Engine Tuning Theory With : Carburetion

[A20A1]

I was reading about booster design, I haven't really had time to read over the article until now.

Anyways some of us that have removed the intake manifold heater, removed the EFE screen, EGR, or other vacuum lines and valves. We're running richer and possibly colder than normal.

I was looking at the article particularly interested in the cooled manifold and how much fuel is broken up to be readily vaporized by different booster designs.

It got me to wondered if the reason the engine would pull harder at night was less because of extra air charge and more because of a larger fuel droplet.


Then I looked at the weird thing sticking into the primary booster of the stock carb and thought that that little reed was there to break up fuel for low speed fuel economy and the secondary lacked this because they wanted to keep the fuel droplets larger.

anymore thoughts you would like to share; here is the article.

http://www.popularhotrodding.com/tech/0511phr_carburetor_boosters_tech/index.html

.
.
.

[2oodoor]

I am glad you still had that article.
I can see how more of a percentage of a finer atomized fuel mist would try to cling to the runners of a hot manifold before it makes it to the combustion chamber as opposed to a cooler manifold it would be in a denser formation even though it was equally atomized.

[2ndGenGuy]

I don't understand what the booster "signal" is that they're talking about? Is it the proper amount of velocity to pull the fuel out into the booster venturi?

[2oodoor]

Think of a MAF , how it works is it measures air flow going past it , hence the air flow is a signal converted to an electronic signal via bi metal instrumentation. Any debris or a contaminated film gets on the bi metal instrument of the MAF and you get delayed or erroneous signals to the ECM for timing and injector dwell corrections. (opps sorry carb people, for the FI analogy)
On the boosters the signal is the air flow going past it to activate the siphon, an "amplified" signal is achieved by enhancing the ID surface of the booster by making it smoother, more defined around the Inner Diameter edge, or even in some cases, cutting steps in it . All very meticulous work needless to say.

[2ndGenGuy]

Aah makes perfect sense. Thanks! :D

[lostforawhile]

Think of a MAF , how it works is it measures air flow going past it , hence the air flow is a signal converted to an electronic signal via bi metal instrumentation. Any debris or a contaminated film gets on the bi metal instrument of the MAF and you get delayed or erroneous signals to the ECM for timing and injector dwell corrections. (opps sorry carb people, for the FI analogy)
On the boosters the signal is the air flow going past it to activate the siphon, an "amplified" signal is achieved by enhancing the ID surface of the booster by making it smoother, more defined around the Inner Diameter edge, or even in some cases, cutting steps in it . All very meticulous work needless to say.good description roodoo

[Accordtheory]

I am glad you still had that article.
I can see how more of a percentage of a finer atomized fuel mist would try to cling to the runners of a hot manifold before it makes it to the combustion chamber as opposed to a cooler manifold it would be in a denser formation even though it was equally atomized.

Did you read the same thing I just did? I don't even know where you got that. What I got was temperature vs vaporization vs droplet size vs displacing air vs power. Where are you getting this clinging shit? Not trying to be a dick, by the way.

[Accordtheory]

an "amplified" signal is achieved by enhancing the ID surface of the booster by making it smoother, more defined around the Inner Diameter edge, or even in some cases, cutting steps in it .

Their definition of an amplified signal in the article was by placing the booster (a venturi itself) in the main venturi of the carb, they were effectively "amplifying" the pressure difference across the jet..2 venturis instead of one.

[Accordtheory]

I don't understand what the booster "signal" is that they're talking about? Is it the proper amount of velocity to pull the fuel out into the booster venturi?

Or the proper amount of pressure drop through the booster venturi, which could be altered by booster design, for the same basic velocity through the carb..?

[Accordtheory]

It got me to wondered if the reason the engine would pull harder at night was less because of extra air charge and more because of a larger fuel droplet.

