Is 12,000 rpm's to high
 

I just swaped my 2.3 4 banger for a 5.0L and the tach reads twice the value. Does any one know is there is an adjustment or do I have to replace the tach with a v8 tach ?

Not sure how to adjust or if it is even possible, but you would be doing yourself a favor if you got a nice new autometer 8k 5 inch monster with shift light. It comes set for 8 cylinders, works great, and looks cool.
You could try calling your local Ford dealer for info if the 4 cyl tach can be adjusted.

I've converted a 4 cyl tach out of a TBird to work in my cougar, it's probably the same tach. You have to take it apart and switch out a capacitor and a resistor with different values. I'm still not sure if mine is quite accurate. It's close. If I were you, I'd recalibrate your 4 cyl (I'll tell you exactly how if you want, email me) and then I'd get an aftermarket tach as well so you know something's accurate. By the way, if you run with the 4 cyl tach on an 8 cyl car and you rev way up, you will eventually blow the tach. It's basically a frequency to voltage converter and then an analog volt meter. So the output voltage from the FV converter is way too high for the volt meter which burns up the coils in it. But you should be okay for a while. Tell me if you want more info on the recalibrating. I'd be happy to help.

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Michael Black
Quantum Motorsports
Norman, Oklahoma

1988 Merc Cougar 5.0 HO, P&Ped heads, 2.25" custom mandrel bent dual pipes, T5 five speed tranny
15.43 @ 91.08mph (not shabby for a 3600 pound car)
60' 2.453 Street tires suck!!!

remove tach and change the selector switch to 8 cyl

THere should be a little adjuster right beside tachometer. if you take off the front plate that covers speedo, tach, and the other gauges, you can change from 4 to 6 or 8 (cylinder) setting using a small flathead screwdriver.

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'79 Mustang Coup
4" Cowl
Weld wheels (15x6;15x8)
Stock 5.8L
C4 w/ shift kit
1.5" MAC full length headers
Holley 750 CFM
Edelbrock intake
2.5" Off road H-pipe
8.8" Rear end w/ 2.73:1 gears (sucks!)
Front: 225/60/15 Rear: 255/60/15 Eagle GT II
Sucky Purolator air filter that's choking my car. http://www.mustangworks.com/interact...gboard/mad.gif

Guess it's different in the TBird because there is no selector switch. If there's a switch that seems fairly self explanitory. If there happens to be no switch, I'll help you out.

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Michael Black
Quantum Motorsports
Norman, Oklahoma

1988 Merc Cougar 5.0 HO, P&Ped heads, 2.25" custom mandrel bent dual pipes, T5 five speed tranny
15.43 @ 91.08mph (not shabby for a 3600 pound car)
60' 2.453 Street tires suck!!!

If you can afford it I would go with an aftermarket tach. I have an autometer and the factory hooked up and the factory tach is close until about 3500-4000 rpms. After that the error grows exponentially. But if you want both or just the factory tach do as the others have said.

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88GT stock shortblock, ported GT-40 iron heads, ported Edlebrock Performer intake, 24# inj, Pro-M 75mm Bullet MAM, 3.73, hurst short throw, F-303, electric fan, alum rad, FMS HD clutch, R134a ac conversion, 70mm TB , and some other stuff I probably forgot, best run so far on ET streets is 13.02@106 with a 1.87 60ft.

I would just get an Autometer. The stock tach's are not only inacurate, but inconsistent.