250 cid rpm

[lgehring]

Good evening all
I bought a dollar box at an auction, in it was a napa balkamp elec tach. I installed it in my 1966 c20 with a 71 250,granny low 4spd, 4.57 rear end. The idle is about 700rpm which seems about right. At 65mph it reads 2100rpm which doesn't seem right. The tach had been installed on something previously. Printed instructions inside said for 6cyl remove lower red resistor. There were 2 resistors, both brown. I'm thinking 65mph should be more like 4000rpm, it sure sounds more than 2100. Any thoughts? Thanks Lowell

[Captainfab]

Yeah, I would say it is still set for a 8 cylinder engine. Sorry I don't know how to switch that particular tach.

[cortcomp]

If both resistors are removable, id hazard a guess that both in is 8cyl, lower removed is six cyl and both removed is 4cyl. Shouldnt hurt anything to pull them and drive and test, if it's the wrong setting it will read wrong. I would think that gear at 65mph would be like 3000-3500?
Posted via Mobile Device

[Sharps40]

My I6 with 3.73 diff turns about 2800 - 3000 in the 60 to 65 mph range.

[TJ's Chevy]

My 6 does 3100 at almost 70. But I think I have a 3.90 gear ratio and I am running 30 inch tall tires. This is with the stock 4 speed. I bought an after market tach made for 4,6, and 8 cyl engines. At 2000 I think it does about 45. My speedo is way off cause it said I was doing 100 when I was only doing about 65!

[lgehring]

Thanks for the input, I think I will snip the lower resistor and see what happens. I can always solder it back on I guess. Lowell

[66Submarine]

Also, it sounds like your truck might have 4.10 gears. Correcting for the 6/8 thing I get 2,800@65, the same I run with 4.10's.

[Vernski]

I have a SW tach I bought long ago and it sat on the shelf for about 4ys then installed it. It doesn't read right either I set it at the recommended setting but it seems like it's reading slower than it should be. I tried other settings and it don't seem to change anything it just stays the same. I'd take it back but the place I bought from is out of business now. I wondered if SW could be of help I sent an email to them long ago asking questions but no answers..Vernski

[lgehring]

I pulled the cover and got the numbers off the gear sometime back. I don't remember what they were but they computed to 4.57 to 1. Thanks for all the replies. Lowell