Two-Stage Power Valves

[Walking-Tall]

Walking-Tall, on your metering block conversion, what are you doing with the mix screws? Aren't the air screws too fat/blunt for idle mix adjustment?

You're absolutely right, the "reverse-idle" mixture screws are too blunt. The block I converted happens to have ~1/16" orifices deep down in there, and so jives fine with the standard mixture screws I've installed into "Frankenstein", lol

[Walking-Tall]

I finally found the "stupid lean" point of the transfer slots. At two turns out on the air screws I picked up a hesitation when cruising with the throttle cracked. Still no hole in the midrange since putting in the two-stage power valve. I'll close up the air screws a bit at a time until the motor is happy again then focus on the accelerator pump. It's better after drilling the bleed hole but still needs a bit of work. No sense fiddling with that until all the "steady state" mixtures are right.

Those are important findings, and goes to show that all that's needed is giving the engine what it wants. The horsepower is there and the best efficiency is also there. Screw EFI and it's 14.7:1, it's got nothing on a dialed in carburetor.

[mrriggs]

It's at 1-3/4 turns on the air screws and it runs NICE. I've only driven it a couple times but the initial results are very encouraging; crisp throttle response, cleans cruise and silky smooth shifts.

With patience and persistence it is possible to dial in a carburetor to run better than a stock EFI. I imagine the same effort spent on a custom EFI would yield the same results. Like you said, give the motor what it wants. As long as you are doing that then it shouldn't matter how you are putting it in there.

[Walking-Tall]

That's good news

True. "Stoich" is a good goal to set for idling, but for the rest of the majority of normal driving conditions where fuel efficiency should be anybody's goal, the air:fuel mixture should get progressively leaner, a fair few numbers leaner than "stoich". Some combinations will work very nicely (crisp, brisk part throttle acceleration, etc.) with upwards of a 16-17:1 air:fuel ratio.

[mrriggs]

I'm still tweaking with this carb. The 0.016" accelerator pump bleed in the metering block definitely helped. I wanted to try more bleed but was hesitant to drill the metering block any further due to the difficulty of un-drilling it should I go too far. Instead, I drilled and tapped a hole under the accelerator pump diaphragm for a #6 brass set screw. I started with a 0.016" bleed in the bowl and keep stepping it up. Every time, the throttle response gets better and better. After each bleed change I try different cams and shooters to find the best combination. I will drive the car for several days with the new cam or shooter to get a feel for it under all driving conditions. Getting a carb dialed in just right takes time.

Right now I'm at a 0.025" pump bleed in the bowl, 0.016" pump bleed in the metering block, pink cam on #2, and 0.031" shooter. It is good but still not perfect.

[xctasy]

I got a Motorcraft CE-126 two-stage power valve and put it in. So far so good. There is a long hill on my way to work where I can hold the throttle between 5 and 10" Hg and it definitely feels smoother and stronger with the little bump from the first stage. Also remembered to measure the PVCRs when I had it apart, 0.052".......

I was kinda busy, but here are the 2 stage power valve details.


https://fordsix.com/viewtopic.php?f=...585198#p585198

I'm back on night duty tomorrow night so I have a little free time.

No need to data base, just bookmark the Falcon Six Performance book, and list this as relevant detail.

There are still about 23 different 2 stage power valves in common production, including one fully adjustable 2 stage from Mikes carbs.

Holley set a truck like 14 pounds per cube limit before you really needed to consider a 2 stage power valve. It was based on the idea that frontal area would also go up from about 20 sq feet in a little Falcon or Mustang II to about 40 sq feet in an E 250 truck. Low power to weight vehicles benefit from being able to lean off the richness in slow, ambling load conditions. So two stage carbs were birthed in the economy verses emissions era, and the 14 pound per cube idea played out like this...

6440 pound shipping weight 460
6006 pound shipping weight 429
5600 pound shipping weight 400
5180 pound shipping weight 370
4900 pound shipping weight 351
4220 pound shipping weight 302
3570 pound shipping weight 255

But the lighter 1983 to 1985 5.0 Mustangs, Capris and 1981 to 1988 5.8 F150 and Bronco trucks were 10 pound per cubes on some versions, and gained exceptional verve and fair economy with a 2 stage power valve 4180 or 4190/4195 Holley carb. So did the 2-bbl 2150 1.21 carb in the 1982 5.0 Mustang GT, and the odd 2150 equiped 400 Bronco or F150's. Jet sizes in big 2150 carbs were squeezed right down to F56 in 2-bbls and H62's in 4180C 4-bbls.


Even below 14 pounds per cubic inch recommendations Holley set, FoMoCo found the 2 stage power valves allowed base jetting to be leaned, and the large V8 style Power Valve channel restrictions left to enrichen 8 jet call sizes.

