I just saw a 636 ci- mellenium hemi with twin 1050 cfm vacuum secondary carbs . I saw a 605 hemi with twin 950 cfm vacuum secondary carbs and a 572 b1 with vacuum secondary carbs. I have never seen big motors like these using using this type of carbs .what is the reason they are using this setup. why r they not using a double pumper or dominators thanks

I have no experience with anything this wild but I will wager a guess.Perhaps to control the rpm that the secondaries come in to aid in traction out of the hole?? I can think of a couple of street scenarios but don't know that they would apply in these applications.

It will be interesting to see the actual reason.

Who`s motors?

I would bet they are low rpm launch engines.. then
the secondaries dump in.... as in foot brake... JMO

That's exactly right. I've been running 2 950's on a 588" HEMI for years now. There's actually an adjustment screw on the vacuum pod to make the secondaries open sooner or later.

I run 2 850 thermoquads on a tunnel ram on my 605, very snappy.Dave

dave, could you please pm me on what mods you did to those thermoquads ? i'm thinking of using a pair on a slightly different intake and could use some guidance. thanks !

The 636 millenium is my motor. Why are they on there??

Simple and honest answer.... Came with the rolling chassis along with some other parts, so i thought i would try them.

Motor was built to be Big inch Low RPM. Also be NSS legal so dominators where not an option.

Jury is still out on them. Its a new combo for me. Motor starts easy, great on the street. very responsive. First track results where good. The 60 foot time was a soft. Leaving on the T brake the Racepak showed a flat spot in engine acceleration in the first second of the run. I believe the secondaries are opening too slow. The former owner of the carbs had the adjustment screws set all the in (in this case super slow opening). on this set after talking with the carb builder found out some vacum pods open faster by screwing in, these are the opposite. I expect to see a significant improvement the next time out. The results will tell.

The carbs where the real trick in NSS racing a few years back to aid in traction etc. I also think they had some advantages when it came to foot braking. On my car i use a T-brake and have a Grid if i need to soften up the hit of the tires, so if i had to do-over i would probably just do a set of 4150's. I did have a set of 4150 vacum carbs on my old car and worked real well on footbrake.

What do you use as a vaccum pump ? I have a 572 ci b1 in a 70 dart that is 2900 poundsI have sheet metal intake hanging around and think on using it . what carb will you recommend for my setup thanks

Use a moroso 4 vane pump. works great. pulls lots of vacuum. we bleed it off at I think 13. I would have to double check my racepak to be sure. Star makes nice stuff also. I have seen mixed reviews on the aerospace one.

As far as carb recommendations it is kind of a broad topic, and I'm not really an expert. Lots of competent carb builders out there. Most of your custom built 4150 carbs are going to run $1000 or so a piece. The carbs I have are from Biggs. He gave me his personal cell to answer questions when I didn't even buy them from him. I thought that was pretty cool. I would probably give him some business in the future. My engine builder uses bob book. Lots of good stuff out there. I do believe there is no such thing as a bolt on and go carb. all need to be tuned for the in a real world setting.