Well, I would not extrapolate that at all, myself.. The article was saying, as I understood it anyway, that if the droplets are too small, a hot IM causes them to become a gas, displacing air, and thereby oxygen, compromising power output. Hot manifold, larger droplets optimal, cold manifold, smaller droplets.
EDIT: Cygnus x-1 is probably right, the cooler air is preventing some of the droplets from turing into a gas, increasing power by displacing less air, but what I wrote about colder air always making more power due to increased density was still valid, too.

[cygnus x-1]

It got me to wondered if the reason the engine would pull harder at night was less because of extra air charge and more because of a larger fuel droplet.

That would only be the case I think if the colder temperature was keeping some of the fuel from vaporizing and displacing air. I don't see how larger fuel droplets would help torque. In fact I would expect the opposite.

C|

[Accordtheory]

So you think that honda could have set it up to vaporize the droplets into a gas for economy at the expense of power production?
You're probably onto something there, I should probably edit my previous post. I didn't think it would be set up like that at first, because I didn't see that making all that big of a difference in economy, but who am I talking about, honda. I definitely see them biasing it in favor of economy..

I wonder how much the a/f ratio changes based on the amount of air displaced by the droplets changing..

[A20A1]

That would only be the case I think if the colder temperature was keeping some of the fuel from vaporizing and displacing air. I don't see how larger fuel droplets would help torque. In fact I would expect the opposite.

C|

kinda of what I mean, less vaporization sorry :(

[2oodoor]

Their definition of an amplified signal in the article was by placing the booster (a venturi itself) in the main venturi of the carb, they were effectively "amplifying" the pressure difference across the jet..2 venturis instead of one.

mY references exceed just that article, sorry to throw you off with terms like CLINGING, maybe synominize that word to fit your imagery. YOu obviously did understand the theory the same as I did so why try to blow my explanation out of the water like that?? The read reminded me of another article solely about Intake manifolds.

Read page two of the article in post #1, about modifiying existing boosters.

[Accordtheory]

mY references exceed just that article, sorry to throw you off with terms like CLINGING, maybe synominize that word to fit your imagery. YOu obviously did understand the theory the same as I did so why try to blow my explanation out of the water like that?? The read reminded me of another article solely about Intake manifolds.

Read page two of the article in post #1, about modifiying existing boosters.

I just didn't get why you brought up the clinging thing. They did not attribute that effect to anything major, or really any of the observed effects. I guess you're just adding it in as yet another factor, which I am not contesting. I also wasn't trying to blow any explanation of of the water at all, or contradict/contest what you wrote about the booster shit, either. I was just referencing the article, and adding their initial description. You're obviously right about removing casting imperfections, etc, amplifying the effect on the booster, but I thought that maybe in the other post, the dude didn't know what they meant in the article as far as the desription of an amplified signal being created by a venturi inside another venturi.

[2oodoor]

Its all good AccordTheory... I was reading the article A20A1 provided and the read brings up something I have not put a lot of thought into. I believe the purpose of the thread is, thinking out the theory of fuel atomization in relation to temperature, air velocity, basically putting it out there for discussion. The PH writer is "revealing" theories applied to performance carbs that were not openly discussed alot previously but since the FI has taken the stage, they found it may be of interest.
Both modifiiying the surface of booster venturis and the strategic placement of them in the carb venturi are methods of amplifying the "signal"
I can't remember if it is in an Edlebrock book or maybe here somewhere I was reading about the design of intake manifolds and the "clinging" example was used, maybe not those same words. :)

