Lets Talk About Double Pumpers

[toobroketoretire]

As my big block '71 is a "street only" C3 and it's never revved beyond about 3500 rpm I wouldn't run a double pumper if you gave it to me. Why? Because double pumpers aren't suitable for street engines because they are intended to be run at 4000+ rpm all the time where venturi velocity remains high. Yes, a lot of C3 owners use them but they meter fuel VERY poorly at low engine speeds under wide open throttle conditions and that's why none of the muscle cars ever used them. They are "track only" carburetors.

I suppose you all disagree with me?

 

[toobroketoretire]

Double Pumpers Aren't Intended For Street Engines.

Double pumpers are one of the reasons why every dyno test using a carburetor is done slowly; the throttle being opened SLOWLY to prevent a massive bog because of low venturi velocity. You can loaf along at 40 mph in 4th gear with a QuadraJet and suddenly stand on the throttle but you can't when running a double pumper. The factory engineers knew "too much too soon" will kill power until the engine can rev high enough to accept the rear two barrels and that's why every muscle car came with a AVS or vacuum secondary style of carburetor. It's much better to use a carburetor that is BARELY big enough than one that is grossly oversized because of the low venturi velocity problem. The lower the velocity is the larger the fuel droplets are and large droplets kill power. That's why double pumpers should never be used on any street engines; especially those with automatics behind them.

 

[Hib Halverson]

As my big block '71 is a "street only" C3 and it's never revved beyond about 3500 rpm I wouldn't run a double pumper if you gave it to me. Why? Because double pumpers aren't suitable for street engines because they are intended to be run at 4000+ rpm all the time where venturi velocity remains high. Yes, a lot of C3 owners use them but they meter fuel VERY poorly at low engine speeds under wide open throttle conditions and that's why none of the muscle cars ever used them. They are "track only" carburetors.

I suppose you all disagree with me?

71 C3, street only and never over 3500 rpm?

For that girlie car you need a two-barrel.

 

[Hib Halverson]

Double pumpers are one of the reasons why every dyno test using a carburetor is done slowly; the throttle being opened SLOWLY to prevent a massive bog because of low venturi velocity. You can loaf along at 40 mph in 4th gear with a QuadraJet and suddenly stand on the throttle but you can't when running a double pumper. The factory engineers knew "too much too soon" will kill power until the engine can rev high enough to accept the rear two barrels and that's why every muscle car came with a AVS or vacuum secondary style of carburetor. It's much better to use a carburetor that is BARELY big enough than one that is grossly oversized because of the low venturi velocity problem. The lower the velocity is the larger the fuel droplets are and large droplets kill power. That's why double pumpers should never be used on any street engines; especially those with automatics behind them.

Expectedly, little of the above is true.

 

[Vettehead Mikey]

I suppose you all disagree with me?

No, irrespective of whether we agree or not, we're just bored to tears with you posting the same garbage over and over.

 

[Antz81]

No, irrespective of whether we agree or not, we're just bored to tears with you posting the same garbage over and over.

At least he's consistent, and sticks to his story. No matter how much evidence there is to prove him wrong.

 

[toobroketoretire]

Using Wrong Parts For Street Engines

I have never understood why people are so bent on using wrong parts for their street engines. Some parts are intended for high rpm track racing and some parts are intended for low rpm street engines that very rarely get revved beyond 3500 rpm. This is why single plane 360 degree intake manifolds and double pumpers aren't suitable for street use because they made specifically for continuous high rpm use. Same goes with headers as they are intended to be run OPEN and at high rpm/full throttle and therefore don't provide any gain for low rpm street use. That's why it's always best to get speed equipment advice from professionals who make their living at it rather than getting advice from forum members who wish they made their living at it.

 

[Vettehead Mikey]

That's why it's always best to get speed equipment advice from professionals who make their living at it rather than getting advice from forum members who wish they made their living at it.

And that explains perfectly why we've learned not to listen to you. :eyerole

 

[Hib Halverson]

Ya know, threads like this are exhausting.

(snip) That's why it's always best to get speed equipment advice from professionals who make their living at it rather than getting advice from forum members who wish they made their living at it.

That final statement begs the question:
Why should we consider anything you post as credible advice, "toobroketoretire."?

As for getting "speed equipment advice from professionals who make their living at it."?

When you say "professionals who make their living at it." are you talking about people manufacture speed equipment, sell it, install it or test it?

By the way, instructions on how to tune a DP for street use can be found by clicking here.

 

[Antz81]

By the way, instructions on how to tune a DP for street use can be found by clicking here.

I believe he has own definition of "street use"

 

[kpic]

Toobroke....
Still at it as usual? As stated earlier, your ignorance is boring.

