Help finding HEI dist. and will I loose my factory tach - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**IT Cowboy** · Today, 03:11 PM

I am looking for a part number or link to which ACDelco / GMC brand HEI ready to run dist. would work in my truck - so far I haven't found one.

After a lot of searching here I can't determine if i would loose my factory dash tach or if it would work with an adaptor.

Willshook · Today, 03:28 PM

Any HEI will work with an analog factory tach, with a caveat. The HEI puts out a square, near digital signal that some factory tachs have a hard time with - either being bouncy or reading further and further off as the RPM increases. MSD (and others) sell a tach filter that cleans up the noise and "rounds off" the signals so it looks more like an analog signal.

By far the best street HEI for a stock/moderate performance engine is the MSD Street Fire. Comes with a kit to adapt the mechanical advance as well as an adjustable vacuum can - makes it easy to get the performance and drivability curves right. You can get it with a black cap so it looks stock ;-)

**Stocker** · Today, 03:45 PM

Decades ago I bought a used GM HEI from a mid-80s vehicle and it's still working. No factory tach though, I hooked up an old Sun Super Tach II that I had laying around. That's still working too.

**58 Special** · Today, 04:11 PM

Put a GM OEM HEI from a late 80's vehicle in my suburban with factory tach 30 years ago. Has never been an issue. Go to auto wreckers and pull one from a van easiest access.

**Steeveedee** · Today, 04:49 PM

I bought a Mallory HEI in '01 to put in a SBC I installed in a Buick Skylark. When I went back to Buick power, I put the HEI distributor in my truck. I have a SUN Supertach also, and it reads fine. It was attached to the top of the dash by my FiL but it looks like it would fit the tach hole. But that has a vacuum gauge in it atm.

**MikeB** · Today, 06:31 PM

This Proform HEI actually has a GM part number. I think it's about the best you'll get for the money. I would runaway, runaway from anything less expensive. I think they are available with different color caps. But I don't know if it will work with a stock tach.

https://www.summitracing.com/parts/pro-141-682

**IT Cowboy** · Today, 07:12 PM

Quote:

Originally Posted by MikeB

This Proform HEI actually has a GM part number. I think it's about the best you'll get for the money. I would runaway, runaway from anything less expensive. I think they are available with different color caps. But I don't know if it will work with a stock tach.

https://www.summitracing.com/parts/pro-141-682

I found that one too but the fitment chart says is doesnt fi tmy 402 bog block?

**jocko** · Today, 07:31 PM

small block and big block distribs are physically interchangeable (however factory advance curves can be different). You'll note this one calls out that it fits both (and the fitment chart includes the 402. I don't know why the others don't include it).

Today, 03:11 PM	#1
IT Cowboy Senior Member Join Date: Jan 2025 Location: Clarkdale, Arizona in a van down by the river Posts: 230	Help finding HEI dist. and will I loose my factory tach I am looking for a part number or link to which ACDelco / GMC brand HEI ready to run dist. would work in my truck - so far I haven't found one. After a lot of searching here I can't determine if i would loose my factory dash tach or if it would work with an adaptor. __________________ '72 C10 / 402 ___________________________________________ Freedom isn't safe, it requires you to take responsibility for your own life, your own safety, and your own success. It carries with it the possibility of failure and the understanding that you're working without out a safety net. If you give the state the responsibility for any of these you also give up the freedom that accompanies the responsibility.

Today, 03:28 PM	#2
Willshook Registered User Join Date: Jun 2019 Location: Chehalis, WA Posts: 122	Re: Help finding HEI dist. and will I loose my factory tach Any HEI will work with an analog factory tach, with a caveat. The HEI puts out a square, near digital signal that some factory tachs have a hard time with - either being bouncy or reading further and further off as the RPM increases. MSD (and others) sell a tach filter that cleans up the noise and "rounds off" the signals so it looks more like an analog signal. By far the best street HEI for a stock/moderate performance engine is the MSD Street Fire. Comes with a kit to adapt the mechanical advance as well as an adjustable vacuum can - makes it easy to get the performance and drivability curves right. You can get it with a black cap so it looks stock ;-)

Today, 03:45 PM	#3
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,791	Re: Help finding HEI dist. and will I loose my factory tach Decades ago I bought a used GM HEI from a mid-80s vehicle and it's still working. No factory tach though, I hooked up an old Sun Super Tach II that I had laying around. That's still working too. __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

Today, 04:11 PM	#4
58 Special Active Member Join Date: Apr 2023 Location: Edmonton,Alberta, Canada Posts: 113	Re: Help finding HEI dist. and will I loose my factory tach Put a GM OEM HEI from a late 80's vehicle in my suburban with factory tach 30 years ago. Has never been an issue. Go to auto wreckers and pull one from a van easiest access.

Today, 04:49 PM	#5
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,879	Re: Help finding HEI dist. and will I loose my factory tach I bought a Mallory HEI in '01 to put in a SBC I installed in a Buick Skylark. When I went back to Buick power, I put the HEI distributor in my truck. I have a SUN Supertach also, and it reads fine. It was attached to the top of the dash by my FiL but it looks like it would fit the tach hole. But that has a vacuum gauge in it atm. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

Today, 06:31 PM	#6
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,654	Re: Help finding HEI dist. and will I loose my factory tach This Proform HEI actually has a GM part number. I think it's about the best you'll get for the money. I would runaway, runaway from anything less expensive. I think they are available with different color caps. But I don't know if it will work with a stock tach. https://www.summitracing.com/parts/pro-141-682 __________________ Mike 1969 C10 LWB -- owned for 36 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- converted from 250-six to roller cam 350, Vortec heads -- sold 1981 C10 Silverado LWB, 305, TH350C -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

Today, 07:31 PM	#8
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,992	Re: Help finding HEI dist. and will I loose my factory tach small block and big block distribs are physically interchangeable (however factory advance curves can be different). You'll note this one calls out that it fits both (and the fitment chart includes the 402. I don't know why the others don't include it).



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