Many people with double pumpers could have a slight bog and never even realize it. I would bet that in lots of cases, you need a dyno with A/F readout to detect it. It depends how rich, how fast you set the pump shot.

I run a 600 dp and you can see it in these dyno plots. I've tried to tune some of this out and have not run a dyno plot since then.



Note the A/F ratio at the bog. The question is, is the bog caused by too much air (and its fuel) too fast, or just too much fuel too fast.

 

If I had your motor even with a 2500 stall thats exactly what I would put in there. Just because you dont hear the sec opening doesnt mean youre losing power the carb only gives the motor what it needs anyways. (this coming from a DP fan)

I will say the VS carb was all around a little "smoother" for lack of a better term. Stick car cammed/geared DP no question.

IMO most overcarb their cars hoping it will be faster.

 

I don't really think that is always true. Yes it will give the max amount it is capable of IF it opens at the right rate so as to not cause a restriction AND actually get WOT. If you have the wrong spring in it you can wind it to the moon and it will never open much. Or if it does open somewhat that in no way means it's "giving the motor all it needs". It just means it's giving it all it can set up as it is. Or even if it eventually does get wide open at say 4000 rpm (if you're lucky)...I can guarantee you that the motor would have wanted more air at lower RPM.

Interestingly I've seen that VS carbs work their best on cars with loose converters and good gearing so that they open very quickly as RPM comes up. In those cases they will run pretty close to a DP.

This whole myth of VS carbs giving it all it needs is just hype to say if you use this it will be safe and not bog. IF they are setup right..a vacuum carb CAN do pretty well...but an equally well setup DP on a tuned motor WILL spank it even at low RPM.

Again...take the safe way...or the fast way.

JIM

 

For some real world experience, I had a 3/4 ton van, nearly stock engine, stock converter with TH400 auto and mid gearing as a dialy driver for over 10 years using a Holley double pumper.
Van weighed around 6000lbs empty and also used it to tow with.
Contrary to popular belief, there was no bogging, despite the fact it wouldn't normally break the tires loose. Ran perfectly under all conditions.
I did however R&R it at least 15 times initially to set it up properly, jets, pump squirts, power valves, bleed drilling etc, but my incentive was the emissions test here in Florida at the time, they were pretty strict and it ended up passing with flying colors.
The nice thing about that setup was that you could tell by the feel of the pedal when you were opening up the secondaries and it was commonplace to cruise at 70mph on just the primaries.
That's probably at the extreme for a dp setup, but it worked well and more reponsive than the qjets that were on there.

Agree totally with 427Hotrod on the vs, just because they may open even properly, doesn't mean you are getting the proper a/f, they must be fiddled with too.
Always a lag with a vs, even if very small.

As an aside, I use qjets with my vettes, and am happy with the demand secondaries, but they are no where near what a stock q jet is either.
They both take a lot of tuning to get it right.

 

I first bought Holley 6210 650 spreadbore double pumper carbs in 1974.
Installed them on my 1968 and 1970 Corvettes to replace the Q-Jets.

Have never regretted gaining positive control of when the secondaries opened, no waiting for vacuum operation to take place. The 68 is 327/350 L79 and I am still using the very same Holley I installed in 1974. Used the same Holley spreadbore purchased in 1974 on my 1970 350/300 turbo 400 automatic 3:08 untill I bought a ZZ create engine. Installed the ZZ engine in early 90's but could not use my old spreadbore Holley because the intake in the ZZ crate engine was square bore design. Bought a new Holley 650 double pumper square bore. Performance is great and I like the added power of the ZZ crate engine in my 1970 Corvette.

Control, control, control, that is what I like about the mechanical Holley double pumpers.