An accelerator pump, AKA a Reo pump, provides a shot of fuel when the right foot hits the floor. People who race cars like them.
About the only bad thing about an accelerator pump is they can hide deficiencies in carburetor tuning.

I do agree a single or dumper pumper for your application is a waste. Might I suggest a nice econo box I4?

 

[toobroketoretire]

Double Pumpers

Double pumpers are okay when used for their intended usage; high rpm track racing where the engine remains at 4000+ rpm all the time. But for street use they fail miserably when the revs are low and a full throttle is given because the venturi velocity drops so much. By preventing the secondaries from opening until the engine can accept the additional air the engine will produce a lot more power. That's why the muscle cars never came equipped with them. And then there's the matter of the "four corner idle screws" that are only useful for racing engines with very long duration camshafts and 1500+ rpm idle speeds; something street engines have no need for. For some reason a lot of people get a kick out of using track racing parts on their street engines even though the parts greatly reduce the engine's power.

 

[Vettehead Mikey]

For some reason a lot of people get a kick out of using track racing parts on their street engines even though the parts greatly reduce the engine's power.

And for some reason a small minority of people just keep repeating the same old broken-record story- even though nobody agrees or cares. Getting pretty tiresome.

 

[kpic]

Toobroke...
When engine vacuum is low, a accelerator pump's shot of gas gets matters moving.

An accelerator pump is a component on a carburetor. It is commonly found on many older vehicles that are equipped with carburetors. The accelerator pump is responsible for providing the momentary additional fuel needed under heavy acceleration conditions. When the pedal is suddenly pressed, the throttle will suddenly open, immediately adding additional air for additional power. That additional air requires additional fuel, especially in the precise moments after the throttle is opened, this is the fuel the accelerator pump provides. When the throttle is rapidly opened, the accelerator pump will squirt a small amount of fuel into the throat of the carburetor so that the engine can continue running smoothly under increased load[/quote]
Symptoms of a Bad or Failing Accelerator Pump | Advice from YourMechanic

My question is how can a self-acclaimed mechanical engineer and self-acclaimed professional engine re-builder be so ignorant of the basics of engines?? The answer is both obvious and screams you aren't what you claim to be which is quite obvious.
Your basting us with your bull manure is well past boring.

Mikely,
No offense intended to you; however, you are being way too kind to a crock of manure.

 

[toobroketoretire]

Track Racing Parts Aren't Suitable For Street Engones.

It seems most people can't understand what the word "suitable" means when selecting performance parts. To me suitable means the best component for the conditions my vehicle runs in. You can obviously run a NASCAR camshaft with 300 degrees of duration and a .800" lift in a street engine but your engine would run awful under 7000 rpm. So for street use a NASCAR camshaft wouldn't be suitable. Same goes with single plane intakes, double pumpers, headers, and other "track racing" components that are intended for high rpm only use. If you want a powerful street engine build it the way the factory built it and use a rear end ratio that is suitable for that engine's torque characteristics.

 

[toobroketoretire]

"Too Much Too Soon" Kills Bottom End Power

The carburetor manufacturers have always made HUGE efforts to prevent a condition known as "Too Much Too Soon" by installing counter-weighted butterflies above the secondary throttle blades to prevent the engine from choking on too much throttle; causing a condition known as "fuel stand off" (a fog of fuel over the mouth of the carburetor that kills power). Holley invented the "vacuum secondary" to prevent Too Much Too Soon and then Carter/Edelbrock and Rochester used an "air valve secondary" (aka AVS) to prevent Too Much Too Soon. The "Three Two's" and dual quads also used a "progressive linkage" to further eliminate the Too Much Too Soon/Fuel Standoff condition. Then 40 years later ignorant people have become determined to have "Too Much Too Soon" because they have been convinced the factory engineers were a bunch of stupid fools. My question is "why are people so determined to prove the factory engineers wrong and end up turning 14 second cars into 16 second cars"? And why are people so determined to do things the wrong way rather than the right way? I just don't understand the insane logic of some people.

 

[toobroketoretire]

Double Pumpers Aren't Suitable For Street Engines

You see, G.M. Ford, and Chrysler would never use a carburetor that produced LESS power and that's why they never used mechanical secondary carburetors on their street engines. At low engine speeds a mechanical secondary carburetor grossly over-throttles an engine which kills venturi velocity AND power. The mechanical secondary carburetors are solely intended for high rpm track racing where the engine is able to spin 4000+ rpm all the time. When an engine is on a dyno the throttle is always opened SLOWLY to prevent a massive bog or backfire. With it's small primaries and AVS secondaries a QuadraJet could be opened suddenly but a mechanical secondary carburetor couldn't and that's why they aren't suitable for street use. And then there's the "four corner idle screws" that are solely intended for racing engines that idle at speeds way above what street engines idle at. Racing parts just don't belong on street engines!