Mostly, simply because it is a modern carb, it has modern fuel circuits.  The other features, I think you can retrofit to older carbs, but older and old style do not come with them.  Those are things like center hung float bowls, dual inlet, quick change secondary spring housing, secondary metering block.  Some of them are available with 4 corner idle.  For more info, check Holley's site.

Just for clarity, I'm talking about the lower end Holley carbs.  I know there are older high end carbs that do come with many of the same features as the Street Avenger.



Lawrenceville, GA

To add to what Charlie has mentioned, the Holley Street Avenger series of carburetors are calibrated for more aggressive camshafts.  Because many of the ‘larger’ camshafts have a reduced carburetor signal at idle, the emulsion holes and air bleeds are sized differently to obtain the correct fuel mixture in the lower rpm ranges.  Many of the universal carbs have fixed emulsion and air bleed holes and are difficult to modify appropriately.  The Street Avenger carbs while still having fixed sizes, are sized for more aggressive camshafts and work better out of the box with modified engines.

Lorena, Texas (South of Waco)

According to Holley tech, the 570 is geared more  toward stock engines.  It is the 670 and bigger which are for modified engines and bigger cams.

What I have is the 570, which Holley would not have suggested for my combo, had I asked before buying, and my engine is not at all radical.  I have acquired a 670 that I wil try soon.  So, if your engine is stock or a basic rebuild, 570.  If it is modified and you've gone up a couple steps or more on the cam from, say,  the standard 1957 cam, 670 or bigger.  And you can always call or email them and ask.



Lawrenceville, GA

Frank/Rebop

Bristol, In ( by Elkhart) 

HI Rob.
My Tbird will go to first of the line if I floor it, since I adjusted the kickdown.

How did you adjust it Ian , did you still line up the hole in the bell crank etc ? I have adjusted the threaded rod [the one direct to the trans] but that had no effect on making it go into first, it does hold the gear slightly longer however it seems to "load up" and clunk into first when nearly stoped.
I did find the linkage I made for the Edelbrock works better and if I floor it will kick to second. before I had to push it through the floor to have any chance.



"Came too close to dying to stop living now!"

It was a long time ago, soon after I got the car but I think it was as the manual says. I remember that just lining up the hole was not enough but  there should be some preload on the kickdown rod. I originally adjusted it because it was a bit sloppy, sounded like it was slipping under very light throttle, when almost coasting. I spoke to an old transmission guy who suggested I look at the kickdown first. That firmed up the shifts and the bonus of first gear when flouring it of the line.
Maybe catch up some day when this rain stops and I'll take you for a spin.

The Fordo transmission manual has some additional advice about setting up the kickdown rod (on my '56) - it involves reading a pressure on the control valve. Shows the proper port to attach your gauge to - but I don't have a reference to it on my computer these days............. I have heard / read that the use of the pressure as a set-point is the best way to get a consistent reaction. Hoosier would know....... 

 
 Steve Metzger       Tucson, Arizona

At least on the 56 Fairlane, the rough adjustment for the trans is to get the kickdown rod to where it lines up with the hole on the bellcrank when pulled all the way up, and then lengthen the rod by 3 turns.  This method has always worked well for me.  The pressure gauge is the better way to do it, but I dont have one of those and havent sought out anyone who can do it that way.

I do believe that if it isnt adjusted properly it will lead to premature wear.

YMMV

Ron Grove

Wauconda, IL

The thing I learned - the hard way as always - is that once you have the rod in the alignment holes - you then must set-up the height of the gas peddle off the floor. Spec was in the Fordo manual. This is so that there is sufficient travel available for the kick-down rod to travel the proper amount to work it's lever in turn. Make sense? When the peddle is too near the floor - mashing it won't result in enough kickdown movement to get the proper shift pressure. Just turn in in the screw on the kickdown raises the pressure OK - but then, back at part throttle the shift may still be harsh.
I've run my outfit with a Holley 600 cfm - and now a Demon 525 - and the internal throttle springs (of the carb) are so different than the linkage was initially designed for - much tinkering is required to balance the spring forces.

 
 Steve Metzger       Tucson, Arizona