Senior Tech Team
Join Date: Apr 2012
Location: Yerington, Nevada
re: ZZ4 upgrades?
As I said, decades ago, I worked out the distributor curves for the ZZ engines, and we did a bunch of them, as Limeworks Speed Shop used those engines exclusively for their built from scratch cars. It works, simple, low cost.
Leave initial timing and mechanical curve alone, speed up mechanical advance with softer springs, start curve 850/900 RPM's, limit 3,000 RPM's. Stock mechanical advance springs look soft, until you stretch them. Stock ZZ mechanical curve rate starts about 1,300 RPM's, limits way past 5,500 RPM's, to compensate for the ported vacuum advance curve added where it shouldn't have ever been in the first place.
Vacuum advance, set up a degrees stop to give 8 to 10 degrees, plug into full manifold vacuum source, idle timing will go to 20/22 degrees, just what that engine wants. FIXED.
Full instructions, with pics are still free, no strings, no ads, address for them is above in another response.
Don't do the mods, live with, and enjoy the over heating, poor performance and rotten fuel economy.
Now, GMPP did NO in car setup/testing/tuning with the ZZ engines, they were all done on a dyno, in which, not one has never been driven around a block, and dyno's love excessive timing and jetting, way past real world settings. The reason no vac adv was used, EMISSIONS reg's were in play, and if GM didn't do that, no engine sales in both Communist Kalifornia and Colorado. NOTHING says you can't modify after you buy it if it is installed in a pre-emissions vehicle.
I have more than 1,500 people that have done these mods to their ZZ large HEI distributors, not one has said to me that it did not wake their engine up, and make it run one heck of a lot better.