BLACK Z

Hi, I read the sticky above but nothing stated why I should use a higher number Power valve, Does a higher Number flow more or less fuel?

What are some symptoms of a too larger or too small power valve?

I have a new 650 DP Ultra carb, I think it has a 6.5 Power Valve in it stock.
Thanks

LSJuan0068

The way I did mine, was hooking up a vacuum gauge and taping it down where i could see it while driving. Now drive around and keep an eye on it and drive in all different throttle positions and see where it has a flat spot and record the reading and use that to determine the power valve.

Others just use the old method of taking the vacuum reading in drive or idle for manual cars and divide by half to determine this.

BLACK Z

What about my other questions in regards to the PV.

sofakingdom

iTrader: (1)

When you are idling or cruising, the vacuum is very high.

When you step on the gas, the vacuum drops.

The power valve is closed when the vacuum is higher than the number, and opens when it goes lower.

If it is too low, then you get the effect where if you give it a little gas, it struggles, maybe hesitates or stumbles or even backfires; but as you continue to slowly roll into it, all the sudden it's like a switch got flipped and it runs right. Very common Holley malfunction. The more tame the motor is (higher idle & cruise vacuum) the worse the problem is.

All PVs flow the same (except for the 2-number emissions ones); the flow is regulated by metering passages in the carb.

Follow the Holley Tuning sticky at the top of this forum, from start to finish, in order, skipping no steps, asking questions along the way if there's anything you don't understand, AFTER getting a good timing curve established. Odds are, your finished product will end up with several size smaller jets, and a MUCH higher # PV.

JaBoT

That sums it up. It's usually not an issue with the carb out of the box because they cruise so rich.
If your cruising at 12.6 afr and you give it a little more gas (not enough to open the valve) then the afr will go up to the 13's or 14's, which is no big deal, you wont really even notice it. But when you tune it to cruise at say 14.7 now when you give it a little more gas you get a very lean condition which is why you need the power valve to come in sooner. Which is where the 2 - 3 inches below cruise vacuum rule comes in.
Usually most street engines need a 10.5 because they draw a lot of vacuum when cruising and the biggest valve they make is a 10.5.

BLACK Z

I'll test the vac this week and post the numbers and let you guys recommend a valve for me. Wish someone lived close enough to come over and give me a hand with this.

The carb has 63 main jets and 72 or 73 in the rear, this is stock from holley on the ultra 650 dP.

BLACK Z

CHecked my Vac I have 17 at Idle. I Didn't get to road test it. What Valve should I try out. Pros and COns of leaving the stock 6.5 in?

JaBoT

10.5

BLACK Z

What is my 6.5 doing or not doing now? I am confused by them, Also is there one in the sec side also?

five7kid

iTrader: (14)

Your 6.5 is staying closed until manifold vacuum drops below 6.5 in-Hg.

I couldn't find anything that said whether or not your carb has a secondary power valve. If you pull the rear metering block, you could answer that for yourself.

BLACK Z

SO it only opens when I am really on the gas then right? Pros cons of this?

redneckjoe

heres a 10.5 "high flow" power valve from summit. might work for ya?
http://www.summitracing.com/parts/hly-125-1005


yup, "should" have 2 power valves, being a DP.

skinny z

If you PV has too low a value (based on what's been posted earlier), then yes, you'll have to get " really on the gas" to drop the manifold vacuum down to the point where the valve opens. That's less than 6.5" for the valve you have and that's a long way into the gas pedal for a gentle passing maneuver. The cons are that the likelihood of a flat spot is greater. The pros of a properly selected valve are something you have to experience to really appreciate. As was posted before, it's like a switch being turned on.
I hope that helps.

