Converting 6 cylinder tach to 8 cylinder

[BluLightning]

Anyone know how to convert a 6 cylinder tach to work with an 8 cylinder? We're working on Donna's 71 Cutlass and got the tach working but is reading too high. When we switched the dwell meter to the 6 cylinder setting, it and the tach read the same numbers. It appears that somewhere along the line, somebody must have replaced the original tach with a tach out of a 6 cylinder car. This is a factory Olds Tick Tock tach so we'd like to get it reading correctly. Any help is appreciated.

Bob

[Barry Donovan]

this is common.
the net and ohms law and resistors is about as insane as....


the 6 is 75% of the 8.
in theory playing with 3v, knowing the ampers.. that could find resistor.
just one.
Don't need a supercomputer and vacuum tubes and that 7 pound hetasinked DRL diode from a gmc that came from a 1950s space program.
No.
you need none of those things.


my subaru tacj went berserk on the msd 6530. I stole the changer that makes 60hz from a computer power supply go safely to ground as 60hz. it still knows 4cyl signals even through the thrashing of the msd.
one gadget, ten seconds with electrical tape.

Not sure what engineer insisted on being such an asshole with the overthunk calculations.

you should be able to dial that in by accident.. playing with resistor.

/rant

[anotheridiot]

Did they actually put something as special as a tic toc tach in something with 6 cylinders?

[BluLightning]

Did they actually put something as special as a tic toc tach in something with 6 cylinders?

No idea but it's reading at a 6 cylinder rate.

[Deaf Bob]

Aftermarket ones I used had a switch inside to choose cylinder nbrs.. Maybe that tach has something like that but not marked?
If not, somebody internally changed it.. OR installed a 6 cyl tach ..

[DanStokes]

I have a 4 cylinder VDO tach in the Volvo. It was converted by the first SBF installer. The process is to add a resistor in the tach input signal on THAT tach. Now I'll wager that someone has posted online how to do that conversion on your tach, too. High likelihood that there's a snipped wire inside the tach that you'll have to reconnect or visa-versa. I'd fire up Google with a possible search term "GM tic-tock tach 6 to 8 cylinder conversion" or something like that.

Dan

[silver_bullet]

From Sean's Memory... I cheated and asked him...
Dakota Digital Tach Signal Interface?

https://www.summitracing.com/parts/dak-sgi-8e

[anotheridiot]

No idea but it's reading at a 6 cylinder rate.

I am not saying you can do it, but I took a sun tach's guts and mounted it behind the stock 67 camaro faceplate. Seems to work fine. Dont know how the tic toc tachs work but the only difference is before you put the pointer on you need to energize the tach since it raises 500 rpms to get to zero.

[DanStokes]

From Sean's Memory... I cheated and asked him...
Dakota Digital Tach Signal Interface?

https://www.summitracing.com/parts/dak-sgi-8e

THAT is a nifty thing to know about!

Dan

[silver_bullet]

Yeah, He found it on the S10 website...go figure...

[Dan Barlow]

What you need is a variable resister . The actual name is potentiometer . Then you can dial it in . My son did this to his 92 RS Camaro .It was originally a V6 car .Think it was less than $3 . If you want I can get more info tomorrow . ( 5-5-17 )