Suitable tacho for EJ20

[asra]

Can someone tell me please if a standard VDO tacho is ok for my Subie EJ20 set-up with the standard car computer which has an input line for the tacho?PeteBairnsdale,Vic.

[NiqueNaque]

Pete,If there is a VDO sensor, use that, it won't cost you any more and it is unlikely to blow up in your face...If not:Be vewy, vewy careful with this, don't plug anything into it without due regard for the following:Most computers are voltage / current sinking devices which rely on a limited amount of current going into it, otherwise phhht, smoke theory of electronics! [It only works because the smoke is held in the device, when the smoke gets out, everything stops, so the thing works on smoke, not electricity! c/- (Doc) John Evans]If you are going to plug anything in make sure you see what it does before you plug it in. Get a multi meter and see what happens with the input point before you do anything, you will probably find that there is no voltage difference between earth and the input point. IE, if you put the probes between the frame and the -ve terminal there will be no voltage with the engine running, this is an indicator the input is voltage sinking.Probably if you switch it on, and run the engine, put the +ve multi meter probe on +ve battery terminal and the -ve lead of the multimeter [set to volts 15 - 0 v DC] to the input, the voltage may vary with revs, if not that then the resistance will vary, probably the faster the engine the lower the resistance and the higher the voltage difference.Try connect all *but* the input on your VDO tacho, turn the ign on and check what the VDO wire is doing - probably it will be 12 V +ve, so don't short it on the frame. Run the engine and see what it does, probably nothing, the voltage may go up and down with the alternator kicking in and out.So if you prove by this it - the subi computer - is voltage sinking, and the VDO is a voltage source, then they may work.. BUT!! the VDO value will most likely not be the same as the subi computer value, you may have to trim it using a fixed and /or variable resistor to make the VDO read the actual revs, you will need a stroboscopic tachometer to when work out what the revs are or a tacho of some description to calibrate the VDO against to get it right. In this even I would start with a Very high resistance 5 watt 1m ohm variable resistor and plug it in series between the vdo and the computer, make sure it is set at 1 m Ohm, start the motor and see what happens. With this level of resistance in series it should not be able to fry anything. You then check the value of the tacho against the calibration tacho and then very, very, very slowly and carefully dial back the resistance until the rpm reading is right.If you want a verbal rendition of this ring me on 0418 811953 and I can talk you through it, in fact I would much prefer you did this rather than trying to interpret what I am saying.Cheers,Nicholas TomlinAlarmist - www.alarmist.com.au - we scare for you

[asra]

Thanks Nick, I will follow your advice and be careful. I'll let you know how I get on. ....hey who let the smoke out....[:I]PeteBairnsdale,Vic.

[asra]

Thanks Nick, I will follow your advice and be careful. I'll let you know how I get on. ....hey who let the smoke out....[:I]PeteBairnsdale,Vic.

[Tim]

Pete, the computer wire at the Subaru computer is actually an output to the tacho, not an input to the computer it is just a voltage pulse thats works a normal VDO tacho fine.Tim McClureBroken Hill

[Tim]

Pete, the computer wire at the Subaru computer is actually an output to the tacho, not an input to the computer it is just a voltage pulse thats works a normal VDO tacho fine.Tim McClureBroken Hill

[asra]

Thanks Tim. That is good news indeed.PeteBairnsdale,Vic.

[asra]

Thanks Tim. That is good news indeed.PeteBairnsdale,Vic.

[asra]

See Pete, you should have listend.Simple carb and adaptor, Gem dissy and adaptor, and coil to suit.And hey presto Chopper Chick's your aunty.[][][]Sam.Melbourne Vic.

[asra]

See Pete, you should have listend.Simple carb and adaptor, Gem dissy and adaptor, and coil to suit.And hey presto Chopper Chick's your aunty.[][][]Sam.Melbourne Vic.

[asra]

Just too sifisticated for that antiquated museum stuf these days Sam. i'm rite into the computa age now.PeteBairnsdale,Vic.

[asra]

Just too sifisticated for that antiquated museum stuf these days Sam. i'm rite into the computa age now.PeteBairnsdale,Vic.

[Ken Watson]

Use a Gokart tacho that just clips onto a plug lead. Cost -about $120Easy to read.You need the one that does 2 and 4 strokes. Ken

[Ken Watson]

Use a Gokart tacho that just clips onto a plug lead. Cost -about $120Easy to read.You need the one that does 2 and 4 strokes. Ken

[asra]

Hi Ken, Would seriously consider that alternative but the EJ20 has its four coils directly on top of each plug so no lead to attach to.PeteBairnsdale,Vic.