let me preface by saying I don't have much carburetor experience and am trying to make an educated guess with recommendations from others. I know every engine / car combo is unique and lots of variables come into play.
I've been running a Quick Fuel Vacuum Secondary SS series 735 CFM carb on my mild cam 451 since new (currently 6500 miles on the motor). The carb performs pretty well with no big issues and I had it jetted and tuned at a dyno shop. The car ran a best 1/4 mile ETA out of 10 track runs of 12.80 sec. Rear wheel numbers are 391 HP / 523 lb-ft torque. Not bad, but would a carb swap make it any better? I know the online calculators often show a smaller carb than what real world results are and I've often wondered if I'm leaving power on the table and have read up quite a bit on using 750 vs 850 carbs. I don't need maximum dyno numbers, but what I am looking for is a noticeable power increase on the street and a better 1/4 mile time would be nice!
The way I understand it, the Quick Fuel Holley type 750 carbs include the 735 and 780 Vac Secondary SS carbs offered. If I don't care about fuel economy, for street driving and a once a year track visit, is there any noticeable driving advantage of a 780 or 850 cfm Quick Fuel Vacuum Secondary carb over my current 735 cfm for my combo?
I've had numerous mopar friends advise me to get away from the Vacuum Secondary carbs and switch to Mechanical for better responsiveness. However, my car is an Auto Trans 727 with 2200 stall converter so I'm hesitant to go with mechanical secondaries. One thing I came across in a separate thread that many don't seem to talk about is the intake manifold effect on vacuum vs mechanical secondaries. I don't know enough on that to comment.
Here's my car info:
727 Auto trans
Lunati Voodoo 60302 Cam (.475" lift, 220/224 at .050")
28" tall rear tires
Eddy RPM Heads
Eddy RPM dual plane intake w/1/2" phenolic spacer
Schumacher Tri-Y ceramic coated headers
2.5" exhaust w/H-pipe/Dynomax Ultraflow Welded (straight through) mufflers
Thanks in advance.
I believe you should pick up a little with a
double pumper (aka mech secondary). I would be looking in the 800+cfm range.
Old combo from the '90s:
8.8:1 1973 440/stock 1973 pistons (hand honed/re-ring)
346 iron heads milled .060, 8.8:1, MP 484 cam, hooker competition headers, 3" short exhaust. Started with 3000 stall, 750 vacuum secondary on a street dominator, first pass [email protected]
ish, ran 12:80s later that day. Switched to a standard 850 DP, 12.70s similar conditions, but did not like how it drove on the street. Tried an annular 850 DP, same ET but drove much nicer on the street, more responsive. Better converter, 12:60s. Tried an RPM intake, still 12:60s but improved streetability/more responsive. Finally went on a cold temp day (low 50s), removed the belt driven fan. 12:50s. coolant temp never got over 180 degrees, it was that cold outside. 106 mph was a pass with good traction, 108 was a pass with wheelspin, it never varied any more.
Good luck with your decision