I've always wondered where the 4500 RPM limit "rumor" about GM's HEI module came from and finally found the source, in a book David Vizard authored called "How to Build Max-Performance Chevy Small-Blocks on a Budget". The relevant pages are actually available on the internet - [h=1][/h]

How to Build Max-Performance Chevy Small-Blocks on a Budget - David Vizard - Google Books

I was a little disappointed after reading all of the the various things that Vizard has written. In the end it seems like he's using the old technique of selling aftermarket products by pointing out "flaws" in existing product. I think that he started by selling MSD product, then went to DUI distributors. He even plugged Pertronix in one article. In some of his latest stuff he's lowered the "weakness" limit to 3300 RPM.

Ignition Systems Cheat Sheet for the Chevy Small Block

Small-Block Engine Build - Popular Hot Rodding Magazine Page 3

Looks like he's "currently" selling Blue Pheonix Plasma stuff -

He's selling oil additives here - Oil Extreme

Just filling in some gaps before I lose all of the links. If you read some of his original writing, it reads like good science but is short on actual measurements. The weak spark limit seems to be a supposition based on "module voltage output". He never actually measured if there was a misfire, just said that there should be.

For the record...

Yeah, that sure starts to sound like marketing propaganda aimed at increasing your own sales by torpedoing someone else's product.

I used to take my GM to 6000 RPM every once in a while and it never gave me any trouble doing that.

Found another Vizard article where he shows actual dyno results with a module change (stock coil though, apparently). Above 5000 RPM (V8 engine, = 6,667 L6 RPM), he shows a dramatic change. But he's still promoting MSD and Performance Distributor products. Just odd that there's not more out there on this.

Chart #9:

Twelve Engine Output Tips - Dandy Dyno Dozen - Stock Car Racing Magazine All Pages

My 280Z has been going strong since I made the HEI mod. Certainly better that the old tiu. It revs to 6000rpm not problems even under full throttle. I don't go about 6000rpm so its good enough for my stock L28.

chas

Someone noticed Vizard is a product whore? Imagine that; A magazine writer skewing an article to sell more products or even, heaven forbid, just reprinting a manufacturer's press release as editorial content. Whoda thunk it?

All these magazine writers are product whores. They are not writing articles to help you out, they write articles to make them and their magazines money.

I've owned several Camaro's that I've Hillclimbed, Autocrossed and Track Dazed. All had HEI ignitions at one point and all used the stock HEI module. Engines were all in the 10.5 - 1 CR range and all made in excess of 420 HP.
 
I could run to 7,000 rpm with no problems at .035" plug gaps. Not on the factory coil though. I used Accel internal coils and Blue Streak HD caps and rotors with Brass contacts. Also, on an HEI distributor you absolutely MUST replace the high resistance carbon button that connects the coil to the rotor with a low resistance bronze button when using an upgraded coil.
 
The factory ignition coils and the high resistance carbon dizzy button are the real weak points of HEI distributor... not the module IMHO.
 
Having said that, I did update the HEI distributor with a Crane Hi-6 CD ignition and LX-92 external coil. Plug gap was increased to .040"  and engine did idle noticably better with the Multi-Spark feature. Seemed to pull harder as well...but I did not do any comparitive Dyno tests between the different ignition systems. Butt Dyno and emmissions testing seemed to show an improvement though.
 
BTW... I love David Vizrds's articles. Great engineer.. but he does tend to pitch the " Product of the moment" . But really, any author of Automotive books does the same thing to different levels.