Boost referenced Power Valves or No Power Valves

[john f2000]

I am running a 572, intercooled, 10-71, 8.5 to1, at around 6 pounds boost, with two dominators with boost referenced power valves, locked out dist at 32 degrees.
The boat runs great, except if I am pulling a wakeboarder or tuber at low speed. It reallly runs fat between 2000 and 2800 rpm. So much so that when I stop and restart, after running in this zone, there is a four foot ring of black soot in the water. The motor is sputtering at this rpm. If you throttle thru it no problem, only a sustained slow pull at this rpm does it load up. To the point that it appears I washed out a cylinder wall and am now getting more blow by.
Do I keep the power valves and adjust them to come on a little latter or junk the entire boost referenced system and eliminate the power vavles?

[acatitude]

I would think you would want your power valves opening at a higher rpm for cruising anyways.... around 32-3300 rpms before they come on... this will help your fuel consuption and shouldnt hurt motor since you shouldnt be making boost at that rpm....
however the best solution is buy a ski boat for that stuff :rollside:
what the hell do I know

[kojac]

Dragboats,
I too am running a 572 with two 1150 dominators on a 871 BDS. Six #'s of boost. When I tried to run the timing Below 36degrees at 3000 rpms the engine would heat up the headers due to unburned fuel in the exhaust.
The motor would run crappy and I had to change the oil after every other time I used it. I run 93 jets in the carbs. because on the dyno that's where the best power was made.
After much trial and error I found that 36degrees of timing at 3000 rpm's helped stop the unburned fuel.
check the fuel pressure. do not run it over 7#.s to the carb because it will over come the needle and seats. causing an over flow.
Check sight glass on the carbs. make sure the levels are correct. I had to install spacers under the carbs with seven degrees cut out to insure the carbs were relatively flat while cruising to help keep the bowl levels close.
If you are tentative about the high timing install a boost retard or timing retard on the throttle for wide open runs. This will help insure detonation does not occur due to high timing.
Now my plugs are clean NKG#v9s AND I run thirty to thirty five miles on a trip using about 9 gallons of 93 octane. Change oil once a season More if I make a high number of wide open blast.
I currently do not use power valves though I am considering them. My carb man said I couldn't install backfire protection on the dominator carbs. I did install progressive linkage on the carbs to cut back on fuel when cruising.. (Normally2500to 3500rpm's)
If I were to use power valves I would check my vac/boost guage and see where the vacuuam falls off and install the appropriate numbered valves.
Hope this helps.
kojac

[john f2000]

Dragboats,
I too am running a 572 with two 1150 dominators on a 871 BDS. Six #'s of boost. When I tried to run the timing Below 36degrees at 3000 rpms the engine would heat up the headers due to unburned fuel in the exhaust.
The motor would run crappy and I had to change the oil after every other time I used it. I run 93 jets in the carbs. because on the dyno that's where the best power was made.
After much trial and error I found that 36degrees of timing at 3000 rpm's helped stop the unburned fuel.
check the fuel pressure. do not run it over 7#.s to the carb because it will over come the needle and seats. causing an over flow.
Check sight glass on the carbs. make sure the levels are correct. I had to install spacers under the carbs with seven degrees cut out to insure the carbs were relatively flat while cruising to help keep the bowl levels close.
If you are tentative about the high timing install a boost retard or timing retard on the throttle for wide open runs. This will help insure detonation does not occur due to high timing.
Now my plugs are clean NKG#v9s AND I run thirty to thirty five miles on a trip using about 9 gallons of 93 octane. Change oil once a season More if I make a high number of wide open blast.
I currently do not use power valves though I am considering them. My carb man said I couldn't install backfire protection on the dominator carbs. I did install progressive linkage on the carbs to cut back on fuel when cruising.. (Normally2500to 3500rpm's)
If I were to use power valves I would check my vac/boost guage and see where the vacuuam falls off and install the appropriate numbered valves.
Hope this helps.
kojac
Thanks that hits it on the head preety good.

[don johnson]

I agree with blowncarrera, at cruise (under 3,000 RPM) you should not be into much boost so there should not be much risk of leaning the mixture down by changing the PV's to have them open later.
I run boost referenced 1150's on my 2 GT 572 CI 14/71 blower motors, each making 1,100 HP. I run 32 degrees locked out. The boost referencing obviously compensates for boost and should allow the power valves to enrichen the motor when it actually needs the fuel, not before. I spend a lot of time at 2,000- 3,000 RPM and my transom is always clean and the motors never load up regardless of what RPM I run them... I have my PV's set so they come open after 3,000 RPM. My motors spent a lot of time on the dyno and in action with an o2 sensor getting the mixture right. It is time consuming but worth the time. You might consider welding an o2 bung into the exhaust, getting yourself a portable o2 sensor and tuning with that. Takes the guess work out as well greatly reduces the risk of getting it wrong and melting a motor!
If you do away with the power valves and jet up you will probably find that your idle to 3,000 RPM is pretty fat. Makes more sense to install PV's that will come open a little later. Additionally, when tuned correctly, by running PV's your motor should run more efficiently and will get much better Gallons Per Hour...
Good luck!

