Emulsion Part 2

[jmarkaudio]

The idle pickup point isn't apparent from here but I believe it comes off of the main well, and you can clearly see the intermediate is fed from the main well. Unlike when the idle circuit is divorced as seen on some methanol carbs, or in the case of a Holley intermediate circuit that is divorced, all the circuits get their fuel through the main jet. That means all three circuits, idle, intermediate, and main will have an impact on each other as well as transitions. Maybe Doug will kick in here.

As far as the SS 780, dry flow on my bench was at 905 CFM at 20.45" H2O, 1.5" HG. At 28" H2O or just a tad over 2" HG it flows almost 1050 CFM dry. As far as going rich at higher RPM, I wonder if it's just a matter of using more available oxygen rather than the carb putting in more fuel to air. You are already running a pretty wide curve rich to lean, I wonder if a better booster might help a little with early vaporization and allow a flatter curve. Another option to lean it up top might be to make the main well exit and booster leg diameter a little smaller. Intakes will make the tune of each different, I would expect more stagger needed with the dual plane.

[Alan Roehrich]

The air flow numbers are of course from the dyno, so we're seeing just the air that we're mixing with fuel, while the pressure drop measurement is of course taken in the manifold.

The dual plane carburetor has considerable stagger in it, the total is between 6 and 8 jet sizes. I think the single plane carburetor is square right now.

We can generate, and run, a flatter curve, say 12.9 to 13.2 or so to 1. The reason for the wide variation is that both engines seem to make more torque with the A/F ratio around 12.7:1, but more HP as lean as 13.2:1. Both cars are relatively heavy cars with automatic transmissions, especially the car with the 441. A lot of torque is required both to launch the cars and to recover from the shifts.

For various reasons, both programs are on hold at the moment, we'll see what happens later this month. I'll talk to my friends at Quick Fuel a great deal at PRI. Johnny and I discussed the possiblity of actually making some boosters to try. One idea was to make some annular discharge boosters that are shaped and sized very much like, if not identical to, the down leg boosters in the SS 780.

[Bob Hollinshead]

Isn't the SS 780 is a first generation 3310? and they flow 905? interesting stuff

[levisnteeshirt]

A lot of ideas and good thinking going on here.

Some of the things I'm wondering about now are the result.

I guess we are all constrained by:

PV = nrT

P = Pressure
V = Volume
T = Temperature
nr = some guys gas constant.

So there are many ways to skin the same cat, but you can only
do each cat once...

Mark, was going to mentioned the type, blend, and additives of fuel affect atomization
but you beat me too it.

Viewing the engine as an air pump, then thinking we are working on the air pumps controller, the carb.
It generally sucks except when something goes arye...then it is a FUBAR. But it should always
suck, not blow, and the sucking should be pulses with minimal reversion...and I guess you
can't get rid of reversion or pulses or oscellation complely, that is there will be a
range where it shows up somewhere in the run, pull, dyno, track etc.

Tune the bad stuff to the range you aren't working in...
and the good stuff to the range you are working in.

Also thinking in the real world, they aren't dyno pulls or chassis dyno pulls...
there is the variation and the deviation from the test world. It only take a
look on the spintron, or in the video of a secondary and seeing the slosch of
fuel or ramming of fuel to realize there is a LOT of CHAOS going on.

So if I understand it correctly....drum roll please, butter, no gravy:

The standard venturis and downleg venturis...are all fine and they
have the fuel sucked into the engine, the mixture is set by the jets,
and bleeds. Get them right and you can make big power, get them
1/2 right and you can have some nagging problems.

Levis I'm not picking on you...BUT you don't like having the jets low
for some reason you like them hi and with air behind them.

However with the metering block Chiseled off my old 855 Corvette carb
the two hold emulsion tubes are there along with my now favorite
LOW IDLE FEED RESTRICTOR. : )

I might be worng on thinking like this its like you either have to [DELETE THIS POST] with the
fuel or [DELETE THIS POST] with the air....

For either to function at its best you have to control process and get it stable.
So as Walter and other's say....I forgot, sorry.

Had some other throughts but dreamland is calling and I can't think any more.

I hope I can remember tomorrotw what I was gong to say tonight so I can.
That extra hour sleepoiing might help.

