I can slam a vacuum secondary carb open and it will run fine.

Slam the double pumper open you will get a immediate surge from both accel pumps dumping the fuel into the engine, but after it uses that all up and the engine is still not turning fast enough to pull fuel through the venturi, you will get a bog. He even admits that.

The original poster can run one of his double pumpers and probably be fine, might even like it. But it's not going to be the ideal smooth running setup that a vacuum sec carb would be.

 

That's the difficulty with the DP - it's getting the "transition" from idle to cruise and cruise to WOT, correctly setup. IMO.

 

On a Holley that is the job of the power valve (PV) and the VS carb also has a PV.


What I see you guys saying is the VS carb can be run on anything and just run, be it right or not where a DP is just a PITA if not right and takes someone who knows how to tune them.


To tell the truth I have not run a Holley DP on the street and the only Holley was a 2300 v2 500cfm on a 304 v8 and even it had a PV I had to "dial in".
All the DP (HP's) were on race motors for drag so if it idled and went to WOT good I was happy. Not that I cant turn it for street just never had the chance to.
Dave ----

 

No way can a power valve overcome all 4 butterflies opening wide open all at once at low rpm. It has double accelerator pumps(double pumper) to try to shoot fuel in there mechanically to overcome this, and it will if the engine is free to rev in a lightweight car. A very high number in the rear would help on a truck.

 

I think if the DP is tuned properly it would work fine on the street in any vehicle. I know a lot of guys that run DP on the street with no issues accept probably gas milage.

 

The PV is does "the "transition" from idle to cruise and cruise to WOT" as you posted and that is what Holley says it does.


Who said they open all at once? Again the carb on the street is not going from idle to WOT like it does on a race motor and even more so if it is a 460.
If your 460 is that weak you need to go from idle to WOT you got bigger issues with the motor than running a DP carb.

You are 100% right.
Would a VS carb be easier to tune? Maybe but only because you can be off on the tune and it will still run pretty good.

If all I had was a DP carb sure as heck I would give it a try and tune as needed.
Let us know what carb you go with and how you make out.
Dave ----

 

Sorry got to call BS on that. It that was the case then no one would use DP's as a drag carb. It all comes down to proper tuning and that means accel pump cams/squirters as necessary to tune the pump shot curve and adjustable progressives linkage for the secondary's . Most all DP's are progressive secondary's, and really only hard core race DP's are 1:1 ratio on the primary's and secondary's

Just cause you have no idea how to tune a DP carb does not mean it is not viable option for street driven vehicles. NO vac secondary carb will out perform a DP in terms of flat out acceleration. Either from a standing start or part throttle.

 

I just drove the truck and haven't done any tuning to the carb and it runs perfect no bogging or stumbling seems to have more top end power.

 

Yup. Probably weak valve springs - so your vales are "floating" above 3,000.

 

He said it runs fine now with the double pumper carb he installed.