Two-Stage Power Valves

[mrriggs]

I've been slowly working through tuning my carburetor and would like to try a two-stage power valve to clean up the mid-range. I've been driving around with a vacuum gauge on it for a few weeks and have determined that the first stage should start at 11 or 12 inches. The second stage timing isn't very important since the vacuum never really hovers at that point, it's either WAY above or WAY below. As long as it's under 8 inches and stays open under full throttle then it'll work.

There are new two-stage power valves available from carburetor-parts.com but I'm leery of no-name aftermarket parts.

NOS Motorcraft two-stage power valves are still available. There is list of Motorcraft part numbers here; http://grantorinosport.org/BubbaF250/carb/carb10.html

What that chart doesn't show is the first-stage orifice size. Does anybody know what the orifice sizes are? There are a few valves on the list with identical opening points so they must have some other difference to account for the part number change.

[Walking-Tall]

If by clean up the mid-range, you mean put smaller jets in it, and increase it's power valve channel restriction sizes to suit, then I get it... but a two-stage power valve by itself does nothing of the sort. Depending on vacuum ratings, it'll bring a first stage in at some part throttle acceleration level (allowing leaner jetting), and then fully open at full throttle.

This is a 2150 (the linked chart is for 2150's...) two-barrel, and what's the engine? So normal cruise vacuum levels never get near 11-12in-Hg? Where does the vacuum go to with what you would judge as light/normal acceleration?

The orifice (power valve channel restriction) size is in the carburetor, near the power valve, but the power valve hasn't any (of relevance) circuit calibration fuel metering orifices. All it does is dictate when the carburetor's power valve channel restrictions' extra enrichment happens.

As well, you would need the much taller (lower) power valve cover and manifold clearance to go with it.

[mrriggs]

Yes, the list is for 2150 carbs but it is the only thing I could find on two-stage power valves. Is there a list that is specific to four-barrel carbs? I was under the impression that they all use the same power valves.

My engine is a stock '84 5.0 and the carb is a reverse-idle 4160 with a 4180 throttle body. Before swapping to the 4180 throttle body I had to run the air screws 1/4 turn out to get it to idle and it was a fat pig at light throttle input (air screws effect transfer slot mixture). After swapping throttle bodies I'm able to lean out the transfer slots with the air screws then adjust the curb idle with the idle screws in the base plate. At 1 turn out on the air screws it runs STRONG but was only getting 10 MPG. At 1-1/2 turns out on the air screws my mileage is up to 15 MPG but I picked up a slight hesitation on moderate acceleration. If I stab the gas it takes off and goes, if I put around it runs well, but at a certain point right in between there is a little flat spot. I'm hopeful that the two-stage power valve will help without having to fatten it up on cruise. The flat spot happens just under 10"hg, cruise vacuum is around 18"hg, mild acceleration and uphill grades dip as low as 11-12"hg. The carb has a 6.5 single-stage power valve now and 64 primary jets. I haven't measured the power valve restrictions yet.

[mrriggs]

... but the power valve hasn't any (of relevance) circuit calibration fuel metering orifices. All it does is dictate when the carburetor's power valve channel restrictions' extra enrichment happens.

The two-stage power valves do have an internal metering orifice, that is how they determine the first stage enrichment. I've seen a chart that shows the various opening points and orifice sizes for Holley two-stage power valves and was hoping someone had the same thing for the Motorcraft power valves.

[Walking-Tall]

A matter of terminology, I suppose. My "of relevance" above, meant, yes, you are right, there's a metering orifice, but I wouldn't really call the taper and seat in a power valve an orifice. That's what gives a wee nudge (tapered seat partially opened... for flow equivalence as to fuel flow, you'd have to do some testing, or figure out the flow window area of a partially and fully open two-stage valve, and on a running engine there's too many variables... if you saw a chart somewhere, for curiosity I'd like to see it too) to the PVCR's at the first stage. Eether, either, yes, a two-stage simply introduces part of the PVCR enrichment, at it's 1st stage.

FWIW, your situation sounds like 9.5 single stage power valve territory to me. I think it's just you found the stupid-lean point, probably with the transfer slots with your "reverse-idle" air bleed adjustment, because your jetting is probably close if not what was factory installed. So, with your adjust-ability, I'd sneak it back rich on the reverse-idle screws by 1/16 turn at a time... *

*Edit: which, with your hybrid situation of "reverse-idle" metering and 4180 base plate (delivering the idle air:fuel quantity), will likely require the base plate idle mixture screws to be snuck back inward, because the "reverse-idle" internal idle feed restrictions and your dialed-in air bled into the idle circuit (up to the idle air bleed maximum) still dictates the air:fuel delivered to the base plate mixture screws.