BLACK Z

Now I have heard there are some that flow better then others. IS there certain ones I should avoid. Sorry for all of the questions, just want to get it right.

skinny z

As sofa pointed out, except for the ones designed for emmisions (which I doubt you'll come across at the speed shop or mail order house) they all flow the same. Back in the old days, there was a slightly different design (with less flow) however as far as I know, they've been long gone for years.

mmadden55

They all flow the same the number is for how many inches of vaccum it opens at , IE 6.5 6 and 1/2 inches of vaccum. Unless you have an engine that doesn't come on till high rpm 6.5 is about right. There are two different styles one with slots and one with holes but they flow the same but they do need different gaskets.

BLACK Z

I have heard for anything over 6.5 Is right now I am hearing 10.5 and just all gets confusing, guess I can try the 10.5 and see if I notice a difference.

skinny z

What's your idle vacuum?
EDIT
Just re-read one of your posts. You say you have 17" of idle vacuum. In that case, a 10.5 PV (which is the highest listed by Holley) will be your best choice. You should notice a difference in part throttle acceleration. Take a vacuum gauge into the car with you and watch as you push to pedal to get below 10" of vacuum (unless of course you have a dash mounted unit).

BLACK Z

I just got some more vac hose, I ll take the gauge in the car with me next time I take it out.

skinny z

Something you may want to note regarding your asking about the differences in flow in power valves. I've copied this directly from the Holley HP Ultra installation manual.

PowerValve Channel Restrictions (PVCR):

These two restrictions are visible when the power valve is removed. They meter the flow of additional fuel into the main well. It is the PVCR diameter, not the openings in the power valve, which controls the amount of fuel admitted in the circuit. Changing the size of these restrictions will lean/enrich the air/fuel ratio at full power, but will have no effect at idle or during part throttle operation, when the power valve is closed.

Having said that, once you discover the changes that the 10.5 PV makes to your fuel curve,you can tune further by changing the PVCR.

On my old Holley, I modified the PVCR (it didn't have a replaceable jet as your does) to the largest spec that any Holly had which is .059". The change is the performance of the car was nothing short of remarkable when the PV was commanded.

skinny z

I stand corrected. I've just returned from the local speed shop where I learned that indeed Holley does make a standard flow and a high flow power valve. There's also a 2-stage PV however it's the emmisions orientated part mentioned earlier.

You heard correctly.

[quote=redneckjoe;5616001]heres a 10.5 "high flow" power valve from summit. might work for ya?
http://www.summitracing.com/parts/hly-125-1005
quote]

The above is the part number for the high flow PV.(125-1005)
The standard flow PV part number is 125-105.
I have no idea what the difference in flow is and I've contacted Holly via e-mail to find out.

sofakingdom

iTrader: (1)

The high-flow one only flows more if you put it in a carb that has high-flow metering orifices. Kinda like putting one of those ginormous mousetrap-looking switches like in the old "Frankenstein" movie to turn on a flashlight bulb. The bulb won't glow any brighter than if you used a normal flashlight switch.

skinny z

Is that the something other than power valve channel restriction?
(By the way, I like your analogy).

BLACK Z

THE PVCR is behind the power valve? I wonder what size is stock and what sizes they offer? I'll prob give Holley a call one of these days. Now I just need to check and make sure i have 2 PV, and to change it all i do is take the bowls off? will I have to reset floats or do a any tuning once i get it back together?

By Tuning I don't mean jets, I mean Idle vac and that kinda stuff.

sofakingdom

iTrader: (1)

Think of the PV as the switch (yes/no), and the PVCR as the resistance of the light bulb (controls how much). Thanks for the thumbs-up on the analogy, I always try to make it as clear as possible.

Yes... you'll see them clearly, little brass plug things with a tiny hole drilled in them, about 10% the size of ones in the PV itself.

The size that is stock, is the size that is in it; and the sizes that they offer, for the carb you have, is also the size that is in it. They are not replaceable in anything less than the $$$$ race-specific carbs. It is VERY RARE in fact that there's any need to change em, in a street situation; (a) they don't come out anyway, and (b) you can get basically the same results some other way.

Good luck with that.

