what is the benefits of progressive linkage on tri-power??
- Thread starter pacer
- Start date
ludwig":29za218s said:
To expand on what Ludwig said, when you have multiple carbs like a six pack setup the center carbs run at normal driving allowing the car to get good gas mileage.
When you depress the throttle the end carbs kick in giving a massive boost to airflow and fuel. The car is now getting enough air and fuel to make good power.
On the Inline six the log head flows like a sewer pipe. Adding the end carbs allows a massive boost in airflow but kills economy. The progressive linkage allows you to run on the center carb to conserve gas and be economical but when you move the linkage more the end carbs open and now you have air and fuel to make more power.
If all three open at the same time, you have to have all three carbs synchronized for it to run right.
With a progressive setup, you run on the center carb only. The outer carbs don't need idle circuit, nor the choke or powervalves from what I understand. All the outer carbs are used for is for dumping fuel only.
With a progressive setup, you run on the center carb only. The outer carbs don't need idle circuit, nor the choke or powervalves from what I understand. All the outer carbs are used for is for dumping fuel only.
I would think that running the 3 carb set in a 1:1 ratio non-progressive manner that the results would be the same as running a 4v 1:1 with all 4 barrels opening at the same time and at the same rate...like trying to flush a mostly plugged toilet...unless it is a max performance engine launching at a very high rpm.
On my home made tri-power I originally ran the small Holley outer carbs and a center YF. Ran OK set up progressive. Wanted more power. Went to 3 YFs. They simply drove the best set up one to one and I always used the idle mixture circuit on all 3 carbs. Just adjusted til it ran best. Being an open plenum it just isn't that critical to syncronize. All 3 carbs used the same jets and power rods. The home made tri-power used 1 7/16" opening at the manifold. Not the small offy opening. Larger carbs do not necessarily "dump" more fuel, the engine has to suck it out after the initial pump shot. I say drill a bunch of adjustment holes in the linkage and try what works best for you.
I think what some people forget is the carb works off a vacuum signal. On a 4 barrel, depending on the manifold design, all 4 barrels are seeing the same signal because they're so close together. On a tri-power set up on our long 6's, the close by carb gets a strong signal so its not exactly like having a 4 barrel all open at the same time.
I think what some people forget is the carb works off a vacuum signal. On a 4 barrel, depending on the manifold design, all 4 barrels are seeing the same signal because they're so close together. On a tri-power set up on our long 6's, the close by carb gets a strong signal so its not exactly like having a 4 barrel all open at the same time.
"Being an open plenum it just isn't that critical to syncronize."
That makes sense. Never thought about that.
On a progessive setup, it also makes sense to keep the idle circuits cracked open a half turn or so because you can't completely seal them off, so they will leak a bit of vacuum. The idle circuits on the outer carbs will help smooth out the idle if the outer carbs are sucking air. At least this is the conclusion I came up with from what I've read researching tri-powers.
I'm in the process of test/tune my 3x1 Offy setup. So far this is all theory to me and I'm currently working on getting the center Holley 1960 to idle smoothly. It idles rough. Swapped it with a known good Autolite 1100 and it idle much better without any adjustments to the outers. I'm thinking that the idle bleed needs to be opened up, but I don't want to modify the carb body unless I know exactly what I'm doing. Any thoughts?
That makes sense. Never thought about that.
On a progessive setup, it also makes sense to keep the idle circuits cracked open a half turn or so because you can't completely seal them off, so they will leak a bit of vacuum. The idle circuits on the outer carbs will help smooth out the idle if the outer carbs are sucking air. At least this is the conclusion I came up with from what I've read researching tri-powers.
I'm in the process of test/tune my 3x1 Offy setup. So far this is all theory to me and I'm currently working on getting the center Holley 1960 to idle smoothly. It idles rough. Swapped it with a known good Autolite 1100 and it idle much better without any adjustments to the outers. I'm thinking that the idle bleed needs to be opened up, but I don't want to modify the carb body unless I know exactly what I'm doing. Any thoughts?
Something to remember / consider.
Non full race 4Vs are progressive, primaries opening first followed by secondaries. Opening of secondaries can be either mechanical or vacuum actuated. Basically the same as a multi carb set-up with all venturi grouped together.
Too much throttle opening drops the vaccum too low to draw fuel in to the venturis. Secondaries, be they additional carbs or venturis, should open when needed.
Think of your progressive multi carb setup as a progressive 4V in sections, center carb is the primary, end carbs are the secondaries.
Cruise on the primary, go for full power on the secondaries.
Non full race 4Vs are progressive, primaries opening first followed by secondaries. Opening of secondaries can be either mechanical or vacuum actuated. Basically the same as a multi carb set-up with all venturi grouped together.
Too much throttle opening drops the vaccum too low to draw fuel in to the venturis. Secondaries, be they additional carbs or venturis, should open when needed.
Think of your progressive multi carb setup as a progressive 4V in sections, center carb is the primary, end carbs are the secondaries.
Cruise on the primary, go for full power on the secondaries.
Similar threads
