to power valve or not......Fiat,gofast,mp???

[396_WAYS_TO_SPIT]

Just curious to see who runs them and why. What do you gain or loose with a blocked power valve? If one were to block the pv, would it be wise to go up in jets? Just trying to answer a few q's before I go into changing a bunch of stuff. I am currently running 6.5 power valves and 64pr/74sec jets. I have 2 braswell holley 750 dp carbs that were fully worked. I am running on the fat side as well. Any info is appreciated.....
396

[Carnivalride]

Just curious to see who runs them and why. What do you gain or loose with a blocked power valve? If one were to block the pv, would it be wise to go up in jets? Just trying to answer a few q's before I go into changing a bunch of stuff. I am currently running 6.5 power valves and 64pr/74sec jets. I have 2 braswell holley 750 dp carbs that were fully worked. I am running on the fat side as well. Any info is appreciated.....
396
396
I'm running a modified 850 double pumper and I run a 3.5 power valve in the primary side and I have the secondary plugged. I've done this because of the amount of skiing and cruising that used to be done with this boat. The powervalve keeps it leaned out for all the idling and cruising and then allows it to richen when stand on it. The reason the secondary is plugged (and jetted up) is because mine is a v-drive runner bottom and the progressive secondary doesn't come in until 4000rpm so if I'm up that high up in the rpm range its to the floor for a full blown pass anyway.
Loren

[steelcomp]

Try it both ways and see how it likes it. If you remove PV's, you need to go up a min. of four jet sizes to compensate for the fuel that the PV circuit adds. If you do a lot of part-throttle cruising, you may find that it will work better with a set-up like Loren's...PV's in the pri's., block the sec's. You can taylor when they open to some extent...sort of like a minin-internal vac. secondary. The smaller the number, the sooner the PV will open.
As far as running on the fat side, do some excercise, porky. :D :D

[AzMandella]

Steelcomp is right except for one thing.It's the larger the number on the power valve that opens sooner.There are alot of things that affect manifold vacume such as high lift long duration cams,duall carbs.the bect thing to do is to get yourself a vacume guage and 6 to 8 feet of vacume hose.Hook it up to one of the vacume ports on the carb and cruise around the lake with the guage in your hand and observe how your vacume changes.What you want to do is to run your boat at a normal cruise speed and read what the vacume is and then choose a powervalve that opens 1 size smaller.For example if you have 9.5 inches of vacume at normal cruise speed then an 8.5 powervalve would be used.

[IMPATIENT 1]

good thread, it answered some quest. i had in my head.

[Carnivalride]

Steelcomp is right except for one thing.It's the larger the number on the power valve that opens sooner.There are alot of things that affect manifold vacume such as high lift long duration cams,duall carbs.the bect thing to do is to get yourself a vacume guage and 6 to 8 feet of vacume hose.Hook it up to one of the vacume ports on the carb and cruise around the lake with the guage in your hand and observe how your vacume changes.What you want to do is to run your boat at a normal cruise speed and read what the vacume is and then choose a powervalve that opens 1 size smaller.For example if you have 9.5 inches of vacume at normal cruise speed then an 8.5 powervalve would be used.
Az
Not sure I agree with you on this. My cruise vacum is much higher than my idle vacum, I have to use a power valve at least a couple numbers below my idle vacum or it doesn't stay closed at an idle. That causes a "rich" condition that eventaully doesn't allow the engine to idle any longer. And yes my cam has some duration & overlap.
Loren

[Taylorman]

Az
Not sure I agree with you on this. My cruise vacum is much higher than my idle vacum, I have to use a power valve at least a couple numbers below my idle vacum or it doesn't stay closed at an idle. That causes a "rich" condition that eventaully doesn't allow the engine to idle any longer. And yes my cam has some duration & overlap.
Loren
Holley recommends your power valve to be half of your idle vaccum. How is your cruise vaccum higher than idle? Vaccum usually drops as rpm's go up.

[AzMandella]

Az
Not sure I agree with you on this. My cruise vacum is much higher than my idle vacum, I have to use a power valve at least a couple numbers below my idle vacum or it doesn't stay closed at an idle. That causes a "rich" condition that eventaully doesn't allow the engine to idle any longer. And yes my cam has some duration & overlap.
Loren
Have you put a vacume guage on and looked at how vacume fluctuates in your particular setup.Vacume will drop drasticly when you first stomp on the accelerator but as RPM'S increase vacume will increase also.It is not uncomon for an perfomance engine to create more vacume once the engine has reached equilibrium(when RPM's have quit climbing) than at an idle.And alot of engines create their highest vacume at an idle.I would'nt be suprised,and would almost be certain of it,that your PV is closing on you as you are increasing in RPM's under hard aceleration.If vacume did not increase as the RPM's increased you would have a hard time getting the main metering system to actuate and continue to add more fuel as needed.When vacume drops to near 0 and fuel begins to fall out of suspension.That is why you have an accerator pump to add fuel to the air until vacume and air flow comes up enough to actuate the main metering system in the same way that vacume comes up you don't want your PV closing under hard acceleration.

