Carb CFM size
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Before you commit to giving up some potential performance, you are aware that a vac 2nd carb will allow you get away with over-carbing it a bit, especially on a 180* intake, no? Set up properly the secondary throttles will never open more than necessary, but you'd still have that extra 100 CFM for top end with a 750 VS. Just making sure you're sure.
Racer
Joined: Oct 2010
Posts: 259
Likes: 3
From: Plano TX
Vacuum Secondaries
Before you commit to giving up some potential performance, you are aware that a vac 2nd carb will allow you get away with over-carbing it a bit, especially on a 180* intake, no? Set up properly the secondary throttles will never open more than necessary, but you'd still have that extra 100 CFM for top end with a 750 VS. Just making sure you're sure.
I'm currently playing around with different secondary vacuum springs in my moderate build 454 (dyno'd at 344 rwhp). I took the car on a gas mileage test run the other day, and with the "heavy" black spring in (which almost promises the secondaries won't open) I managed 14.5 mpg with 3:08s at a steady 65 mph. I thought that was pretty good. Now I've got the long yellow spring in, and will be going to a local "dyno day" this weekend just to see what the curve looks like on a dyno.
The carb is a Holley 770 Street Avenger (you'd probably want the 670) and the cool thing about it is that it comes standard with the quick change secondary vacuum spring capability....give you all kinds of options to play around with.
