ZZ4 swap and resulting tachometer issue

[TWINRAY]

What are you guys that put crate motors in doing about a tachometer? Swaping a tach drive distributor in or running with an add-on unit on the steering column? Thanks, Fred

 

[Hib Halverson]

I'd go with the tach drive distributor.

MSD makes really good, billet, tach drive distributors for Corvettes. I have one in my 71. Big improvement over the stock T/ign. distributor I had previously.

If you insist on HEI, I recall there is an aftermarket company that sells an HEI distributor with a tach drive body.

If the car in quesiton is a C3, I've, also, heard of people installing an Auto Meter electronic tach in into the stock tachometer location in the IP.

 

[TWINRAY]

I'd go with the tach drive distributor.

MSD makes really good, billet, tach drive distributors for Corvettes. I have one in my 71. Big improvement over the stock T/ign. distributor I had previously.

If you insist on HEI, I recall there is an aftermarket company that sells an HEI distributor with a tach drive body.

If the car in quesiton is a C3, I've, also, heard of people installing an Auto Meter electronic tach in into the stock tachometer location in the IP.

Thanks Hib,

It is a C3 and I will look into option #3.

thanks, Fred

 

[loup68]

Tach drive distributor in ZZ-4

I bought a DUI (Davis unified Ignition) distributor for mine with the tach drive HEI, from Eckler's.

 

[orlandjoe]

I run the Mallory with tach drive and no vacuum advance, Works well, uses a coil since it's ot HEI.

 

[Jack]

First ... GMPP ZZ4 crate has a steel roller camshaft & requires correct dist gear ... a "melonized" gear. You can buy the dist gear separately from GM & install it on any GM HEI or clone thereof with .491" od shaft.

The msd td dist requires an additional cd spark box & wiring & place to mount box ... all total dist +box probably near $500 - $600 retail. MSD does offer equivalent to "melonized."

OR - Several speedo-tach resto/calibration shops can retrofit old mech tach face with new electronics ... then run a conventional HEI without tach drive.

OR - A 75-77 C3 elec tach will fit 68-74 C3 dash with minor mods to tach ... then run a conventional HEI without tach drive.

OR - several sources offer a clone of GM HEI dist also having a mech tach drive ... AFAIK, ALL are asian with exception of Davis Unified at nearly $500 ... the rest range from less than $100 (fleabay) to almost $400.

FYI ... 68-74 chrome dist shroud/box/lid will not fit larger HEI ... but same tin from 75-77 will.

FYI ... most OE 68-74 GM tach drive points dist can be rebuilt to like new for under $200 ... sometimes much less. Points work AOK for most street vette.

If original points dist cannot be salvaged ... and If cost is no issue, suggest Davis Unified tach drive HEI ... otherwise, fleabay asian tach drive HEI ... MANY run the cheap asian pieces with rare complaint.

 

[Hib Halverson]

"jack" makes a very important point which I missed.

When I posted about the MSD distributor, I was thinking about the Crane roller in my Big-Block which has a cast iron gear bonded to the steel roller cam. Rollers with cast iron dist. gears can use a conventional distributor driven gear.

If GM's crate motor roller cams are ground on steel blanks w/o cast iron dist. gears, you definitely need to change the gear. In olden times we used bronze gears but they wear fast so the GM Melonized gear (PN10456413) is a must.