Help with Power Valve

Dennis Kelley · #1 (**permalink**) 02-28-2006, 07:04 PM

hey Guys,

Went to the dyno and car ran good but the A/F indicates a big lean spot when I first get into the gas. Tried to up the squirters and the engine would bog. Engine man said needs a larger power valve. Currently running 6.5. 15 inch of vacuum at idle. Would a 8.5 help or should I go higher. Any advice appreciated. Happy motoring.

Later Dennis

wtm442 · #2 (**permalink**) 02-28-2006, 08:45 PM

Power valves are not sized by fuel flow. The number is where they open in regards to the amount of vacuum. You may want to try a 10.5 power valve because it will open a fraction sooner than the 6.5 you have now.

What did you do in regards to the squirter? Larger squirter? If so, from what to what regarding size? Use a different squirter cam?

What kind of carb do you have? Do you notice any bog or hesitation when driving around?

What was the A/F ratio at full throttle? OK/rich/lean?

Dennis Kelley · #3 (**permalink**) 03-01-2006, 12:14 PM

The carb is a 650 dp holley. I went to a larger squirter 31 and the motor would bog. No change to pump cam. I was told that a larger (number) power valve would richen the low fuel a/f ration up. The car drives very well most of the time but when you run at 2000 rpm on the dyno and floor it you have a extremely lean spot on the a/f graph. once the power valve opens a/f is very good at 2500rpm 12.0 to 13.0 at WOT. I'm getting ready to go to the drag strip on the 18th and my engine man said that it would pick up some time if I get that lean spot out of it. Engine man said to go to bigger power valve. Just trying to get the last bite of reponse out of this little motor.

later

dennis

trularin · #4 (**permalink**) 03-01-2006, 12:59 PM

Unless you have a data logger and the engine is fitted with sensors, trial and error is about the only way to find out if your whole car likes your carb changes.

Warren is right about the numbers. You might want to try the 8.5 and see if the bog goes away. Then you need someone to follow you to see if you are pumping black smoke out your side pipes ( too rich ).

BTW, you can call Holley and they will get you 90% of the way there if you give tham all the info they ask for.

Just my $0.02 worth

HighPlainsDrifter · #5 (**permalink**) 03-01-2006, 12:59 PM

Hi,
Normally you would size a power valve 4 to 6 sizes less than your vacuum reading at idle.If you have 14 to 15 inches of vacuum at idle I would try a 8.5.
Also a little more initial timing will help.
Perry.

wtm442 · #6 (**permalink**) 03-01-2006, 01:02 PM

Power valve numbers only denote when it opens, so larger number does NOT flow more gas - it just opens a fraction of a second sooner when you hit the loud pedal.

1) Change to a 10.5 power valve.

2) make sure that both squirters open as soon as the gas pedal moves (you did say you have a double pumper). But you said squirter (singular). If you actually have vacuum secondaries, you might want to go to a lighter spring.

Test it by running at 3500 RPM and then flooring it under a load. If there is NO hesitation/bog like there is at 2000 RPM, the problem is in the squirter circuit and/or when the secondaries open up.

3) What ever, write down the changes and then record your thoughts.

4) Do NOT make more than one change at the same time. Repeat - only ONE change at a time.

Good Luck at the drags

wtm442 · #7 (**permalink**) 03-01-2006, 01:06 PM

Just remebered I had a slight hesitation once and a tune up (plugs, cap and rotor) eliminated 90% of what I thought was a carb problem.

Moral - do a tune up BEFORE f***ing around with a carb.

Dennis Kelley · #8 (**permalink**) 03-01-2006, 03:55 PM

Yes the carb is a double pumper and has two squirters. I went to get some different power valves and I'm just going to go back to my buddies dyno and try a few different power valves. The air fuel ratio is very good it just seems that the power valve is not opening fast enough. I"ll keep you guys informed after I run the Wide band O2 on the dyno. My typing is poor but I appreciat the help and will try a 8.5 through 10.5 Power valve. The car is in very good tune but I'll also check ever thing. I can use the dyno most of the day saturday.

Later

Dennis

Dennis Kelley · #9 (**permalink**) 03-01-2006, 04:00 PM

WTM442 thanks also and I'll try your suggestion on the dyno with the wide band. I never thought of taking it up to 3500 rpm to narrow down whether its power valve or squirter problem.

thanks

dennis

mstngjoe · #10 (**permalink**) 03-02-2006, 07:34 AM

What color is the pump cam and what position (1 or 2) is the screw in?