PowerValve Selection II
 

O.K. decided on a 7.5 on the PRIMARY side of my 4010 VAC SEC Holley. Im pulling 11.5 at idle in gear. I NEED HELP WITH THE SECONDARY Powervalve. How do you decide the rating on this one. What readings do you taks AND WHEN? This carb was built for Crusader Marine and was built for HP Bigblocks(Im using a 375horse SBC)...Holley said it came with 10.5 powervalves on the front 6.5 on the rear......

BH

BH what is the vac, crusing ?? if your set on the 7,5 the rear has to be that or less 6.5 ,need more data you gotta have it to do it right ;) ;) ;)

Best way to get the data is to plot your vac. reading vs RPM, say every 1000 rpm or so. Do this at your optimum trim angles and with the correct prop. Then repeat this process with the trim down and tabs buried. Carefully observe at what RPM the secondaries begin to open for both the optimum trim and buried settings. There will be a difference. Then Bobby or another knowledgeable carb guy can set you straight. You got to know this stuff or else you are just shooting in the dark.

Gonna try the 7.5 in the primary and a 6.5 in the secondary. When I get it out I will check the vaccum at my cruise (3500 rpms)and get back with you all. I really only see three rpm levels 90 percent of the time... Idle,3500-cruise and w.o.t-5200. And of the three probally 40 percent is idle 40 is 3500 and 20percent @5200
Thanks guys I will get back with a full report!:D

BH

Well got out last evening.....Readings were 15in at idle,11.5 at idle in gear and 8 in at my cruise. I figured that it would be higher than that at my cruise (3500).Oh well....... So what is everyone's recomendations? Remember I have TWO powervalves. I am leaning towards a 7.5 or 6.5 on the front and either 6.5 or 5.5 on the rear.....Holley's reccomendations would put me at a 6.0 front and rear.......Bobby what's your call?


BH