The Holley "Trick Kit" literally

[78_Elky]

take a fluid dynamics class and it will make a lot of sense as to why the venturi is designed the way it is, and also the way that inserting the fuel into the air stream at different points will allow more power or better performance. I also would say that the rating they put on their carbs may be more for marketing than from actual specs. But if you know how it works and have the access and ability to test them you will be able to pick the right one (Who is going to go buy 5 carbs to test though LOL).
Oh and IIRC then a smaller venturi may be on a larger carb and rated at a higher cfm because it could be that the air and fuel get to that small section they flow faster and therefore more gets into the engine than with a fuel toilet design. Also the design of the venturi will dictate wether the air is in a primarily laminar or turbulent flow and how it will atomize the fuel, this goes so far as to the design of the manifold when the fuel hits that it needs to be flowing well enough and not hit the bottom of the plenum like a rock. I hope this helps, if you need anything specific I have a fluid dynamics book and know how to use it and do the math for it and can try to explain some things in more detail.

-Josh

 

[Goob]

Tru Dat!!
When you add fluids to the flow, it changes everything, then you have to consider what condition the fluids are in.

That is the reason for the emulsion holes and air bleeds, to deliver the liquids to the booster in a more emulsified/atomized state.

I know I've had very little luck with the stock annular booster carbs. lazy mixing is my theory.

Injection systems with down nozzles produce more HP because there are no fluids introduced in the incoming air, and Alky systems resist performance swings with weather because you're filling the cylinders with half the atmosphere you do with Gasoline....the nozzles and delivery pressures do the atomization at the delivery point.

For what all that is worth....... :roll:

 

[NoMoore]

All this makes me wonder what misconceptions are out there!

The more I am learning now, the more I find that what I have been taught is all wrong.

 

[NoMoore]

Now, one thing that I have never heard or seen mentioned is related to a rear power valve. Some holley's come with them, some don't.

In general Drag racers take both power valves out to ease tuning, and reduce variables.

The thing that's not mentioned(at least to me!) is relating to fuel slosh. I always hear about jet extensions to prevent your jets from coming uncovered, which may be exagerated, but not one time have I heard about a secondary power valve coming uncovered. It sits higher than the jets and would be more suseptable to being exposed to air on the launch.

I believe it is important to block the secondary for a drag race or street strip application. For that matter, why have one there in the first place? If you are into the secondaries you are most likely not worried about fuel consumpotion.


I have a friend whose camaro comes out of the hole and dies off for a split second, he has a secondary power valve, and I bet this is a contributing factor.

On to misconceptions, one thing I was taught early on was that having the correct powervalve helped clean up your idle. I can not see how it could. It is part of the main circuit, which should not be activated at idle.

This is the kind of stuff that makes learning about carbs difficult. The information we are exposed to is in limited supply, and not always credible.




One neat hing though, is I just reached the point where understanding Holley carb's operation just "clicked." Now learnig about them makes even more sense easier than before.





Thanks for posting guys, this is a great thread so far!

Anyone have any misconceptions they'd like to add?

 

[CutlassRacer]

I get people all the time at work that think that they can "jet up" their carb to any size that they want.

"Yeah we put 750 jets in my 600 so its a 750 now". Dead serious and I cannot believe how often this happens.

A power valve should have nothing to do with the idle circuit, you are correct. If you have one that is too high of a rating, you might get a rich stumble during the transition to the main circuit because the vacuum in the intake drops below the power valve opening point and adds the extra fuel to the motor, but that is as close as you can get to having it affect the idle.

On the secondary power valve thing, I know of a couple very high hp blow through carburetors (as in 1800-2000 hp) and they have some trickery done in them to keep fuel going to the rear power valve. With the massive amounts of fuel that needs to be metered into the engine on a setup like that, bringing the extra fuel through the power valve channels is necessary.