Not really necessary... THINK... when the secondaries are open, what else is going on? is the accelerator floored? Maybe? Ya THINK? I'm not sure why Holley ever bothers putting one in the secondaries, for PRECISELY that reason: in this universe, there is basically NO POSSIBLE SCENARIO EVER in which the secondaries will be open, but the vac will be high enough to close it. NASCAR on a road course, maybe; the rest of us, probably NEVER ONCE in our entire life. Just FYI, rule of thumb is, block it and increase the jet sizes by about 8 - 10 #s; feel free to try it.

Pretty much.

Probably not, if you're careful.

Of course.

That's not "tuning", that's mostly just piddling. YES you will have to do some actual "tuning", which of course, is PRECISELY what changing the PV # is part of. As per the Holley sticky, you'll probably end up leaning out the jets several sizes to get that part right, and then raise the PV # in response to that. Do that stuff in the order it's given in the sticky, not just plow in right in the middle someplace; because once you DO go back and change the stuff that's supposed to be done FIRST, you'll just have to go back and re-visit the stuff that's supposed to be done AFTER the other. That's the whole point: do the stuff that affects everything FIRST (jets), then do the stuff that affects fewer and fewer other things (PV) until you get to the point where you're working on stuff (idle system) that receives effects from all that other stuff but only affects itself.

BLACK Z

The jets are are in the Primary's are 63's, the jet kit the tuner had started with 64's ( I had taken the car to two local race shops ) There are 63's in the front and 73's in the rear not sure how much smaller i should go on the Primaries. The car seems to be running pretty good. How do the PV's Affect the Idle circuit? Changing them I'll have to go back and adjust the 4 Idle Screws.

skinny z

The PV doesn't affect the idle circuit. The fact that it remains closed below the level of your idle vacuum is why. You say you have 17" of idle vacuum and if you install a 10.5 PV, then that valve will not open and provide enrichment until you get on the gas and drop your vacuum below 10.5". Once you bring your vacuum gauge into the cabin with you, you'll see very clearly how the whole thing works.

If that's the case, just swap out the valve(s) and take it for a spin. Chances are you'll feel a strong improvement in part throttle acceleration. Watch your vacuum gauge on your test drive. Even better, go for a test with your current power valve and see what it takes to get the vacuum below the point where PV kicks in. That would be 6.5". Then do the same test with the new PV.

Remember, this is all relative to Sofa's sticky. It's a well thought out plan for tuning your Holley and if you start to tune this way, it's in your best interest to follow it exactly and completely.
There are so many complexities in a carb and so much overlap in the various circuits that keeping it as simple and direct as possible is your best chance of success.
Once you've been into the tune for a while, you'll soon see what relates to what and how to affect changes. Your Holley Ultra, if the catalog description is accurate, is fully tunable. This includes: idle air bleeds (IAB), high speed air bleeds (HSAB), idle feed restrictor (IFR), power valve channel restriction (PVCR) and a few others including the usual jetting, accelerator pump and PV.
Keep asking questions if you're unsure. Someone is bound to offer assistance.

BLACK Z

Thanks for all of your guy's help, Some ? I ask I know the answer to but just want to check. I'll Take a Vac gauge with me next time i take it out just so I can see what it is doing. I'll order up 1 or 2 PV Once I figure out how many I have.

JaBoT

The power valve doesn't affect the idle circuit even if the pv number is below idle vacuum. You can still run a 10.5 valve on a car that makes 9 inches of vacuum at idle and not be rich because the pv circuit does not really affect the idle circuit.
Back in the day this was a common issue with cammed cars but all due to the fact they were not actually idling on the idle circuit because the idle transfer slot was uncovered because they had to turn the idle screw in so far to get it to idle.

You don't need a couple different power valves, you just need a 10.5.

You can actually use one that's a few inches higher but no one makes it.

skinny z

Not according the Holley tuning manual. The PV discharges through it's own port below the throttle blades and will provide enrichment at idle if opened.



That's true. A 10.5 is all Black should need.

