[What'saCobra?]

At the risk of being redundant to my own remarks and those of others, i would like to re-iterate a particular feature of both the Holley HP series carbs and some of the Demon carbs (although i don't really know which of the Demon's).

A few years ago the results of considerable experimentation at Holley resulted in a major break-through in venturi design and flow characterists creating the vacuume sensitivity and the increased strength of the vacuume signal used to tell/pull fuel into the airstream.

An electrical engineer might say that the carb now has significantly higher signal gain. A physicist might say the signal circuit had increased Q or ratio accuracy.

This higher signal strength was a very important issue to us rodders, but we didn't know it. With a tiny signal, which occured at very wide throttle openings and low rpms, it wasn't possible on the old carbs to put enough fuel into the very slow moving air mass. Once the rpms increased enough, the air mass flow increased enough to result in a large enough signal to add enough fuel to the air, so the engine ran better. This effect almost always required a vacuume operated secondary on the street, to keep the flow high enough past the venturi(s) on the only two open barrels. It was pretty straightforward enough to set the secondary linkages, vacuume pot sensitivity and diaphragm springs to open the second pair of barrels properly. But, the total hp developed under the two barrels wasn't as high as possible as if they were all open.

And, of course, the vacuume system could hang up (often the cause of serious accidents in the 'Vette 3 X 2bbl set-ups on the first 427's, but don't ask me how i know) and then flip to WOT with a bump in the road. Neither did the engines pull hard off the line, running only the two barrels.

This problem was oh so common to see in the older Holleys, a real pain in the buttinski. You could try to fix it with bigger pumpers, excess richness, etc, but the problem was that the mechanical 'amplifier' in the venturi system was too weak at low air mass flows. So you 'feathered' the throttle open all the time and tried to keep high rpms so you could slam it when necessary. And cold operation was ugly.

When Holley finally decided to get some fluidic people on this, in addition to their regular folks, significant discoveries resulted in much better gain designs, higher signals and more precise control accuracy at a wider range of air mass flows, especially in the dreaded WOT at low rpm region.

So, naturally, other carb companies 'discovered' the same improvements soon enough. OK by me. i still stick with Holley, i guess, because of such a long history of use and the smart applications engineers on the other end of the phone.

i've also found the same throttle response issues in race-boat engines, plus special safety issues, better served by Holley. i see guys out there with their 7 liter hydros and old design carbs, running just as awful as they used to run twenty or thirty years ago. They are simply such poor mechanical amplifiers that too much fiddleing is necessary to get them to work. And SOME of them don't even use center pivot float systems, which means that the float bowls are at the wrong levels. As the props grip, the hard acceleration pushes the fuel to the rear of the bowls and expose the main jets to air-sloshed (and entrained) fuel and they have no extensions from the jets to the rear of the bowl. You don't have to be a genius to fix those problems. But, instead of getting with the program, they suffer with ill-tempered engines, popping and dying and then generating lots of power in the range it will finally work. Painful to watch.

My opinion, sell them (non-HP's) to a collector and go all new. Or keep it in a nice box for the next 'nostalgic' owner of your rig, include it in the sale and for pete's sake don't waste your time and energy trying to make that pig work; unless you are really very, very sharp and can make big time changes correctly.

Now, there are specialists out there that have improved on Holley/Demon designs for even wider ranges of rpm's. And their designs improve the total amount of HP available in a very wide range of rpms, particularly from 3500 to 9000 rpms. These proprietary designs are de riger in NASCAR (and other places); where frequently, you can neither buy or examine the carb in detail, but you rent carbs (and the engineer/tuner that comes tethered to them) only. Hey, if you want the best, it is always much more money because they invested that much R&D/test/set-up time in it and they are not going to let you copy or reverse engineer it. Would you?

However, you might be able to buy one 1-2 years old and don't be surprised at the $3-5K price for a used carb...that might have the proprietary bits in it, but might not have them all and certainly not the latest...

Summary: Holley HP's forever (or at least until i find something better).

My 2¢.