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**Joe Pass** · 02-15-2015, 05:40 PM

I also used the Classic Parts tach conversion but I'm not completely satisfied...That being said I ran into a issue with it not being close to accurate. My first one wouldn't read so they replaced it and the second one isn't accurate. I worked with the Classic's tech and they said sometimes an aftermarket HEI doesn't send the right signal and reads half of what it should. I have an MSD HEI so I contacted them and they suggested a resister that didn't help either. I tried a new HEI from GM and that failed to read correct also. They have a filter available and even though they say its not need for HEI, they suggested that I try it. I ordered it at the tune of $27 and it made no difference.
Just for the record I have been installing aviation navigation and worked with a lot of instrumentation and I'm fully aware of proper installation and grounding etc..

02-15-2015, 05:40 PM	#5
Joe Pass Senior Member Join Date: Aug 2013 Location: Windsor, California Posts: 1,042	Re: tach question I also used the Classic Parts tach conversion but I'm not completely satisfied...That being said I ran into a issue with it not being close to accurate. My first one wouldn't read so they replaced it and the second one isn't accurate. I worked with the Classic's tech and they said sometimes an aftermarket HEI doesn't send the right signal and reads half of what it should. I have an MSD HEI so I contacted them and they suggested a resister that didn't help either. I tried a new HEI from GM and that failed to read correct also. They have a filter available and even though they say its not need for HEI, they suggested that I try it. I ordered it at the tune of $27 and it made no difference. Just for the record I have been installing aviation navigation and worked with a lot of instrumentation and I'm fully aware of proper installation and grounding etc..