(image photographed from the SA-Design book, "Volume One - Carburetors: Holley Carburetors", by Dave Emanuel, ISBN 0-931472-08-03)

[xctasy]

http://vb.foureyedpride.com/showthre...ies-right-away

Post 10, post 13.

PVCR size in the carb, and just the internal spring rate on Holleys controls secondary points.

On old flathead Holley's and all the Weber 5200/6200/6500 series carbs you can externally measure a single stage crack off point by drilling a passage, and fiddle with the spring and oriface sizes.


Holley 2300/41xx's and Autolite 210/4100 /Motorcraft 2150/ use a first stage crack off intial step based on a PVCR in the carb of 40 thou on 4-bbls. The interplay is primarily spring rate. Jeeps used the Motorcraft 2 stage power valve and carbs.


Lower PV in this picture..



http://www.ifsja.org/forums/vb/showthread.php?t=174374


Holley 2 stage...




Motorcraft and Holley will be the same internally, I'd guess.

But your gonna have to check statically.

The actual Laboratory set crack off Hg can be measured by doing a vac check on a striped out 1/2 to 3/4" NPT Solvent Trap Adapter.


The same 1/2", 28 thread per inch thread a tennis ball launcher http://adbe.us/500NPT.html


You then load it with a Carb Pulldown Hand vac pump like Ford uses for 80's CFI and carb vehicles.




I'm sure you've seen the references


Post #26 and 29

http://vb.foureyedpride.com/showthre...my-4180C/page2


Post #11

http://vb.foureyedpride.com/showthre...identification

[Walking-Tall]

I went lookin' in my reference materials, and I stand corrected, there is indeed an internal 1st stage fuel orifice inside a two-stage power valve. Are there differences between two-stage valves and are those differences listed anywhere? No idea. I haven't ever seen anywhere any specifications other than the two vacuum levels for the 1st and 2nd (full) stages of enrichment. For that reason, I'd imagine there isn't any internal orifice size (flow rate) differences between the different ones, and that it's simply vacuum levels that allow that restricted 1st stage to become functional, enriching the main circuit by some varying percentage. Listed in numerous places though, as to flow rate generally, is the indication that past a certain necessity of fuel flow rate, either with PVCR sizes or horsepower potential, a two-stage valve shouldn't be used. At least for the most part, it's those vacuum levels (load) that are the reason for choosing/specifying which two-stage power valve to use.




Here's the only kind of description, specification chart, and theory I've ever seen for them:




Here's the rest of the page from the above image, with some good theory and guidelines for choosing a power valve:



(these images photographed from the SA-Design book, "Volume One - Carburetors: Holley Carburetors", by Dave Emanuel, ISBN 0-931472-08-03)

[mrriggs]

I do remember seeing a list that showed the restriction sizes but can not for the life of me find it now. It's funny, that book was the first one I grabbed to look for it. Definitely a great book. Proven by the fact that they aren't telling you you pick a power valve based on half-manifold-vacuum-at-idle.

FWIW, your situation sounds like 9.5 single stage power valve territory to me. I think it's just you found the stupid-lean point, probably with the transfer slots with your "reverse-idle" air bleed adjustment, because your jetting is probably close if not what was factory installed. So, with your adjust-ability, I'd sneak it back rich on the reverse-idle screws by 1/16 turn at a time... *

I may end up going with the numerically higher single stage power valve but wanted to at least try the two stage first. "Performance" is a relative term, it's meaning changes based on what it is the car is expected to perform. This car is my daily driver and has never seen a race track. In the arena that this car competes, gas mileage is the primary measure of "performance." I don't think I've found the "stupid-lean" point yet, it runs very well, high and low, just has one little bad spot in the middle. If anything, I think I need to continue leaning the transfer slots until it is too lean at low throttle settings then richen it up just enough to be happy.

*Edit: which, with your hybrid situation of "reverse-idle" metering and 4180 base plate (delivering the idle air:fuel quantity), will likely require the base plate idle mixture screws to be snuck back inward, because the "reverse-idle" internal idle feed restrictions and your dialed-in air bled into the idle circuit (up to the idle air bleed maximum) still dictates the air:fuel delivered to the base plate mixture screws.

Yep, I've had to readjust the base plate idle screws any time the air screws are changed.

[Walking-Tall]

I do remember seeing a list that showed the restriction sizes but can not for the life of me find it now. It's funny, that book was the first one I grabbed to look for it. Definitely a great book. Proven by the fact that they aren't telling you you pick a power valve based on half-manifold-vacuum-at-idle.

I may end up going with the numerically higher single stage power valve but wanted to at least try the two stage first. "Performance" is a relative term, it's meaning changes based on what it is the car is expected to perform. This car is my daily driver and has never seen a race track. In the arena that this car competes, gas mileage is the primary measure of "performance." I don't think I've found the "stupid-lean" point yet, it runs very well, high and low, just has one little bad spot in the middle. If anything, I think I need to continue leaning the transfer slots until it is too lean at low throttle settings then richen it up just enough to be happy.

