Is it possible to cut the voltage in half going to the speedo and what effects would it have? If it slowed everything down to half its stock calibration ie. reading 30mph while actually doing 60mph, wouldn't this bypass the govenor and at the same time make the speedo functional up to 220mph?

Just a thought.

Steve

 

I think the VSS signal is pulse modulated, not amplitude modulated, so no, this wouldn't work.


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1984 Silver Z28, 383 cid 4 bolt, ARP Fasteners, 2 1/2" Cowl Induction Hood, 600 cfm Performer Carburetor, Torker II Intake, Performer RPM Heads, XE268H Cam, Magnum Roller Tip Rockers, MSD6AL Ignition, Blaster2 Coil, Recurved HEI Distributor, 700R4, TransGo SK, 2.73:1 Limited Slip Dana 44, Terminator Headers, Custom 3" TIG Welded Stainless Exhaust, Flowmaster Muffler, 4 Wheel Disc Brakes, Oil Cooler

 

Hmm... but I suppose if you wanted to you could build a divide-by-2 pulse counter to put in the input to the speedo. Parts would probably only cost you about a buck.

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1984 Silver Z28, 383 cid 4 bolt, ARP Fasteners, 2 1/2" Cowl Induction Hood, 600 cfm Performer Carburetor, Torker II Intake, Performer RPM Heads, XE268H Cam, Magnum Roller Tip Rockers, MSD6AL Ignition, Blaster2 Coil, Recurved HEI Distributor, 700R4, TransGo SK, 2.73:1 Limited Slip Dana 44, Terminator Headers, Custom 3" TIG Welded Stainless Exhaust, Flowmaster Muffler, 4 Wheel Disc Brakes, Oil Cooler

 

As a matter of fact, I am working on that type of circuit. Its function is actually to double the range of a speedo, and correct it, too, if necessary. In the case of my '92 Z, the speedo only goes to 145, so this circuit uses a digital frequency detector, running a at 10 mhz, to sample the speedo input signal, and divides the signal by 2, if the speed is over 140 mph, and reverts back to 1:1, when the speed input drops back below 130 mph (10 mph hysteresis). So, now the range of the speedo is 290 mph. Also, since a 21 tooth driven gear is not available (for 3.73:1 gears) for a T5 electronic speed sensor, my speedo reads 5% high, so the circuit will remove 1 of every 20 pulses to correct the signal by -5%. I'll let you know how it works.

To answer your question, if the VSS signal to the ECM was divided by 2, you would have twice the speed limiter range. It would be easier to disable the speed limiter in the PROM, though. If you have a '89 or older ECM, the VSS signal to the ECM comes from a speed buffer in the cluster, so a divide by 2 circuit would be simple. If you have a '90 or newer ECM, the VSS goes directly to the ECM (the VSS is built into the ECM) & the ECM outputs a 4000 pulse / mile signal to the speedo & a 2000 pulse / mile to the cruise control module, so you would have to build a "speed buffer" & run the VSS to it, then do the divide by 2 function & convert the divide by 2 signal back to a level suitable for the ECM's VSS input.

Tim