HEI with factory tach - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ic1480 · 02-17-2015, 01:53 PM

OK so first post. be kind. have done a few searches and am still a little confused about HEI Petronics III and factory Tach. brand new gauge cluster with tach. BBC. I need an all new wiring harness and some say there is a trick to getting the tach to function correctly. What say you.
thanks
IC

**leddzepp** · 02-17-2015, 02:02 PM

I've used several factory tach dashes with HEI, no problems.

**FirstOwner69** · 02-17-2015, 02:16 PM

My factory tach works fine hooked with the GM HEI distributor. However, I seem to recall reading some threads where people had problems with the reproduction tachs that look like the originals. Do you know that yours is an original?

ic1480 · 02-17-2015, 02:18 PM

brand new repop gauge cluster

BrianG · 02-17-2015, 03:53 PM

I believe that the petronix III does have issues with tachs. Seems like the model II was better. I believe its something with how it issues the spark. Sends a double pulse or something. I'm completely talking from what I seem to remember, have heard before so don't kill me with what I've said wrong.

Are you familiar with the search at the top yet? type in Petronix, then click the 67-72chevytrucks.com button and then hit google.

It will bring up another window with a google search on Petronix (or whatever you type) for hits on this forum. It works really good and there are many many posts about them.

Happy reading and good luck.

**'68OrangeSunshine** · 02-17-2015, 06:12 PM

I have the Pertronix II and have no Tach problems. A buddy has a '72 Ford F250 w/429 V8 and a Pertronix III. He can't use his tach. The PIII is a multi-spark set up and interferes with the tach signal, I guess.
I suppose if you have the Corvette-style mechanical tach, it would work, but electronic tachs aren't compatible.

snipescastle2 · 02-18-2015, 09:21 AM

If you are having problems with the tach not operating correctly, you may have to run a "Tach Filter" the signal interference from the HEI ignition systems may cause the tach to operate erratically, and a filter will sort that out. I know most places- LMC or Classic parts,etc...have them, not too expensive, or you could make one yourself......here's a post on the subject:

http://67-72chevytrucks.com/vboard/s...d.php?t=568274
HTH,
Ben

02-17-2015, 01:53 PM	#1
ic1480 Registered User Join Date: Feb 2015 Location: ND Posts: 20	HEI with factory tach OK so first post. be kind. have done a few searches and am still a little confused about HEI Petronics III and factory Tach. brand new gauge cluster with tach. BBC. I need an all new wiring harness and some say there is a trick to getting the tach to function correctly. What say you. thanks IC

02-17-2015, 02:02 PM	#2
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 20,016	Re: HEI with factory tach I've used several factory tach dashes with HEI, no problems. __________________ 1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man RIP FleetsidePaul

02-17-2015, 02:16 PM	#3
FirstOwner69 Senior Member Join Date: May 2010 Location: Wisconsin & Arizona Posts: 4,846	Re: HEI with factory tach My factory tach works fine hooked with the GM HEI distributor. However, I seem to recall reading some threads where people had problems with the reproduction tachs that look like the originals. Do you know that yours is an original?

02-17-2015, 02:18 PM	#4
ic1480 Registered User Join Date: Feb 2015 Location: ND Posts: 20	Re: HEI with factory tach brand new repop gauge cluster

02-17-2015, 03:53 PM	#5
BrianG Registered User Join Date: May 2011 Location: Oakley, Michigan Posts: 735	Re: HEI with factory tach I believe that the petronix III does have issues with tachs. Seems like the model II was better. I believe its something with how it issues the spark. Sends a double pulse or something. I'm completely talking from what I seem to remember, have heard before so don't kill me with what I've said wrong. Are you familiar with the search at the top yet? type in Petronix, then click the 67-72chevytrucks.com button and then hit google. It will bring up another window with a google search on Petronix (or whatever you type) for hits on this forum. It works really good and there are many many posts about them. Happy reading and good luck.

02-17-2015, 06:12 PM	#6
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,379	Re: HEI with factory tach I have the Pertronix II and have no Tach problems. A buddy has a '72 Ford F250 w/429 V8 and a Pertronix III. He can't use his tach. The PIII is a multi-spark set up and interferes with the tach signal, I guess. I suppose if you have the Corvette-style mechanical tach, it would work, but electronic tachs aren't compatible. __________________ Every 25 years I like to rebuild that 292, whether it needs it or not.

02-18-2015, 09:21 AM	#7
snipescastle2 Registered User Join Date: Mar 2009 Location: WARRENSBURG,MISSOURI,64093 Posts: 1,518	Re: HEI with factory tach If you are having problems with the tach not operating correctly, you may have to run a "Tach Filter" the signal interference from the HEI ignition systems may cause the tach to operate erratically, and a filter will sort that out. I know most places- LMC or Classic parts,etc...have them, not too expensive, or you could make one yourself......here's a post on the subject: http://67-72chevytrucks.com/vboard/s...d.php?t=568274 HTH, Ben



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