[Carnivalride]

Holley recommends your power valve to be half of your idle vaccum. How is your cruise vaccum higher than idle? Vaccum usually drops as rpm's go up.
Taylorman,
Mines a v-drive, very little load at cruise speeds. 268/278@.050" duration on a 110ls. Idle vacum is 6.5inches, cruise vacum is about 9-12inches depending on rpm and skier/no skier. The cam has lots of reversion at idle rpm and it runs considerably smoother with very little load unlike your jet (if its like the Taylors I'm used to) around 2500-3500rpm. I assume it's coming into the powerband where the combination is starting to work together.
Loren

[058]

Az
Not sure I agree with you on this. My cruise vacum is much higher than my idle vacum, I have to use a power valve at least a couple numbers below my idle vacum or it doesn't stay closed at an idle. That causes a "rich" condition that eventaully doesn't allow the engine to idle any longer. And yes my cam has some duration & overlap.
LorenPower valves have no effect on idle mixture if they are not blownout and leaking. A good working p/v only enrichens the main circuit and it can be wide open at idle and will have no effect on the idle mixture. If you have fuel flow thru the booster venturis at idle then there is something else wrong with the carb and should be repaired and/or set up for low idle vacume. Look at the circuits of a Holley and you will see that the p/v has nothing to do with the idle circuit. Holley only says to use idle vacume as a starting point to select a power valve value.

[SUI-CY-COLE]

if those are braswell carbs...call braswell..PERIOD!!!

[SmokinLowriderSS]

I tried it last spring 396, here's how it went
Started with 700 CFM 4150 Holley Mech Secc, jetted 66/76 with 6.5" PV Ran perfectly, no holes/bogs/soft spots, decent mileage, reved fast and hard (26 years)
plugged the PV, jetted up 8, 74/84
Rich as snot, but it ran decently, was hard to get an idle mixture stable, tended to load up, reved somewhat slow and ran weak on top. Man did she eat gas up too.
Jetted down to 72/82 (still up 6)
Ran better, still acted rich but cannot confirm, now had a hole off idle that the 30 & 50CC accel pumps couldn't cover if nailed from idle. Not enough to stall it but a BIG leanout hole.
Said F-it and went back to orriginal, and ran her hard and happy all summer. Not gonna bother that P.I.T.A. route ever again.
Currently running 67/77 (up 1) with the new headers and will see just where my mixtures are this weekend.

[GofastRacer]

Vacuum holds the PV closed and it must reamain closed on the idle, take a check of the vacuum at idle, use next step lower on the PV done deal!..

[Carnivalride]

Power valves have no effect on idle mixture if they are not blownout and leaking. A good working p/v only enrichens the main circuit and it can be wide open at idle and will have no effect on the idle mixture. If you have fuel flow thru the booster venturis at idle then there is something else wrong with the carb and should be repaired and/or set up for low idle vacume. Look at the circuits of a Holley and you will see that the p/v has nothing to do with the idle circuit. Holley only says to use idle vacume as a starting point to select a power valve value.
058,
Ok once again my typing gets me in trouble, the power valve is in it for the off-idle and cruising, to keep it from loading up and fouling plugs while pulling tubers and skiers. The butterflies are drilled to help "lean out the mixture at idle. It has thinned throttle shafts and modified downleg boosters, but yes it does pull about 1/2" of vacum at 7200-7300rpm. It's not perfect but I'm making it work for now, just trying to give a guy some input on something that does work for me.
Loren

[Carnivalride]

Have you put a vacume guage on and looked at how vacume fluctuates in your particular setup.Vacume will drop drasticly when you first stomp on the accelerator but as RPM'S increase vacume will increase also.It is not uncomon for an perfomance engine to create more vacume once the engine has reached equilibrium(when RPM's have quit climbing) than at an idle.And alot of engines create their highest vacume at an idle.I would'nt be suprised,and would almost be certain of it,that your PV is closing on you as you are increasing in RPM's under hard aceleration.If vacume did not increase as the RPM's increased you would have a hard time getting the main metering system to actuate and continue to add more fuel as needed.When vacume drops to near 0 and fuel begins to fall out of suspension.That is why you have an accerator pump to add fuel to the air until vacume and air flow comes up enough to actuate the main metering system in the same way that vacume comes up you don't want your PV closing under hard acceleration.
Az,
Yes I have run with a vacum gauge on this set-up, idle is the worst except for hard accelration. Like I said idle vacum is 6.5inches and unstable, thats one of the reasons I'm running the 3.5 PV, cruise is around 9-12inches depending on load and speed. Now this is a hotrod (for me anyway) so there's not much easying into it unless I'm cruising or pulling. When I mash it it zeros out the vacum gauge untill about 7100rpm you can see it start to move and by the 7200-7300rpm range (my max) it's pulling about 1/2" of vacum, this is too much for a hotrod in my opinion but I can't afford to do anything about it right now.
Loren

