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.

[xs-cash]

Originally Posted by 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.

Same here on my 71

[IT Cowboy]

Well re-timing it made a pretty decent difference. I turned it up to @ 15 degrees BTDC and of course the idle picked up right away and I adjusted that down. The air/fuel really didnt need much adjusting maybe a 1/4 turn out on each side and the vacuum picked up a little to around 18.

I took it for a spin and when I mash on the throttle it pulls and keeps pulling like I would expect it to. When I stab the throttle it jumps up to @ 4000 rpm and giddys right up. It doesnt snap me in the seat but it does have some jump and what I expect a 50 yr old truck with a 402 to do.

I stopped and spoke to a neighbor who is a car guy and he said "aren't you worried about it overheating at that timing setting". I let it idle in the drive for quite a while while I messed with it and the temp stayed just a hair below 1/2. When I was driving around the temp gauge was around 1/4 consistently. Oh and it doesn't smell like it is super rich now and doesn't burn my eyes and throat from idling.

The throttle wants to stick just a bit at a higher idle of @900 but I think some cleaning and adjustment of the linkage will take care of that.

[Steeveedee]

It's possible that the primary throttle shaft is worn, not necessarily giving a vacuum leak, but enough to keep the idle up. You can wiggle the throttle lever at the shaft and see if the idle drops. It's common for an HEI to bring the idle up due to improved combustion. It is worth checking what the total advance is, just in case the 15 BTDC at idle is too much. That's what your neighbor is talking about, I think.

[IT Cowboy]

Originally Posted by Steeveedee

It's possible that the primary throttle shaft is worn, not necessarily giving a vacuum leak, but enough to keep the idle up. You can wiggle the throttle lever at the shaft and see if the idle drops. It's common for an HEI to bring the idle up due to improved combustion. It is worth checking what the total advance is, just in case the 15 BTDC at idle is too much. That's what your neighbor is talking about, I think.

For my idle if I let the throttle return by itself it stays about 150-200 rpm too high. If I grab on the throttle on the carb where the link is and give it a nudge forward then it will fully return and the idle drops. Is the bushing worn or sticking or would a tighter return spring fix that.

When I spray carb cleaner on the throttle link area the idle drops a bit but I need to srpay direct and quite a bit. I dont think there is a huge leak. Setting the timing bumped the vacuum about 5 points.

[Steeveedee]

I doubt the carb has bushings. I'd check that the fast idle cam isn't holding the primary throttle pates open slightly. Otherwise, I'd put the bushings in. When the throttle plates are that close to closed, a little mispositioning can make a noticeable difference.