Vacuum Secondarys ???
 

I know Holley offers Marine carbs with vacuum secondarys, but does anyone use them? I think they would probably give better fuel economy over a double-pumper, but can you tune one to give as much power?

I'd like to know the same as well.

I am using them in my warmed up 454's. it took me years to get the right combination of accelerator pump size, squirter size, ramp (cam) size, diaphram spring size, but I have put other carbs on to see if they made more power and they didnt. I think the vacuum secondarys work fine for me. On the other thread regarding carb size, someone mentioned a very interesting difference about them regarding response in turns. Since I dont race, I could care less but he had a good point. I am always scared of running lean just before the secondarys open ( a known Holley trait) so I stay away from the 4000-4200 range. Im either at 3500 or WOT.

formula31, So is what you're saying true more on the vacuum secondary Holley's or the mechanical secondary Holley's?---Or both? Thanks

That I dont know, Ive personally never burnt a piston as a result but know people who said they have. Dennin Moore knows I think. He said something about a change to the metering plate that prevents that problem. He listed a specific carb that had that change. I dont remember what thread it was on, couple months ago I think. MIne are 1960's vintage 3310 780's built for GM for the big hp vets. I build my own vent loops and throttle shafts to marinize them. Was a fun project and I learned a lot. There were some really good engineers at Holley that helped me out. Of course, that was in the late 80's.

I have a pair of 3310's on a blown 502. They have been worked on and boost referenced, and work perfectlly, at idle and all speeds. Theses carbs have been on this motor since 1992, and I went thru them when I rebuilt the motor 2 years ago.

Mine are 9029's that came with the 86' KAAMA engines. (Hardin Marine used to build them). They are a 716cfm, vac secs, elec choke......but seem to run great. (granted the motors are just the older style 454/450hp gm stuff).


Bob