I installed an autometer tach on my dads 91 350 with 5 speed and 215 tires and 3:50 gears. I need to know what some of you guy's are turning rpm wise at say 55 and 60 in fourth or fifth so I can set the tach it works off of the alternator and works pretty well I set approximate by my truck but I have 4.10's

 

I went to the truck shop up the road from work. I walked into the office and explained what tach I had installed and that I was all ready to do the adjustment (gauge easily removed and screwdriver in hand) and I needed someone to check it with an optical tach.

He told me to follow him back to the truck shop and grabbed the reflective tape and the tach. He threw the tape on and we went to 2000 rpm via the digital tach and I set mine. I was off by around 50 at idle with my guess adjustment.

We talked about the truck and diesel performance in general and I asked how much. He said "no charge". Offered to pay for his lunch or beer and he passed.

I think being ready and knowing what I needed done helped a lot. It's a basic job and you can prolly get it done very cheap.

Den

 

well i have got a 90 with 3.54 gears and at 70 i am right at 2000 rpm in 5th and i think 2000 rpm at 57 or so in 4th. tire size won't make a difference on what your speedometer reads so. the reason i say that is i have 35s. and i am going off speedometer speed not actual.