JaBoT

Forget the manual. There are a lot of things in there that are not correct for proper street tuning.
If the power valve opens while the carb is running on the idle circuit, it will have minimal to no affect on idle afr. Maybe .1 to .2 difference in afr at idle. Plus you would have adjusted the screws to tune it out anyway.
If your not idling on the idle circuit then it will be dumping a lot of fuel when the car is trying to idle. Just another reason why having the proper transition slot adjustment on the mains is so important.

skinny z

It's actually the aftermarket book by Dave Emanuel. Having said that, not everything in print is true either.
I can say this though, I'll be doing a little power valve tuning myself (that's for the thread BlackZ!). My idle vacuum is around 11-12" depending on the amount of heat that's built up in the engine (another reason for a functional cowl hood) and I'm going to experiment with a 10.5 PV. Under certain conditions, my idle has dropped to around 10" of vacuum. While some argue that a wide band gauge isn't very reliable at idle due to mixture dilution etc. etc., I have a good correlation between what my gauge reads and what's happening engine wise. (As an example here, I had my engine fully warmed up and the electric choke mechanism had been removed and was sitting on my bench. Installing the stone cold choke on the warm engine, with the choke valve closed, immediately brought my afrs to 11:1. As the valve opened I could see the afrs slowly lean out to what was the previous afr at idle without the choke. Accurate? I can't say. A relationship? Most definitely.)
Anyway, my point here is, pending the accuracy of my gauges (vacuum and afr) I'll know soon enough if the PV is opening. By the way, I like watching the goings on regarding the gauges when I'm cruising and pull the PV open. It's obvious what's happening and you can feel it too.

BLACK Z

What I mean by a couple PV is if I have one for the front and one in the rear, I Have heard that I have 2 and I have heard there is also one.

skinny z

You and I will be testing power valves at about the same time (if I can get around to it before I head out of town next week). I'm picking up a 10.5 and a 9.5 (PN 125-105 & 125-95).
The results should make for some interesting reading.

BLACK Z

I may be a few weeks behind you, I have a full plate the next few weeks,not sure how much time i'll have. What set up are you running.

skinny z

If I don't get to it on the weekend, then it won't happen until September.
As for my setup, I'm working with a new Barry Grant/Speed Demon 750 vacuum secondary carb. I've modified it to have all the adjustments that your Holley HP Ultra has. IABs, HSABs, IFRs, etc. Almsot too much to work with however if I can get this thing dialed in like my last Holley, which had practically no adjustability, then I'll be in great shape.
As for the rest of my combination, I've copied my signature below.

86 Sport Coupe, gunmetal grey, black interior, IROC rims, AMD cowl hood, 355, 10.25:1 RHS PRoTorker heads, roller valve train w/ custom hydraulic cam, Air Gap intake, 750 Barry Grant/Speed Demon Vacuum Secondary, MSD 6 AL Ignition and billet distributor, Canton road race oilpan, Hedman LT headers, Griffen rad, 700R4 w/10" convertor, TransGo Stage 2 kit, Hurst Dual Gate shifter, 1350 u-joints, 3" steel shaft, Dana 44 w/3.73 TracLoc, LS1 front brakes, PBR rear, Intrax 2" drop springs, poly bushings throughout, Del-Alum bushed front A-arms, on board data logger, full AutoMeter gauge cluster.
Blah, blah, blah...
I just want to go racing.

BLACK Z

Sounds like it'll run, I had a Summit Built 355 before this motor that would run, Sold the motor to a friend, Should have kept it.

JaBoT

You shouldn't have a rear power valve. And if for some reason you do put a plug in it and go up 8 jets. There is no reason to have a rear power valve. But i'm pretty sure you don't have one

skinny z

12.6 @ 108 so far with a weak 1.8x 60'. Based on that, and that it was running with heads that had wiped out valve guides (really wiped out!), I think there's more in it.
20+ mpg too.
I'm hoping October will be a decent month at the track.

BLACK Z

Ok, I have 73 Rear Jets in it now. Do they make a plug if need be or do you just use a reg bolt?

skinny z

A plug for...? I hope you're not thinking of eliminating the secondary power valve.

