Senior Tech Team
Join Date: Feb 2013
Location: Lloydminster, Alberta
Re: Mechanical or Vacuum secondaries
Your 4 speed and gear, I would go with a AED 950HO. If you want to have a choke, then a FST 750 RTX vacuum secondary.
I have a 630hp MJ engine in a 71 Nova. 3.42 gear, 27" tire, 2500 10" converter. I run a AED 950HO Modified, and 770 street avenger (actually a 750 after measuring the throttle bores and venturis). The double pumper hits way harder, and with normal street tires they don't have a chance, especially since I changed the converter from one that would flash to about 2200. The few more rpm this converter flashes to made the difference that the tires light up instantly. That includes a Hoosier drag radial that with the other converter would stay right on the edge of traction, hazing the tires, but staying hooked up.
Now with a tire change to a regular Nitto NT555G2, I put on the avenger to gain a choke which is nicer for cold starts, and give the tires a chance to hook. They still light up at will but I can roll into the throttle fairly aggressive, and keep them hooked. With the AED carb, as soon as the secondaries would open the tires would light up.
I have ran the car at the track with both carbs. The avenger is only 1-2 mph and about .1 to .15 slower. And that is using the stiffest black secondary spring.