[VD CRUISER]

I run two 1050's, on my 548ci with a 10:71 and 32 deg timing, without power valves and 98 jets all around and it seems to run pretty clean at all rpms. According to the Hot Boat article a couple months ago this is all wrong. I just had a problem with sooting up the transom last week, but found one float level to high. Engine has been together now for almost 6 seasons,(knock wood). I've thought about going to pv's but not sure I should mess with it.

[kojac]

I agree with blowncarrera, at cruise (under 3,000 RPM) you should not be into much boost so there should not be much risk of leaning the mixture down by changing the PV's to have them open later.
I run boost referenced 1150's on my 2 GT 572 CI 14/71 blower motors, each making 1,100 HP. I run 32 degrees locked out. The boost referencing obviously compensates for boost and should allow the power valves to enrichen the motor when it actually needs the fuel, not before. I spend a lot of time at 2,000- 3,000 RPM and my transom is always clean and the motors never load up regardless of what RPM I run them... I have my PV's set so they come open after 3,000 RPM. My motors spent a lot of time on the dyno and in action with an o2 sensor getting the mixture right. It is time consuming but worth the time. You might consider welding an o2 bung into the exhaust, getting yourself a portable o2 sensor and tuning with that. Takes the guess work out as well greatly reduces the risk of getting it wrong and melting a motor!
If you do away with the power valves and jet up you will probably find that your idle to 3,000 RPM is pretty fat. Makes more sense to install PV's that will come open a little later. Additionally, when tuned correctly, by running PV's your motor should run more efficiently and will get much better Gallons Per Hour...
Good luck!
Don,
Do you have the ball checks in your carbs to prevent the power valves from blowing in case of backfire? My carb guy says there is not enough meat in the carbs to install the backfire prevention ball check. Just wondering if you or one of the other guys have it and how it was working.
I would like to use the power valves but my rig has a tendency to backfire on startup when it is cold and that destroys them.
Kojac

[don johnson]

Don,
Do you have the ball checks in your carbs to prevent the power valves from blowing in case of backfire? My carb guy says there is not enough meat in the carbs to install the backfire prevention ball check. Just wondering if you or one of the other guys have it and how it was working.
I would like to use the power valves but my rig has a tendency to backfire on startup when it is cold and that destroys them.
Kojac
Dale,
I do not think so. My engines never backfire, even cold, so it would not be a concern.
I assume you have a blower motor... What kind of timing do you run? I run 32 degrees locked out. Locking out the dist and having full advance takes much of the "cold bloodedness" out of a motor.. Also makes the motor much happier at lower RPM's.

[don johnson]

Dale,
I do not think so. My engines never backfire, even cold, so it would not be a concern.
I assume you have a blower motor... What kind of timing do you run? I run 32 degrees locked out. Locking out the dist and having full advance takes much of the "cold bloodedness" out of a motor.. Also makes the motor much happier at lower RPM's.
Dale, I was thinking about your backfiring problem a little more.... Backfiring when cold can also be caused by it being lean. If you are locked out with timing at 36 degrees then consider richening up with the idle screws or better yet air bleeds on top of the carb.
JohnF2000, one thing no one has considered is you may want to think about tuning with the air bleeds as those can have drastic air/fuel affect on the off idle and transition to intermediate circuit of the carb. However, these adjustments get tricky. Best to get an O2 sensor and adjust that way. Again, takes the guess work out of it and you get very specific readings for each change.

[kojac]

Dale, I was thinking about your backfiring problem a little more.... Backfiring when cold can also be caused by it being lean. If you are locked out with timing at 36 degrees then consider richening up with the idle screws or better yet air bleeds on top of the carb.
JohnF2000, one thing no one has considered is you may want to think about tuning with the air bleeds as those can have drastic air/fuel affect on the off idle and transition to intermediate circuit of the carb. However, these adjustments get tricky. Best to get an O2 sensor and adjust that way. Again, takes the guess work out of it and you get very specific readings for each change.
I set my timing to 36 degrees at 3000 rpms. it is not locked out.
I have increased the size of air bleeds to help eliminate the lean condition at idle, Maybe I have to go up in size? Definitely something wrong.
Once the motor has built up some heat it idles fine.
Kojac

[don johnson]

I set my timing to 36 degrees at 3000 rpms. it is not locked out.
I have increased the size of air bleeds to help eliminate the lean condition at idle, Maybe I have to go up in size? Definitely something wrong.
Once the motor has built up some heat it idles fine.
Kojac
Sounds lean at low RPM to me, maybe fatten it up some more with the air bleeds and idle circuit adjustment. I cannot remember if rich = larger or smaller air bleeds... For what it is worth.... my motors will idle immediately when I start them cold.
You may also want to consider locking the dist out which will help your low RPM issues. However, it will also lean the mixture out a little more but that is not a big deal as you need to fatten it up anyhow...