Cheers,

Spike

range

if that worked for me buddy I'd do it ,,, when i drop a cars lap time .3, .4 , or better ,, its usually the opposite, using low jets , low emulsion , ,, anything should be acceleration tested on a dyno to see if its worth having , IMO ,,

[jmarkaudio]

Isn't the SS 780 is a first generation 3310? and they flow 905? interesting stuff

The SS 780-VS is a vacuum secondary carb made by Quick Fuel that is Stock, Super Stock, and Comp legal as a replacement for the original 3310. They make a legal replacement for the 750 and 850 DP carbs as well. We put one on a B/S Camaro with favorable results, only jetting it up from stock. I think when they take the time to dyno tune it with any needed stagger it will net some more.

[Walter R. Malik]

The dual plane carburetor has considerable stagger in it, the total is between 6 and 8 jet sizes. I think the single plane carburetor is square right now.

We can generate, and run, a flatter curve, say 12.9 to 13.2 or so to 1. The reason for the wide variation is that both engines seem to make more torque with the A/F ratio around 12.7:1, but more HP as lean as 13.2:1. Both cars are relatively heavy cars with automatic transmissions, especially the car with the 441. A lot of torque is required both to launch the cars and to recover from the shifts.

I have had good luck attaining near the fuel curves you are after using the older Holley 780 main bodies with stepped downleg boosters installed, (.150" passage), using newer, SLIGHTLY re-tuned lower emulsion diameters, HP metering blocks with their relocated 3 step emulsion, (convert the throttle body to 4 corner idle), with the HSB up around .033" to get it really close.

Believe it or not ... modified "straight leg boosters" got it even better.

[Alan Roehrich]

The dual plane carburetor has considerable stagger in it, the total is between 6 and 8 jet sizes. I think the single plane carburetor is square right now.

We can generate, and run, a flatter curve, say 12.9 to 13.2 or so to 1. The reason for the wide variation is that both engines seem to make more torque with the A/F ratio around 12.7:1, but more HP as lean as 13.2:1. Both cars are relatively heavy cars with automatic transmissions, especially the car with the 441. A lot of torque is required both to launch the cars and to recover from the shifts.

I have had good luck attaining near the fuel curves you are after using the older Holley 780 main bodies with stepped downleg boosters installed, (.150" passage), using newer, SLIGHTLY re-tuned lower emulsion diameters, HP metering blocks with their relocated 3 step emulsion, (convert the throttle body to 4 corner idle), with the HSB up around .033" to get it really close.

Believe it or not ... modified "straight leg boosters" got it even better.

Walter, the Holley carburetors we have actually use the metering block from the HP two barrel on both ends, with some modifications. Those carburetors are so good that they are about as fast, and make about the same power as the Quick Fuel carburetors. The Quick Fuel carburetors do not have as much tuning time on them, nor are the metering blocks modified as much. We are not allowed to use true 4 corner idle on our carburetors, all adjustments must be blocked with staked in lead balls. The high speed bleed is up to around 34-37. With the stagger jetting, the jets 78, 80, 82, 84, the stagger is extremely similar to that listed in the Chevrolet Power service manual.

[n5ifi]

I have a couple questions that I would like to ask but they are slightly off topic and I hesitate to do it here.

1. Is there a rule of thumb about jetting up or down with these main air bleed changes?
If I start with a 36 MAB and end up at 28 MAB and I have a 73 jet in the car for best performance at 36 MAB, how do you make a educated guess about how much to drop the Main Jet to get everything back square again?
If you look at some of the older Holley's, that have (I assume) smaller MAB's and low IFR's they also have smaller main jets than the newer stuff. I know there is a lot of things that mat have to be considered and I may not be taking ever thing into account but this just bugs me. I see others having problems with this too. They reduce the size and restrict the emulsion and the changes help but when they reduce the main air bleed size they loose power and go right back to where they were. Wouldn't they also have to reduce the main jet size to get everything back to square?

2. Given a stock metering block locations for PVCR how do you know how to calculate it's size compared to jets size?
Obviously, the same size hole or orifices will not flow the same at different heights in the block (right).
The jet might be tapered and flowed too. The PVCR is not. I've seen all kind of numbers about it but nothing that ever made sense to me.

[Walter R. Malik]

1. Is there a rule of thumb about jetting up or down with these main air bleed changes?
If I start with a 36 MAB and end up at 28 MAB and I have a 73 jet in the car for best performance at 36 MAB, how do you make a educated guess about how much to drop the Main Jet to get everything back square again?
If you look at some of the older Holley's, that have (I assume) smaller MAB's and low IFR's they also have smaller main jets than the newer stuff. I know there is a lot of things that mat have to be considered and I may not be taking ever thing into account but this just bugs me. I see others having problems with this too. They reduce the size and restrict the emulsion and the changes help but when they reduce the main air bleed size they loose power and go right back to where they were. Wouldn't they also have to reduce the main jet size to get everything back to square?