Yep, I've had to readjust the base plate idle screws any time the air screws are changed.

Yup, it's a good book for a solid understanding of the basics.

In the middle... restates better: at or near stupid-lean of transition. Same thing with mine, efficiency. Mine's light years more efficient than it ever was! Though I dialed mine (3.8L w/500 Holley 2-barrel) in (averages 27 US MPG) with adjustable idle feed restrictions and idle air bleeds, then jetting and adjustable PVCR's, and needed a 4.5 power valve due to the cruise and normal acceleration loads with the car's meager power.

You're well on your way to dialing 'er in real nice.

[mrriggs]

Here we go. http://www.catalograck.com/ImgVD/HOL/125-208.pdf

It's not the list I remember seeing but it does show the restriction sizes. Any chance these Holley part numbers cross reference to any of the Motorcraft ones?

[dynodon64]

[QUOTE=mrriggs;1822371}At 1-1/2 turns out on the air screws my mileage is up to 15 MPG but I picked up a slight hesitation on moderate acceleration. If I stab the gas it takes off and goes, if I put around it runs well, but at a certain point right in between there is a little flat spot.[/QUOTE]

The slight hesitation problem your talking about here sounds like a lean accelerator pump shot. Now if the hesitation continues as the car is accelerating at steady throttle setting, then you need to reduce the bleed air setting. You may even want to look at the float level setting. I little more fuel level may help out. Fuel level effects when the main jets start flowing. Higher fuel level will allow main jets to flow sooner. If this lean condition is at part throttle, how far open are the butterflies? The transfer slots may not even be in play here. you may be into main jet flow at this point. Transfer slots work mostly just off idle. Above that and you are into the mains.

[Walking-Tall]

Here we go. http://www.catalograck.com/ImgVD/HOL/125-208.pdf

It's not the list I remember seeing but it does show the restriction sizes. Any chance these Holley part numbers cross reference to any of the Motorcraft ones?

Great digging, lol! Downloaded, thanks Ultimately, by those listed orifice sizes, what they do is give let's say ~25% of the carburetor's full PVCR's enrichment, at the higher vacuum number.

Let's not kid ourselves here though: you have established that leaning the "reverse-idle" air screws gave you a miles/gallon improvement as well as made the moderate acceleration hesitation show up, so we are talking about the idle/transition circuits (which is why I can be seen stating what a dog'n'pony show the two-stage valves were). You said if you step on it harder, away she goes, telling me your main circuit is fine. The issue is a small window of the upper of the idle/transition circuit and the beginning of the main circuit taking over. Power valve enrichment doesn't mean or do anything unless the main circuit is activated and flowing, doing the fueling. The idle/transition circuit can be and usually is doing the fueling (depending on gearing and load of course) well up into highway speeds. I think you're on the right track, keep after it.

By the linked document's vacuum ratings of 12.5/5.5, 10.5/5, and 10.5/5.5, they cross reference with the three I posted above.

[mrriggs]

...By the linked document's vacuum ratings of 12.5/5.5, 10.5/5, and 10.5/5.5, they cross reference with the three I posted above.

The others match up with three of the 4165/4175 valves on your list as well.

[Walking-Tall]

The others match up with three of the 4165/4175 valves on your list as well.

Yes, and Holley and Autolite/Motorcraft both take power valves with 1/2"-28 thread size.

[mrriggs]

The issue is a small window of the upper of the idle/transition circuit and the beginning of the main circuit taking over. Power valve enrichment doesn't mean or do anything unless the main circuit is activated and flowing, doing the fueling.

That's what I picture is happening, by reining back the transfer slot mixture I've lost the overlap with the main circuit. I'm assuming that by opening the power valve the main circuit would have less restriction and start flowing sooner. Most guys never even touch the transfer slots or power valve, when they get a hole in the transition they just stab bigger jets in there and the problem goes away. Of course, their mileage goes away too but they aren't driving it everyday so it's no big deal. I was hoping to apply the same "bigger jet" trick but only in the spot that needs it.

[dynodon64]

Emulsion tubes are different just for these problems. Since you are using two different carb parts, you have altered the stock design and now you are the new designer. So it only stands to reason, there will be issues. Again, fuel level will effect this problem without effecting WOT fuel. Look into emulsion tube tuning.

[mrriggs]

Again, fuel level will effect this problem without effecting WOT fuel.

Thanks for the suggestion. I've always just set the level to the bottom of the sight plug hole. This may be a silly question but how do you measure the fuel level when it's higher than the hole? Do you set it to the bottom of the hole, put the plug back in, then raise the needle by counting turns? Or do you use those cheesy plastic sight plugs? I tried those once but couldn't really see anything through them.

