wiring in a tach?

[fastpakr]

Wait... if it's getting half the pulse count, wouldn't you need the tach set for half the cylinders, not double? If so, an automotive tach wouldn't work.

[Anonymous]

Wait... if it's getting half the pulse count, wouldn't you need the tach set for half the cylinders, not double? If so, an automotive tach wouldn't work.

The GS's give 2x the pulse counts that a 4 cylinder car generates. If you used a tach set for an 8 cylinder car, then it should give the correct RPM reading.

[Anonymous]

If im not mistaken dont four cylinder engines fire 2 cylinders at a time? same as a four cylinder on a gs motorcycle right?

So if this is true wouldnt the tach get the same reading in a car or a bike.

And with this topic comes a question..Does the size of the stroke influence the rpm reading or it doesnt matter, cuz not all engines have the same crank and stroke size so is a tach specially made for each engine or it doesnt matter as long as it knows when the spark is?

[duaneage]

Wait... if it's getting half the pulse count, wouldn't you need the tach set for half the cylinders, not double? If so, an automotive tach wouldn't work.

The GS's give 2x the pulse counts that a 4 cylinder car generates. If you used a tach set for an 8 cylinder car, then it should give the correct RPM reading.

8 cylinder = 4 pulses /rpm
6 cylinder = 3 pulses /rpm
4 cylinder = 2 pulses /rpm
2 cylinder = 1 pulse/rpm

Look at the crankshafts of these engines and it becomes apparent.

[gtsg01]

If I may offer a suggestion. While everyone seems to have a grasp on the number of pulses per revolution, you only need to monitor One coil to get the tach to work properly.

So, if you hook the tach to the 1-4 or 2-3 coil and set the tach to 4 cylinders, it should read correctly.

I will hook my dwell/tach tester (Yes, I am an old fart and still have one) to my 1100 this afternoon to verify.

I will let you know how it turns out.

[Detman101]

If I may offer a suggestion. While everyone seems to have a grasp on the number of pulses per revolution, you only need to monitor One coil to get the tach to work properly.

So, if you hook the tach to the 1-4 or 2-3 coil and set the tach to 4 cylinders, it should read correctly.

I will hook my dwell/tach tester (Yes, I am an old fart and still have one) to my 1100 this afternoon to verify.

I will let you know how it turns out.

That is exactly what I was thinking. However. How would you go about wiring the tach into the coil?
Explain please, I plan to pick an electronic one up after work today.

Thank you,
Dm of mD

[fastpakr]

Automotive tachs just connect to the negative side of the coil. I was talking about only using one coil as well, but hadn't been aware that they fired on compression AND exhaust.

[DMPLATT]

So, what's the prognosis here? Still deciding?


Billy Ricks said he wired in a GSXR Tach, how hard is that and how much configuring is needed?

Sorry to hijack, but sounds like lots of Tach trouble going around. :?

Thanks

[Anonymous]

Automotive tachs just connect to the negative side of the coil. I was talking about only using one coil as well, but hadn't been aware that they fired on compression AND exhaust.

That's correct - wire to the negative side. If an automibile has 8 cylinders and one coil it fires 8 times for every two revolutions of the crank. A 4 cylinder car fires the coil (single coil) 4 times for every 2 revolutions. The GS fires each coil 2 times for every 2 revolutions or 1/2 the count for a 4 cylinder tach wired to the coil. You then get 1/2 the RPM reading on the tach.

If you are using a tach that reads from a single coil for each cylinder, then you will get an RPM reading of 2x since the GS fires for 2 cylinders.

It all depends on how they indtend the tach to operate in the first place. Put it on and look at it.

[Detman101]

So you would have to run the tach negative to the negative on both coils right?

(I'm so confused by this electronic tach theory)


Dm of mD

Automotive tachs just connect to the negative side of the coil. I was talking about only using one coil as well, but hadn't been aware that they fired on compression AND exhaust.

That's correct - wire to the negative side. If an automibile has 8 cylinders and one coil it fires 8 times for every two revolutions of the crank. A 4 cylinder car fires the coil (single coil) 4 times for every 2 revolutions. The GS fires each coil 2 times for every 2 revolutions or 1/2 the count for a 4 cylinder tach wired to the coil. You then get 1/2 the RPM reading on the tach.

