I found this to be a good read. I have a DUI distributor on my 69 Riv with a 455 and didn't really know much about it nor do I know much about the HEI systems but have read alot on here about them and guys seem to love them and the stock points distributors. What's everyone's take on these two ignition systems, pros/cons, real world use and experiences etc.?? https://www.hotrod.com
The DUI is a big cap GM HEI distributor. Not sure what you are asking. DUI maybe has better components than a stock GM HEI, maybe?
Larry, I'm asking what the difference is between the two and why most guys favour the stock HEI system or points distributors? My car came with the DUI. I reallly don't know much about ignition systems at all I remember helping my dad rebuild the points distributors in his old cars/trucks as a kid sitting on the fender sanding the parts to clean them up and putting it back together. I read the article above out of curiosity and it seems to me that the DUI is a simpler and more efficient system. Also to ad to this what does the MSD ignition box do? Can it also be used with a DUI distributor?Learning is fun
The stk big cap hei coils run out of spark on top rpms, the factory module doesn't better job a dwell control then the big box store parts, but with a good module and coil they are good system for street. I ran one for years on the strip
Your link only takes me to the Hot Rod home page, not to any article. The two distributors are the SAME design, a GM HEI. The DUI is the same distributor with maybe better components and a better advance curve. It's an apple to apple comparison with the DUI maybe a better tasting apple.
Is this the article? https://www.hotrod.com/articles/dui-ignition-need/ The article really answers all the questions you asked.
No that wasn't the article that I read but the one you posted Larry was way better at explaining it. Wish I had read that one first lol. The article I tried posting was why the DUI was better than stock HEI and how it helped with low rpm dwell and bumped up hp a bit
Larry where does the MSD box come into play with all this? Also guys running the points system is that because they're after stock/factory original equipment looking cars? From what I understand points system is very finicky so other than being "correct OEM parts" why would they still use them? Are there tuning benefits of points that the HEI doesn't have?
MSD is a different kind of ignition. Points, GM HEI, Pertronix, Crane points replacement systems are inductive ignition systems. MSD ignition is a Capacitive type system. Another Hot Rod article, https://www.hotrod.com/articles/inductive-vs-capacitive-discharge-ignition-systems/ Points work just fine, but require periodic adjustment to dwell. Dwell directly affects timing, so a dwell changes from wear, so does timing. Points replacement systems control dwell with microprocessors, so dwell is more stable and so is ignition timing.
Awesome info Larry! That was a good read. So if I understand this correctly basically the msd box is an aid in the points ignition system to help with efficiency and performance of the spark and timing which still requires adjustments here and there of weights, bushings and springs. Where as the HEI/DUI system has everything built into it, do not require the additional box and can be set up to whatever specs the user requires and dropped right in with no further adjustments other than setting the timing up with a timing light.
Think on the msd box as an add on booster the the ignition. The box needs a signal from the distributor. Points basically control dwel......the amount of on time for the coil......to little dwel and the coil wont be able to generate enough spark all the time. The HEI module has the dwel programmed in and is not adjustable. The msd box take the signal from the dist and uses it to amply the spark by adding multiple sparks under a certain rpm and by supplying more power to the coil..... Different coil can also effect spark anger output by having a better ratio of windings inside to generate more output Some boxes allow you control the actual timing, some the timing is still set by the dist or external magnetic pickup. The fancier boxes you could have your base time set at say 40......but the engine could be running at any number under that base setting
This all makes better sense to me now. I've found myself reading different posts on here about guys having issues and others saying check you coil, adjust your dwell etc etc and I've been lost since my car doesn't have that stuff anymore. Atleast now I know what they're talking about . For the record I'm not having any issues with ignition or timing I just wanted to be better educated .