14 pounds per cube is a 170 2380 pound Round Body Falcon,
a 200 cube a 2800 pound Fox body Zephyr, Fairmont, Capri or Mustang,
a 250 cube 1968-1973 Fairlane, Ranchero or Torino, or 75-80 Granada/Monarch.

A 79 or 82 5.0 Mustang can have as little as just 9 pounds per cube to lug around, and gets better economy and drive-ability with the two stage power valve; they kept it right up until the last carbed 5.0 V8 in 1985. The two stage PV is just an added bit of extra tuning to the whole kit. Ford found the 255 engine saved 1.5 mpg, but the 1982 5.0 gained 35% more power with a 1.5 mpg highway gain at 55 mph; no mileage penalty, and much of that was the ignition, power valve and gearing. So the annular booster 2150 and 4180 carbs with those valves were exceptionally distinguished economy engines, as well as being quite exceptional performers.

P/N, 1st Stage Opening, 2nd Stage Opening, and any known 1st stage restriction

Holley Lists 3 now, down from 7 a while ago, down from 21 a long time ago.
125-206 12.5” Hg 5.5” Hg .028”, like the old Holley PN 2-4311 (later 25BP-475A-12)
125-207 10.5” Hg 5.0” Hg .021” like the old Holley PN 2-4312 (later 25BP-475A-25)
125-208 10.5” Hg 5.5” Hg .028”
Others

125-213, 11.5, 5.0
125-212, 12.0, 6.5
125-215, 10.5, 6.0
125-218, 11.0, 5.5 (23 means a 125-218 )

Holley had 21 total if you include the unlisted “24” we found lurking under the hood of an 83 Mustang 5.0 GLX



Examples:-There are date prefixes before the Holley 2 stage call number
A6-7 Stock AMC 304 Motorcraft 2100 1.08 model 5.5
8 '85 Capri/Mustang 5.0 Holley 4180C stamped "8", means the 2nd stage would come in at 4.5
B1 8 Ford 460 F250 4X4 with 4180c come in at 4.5
13 On some IH 2300C truck carbs come in at 6.5
16 carbs with this PV come in at 6.5
23 = 1984 Capri/Mustang 5.0 Holley 4180C F1 23, or 125-218, 11.0, 5.5, but says it comes in at 6.5
24 = 83 Mustang 5.0 GLX 5.0 not on list
Standard rebuild Capri/Mustang 5.0 Holley 4180C 3-1346 kits = 10.5/6.5, no traditional stamping

MIKES Carburettor Parts Has 11or 12 generic Number:70-1000 2 Stage Power Valves




Napa offers a total of 8 diff. 2-stage power valves.

PN 2-4311 1st stage opens @ 9.0"Hg, 2nd stage @ 2.5"Hg 1st stage restriction .035

PN 2-4312 1st stage opens @ 10.5"Hg, 2nd stage @ 5.5"Hg 1st stage restr. .021

PN 2-4405 1st stage opens @ 9.0"Hg, 2nd stage @ 2.5" Hg 1st stage restr. .028

PN 2-4406 1st stage opens @ 10.5" Hg, 2nd stage @ 5.0"Hg 1st stage restr. .020

PN 2-4409 1st stage opens @ 11.0"Hg, 2nd stage @ 7.5"Hg 1st stage restr. .028

PN 2-4410 1st stage opens @ 10.5" Hg, 2nd stage @ 5.0"Hg 1st stage restr. .028

PN 2-4412 1st stage opens @ 11.0"Hg, 2nd stage @ 6.0"Hg 1st stage restr. .0225

PN 2-4413 1st stage opens @ 11.0"Hg, 2nd stage @ 7.0"Hg 1st stage restr. .024

Ford had five Motorcraft 2150 2 Stage Power valves from 1974 to 1979. Since it has a wide range of crack off vacuums, I've listed them as Nominal so you can determine the pattern in power valve rank.

CE105 Nominal 7.0”Hg/ 2.0”Hg
CE120 , CE123 & CE122 Nominal 7.0”Hg/ 2.0”Hg
CE126 Nominal 10.0”Hg/ 3.5”Hg
CE130 Nominal 10.25”Hg/ 5.0”Hg
CE132 Nominal 10.25”Hg/ 6.0”Hg

[mrriggs]

Carb tuning 101: When you're sure you have a carburetor problem, check your ignition system.

I figured since this car has a Duraspark system with new plugs, wires, cap and rotor then the ignition system must be alright. The results I was getting when trying to tune the accelerator pump didn't add up. For piece of mind, I hooked up a TFI module and coil, using the Duraspark box as a trigger.

Wouldn't you know it? My mysterious carburetor troubles disappeared! In fact, I was even able to open up the air screws further without experiencing a "lean" stumble.