If you are using a tach that reads from a single coil for each cylinder, then you will get an RPM reading of 2x since the GS fires for 2 cylinders.

It all depends on how they indtend the tach to operate in the first place. Put it on and look at it.

[fastpakr]

Swanny, I really think you're mixing yourself up in that logic somewhere. Using the info you just gave that the GS justs divides the job across two coils (but total pulse count is no different from a single coil auto system that fires each time a cylinder is coming up on compression stroke), then the coil reading of a single coil on a GS will be 1/4 that of the only coil on a typical 8 cylinder car. To get the readings to match, you'd need an auto coil for a 2 cylinder car (yes, i realize that's not going to happen).

That is, unless each coil on a GS fires every time either of the cylinders it powers is on the compression stroke, as some others seem to be indicating?

random numbers...
8000rpm = 64000 pulses/minute (8 cylinder, single coil)
8000rpm = 32000 pulses/minute (4 cylinder, single coil)
8000rpm = 16000 pulses/minute PER COIL (4 cylinder, 2 coils)
8000rpm = 16000 pulses/minute (2 cylinder, single coil)

[Anonymous]

Correct me if I'm wrong here guys but......

If you look at the pickups you'll get some idea of how it works. There are two pickup coils and one rotor. Every time the rotor passes a pickup it sends a pulse to the ignitor.

This means two pulses per crank rotation.

The Ignitor sends out one pulse per crank rotation to each coil, ergo each spark plug gets a jolt every time it passes TDC, therefore each coil gives out the same number of pulses as the crank revolutions.

The reason I need to put a frequency divider in is that I've fitted a Boyer branson electronic ignition to my GS550ES. The rotor arm on this has two magnets and the pickups wired together in series which effectively doubles the pulses sent out to the ignition module. Which means each sparkplug gets a whack on every half crank revolution.

[Anonymous]

So you would have to run the tach negative to the negative on both coils right?

(I'm so confused by this electronic tach theory)


Dm of mD

You can't do that.

[gtsg01]

Here is the result of my Dwell/Tach test on my GS1100.

Meter connected to the White wire of the 1-4 coil.

Engine idling at 1000 rpm indicated on mechanical tach

On 8 cyl scale = 250 rpm

On 4 cyl scale = 500 rpm

On 2 cyl scale = 1000 rpm

These readings are from an analog meter and are approximate, but in the ballpark.

The 4 cyl GS engine has 1 pulse per rpm. So you need a tach with a 2 cylinder setting.

I was quite surprised at the results. I have tried to work it out in my head and always came up with 2 pulses per rpm

Most of the inexpensive Tach's I have seen only have 8-6-4 cylinder settings.

[Anonymous]

Swanny, I really think you're mixing yourself up in that logic somewhere. Using the info you just gave that the GS justs divides the job across two coils (but total pulse count is no different from a single coil auto system that fires each time a cylinder is coming up on compression stroke), then the coil reading of a single coil on a GS will be 1/4 that of the only coil on a typical 8 cylinder car. To get the readings to match, you'd need an auto coil for a 2 cylinder car (yes, i realize that's not going to happen).

That is, unless each coil on a GS fires every time either of the cylinders it powers is on the compression stroke, as some others seem to be indicating?

random numbers...
8000rpm = 64000 pulses/minute (8 cylinder, single coil)
8000rpm = 32000 pulses/minute (4 cylinder, single coil)
8000rpm = 16000 pulses/minute PER COIL (4 cylinder, 2 coils)
8000rpm = 16000 pulses/minute (2 cylinder, single coil)

Corrected random numbers...
8000rpm = 32000 pulses/minute (8 cylinder, single coil)
8000rpm = 16000 pulses/minute (4 cylinder, single coil)
8000rpm = 8000 pulses/minute PER COIL (4 cylinder, 2 coils)
8000rpm = 8000 pulses/minute (2 cylinder, single coil)

Check my post again. I think we are saying about the same thing. The correction is due to the fact that the crank turns twice for each firing. (4 cycle)