[GofastRacer]

058,
Ok once again my typing gets me in trouble, the power valve is in it for the off-idle and cruising, to keep it from loading up and fouling plugs while pulling tubers and skiers. The butterflies are drilled to help "lean out the mixture at idle. It has thinned throttle shafts and modified downleg boosters, but yes it does pull about 1/2" of vacum at 7200-7300rpm. It's not perfect but I'm making it work for now, just trying to give a guy some input on something that does work for me.
Loren
Well I'd tell ya the solution to all that crap, but I think you already know what I'd tell ya so I won't!... :D :D :D :D

[Carnivalride]

Well I'd tell ya the solution to all that crap, but I think you already know what I'd tell ya so I won't!... :D :D :D :D
Let me guess Art...... could it be possibly :p perhaps mechanical fuel injection? :)
Do I get to move on to the bonus round now? :rolleyes: :D :cool:

[Blown 472]

Take a vacuum gauge and a note pad, have some one drive the boat and make a graph with rpm on the left side and vac across the bottom, and go say every 200 rpm and chart what the gauge says.
Then figure out where your "cruise" rpm is and see what the vacuum is, then pick a valve that will stay shut at that rpm but will open when the vacuum drops below that set point.
You can do this on the primary side if you are "cruising" on just the primarys, then if you can put a pv in the secondary side pick one that will open a few hundred rpm before wot as jet boats like to get fat on the top end due to the load of the pump coming up.

[steelcomp]

Az, you're right on all accounts. My bad...bigger number, sooner opening.
058's right about idle mixture and PV. We had a long thread about this a while back, and there's no connection between PV staying open and idle being too rich. It may cause other drivability issues, but not idle.
Idle vac and cruise vac are typically two different things. Idle vac is manifold vac, and cruise vac is pressure drop in the venturi, (port vac) not necessarily in the manifold. Depends where you're checking it.
If you want foot to the floor mash and go performance, ditch the PV's. If you want some part throttle cruisability and economy, then set the PV's just below your cruise vac. Idle vac means nothing here.Steelcomp is right except for one thing.It's the larger the number on the power valve that opens sooner.There are alot of things that affect manifold vacume such as high lift long duration cams,duall carbs.the bect thing to do is to get yourself a vacume guage and 6 to 8 feet of vacume hose.Hook it up to one of the vacume ports on the carb and cruise around the lake with the guage in your hand and observe how your vacume changes.What you want to do is to run your boat at a normal cruise speed and read what the vacume is and then choose a powervalve that opens 1 size smaller.For example if you have 9.5 inches of vacume at normal cruise speed then an 8.5 powervalve would be used.

[396_WAYS_TO_SPIT]

if those are braswell carbs...call braswell..PERIOD!!!
great advice :rolleyes:

[396_WAYS_TO_SPIT]

THanks for all the advice and ideas guys. I am up for trying new things but dont want to phuk anything up. I will be bringing the vacuum guage this weekend to the lake and check numbers. I only have pv's in the primarys so I dont have to worry about secondaries......

[SUI-CY-COLE]

great advice :rolleyes:
best one on here so far....with all the advice thats been on here now...you will be messing with it for the next two months....call braswell with your info they will tell you what to do.....PERIOD!,,,,btw i run no p.v..... :)

[U.T.B.A.V-Drive man]

Does the hi-rise or the tunnel ram manifold make any differance? I had a tunnel ram w/ 2 750 dbl pumpers W/ blocked off power valves. It ran a little fat @ idel, so teaching someone how to ski wasn't good. Check this out, 5,7,6and 8 ran fater then 1,3,2 and 4.(nothing to do w/ the pv's) the plugs in the front always read differant (v-drive) Carbs sit on the manifold sideways. :rollside:

[469 the coyote]

I have a braswell on my moms boat. It is a 930 cup carb that I got from grose racing. It has power valves on both sides and they are 6.5 with 85 jets and works great. The braswell 1050 on my motor does not have any. But remember if you take the powervalve out you have to jet it up ten sizes.