[dynodon64]

If you had see through plugs, that would help. It would just have to be adjust and test. Maybe 1/4 turn of the float adjuster at a time.

[Walking-Tall]

That's what I picture is happening, by reining back the transfer slot mixture I've lost the overlap with the main circuit. I'm assuming that by opening the power valve the main circuit would have less restriction and start flowing sooner. Most guys never even touch the transfer slots or power valve, when they get a hole in the transition they just stab bigger jets in there and the problem goes away. Of course, their mileage goes away too but they aren't driving it everyday so it's no big deal. I was hoping to apply the same "bigger jet" trick but only in the spot that needs it.

Exactly You've got pretty much limitless (IFR & IAB are the limits) adjust-ability of the idle/transition circuit with your hybrid to address this, it just needs some itty-bitty tweaking. Big swipe 1/4 or 1/2 turn changes with it will and have shown you where the limits are. Finding out where the limits are, safely at low and cruise speeds, is important for dialing something in. It's identical to finding the right size idle feed restrictions and idle air bleeds. IMHO, all the addition of increased main well emulsion and emulsion-tuning-gone-wild 3-ring circus of late, which has little to nothing to do with the idle/transition circuit, coupled with high-mount idle feed restrictions, is just that, a completely unnecessary circus of marketing and a price-increasing tool, and creates unstable, erratic, and rich low and mid speed flow and usually an adequate or bad lean-out up top, tuning for WOT numbers and BSFC, which rarely has any connection with reality and the variations of a vehicle motoring down the road. Thankfully, lots of that "technology" is quietly going away.

What is the list # of that reverse-idle carburetor?

[mrriggs]

What is the list # of that reverse-idle carburetor?

It's a List-6619-1 carb, the throttle body came off a List-50003 truck carb.

[Walking-Tall]

It's a List-6619-1 carb, the throttle body came off a List-50003 truck carb.

Good combo. If secondary metering plate #39 is still out back, it's got Ø0.073" secondary "jet" holes. A 6619 600cfm came originally with #64 primary jets and probably has approximately Ø0.050" PVCRs.

Not to hijack your thread, but thought this stuff might interest you...
I'm converting an old LIST-4668 (an oddball typical '60s-'70s Mopar-engineered somewhat spread-bore ~700cfm vacuum secondary), originally from a '70 Dodge Challenger w/383 Magnum, over to standard from reverse-idle, and to 4-corner idle with a 3310 750cfm primary metering block out back. Here's the original reverse-idle primary block:




Again, the original primary metering block. The red lines indicate the new passages that I drilled, new idle wells and connecting passages that are needed for conversion to standard idle, and drilled and tapped 6-32 for adjustable screw-in IFRs and 8-32 for adjustable screw-in PVCRs:




Connected/added new passages to the throttle body and main body necessary for standard idle, and tapped the four idle air bleeds for adjustable screw-in bleeds (brass 8-32x3/16" socket set screws):

[mrriggs]

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".

Without access to an eddy brake chassis dyno it is really difficult to isolate steady-state high-load conditions. I suspect that dynodon64 was right when he suggested that the flat spot was due to the accelerator pump. However I think it was too rich and not too lean. I've tried three or four different pump cams and have gone up and down on shooters with each. No matter what I tried, I could not get a small enough pump shot. I could move the problem around with the shooters; a smaller shooter would take off crisp but I'd get a delayed stumble, a larger shooter would be more sluggish on initial hit but accelerate with no stumble. It needs less volume but pump cams alone weren't getting me there.

The solution [I hope] is more pump bleed. I opened it up to drill out the pump bleed only to find that this carb didn't have a pump bleed. I've never messed with pump bleeds before so I wasn't sure where to start. I checked a "universal" 600 Holley from the junk box and it didn't have a pump bleed either. I tore into the 4180 that I robbed the throttle body from and it has a 0.016" bleed in the metering block right in front of the transfer tube. So I drilled a 0.016" hole in my metering block. This was the last change I've made and I haven't fooled around with the cams or shooters yet but it seems like a step in the right direction.

[Walking-Tall]

Good stuff.

Yes, shooters can control volume, but only as to when the most of it is injected, sooner (bigger) or later (smaller). Pump cams are your only true control of the volume of fuel sent with acceleration. If you haven't yet, I'd try the smallest white pump cam in it and then adjust shooter size to suit.

Not many have an accelerator pump bleed. What you did will do the trick. Another easy option for that, with bowls that have the red accelerator pump "umbrella", is to drill a Ø0.025" hole in the pump chamber straight up into the float bowl. There's usually a small dimpled spot for adding one. After that you normally have to go up with shooter size some. The bleed also helps with quick chamber refilling, because the "umbrella" versions only refill when the pump is stroked, but with the ball bearing and strap style, there's always venting/refilling when at idle. Good luck with it.

[mrriggs]

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.

[mrriggs]

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?