I know this topic has most likely been beatin to death but what do i need to put a tach on a 2002 Scrambler H.O. I was most likely going to pick up a Sun Pro Tach from auto zone or kamaprt (KMart) How many ignition Pulses do i need? what wires need to be Tapped? Thanks guys! Jason

 

Jason, the 4-strokes use 6 pulses per revolution compared to 2 pulses on a 2-stroke. I havent tried hooking one up to a 4-stroke, so I cant help you with that. I dont think it will work, but maybe someone can shed some light on it. Bubba

 

Scramblin2002ho

Sorry but it won't work. I don't unstand why, but after buying one and talking to Sun, I was told it wouldn't.

We ended up with a digitron playback tach.

 

so if i get one set up for six pulses it wont work? any other choices besides the "mini" tachs i want a dial insted of a LCD screen, Jason

 

BuMp!

 

I'll explain how it works as I think this through for you.

First auto background: A 4 stroke fires every other rev. A distributor spins w/the cam, or half speed, hence its already doing a 2:1 reduction. The car tach wants to crank revs though, not ditributor revs, so we need to take our ignition impules and to a X 2 in the car. Thus a car auto "senses" half the revs of the number of cylinders it has. so a 4 cylinder car senses 2 "impulses"

As is happens, most 1 or two cylinder 2 stroke engines are set to fire every 180 degrees. Yes, that means they fire at bottom of stroke too. The net of it all is that they fire at 2 impulses per rev, or they match the 4 cylinder auto setting works.

P 4 stroke ignitions seem to fire 6 pulses per rev. Don't know why, but I wonder it its not sensing off the alternator magnets....

Anyway, it seems to me you'd want a tach for a 12 cylinder auto. Unusual, but not un-heard of. the closest I know of price wise is the stewart warner @ about $100, or perhaps a VDO @ $200.

Finally, the sun performance series is documented @ a max of 10 cylinders. Can't help but notice that dip 1 is a x2 multiplier and dips 2-5 are for values 2-5. By flipping on and off the x2 dip they get up to 10 cylinders. I also note dip 6 isn't documented. Course, if it was active that would be for a 6 cylinder (which they didnt' need, they just did a 3 cyl x2) and with the x2 dip on that would be a 12 cylinder setting. hm... but then the stewert warner is documented and cheaper too!

luck.

dan

 

well the tach i was lookin at was 30 to 40 dollars at Autozone and as mentioned it was set for up to 10 cylinders im advanced in like auto shop so sum makes sence sum doesnt could you simplify? im only 15 thanks!, Jason

 

Wow, the best I could get from autozone for $35 was the pro II, and it only did 2-4-8 cylinders.

Anyway, to net it out for you, you need a tach that supports a 12 cylinder car.

Now, MAYBE a sun tach will work...

Assuming you have a sun tach, and that its one with 6 dip switches (if not you need a different tach):

Switch two turns on "sense two pulses"
Switch three turn on "sense three pulses"
Switch switch four turns on "sense four pulses
Switch Switch five turn on "Sense five pulses
Switch switch six is unmarked

For a six cylinder the have you turn on switch3, and the "impulse doubler" switch, switch #1
They have no 7 cylinder setting
8 cylinder is same as a 4, but with #1 also turned on.
10 cyl is same as a 5, but also with #1 turned on.

All that will be in your owners manual

I'm wondering what dip switch #6 does. It sorta follows that, had it been enabled, dip switched #1 and #6 being on (and only) would have allowed for 12 cylinder operation. I've no idea of course.

 

Well i guess that idea went down the tubes i wanted a tach with out spendin $100 cuz well i just dont have that but if you think of somthing PM me if ya like thats for all your help guys!, Jason