Thread: V8 Conversion
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Old 10-01-2015, 12:25 PM   #81
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Join Date: May 2015
Location: Lake Orion, MI
Posts: 55
Originally Posted by BoxsterLS376 View Post
It took pulling some teeth from Renegade but apparently someone who did this conversion ran into this problem as well and created the solution I had envisioned~

All your tachometer worries can be solved by spending a few more bucks... about $80 of them I believe...

Check out Ashlock Technologies~

I'm pretty sure you can achieve the same results by re calibrating the GM PCM.

This is how I plan on doing it:

Originally Posted by
I did a search for this information and could not find it using keywords Tachomter and Tach.

I am looking into adjusting the tach output for my 98 VCM due to putting the motor into a 6 cylinder BMW. The stock setting for high & low resolution is 6. What is the proper adjustment to make the tach output the same as a 6 cylinder motor? I know the LSx output is seen as a 4 cylinder by tachometers. Nothing else on the car uses the tach output.

Did some math & research & some more math, this looks to be correct:
The number of crankshaft medium resolution pulses (24x pulses) to hold the tach output high (should match {G1205} "Tach Pulses Low").
The number of output pulses P is calculated as P=24/(N*2) where N is the value of this calibration.

Sample values for this calibration:
For 12 pulses, use N= 1
For 6 pulses, use N= 2
For 4 pulses, use N= 3 (Note- 8 cylinder tach setting)
For 3 pulses, use N= 4 (Note- 6 cylinder tach setting)
For 2 pulses, use N= 6 (Note- LSx 8 cylinder & 4 cylinder tach setting)
For 1 pulse, use N=12

N=6 same as you see in HPT (for Gen 3 motors)

Pulse Calculator: V8 tach reads 4 pulses per revolution, so 24/8=3. 6 cylinder reads 3 pulses per revolution, so 24/6=4. 4 cylinder reads 2 pulses per revolution, so 24/12=2. These are the "N" numbers for above that are plugged into the HP Tuners Tach Output fields.
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