There is no real "rule of thumb" for any of this and an educated guess as to what has already been done in the past is the only recourse for most people to getting it right.
Most emulsion changes won't alter main jetting very much; however, WILL alter the off idle slot fuel demands ... the main HSB is what alters the main jetting most.

Alan;
YES, some of my oval track customers can't have 4 corner idle either so, those rear idle screws are cut to about half their length and fully seated. The secondary IDLE air bleed then must remain on the small side and the sizing of that .025" constant idle feed hole in the secondary bore is REALLY important to the drivability tune; (you may not need this in a drag race situation; especially a trans brake car).

Is that class allowed billet metering blocks...?

[levisnteeshirt]

the kill bleed functions like an emulsion bleed once the booster starts ,,, so in effect ,, the old blocks have 3 emulsion holes , energy looks for the least path of resistance , so I have to believe alot of the air stream flowing past the idle air bleed goes through the kill bleed

[levisnteeshirt]

I'd love to hear the theory behind all of this ,, it makes me wonder in the time constraints of a pro stock pass , how much of this is useful

[Walter R. Malik]

the kill bleed functions like an emulsion bleed once the booster starts ,,, so in effect ,, the old blocks have 3 emulsion holes , energy looks for the least path of resistance , so I have to believe alot of the air stream flowing past the idle air bleed goes through the kill bleed

???????, I think that is a misprint to your thoughts.

[Tuner]

the kill bleed functions like an emulsion bleed once the booster starts ,,, so in effect ,, the old blocks have 3 emulsion holes , energy looks for the least path of resistance , so I have to believe alot of the air stream flowing past the idle air bleed goes through the kill bleed

???????, I think that is a misprint to your thoughts.

You don’t think he leaked one of those majik carb secrets he only knows?

[levisnteeshirt]

the kill bleed functions like an emulsion bleed once the booster starts ,,, so in effect ,, the old blocks have 3 emulsion holes , energy looks for the least path of resistance , so I have to believe alot of the air stream flowing past the idle air bleed goes through the kill bleed

???????, I think that is a misprint to your thoughts.

You don’t think he leaked one of those majik carb secrets he only knows?

think about it ,, if thats possible ,, I had a carb here that someone drilled a hole back to the main body, beside the booster , then drilled a coresponding hole at an angle in the metering block to the top of the mainwell , below the top plug , then drilled a connecting hole above the kill bleed ,,, most bizare carb mod I've saw ,, I don't know what he had in mind ,, the guy that sent it to me was having a hard time getting it to act right,,, looking at this thing got me to thinking about that ,, I guess this placed atmospheric in the top of the main well , which then the kill bleed would more than likely feed off of that instead of whats coming , if anything like this , from the IAB

maybe if there was a valve mechanism , like a power valve of sorts , to only allow this extra flow of air at higher vacume levels inside the main well ,, but to only let this source discharge into the booster , so it will force the fuel faster to the booster , ,, but then who knows what would happen to the signal ,,,, this person whoever did this spent a good bit of time doing this ,, and I was trying to imagine some way to make this work ,,, they also messed with the top of the venturi ,, I told the owner that might be a problem once I built new blocks and plugged those holes in the mainbody , and its came true ,, the carb goes crazy lean on top so I have to believe the venturi effect has been destroyed ,, they had placed those old truck style boosters that were in 700 dp's back in the day to try to get it to work , but they were in crooked so I took them out and put in a stepped down leg, but it didn't work ,, fixing a new mainbody up to send him

[Alan Roehrich]

Alan;
YES, some of my oval track customers can't have 4 corner idle either so, those rear idle screws are cut to about half their length and fully seated. The secondary IDLE air bleed then must remain on the small side and the sizing of that .025" constant idle feed hole in the secondary bore is REALLY important to the drivability tune; (you may not need this in a drag race situation; especially a trans brake car).

Is that class allowed billet metering blocks...?

I don't think we can use billet blocks on the Holley carburetors. They probably would never be able to tell on the Quick Fuel carburetors.

We do not use a trans brake, it would be legal on the Super Stock car with the 411, but not on the Stock Eliminator car with the 441. To keep the cars
as close to exactly the same with regards to driving, we did not install a trans brake in the Super Stock car. Usually the cars in Super Stock are faster
without a trans brake anyway.