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#1 |
Not a bad nut after all..
Join Date: Dec 2000
Location: ND
Posts: 1,756
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How to Adjust Factory Tachometer?
I picked up a factory tach from a big truck and just finished installing it and a reproduction vacuum gauge in my Blazer. Unfortunately the tach feels like it reads a few hundred RPM high. I have HEI and a late 1970's Camaro tach filter. I'm going to temporarily hang an aftermarket tach under the dash for comparison. I read in other posts about the calibration screw on the backside of the factory tachs:
1) Can I reach this screw without removing the gauge cluster (is the circuit board in the way, do I need Ethiopian arms, etc)? 2) Is this screw a flat head or Philips head? The tach currently sits nicely at zero RPM with the ignition off.
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'05 Chevy 2500HD 4x4 '72 GMC LWB 4x2 driver '72 Chevy LWB 4x4 plow truck '71 Blazer 4x4 driver '70 GMC LWB trailer |
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#2 |
Not a bad nut after all..
Join Date: Dec 2000
Location: ND
Posts: 1,756
|
Re: How to Adjust Factory Tachometer?
I hooked up this old (50+ years old according to Snap-on tech help)tach/dwell meter first to my other truck with a new Sun tach on the column. Difference was a consistent 200rpm across the board.
Next I hooked it up to my Blazer with the factory tach; the factory tach is 500-700rpm low and the difference gets even greater with rpm.
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'05 Chevy 2500HD 4x4 '72 GMC LWB 4x2 driver '72 Chevy LWB 4x4 plow truck '71 Blazer 4x4 driver '70 GMC LWB trailer |
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#3 |
the boat guy
Join Date: Jul 2007
Location: springfield mo
Posts: 2,339
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Re: How to Adjust Factory Tachometer?
If you have a 6 cylinder engine and a v8 tach it will read 25% lower at all rpms.
If you have a v8 with a 6 cylinder tach it will read 33% higher at all rpms. I may have my % off, its been a while since math class. Posted via Mobile Device
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67, swb, fleet, tach, throttle, 5.3, 4l60e, 3.73's, fuel cell, 5 lug, p.d.b., 4-6 drop. great little truck 66, stevens drag/ski 18' silouette, 350, 2.02 doublehump heads. comp extreme marine 278 cam, vette 7 fin valve covers, old polished edelbrock intake, velvetdrive, casale v-drive, adj cavitation plate. 28, model a rpu project, |
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