JaBoT

absolutely!! but he probably doesn't even have one anyway. Most carbs don't.

Yes they sell a plug. But take the carb apart first to see if you even have one.

skinny z

I'll have to confess, my experience is with vacuum secondary carbs.
I understand the concept and the procedure but I've never tuned one that way.

sofakingdom

iTrader: (1)

Reading back through, I see where you say this is an "Ultra DP" carb; not something I am specifically familiar with. Posting the list # would be worthwhile.

However, if it's a DP, it's also manual secondaries. Whether it's a 4150 (sec metering block) or 4160 (metering plate) is a different question.

Since there is, for all practical purposes, NO circumstance under which the secondaries would be open but the vacuum high enough to close the PV, the PV adds NOTHING to their functionality. That's the philosophy behind plugging it and increasing the jet size: it eliminates a moving part and point of failure.

But you're A LONG WAY off from being to the point of tuning the secondaries, from what I'm seeing here. We haven't yet heard the results of the first step of sizing the carb's fuel delivery to match the engine's demands, which is, finding the size of the jets where high-speed cruise is on the ragged edge of too-lean. That's THE FIRST thing you gotta do to tune a carb, is isolate the main system (eliminate the effects of all the other systems) and get it set up properly. You can't work on the power system until the main system is right, because if you do, then sooner or later you're going to have to work on the main system, but since that affects the power system, you'll just have to go back and re-do that. This is the reason for using PROCESS, LOGIC, and ORDER, rather than just jumping into it a tweeeeking on stuff randomly. Same deal with the secondaries: leave em alone until the primaries are PERFECT, from start to finish; because no matter how good you dial em in, if you go back and change the primaries, then they'll be wrong again.

TreeFiddy

Sofa, just a question on the process - while setting up the primaries, where should the secondaries be set at for idle? Completely closed to elimate any effect on idle, or cracked open a bit?

sofakingdom

iTrader: (1)

Rough in the "transition slot" situation; which is, set the idle about right, then take off the carb and turn it upside down and adjust the pri throttles to set the transition slot to about .020" - .030" showing (approx. a square) below the blades, while observing how far the blades moved to get it there; then adjust the sec idle about the same amount in the opposite direction.

Most often you'll find that the pri is too far open, and there'll be like .080" of transition slot showing, meaning you'll need to let the pri throttles down and open the sec ones up. Should make a SIGNIFICANT difference, all by itself, to the "feel" of the engine on throttle tip-in.

After the main and power systems are dialed in, you'll probably want to go back and finesse that, but it helps to start out with it somewhat close.

TreeFiddy

Logical. Thanks!

mmadden55

The reason you have a power valve set for say 6.5 inches of vacuum is that when you accelerate your vacuum drops, a power valve set for 6.5 will open when your vacuum level reaches that point and stay open in till it goes back above it. You don't need 10.5 on anything that isn't drag race only, your valve will be open way too much and you will be wasting gas.

BLACK Z

I need to find a good tuner around here, I just don't have the time, or all of the knowledge, One time going though this with some one in person and Id have it down pretty good.

JaBoT

That is just 100% incorrect for a street car that has been properly tuned at cruise. If the car is cruising at around 14.7 when you give it light throttle to accelerate past someone on the highway it will create a bad lean condition causing a lean buck due to the power valve not opening soon enough. You obviously have never set the mains to cruise at a proper afr for a street car otherwise you would know this. Race cars can use a lower pv because they are cruising in the 12's to 13's.

The reason they come with 6.5 power valves is because
1 Out of the box they cruise at a rich afr so it doesn't matter. If your cruising at 12.5 and you give it a little gas to accelerate it will just lean out to like 14. no big deal.
2 most people don't know how to properly set the idle so it's actually not idling on the idle circuit and the pv opens when its not on the idle circuit it will be crazy rich. By putting a 6.5 in it this problem does not exist.