Power Valve selection

[hydroguy]

I am rebuilding my 750TR Barry Grant's and am wondering why the power valves in the metering blocks are not valves at all but just threaded plugs albiet they look like Barry Grant parts. The power valves that came with my rebuilding kits are actually valves. Why would you restrict the flow of fuel to nothing in these carbs at the power valve? :confused:

[ABBOTTCRAFT]

They are setup to run without Powervalves, so they are plugged..:D

[hydroguy]

O.K. but what is the reasoning behind the selection of power valve or no power valve?

[poncho]

From what i understand when using a tunnel ram there is little or no vacuum and power valves respond to vacuum at low idle so they are not relative to a high rpm no vacuum deal, dont bust my butt if i am wrong;)

[hydroguy]

O.K. That makes sense, no vacuum, no need for a power valve. I didn't want to be sticking the valves in there if they werent tuned for them. Probably wouldn't make much difference anyway, if there is no vacuum they wont work.

[ABBOTTCRAFT]

O.K. That makes sense, no vacuum, no need for a power valve. I didn't want to be sticking the valves in there if they werent tuned for them. Probably wouldn't make much difference anyway, if there is no vacuum they wont work.

You would run fat on the top end if you put them in & if tuned for top end you would be lean on the bottom end....

[RiverRacer]

And now for the simple no brainer solution, put a hat on it!..:D:D

[hydroguy]

I'm getting closer. Next season for sure!

[RiverRacer]

Yeah, if you want to keep you're sanity, LOL...:D:D

[gfinishline]

I wish tuning carbs were that simple.

[e-PerformanceMarine.com]

Now I know I am not the smartest guy here, but I really like the option of a Power Valve. In a family boat you can set it up so you have a real good idel and midrange responce without being fat, but have all the fuel you need to run up top. Take a engine that makes 10" at idel and at cruise it makes 13"+ as soon as you drop the hammer you want more fuel right ? Well if you were to leave the stock 6.5 pv in it would take more time to enrich the system than if you had a 9.5 pv. Now if you try a high flow pv you can actually make more power as well. I have found the highflow versions give me about 100rpm over the standard version. I also hate fouling plugs at the races waiting for a heat to start. The power valves have given me the ability to run less main jet till I need it. A 6.5 pv opens when vacume drops below 6.5"s and closes when vacume returns to above 6.5"s. That is how all of them work, even the high flows.
I hope this helps a bit.

[gfinishline]

One of the problems found on "ski boat V-drives" is the prop load at idle. The motor may idle at 850 RPMs with 9" of vacuum out of gear, but drop to 3" while in gear. Then at the first opening of the throttle, no vacuum, for a split second. This usually happens with 3 blade props. Often I've had to plug the power valves, and up the jets just to get a boat running on the water. After the idle and low speed settings are found, I will start working on the 'over all power band' and often go back to "lower value" power valves, just for economy. Most boats with 2 blade props don't suffer this problem because the prop 'slips' at low RPMs and it isn't such a severe load on the motor "down there". (just like jet drives) Not all tuning can be done on a dyno. A number of Holley Competition carbs also have adjustable 'mid range' power systems, channel restrictors, air bleeds and jets, along with all the regular adjustments. Easy to talk about and teach, more difficult to actually do and gain power.

[FC-Pilot]

Easy to talk about and teach, more difficult to actually do and gain power.

George, that is the quote of the year! That not only applies to carbs, but everything in this performance world.

Paul

[RiverRacer]

If you have a stock or slightly modified motor, get the right size carb for the motor and try it right out of the box, be surprised at how close it could be!..