 

[boyzbad]

Your trying to understand something older than the hills. Go EFI and never look back. A person that used to do head work for me (vey knowledegable)
once told me that 1 in 12 Holleys were good. Maybe true considering mass production. My personal opinion is that every single combo is different even if it's been duplicaTed.

 

[NoMoore]

I get people all the time at work that think that they can "jet up" their carb to any size that they want.

"Yeah we put 750 jets in my 600 so its a 750 now". Dead serious and I cannot believe how often this happens.

A power valve should have nothing to do with the idle circuit, you are correct. If you have one that is too high of a rating, you might get a rich stumble during the transition to the main circuit because the vacuum in the intake drops below the power valve opening point and adds the extra fuel to the motor, but that is as close as you can get to having it affect the idle.

On the secondary power valve thing, I know of a couple very high hp blow through carburetors (as in 1800-2000 hp) and they have some trickery done in them to keep fuel going to the rear power valve. With the massive amounts of fuel that needs to be metered into the engine on a setup like that, bringing the extra fuel through the power valve channels is necessary.

Do they need the secondary powervalve because 99 jet is the highest, and is not enough for them? The PV would provide some extra enrichment.



And LMAO at the jetting it up to a 750. I swear I've heard that one too.

 

[Goob]

I believe it is important to block the secondary for a drag race or street strip application. For that matter, why have one there in the first place? If you are into the secondaries you are most likely not worried about fuel consumpotion.

Correct, the rear power valve should always be removed in a drag car,(with standard mounting, single carb) I like to use the front power valve with a footbrake car to keep the plugs clean and throttle response crisp, BUT, there were certain older Holley metering blocks that would not flow enough fuel without a power valve or modification of the well tubes and emulsion holes.

I use nothing higher than a 3.5 power valve because the extra fuel is for sure never needed at anything less than wide open throttle, but if the carb is actually too small CFM wise, you can pull a power valve shut during a top end charge.

And now for something completely wacky.....

I once traded out some stuff to a circle jerker and ended up with this really cool tricked out 500 2-barrell, it had NO booster venturi, the bore venturi had an annular ring around it that the fuel pulled through, I'd have to guess the thing would flow 800 CFM +, always wanted to try it out, but some guy wanted it REEEAAL bad one day when I wanted some money REEAAL bad.....

Ooops, I've digressed....... :lol:

 

[NoMoore]

I'd love to hear more about your "lazy mixing"theory with stock annular boosters. I have yet to learn much about atomization. My booster research has been pretty limited to sensitivity.

 

[NoMoore]

I believe it is important to block the secondary for a drag race or street strip application. For that matter, why have one there in the first place? If you are into the secondaries you are most likely not worried about fuel consumpotion.

Correct, the rear power valve should always be removed in a drag car,(with standard mounting, single carb) I like to use the front power valve with a footbrake car to keep the plugs clean and throttle response crisp, BUT, there were certain older Holley metering blocks that would not flow enough fuel without a power valve or modification of the well tubes and emulsion holes.

I use nothing higher than a 3.5 power valve because the extra fuel is for sure never needed at anything less than wide open throttle, but if the carb is actually too small CFM wise, you can pull a power valve shut during a top end charge.

And now for something completely wacky.....

I once traded out some stuff to a circle jerker and ended up with this really cool tricked out 500 2-barrell, it had NO booster venturi, the bore venturi had an annular ring around it that the fuel pulled through, I'd have to guess the thing would flow 800 CFM +, always wanted to try it out, but some guy wanted it REEEAAL bad one day when I wanted some money REEAAL bad.....

Ooops, I've digressed....... :lol:

That 2 barrel would have made for one heck of sleeper look.

I recently got a carb from TMP carbs. He has a 2.5 PV in it. I am curious to see if it could be plagued with the problem you just spoke of with the PV pulling shut.

Troy at TMP has been one of the people helping me understand these things a little better, and definitley the one who is inspiring me to take a hard look at them. He is a little unconventional when it comes to sizing. I'll try to find some quotes to post this afternoon.