[kojac]

Sounds lean at low RPM to me, maybe fatten it up some more with the air bleeds and idle circuit adjustment. I cannot remember if rich = larger or smaller air bleeds... For what it is worth.... my motors will idle immediately when I start them cold.
You may also want to consider locking the dist out which will help your low RPM issues. However, it will also lean the mixture out a little more but that is not a big deal as you need to fatten it up anyhow...
Thanks for the input. I'm going to try the bigger bleeds and do a little more adjustment to fatten it up.
Kojac

[JMC]

The bigger the number and hole size in the air bleeds the leaner it will run.

[DUCKY]

I would agree that 32* is a little soft on the timing. What you need to know if what the vac/boost gauge is saying when you are pulling the toys. Figure out how much vacuum the motor is pulling at that rpm and go 1/2 to 1" lower on the power valves. (if it pulls 5" vacuum, put in a 4.5 or a 4 valve) If you are unlucky enough to be at the 0 mark during this point, you are hosed.... Bumping the timing a little should increase the part throttle vacuum though. Good luck getting her fired up... I hate locked out distributors!

[kojac]

The bigger the number and hole size in the air bleeds the leaner it will run.
Thanks JMC, I just finished reading that in my Holley carb book.

[john f2000]

Dale, I was thinking about your backfiring problem a little more.... Backfiring when cold can also be caused by it being lean. If you are locked out with timing at 36 degrees then consider richening up with the idle screws or better yet air bleeds on top of the carb.
JohnF2000, one thing no one has considered is you may want to think about tuning with the air bleeds as those can have drastic air/fuel affect on the off idle and transition to intermediate circuit of the carb. However, these adjustments get tricky. Best to get an O2 sensor and adjust that way. Again, takes the guess work out of it and you get very specific readings for each change.
To correct myself I was mistaken I have holley 950's. These do not have an intermediate circuit. However this weekend I learned that I am pulling 11" vacume at idle at about 2k I start running crappy and my vacume drops to around 6 to 7 it runs crappy or fat until about 2,900k then the vacume picks up to 11" again and it runs great from there on up. This only happens when throttleing slowly. If you hammer it it misses this transition and runs great. Mainly comming off plane slowing down or pulling wake boards etc... Obviously when I come up to boost the vacume goes to 0 then positive.
I agree with you on the air bleeds. My twin turbo big block in my truck with a blow thru carb, is tuned best thru transitions and on the mains with the air bleeds.
thanks
john

[john f2000]

I forgot I have 6.5 power valves.
To correct myself I was mistaken I have holley 950's. These do not have an intermediate circuit. However this weekend I learned that I am pulling 11" vacume at idle at about 2k I start running crappy and my vacume drops to around 6 to 7 it runs crappy or fat until about 2,900k then the vacume picks up to 11" again and it runs great from there on up. This only happens when throttleing slowly. If you hammer it it misses this transition and runs great. Mainly comming off plane slowing down or pulling wake boards etc... Obviously when I come up to boost the vacume goes to 0 then positive.
I agree with you on the air bleeds. My twin turbo big block in my truck with a blow thru carb, is tuned best thru transitions and on the mains with the air bleeds.
thanks
john

[TIMINATOR]

3 circuit carbs and annular discharge boosters will cause the low/midrange to be quite rich. Both of these "fixes" were used/designed to help transition with tunnel rams or over carbed drag motors. Both deals allow a lot more fuel flow with little airflow. Some guys run these type carbs on blowers, they usually don't transition very well. The last boat that I worked on for a severe rich midrange, would hardly get the boat on plane, it was so fat. Above 3000 rpm it hauled ass though. We got a set of 2 circuit, standard booster dominators and now the fuel mileage has tripled! If you don't care about mileage, then you can run plugged power valves too. It hurts nothing but your wallet. P.S. the more boost you run, the less difference plugged power valves make. That is because you have boost at all times under power. TIMINATOR

[VDRIVERACING]

You need to hook up with John Avery. I had a similar setup and he made a boost reference circuit that did the job. No more loading it up, smooth transition, no downside on top end. He does tend to want to jet too lean, IMO, but they worked great. He is THE man for those carbs. I dont have his number, but if you ask David Rankin, he might. Now that I think about it, John set up boost refernce circuits on Dave's offshore boat and it purrs.

[john f2000]

You need to hook up with John Avery. I had a similar setup and he made a boost reference circuit that did the job. No more loading it up, smooth transition, no downside on top end. He does tend to want to jet too lean, IMO, but they worked great. He is THE man for those carbs. I dont have his number, but if you ask David Rankin, he might. Now that I think about it, John set up boost refernce circuits on Dave's offshore boat and it purrs.
Great. how do I get ahold of David Rankin. Do you have his number you could pm me?

[VDRIVERACING]

I found John's card...
Engine Dynamics
4152 N Puente Ave
Baldwin Park, CA 91706
626-337-4614

[don johnson]

Is this the same Engine Dynamics that used to be in Garden Grove right off the 22 freeway?

[VDRIVERACING]

Is this the same Engine Dynamics that used to be in Garden Grove right off the 22 freeway?
I do not know... Sorry.