[Hauntd ca3]

inlet manifold design, fuel droplet size have always been cause of arguement for years.
but the fairly common concensus on droplet size is smaller is generally better.
it does vaporise easier but is easier to ignite and burn completely.
i personally dont believe in manifold heaters but they are designed to help vaporising of the fuel to enable a more complete burn.
once the fuel and air is past the butterfly it doesnt matter if it vaporises completely and take up more room thn air, coz its already been metered into the air stream in the correct ratio.
the smaller venturi at the top of the carb out in the air stream on a wee outrigger is the main fuel discharge into the carb.
the tube in the top of each barrel on an angle are the main air bleeds into the jets.
fuel and a metered amount of air are mixed before it comes out of the discharge nozzle.
the air is mixed into the fuel by what is called the air correction or emulsion tube /
the emulsion tube has the fuel orifice/jet in the end of it.
atmospheric pressure in the float bowl forces fuel thru the jet.
air is drawn in from an air bleed to the emulsion tube where it mixes with the fuel to partially
atomise it.
the air passing thru the secondary venturi lowers the air pressure at the discharge nozzle and the partially atomised fuel is drawn out into the air flow to the cylinders.
the ways to change droplet size are change the emulsion tube to allow more or less air into the fuel.
change jet size to chnge the amount of fuel being drawn into the motor
or change the secondary venturi size to have bigger/smaller discharge nozzle to allow more or less of the partially atomised mix into the motor.
some parts of this may be not quite right but its pretty close i hope.
if you can get you're hands on a dcoe webber crab or a dhla dellorto you can easily remove all these parts and see how it all works and where everything flows to make carbs easier to understand.

[A20A1]

The Air Correction is a way to put resistance on the flow of fuel
or else I think I read that the metering of fuel would be too linear, creating an overly rich mixture at WOT.

I think I saw it in the weber book I had but I can't find it to double check.

[cygnus x-1]

With my Weber 38 at least, the emulsion tubes change how the fuel is aerated at different levels of venturi pressure. The tubes have various holes of different sizes along their length and changes in the amount of fuel flowing through the tubes changes which holes are submerged in fuel or not. The emulsion tubes are used to make more subtle changes in the air fuel mixture under various operating conditions versus changing fuel jets for example. The air correctors are jets that change how much air gets in to the emulsion tubes, mostly at higher RPMs. A larger air jet allows more air in sooner making for a leaner mixture. I've heard them described as sort of "fuel brakes".
The Weber book has some good info on emulsion tubes.
There is also a really fantastic thread on another forum about the Weber 32/36 and 38/38. Wait, here it is:

http://forums.off-road.com/engines/205097-weber-32-36dgv-verses-weber-38dges.html

I spent MANY, MANY, hours reading and rereading this. One of the guys, 'Sarge' I think is even quoted in the Weber FAQ here. Highly recommended reading.

It's interesting going back to think about carbs after having gone through the exercise of setting up a fuel injection map from scratch. The difference in fuel required at WOT between 2000RPM and 3000RPM is much greater than the difference between 5000RPM and 6000RPM. It didn't really sink in until I tried tuning FI.

C|

[Hauntd ca3]

what you said is sort of what i was trying to say.
i didnt really feel like digging out the text books to get it spot on.
that fuel getting aerated does have alot to do with end size of the fuel droplet getting to the motor tho from what can remember.
i would say to that as far as tunng with carbs goes, you prob couldnt go past a couple 45 dcoe webbers.
sure the 32/36 down drafts would give better scope for tunig over the oem carb but the amount of airflow available wouldnt allow for more than minor mods i'd think.
might be wrong as never used 32/36s or anyother down draft carb for tuning before
only side draft webbers or dellortos

[A20A1]

I probably have that book... and sarge is awesome. :D

[cygnus x-1]

As I recall a single Weber 38/38 is good for about 150HP. The 32/26 maybe 140HP or less. Twin DCOE 45s I'm sure at least 200HP. Side drafts have the added advantage that the airflow doesn't have to turn a corner.

And yeah, Sarge is THE man.

C|

[A20A1]

Thats not really it's biggest advantage, even down drafts can have decent transitions, especially on tunnel rams, the advantage for the side drafts are they are usually setup to run IR (Individual runners) so it has better metering or something like that. :D I wrote it all down somewhere when I was going to do a IR setup.