Make your own Tach Recorder

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Posted by Kevin Greer Racing on March 12, 1997 at 22:03:07:

OK, I don't usually do this, but this forum deserves this! A couple of years ago I discovered that you could use a personal (mini) cassette recorder to record your tach readings. Please keep in mind that this requires an DT-6E for playback, but most of us have one laying around.

• 1. Purchase a mini cassette recorder with AN EXTERNAL MIC JACK and an EARPHONE & JACK(about $50)
• 2. Take a regular Digitron tach lead and cut it about 6" from the pigtail & connection end.
• 3. Buy two mic jack plugs from Radio Shack. The kind with the cover that screws on over the solder connection area.
• 4. Strip back the outer covering about an inch on the tach lead ends.
• 5. Solder in the center wire to the hole on the plug and then squeeze the grounding part around the braided shield of the tach lead.  

What you will be doing is recording the "beeps" of the spark plug firing. First, run the engine at idle with a regular tach lead and check to see what the idle rpm is. TO RECORD: Attach the long lead that you made to the plug wire in the normal manner. Plug the other end into the EXTERNAL MIC. Turn the volume up as high as it will go on the recorder. Hit PLAY/RECORD and record about 30 seconds of idle. Shut everything down. Take the short end and attach to the DT-6E... the other end goes into the EARPHONE JACK. Rewind and play back what you just recorded on the tach display. YOU MUST CHECK TO SEE THAT what you noticed on your first idle run matches what you recorded. If they don't, you must adjust the recording volume on the recorder. The recorders that I buy, record and play back fine at highest volume, but I have had a few that have been VERY volume sensitive and thus took some playing with until you find the match point and then make a paint mark on the volume control so that the setting is always right! Ya, its not as easy as hitting the recall on the memory tach, but this will tell you EXACTLY what the engine is doing for the entire lap!...LOW RPM, HIGH RPM, CLUTCH ENGAGEMENT, etc...in real time! You know how long it takes to make a lap, so as you replay you laps, you will be able to see what the engine was doing where! I have made and sold over 50 of these and they have proved to be very valuable. Hope this helps someone to gain a 1/10!

Kevin Greer