[bigblockbill]

First thing I do..especially in a jet is take the powervalves out and throw them in the trash (not sure on my I/O yet).
I was under the understanding that powervalves were only worth about 6 jet sizes but who knows. It is just one more variable that is not worth your time to mess with when trying to dial a carb in. Run the boat make a jet change and run again. Start rich and keep leaning it out 2 sizes at a time until you loose RPM, then fatten her up some and you got it.
The other day we had one that was close and did not know which way to go... took a guess and leaned the front and back by 2... and it started lean popping... turns out from the lean pop condition that +4 jets front and rear was perfect.
Also found out that the air bleed screws make more of a difference then I had previously belived. I thought they really only changed things at idle and just off idle, but they make a huge difference at speed. Once you get the boat jetted right they should be between 1 and 3 turns out.
One other thing I learned is carb spacers and different intakes make a difference in jetting. Took a 2" alum spacer off and had to go down in jets approx 3-4 sizes. I think it made for faster air through the carb and hence drew more fuel. I sold the boat before I really got it dialed in w/o the spacer so I don't know which way was going to work better.
my .02 worth

[SUI-CY-COLE]

I have a braswell on my moms boat. It is a 930 cup carb that I got from grose racing. It has power valves on both sides and they are 6.5 with 85 jets and works great. The braswell 1050 on my motor does not have any. But remember if you take the powervalve out you have to jet it up ten sizes.
yep your right,,i went 8 sizes up...

[058]

First thing I do..especially in a jet is take the powervalves out and throw them in the trash (not sure on my I/O yet).
I was under the understanding that powervalves were only worth about 6 jet sizes but who knows. It is just one more variable that is not worth your time to mess with when trying to dial a carb in.
To run without power valves on a boat that sees less than WOT throttle all the time is a waste of fuel, will load up the plugs, wash the cylinders and dilute the oil. There are rare exceptions such as trying to run a pair of 450 Holleys that has enough flow velocity and restriction that the p/vs would close at the upper rpm range further leaning out the engine. MOST Holleys will benefit using power valves. If a power valve is eliminated you must check the PVCR hole area [sq/in] before just sticking in a jet thats 6 or so sizes bigger. Some metering blocks have PVCR hole diameter of .070" or more so a 6 step jump would not be enough fuel to compensate for the lack of PVCR fuel.

[SUI-CY-COLE]

To run without power valves on a boat that sees less than WOT throttle all the time is a waste of fuel, will load up the plugs, wash the cylinders and dilute the oil. There are rare exceptions such as trying to run a pair of 450 Holleys that has enough flow velocity and restriction that the p/vs would close at the upper rpm range further leaning out the engine. MOST Holleys will benefit using power valves. If a power valve is eliminated you must check the PVCR hole area [sq/in] before just sticking in a jet thats 6 or so sizes bigger. Some metering blocks have PVCR hole diameter of .070" or more so a 6 step jump would not be enough fuel to compensate for the lack of PVCR fuel.
oh,,i misunderstood,,i thought you wanted to go from idle to full throttle,lololol
......beer

[bigblockbill]

To run without power valves on a boat that sees less than WOT throttle all the time is a waste of fuel, will load up the plugs, wash the cylinders and dilute the oil. MOST Holleys will benefit using power valves.
So for my I/O application which will see a lot of part throttle cruzing I am guessing would you recommend power valves in both the front and back...or can I get away with one PV in either the front or the back??? Its a holley HP 1000, with 4 corner idle....not sure of the PVCR hole size.

[058]

So for my I/O application which will see a lot of part throttle cruzing I am guessing would you recommend power valves in both the front and back...or can I get away with one PV in either the front or the back??? Its a holley HP 1000, with 4 corner idle....not sure of the PVCR hole size.
I'd run p/vs in the primarys only. Only time I can see running p/vs in the secondarys is on road race car applications where precise fuel control is required thru a wide variaty of throttle applications and a broad rpm range of the engine. Most all other applications the secondarys are either open or closed and very little in between.

[058]

oh,,i misunderstood,,i thought you wanted to go from idle to full throttle,lololol
......beerRich...you didn't mis-understand, some of us live at WOT :D :D :D

[bigblockbill]

I just got this thing and still working at getting it dialed in, so I will give it a try.
Thanks, Bill

[SUI-CY-COLE]

Rich...you didn't mis-understand, some of us live at WOT :D :D :D
bob hows busines????
im hungry...you got any pastrami down at that shop?

[396_WAYS_TO_SPIT]

this is some killer info. THanks fellas;) I think I will just leave the pv's in my motor;)
396

[058]

bob hows busines????
im hungry...you got any pastrami down at that shop?
Business is ok.....still a little slow but liveable. You want pastrami?? We got Pastrami, we got 2 or 3 types of copa, we have prosciutto, we have 3 or 4 types of salami and all the usual regular stuff...whats your pleasure??

[Blown 472]

Business is ok.....still a little slow but liveable. You want pastrami?? We got Pastrami, we got 2 or 3 types of copa, we have prosciutto, we have 3 or 4 types of salami and all the usual regular stuff...whats your pleasure??
All of the above. :boxed: