View Full Version : HEI vs. Thunderbolt?

03-18-2011, 09:38 AM
I'm gettin ready to drop the newly freshened up 350 Vortec in my 16. I have an original mercruiser distributor and wiring but not sure if it is any good. The module is expensive as hell to replace. Was thinkin about going to a Davis Unified Ignition (D.U.I.) marine distributor. One wire hook up on it just like a standard Chevy HEI, coil is intergrated into the cap, and since all the wiring in the boat was stolen when I got it I figured it would be an easy setup. Any advice? Also running IMCO risers so mounting brackets for modules and wiring not there.

03-18-2011, 02:05 PM
HEI is a gret set-up. Make sure it gets a constant operating voltage. This is why the GM ran a short heavy wire to power the HEI. I have used it for years with great resaults. I usually mod the ignition curve to run 15 degrees @ idle and try and have all advance in at 3000 rpm which is 36 degrees total. Being a marine DUI it probably doesn't have a vac advance which you dont want to use. Using only mech. advance with weights and springs. I also use a continuous duty relay to power the dist. I like the merc as well but are costly. Good luck!

03-18-2011, 05:47 PM
Thanks for the input. Have used them on vehicles for years. Didnt know about the mechanical advance. So I can use a basic HEI just remove the vacuum advance.

03-18-2011, 06:25 PM
Had my DUI for 6 yrs. without issue. Dui will set up total timing and rpm to your liking. Mine was set up with 22* @3200, with 12* initial.

Need a ground wire hooked up to the beige wire to activate the shift interrupter. Need help, let me know. Have pics of hookup.

03-19-2011, 07:28 AM
I prefer the Delco marine HEI unit.. Pretty easy install & parts are usually readily available. They arent too bad $$$ wise either to buy the kit. We sell a decent amount of them with repowers.. Feel free to give me a shout if it may interest you.. :) Jamie / Lakeside

03-19-2011, 09:14 AM
The Merc ignition is a very good unit, yes parts can be but do not have to be expensive. Why dump a running item before you have an issue, when was the last time any member blew a pack? I an tons of others have been running the Merc stuff for many years with -0- problems, I wanted more spark for my 383 so I swapped out the stock coil for a hot one. I have since picked up an extra pack for $50 and an almost new distributor also for $50, I drag it along on trips. Not knocking after market most of which is good but is it better? Don't ask Maddad about AM stuff he had a baddy!