Help finding HEI dist. and will I loose my factory tach

[IT Cowboy]

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]

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]

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]

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]

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]

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 the Proform is 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]

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]

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).

[Myself]

I've used several of the cheapy aftermarket "hi-performance" HEI distributors through the years and never had an issue.

[PbFut]

OP, You asked about EFI systems in another post. If you are going EFI, then hold on the HEI distributor until you decide on the EFI. If you go EFI, and you incorporate spark control, the correct distributor is important. Many EFI systems will allow connection into a HEI distributor. Some will not and all will need lock out capability if you want the EFI box controlling the spark curve. Most low cost distributors will not allow lockout or make it difficult to do so. With the right parts you can turn a Small or BB chevy into a modern controlled engine with all the moder adjustments on your laptop. FiTech and Holley EFI systems play really well with MSD billet type distributors. The MSD 8579 is a small diameter magnetic type distributor that easily locks out that is necessary the EFI box to spark control. A MSD 6al will provide multi spark ability and some EFI boxes are now adding multi spark. Paired with a MSD blaster or similar coil and your spark will light anything you through at it. It will also knock you across the garage if you grab a hot end of a open spark cable and have your other hand on a ground.

['68OrangeSunshine]

Tach works fine with my HEI on an L6 292 in a '68 C/10 Stepside. My tach, an AutoSun, hose-clamped to the steering column, also worked fine on points and even Pertronix Ignitor II [when I had that].
I heard Pertronix Ignitor III will not work with any tachs. A friend put a Pert III on his 429 in a '72 F250. No tach. Called Pertronix. They told him to go back to a Pert II if he wanted a tachometer.

[tim_mc]

I installed a new ACDelco HEI, P/N 93440806 when completing my '67 C20 project, however, after about a year of use I had to replace the coil due to weak spark. I went with Davis Unified Ignition coil and their Dyna-module as drop-in replacements. The hotter DUI coil and longer dwell in their module is a huge improvement over a stock HEI. I even swapped back to a stock module just to check the difference. Throttle response and acceleration is much better with the DUI module. If I needed an HEI now, I'd probably find a good OEM HEI core (not a new Delco) and upgrade the coil and module, or just spring for a whole new DUI assembly:
https://performancedistributors.com/...reetstrip-dui/
It works with the 5K tach on my reproduction gauge cluster from Brothers/Holley with no mods needed.