I need some help, I need to either change an 85-86 TC tach to work on a V8, or I need to change the sweep on the V8 tach to read 7000 rpm like the '85-86 TC tach. The article on coolcats says that mod only works on 87-88 tachs. Somehow I need to get a tach to read up to 7000, but on a V8. Any help is appreciated.
Thanks, Herb :D
isnt their a thread on this somewhere? or was that to convert a 7k tac to a 6k v8 tac? i'll look around, worst comes to worse i think its a matter of pulling out fun things like diods and capicators from the bord on the tac and replacing them with something different.
found it http://www.coolcats.net/tech/advanced/4to8tach.html now if somebody has a aftermarket tac, and one of these to experiment with, maybe we can find a way to calibrate an extra thousand rpm in their. other than that it looks like you may need a different tac, at least a 87-88 tc tac, which i have one of by the way.
I already know about the coolcats article, as I said, but the 87-88 TC tach only goes to 6000, and my custom gauges are 7000.;)
what i was getting at is using one of the tac's not a early one because they cant be modded apairently, and replacing the resistor with a slightly different one. put it back in a car with a after market tac ghetto'd in or a multimeter set to rpm and see if its calibrated correctly. its going to be alot of trial and error tho.
YOu should eb able to modify the sweep of the V8 tach easily enough. We know that with a 100k resistor the tach is calibrated for a 4cyl, which would make the needle move twice as far on a V8 engine. We also know that a 51k resistor will recalibrate that 4-cyl tach so that it will be accurate with a V8. What you need is a resistor that will lower the V8 readings even more but only slightly so (so that you can cram 7k rpm worth of measurement into the same sweep that used to be 6k). I would recommend trying a 47k ohm resistor, since it's the next common step below 51k. It may not be 100% accurate, but no factory tach in these cars ever was...
Thanks. :D Hey no one ever said I was smart...lol:hick: I just noticed that the 97-88 TC cluster has the 7000 sweep, just stops at 6000 to make room for the firm ride light. Duh.:crazy: :bricks1:
T Chicken is correct, but my guess is you'll need a resistance in the range of 43K- 47K ohms. Its easy enough to put a pair of 22K in series to get 44K. Or 18K and 27K in series to come up with 45K. Then you never know 47K may be fine.
6/7th of 51 is 43.7 so you need 44 ohms.