my R32 analogue tacho. I then changed the setup to a 4 cylinder input which when idling at 900rpm gave a reading of between 1200 and 1300rpm on the digital tacho (the digital tacho changes in 100rpm increments). At about 3000rpm on the R32 tacho the digital tacho had a reading of about 4600rpm.

The speedo corrector kit can be used to correct a pulsed digital signal from a speed sensor to compensate for any speed inaccuracies generated by diff or gearbox changes etc. This would be ideal for R33 owners who convert from an auto to a manual. The unit can also be used to correct tacho pulsed signals.

The unit is very flexible as it will adjust the output signal from the unit between 1% to 99% of the input signal with changes in 1% increments possible. It can adjust either up or down. In the case of the Silvia tacho, the drive signal needs to be adjusted to approximately 2/3 of the signal coming from the ECU.

To test I set the digital tacho to receive a 4 cyl input and connected the corrector unit in between the ECU and digital tacho. I then proceeded to adjust the corrector unit until the digital tacho read the same as the R32 analogue tacho. I compared between idle and approx 5000rpm.

The speedo corrector kit can be purchased from Jaycar for about $45. The kit number is KC5380 (have a look on the Jaycar website).

As mentioned in my earlier thread if there is someone in Brisy who would like to trial run the unit then I’d be happy to install my unit in their car.

Hope this helps.