Powervalve size?

[elimination]

What sized powervalves should I be running? Currently I am running two Holley 750's HP's with 6.5 valves. The motor is a 468, 10.5-1, Weiand Tunnel, Rec. Port Heads. The reason I am asking is because I was told to drop down to 2.5 P.valves due to the vacuum with a tunnelram causing it to dump fuel at an idle. My concern is the possibility of the motor running too lean. Thanks for the help!

[HighRoller]

I have heard that the size of your powervalve can be calculated through this formula.Hook up a vacuum guage on your engine and measure it at idle then divide this number by 2 and that's your number.13 inches=6.5 power valve and so on.Maybe someone could correct me if I'm wrong and maybe it's different with dual 4's.If so I'd like to know.....

[Blown 472]

If this is a jet boat, put a vacuum gauge on it and record your vacuum at wot, then back it down 500 rpm and record the vac and put a valve in that matches that rpm/vac reading this will bring the power valve in on the top end as jet boats need more fuel at top end due to the increase in load. You will not add fuel at idle unless the diapham is broken as the pv only enrichens the main circuit.

[Racing Ray]

The standard way to select the proper power valve can be found right here.
Holley (http://www.holley.com/HiOctn/TechServ/TechInfo/CI-121.html)

[Blown 472]

Racing Ray:
The standard way to select the proper power valve can be found right here.
Holley (http://www.holley.com/HiOctn/TechServ/TechInfo/CI-121.html) Now all we need is 058 in here, dont forget bout the low pressure area too. :D :D :D
What do you drag race Ray?

[Hotcrusader76]

elimination:
What sized powervalves should I be running? Currently I am running two Holley 750's HP's with 6.5 valves. The motor is a 468, 10.5-1, Weiand Tunnel, Rec. Port Heads. The reason I am asking is because I was told to drop down to 2.5 P.valves due to the vacuum with a tunnelram causing it to dump fuel at an idle. My concern is the possibility of the motor running too lean. Thanks for the help! You're right. Most set-ups like yours only need 2.5 or none at all. Consider just blocking them off and jetting up 3-4 sizes to compensate for the lean condition.
~Ty

[Racing Ray]

Blown 472
Now all we need is 058 in here, dont forget bout the low pressure area too. :D :D :D
What do you drag race Ray?
66 Chevelle S/C S/G
That low pressure area is pretty wicked. eek!
http://highperformancecars.com/collinsracing/rr1.jpg
Ty
Help me understand why a Jet application is so much different. I am trying to learn here too.
[ July 09, 2003, 07:23 AM: Message edited by: Racing Ray ]

[Blown 472]

WHat are you running in that car?? Super gas??
I was talking about the jet aplication, due to the load increasing on the motor from the rpm increase I was told it is best to add fuel to the motor rather than lean in out on top end like a prop boat, and the powervalves can be used as a switch to do this. It is easy to map the rpm to vac chart and then pick where you want to add fuel.

[Racing Ray]

The car is capable of and I am licensed to compete in Super Comp and Super Gas but running a door car in S/C is tough so I pretty much stay in Gas. I understood your post and what you were saying about trying to enrich at a certain RPM band. I was asking Ty why you would size a power valve so small or remove it and go up only jet 4 sizes which to me appears would cause a severe lean condition on the top end.

[Blown 472]

Racing Ray:
The car is capable of and I am licensed to compete in Super Comp and Super Gas but running a door car in S/C is tough so I pretty much stay in Gas. I understood your post and what you were saying about trying to enrich at a certain RPM band. I was asking Ty why you would size a power valve so small or remove it and go up only jet 4 sizes which to me appears would cause a severe lean condition on the top end. Gotcha, tube chassis car?? what engine you running?? I used to work at Ken Thurm race cars and we ran a s/c camero.

[Racing Ray]

In that picture I was running my back up motor a 511 w Dart 320s and a single 1050. My big motor a 565 Merlin Lite. (I always say have a Lite)
http://www.highperformancecars.com/newmotor.jpg

[Blown 472]

Hot damn, that is bitchen. You run a glide behind it?

[Racing Ray]

Yes I run a glide 1:76 6200 stall I shift at 7600 and cross the line at 7800. My son and I built the car a few years ago and I started in S/ST with a back halved chassis then we extended on with a strut front end when we decided to step up. I let my son run it at Super Chevy last year with the throttle about 1/4 open he was running 10.30s @133 normally I run 9.90s @153-157 depending on the air.

[Blown 472]

Very nice.

[Thunderbutt]

I have the same set up as you and I blocked mine off. Mine doesn't run lean, in fact its a little rich.

[Budweiser]

The way I understand it (Holley's), the way you have it set up would create a very rich condition at cruise/part throttle, especially if you're already fat on the top end. Is this the case for you? It's been a few years since I read all my "tune and rebuild your Holley" books, but I have a story in my mind about how and why they work... Idle has it's own circut that becomes un-operational once the throttle blades open a certain ammount. Then you're running on the main circut which is metered by the jet size which should be tuned perfectly for cruise/part throttle. And finally there is your power valve enrichment circut which adds fuel at full throttle (low vacuum)to maintain an ideal air/fuel ratio. The ammount of fuel delivered by the power valve is metered within the metering block and can be adjusted, but I understand it's best to leave this part to the Pro's. The sudden transition from the idle circut to the main circut creates a lean period while air velosity builds for the main circut to opperate properly, this lean condition is eliminated or masked by the accelater pump (circut). All of the circuts are designed to create an ideal air/fuel ratio most of the time and in most conditions and throttle positions.
Sorry to be so long winded guys, just thought this might help a little. And by all means, PLEASE correct me if this is at all inaccurate.

[Thunderbutt]

YES

[BK]

Hotcrusader76:
elimination:
What sized powervalves should I be running? Currently I am running two Holley 750's HP's with 6.5 valves. The motor is a 468, 10.5-1, Weiand Tunnel, Rec. Port Heads. The reason I am asking is because I was told to drop down to 2.5 P.valves due to the vacuum with a tunnelram causing it to dump fuel at an idle. My concern is the possibility of the motor running too lean. Thanks for the help! You're right. Most set-ups like yours only need 2.5 or none at all. Consider just blocking them off and jetting up 3-4 sizes to compensate for the lean condition.
~Ty OK im a little confused on this. Im running a tunnel ram with 600 Holleys (1850's) and am using 8.5 pv's. I adjusted my idle with a vacume gauge and have 10-12 inches at idle and 15-17 at cruise, soon as I get on it the vacume drops off below 3 or 4. What would be the advantage (if any) if I ran a 2.5 pv or blocked it off?

[Budweiser]

BK
I'm curious too. Assuming your carbs are delivering your desired air/fuel ratio, it doesn't make sence (to me anyway) to change it.
Guys am I missing something?? Maybe specific conditions that occur in a jet application. Please fill me in.
By the way BK, what are your idle/cruise/WOT rpms? And I'm just assuming you have a jet.

[Hotcrusader76]

BK:
Hotcrusader76:
elimination:
What sized powervalves should I be running? Currently I am running two Holley 750's HP's with 6.5 valves. The motor is a 468, 10.5-1, Weiand Tunnel, Rec. Port Heads. The reason I am asking is because I was told to drop down to 2.5 P.valves due to the vacuum with a tunnelram causing it to dump fuel at an idle. My concern is the possibility of the motor running too lean. Thanks for the help! You're right. Most set-ups like yours only need 2.5 or none at all. Consider just blocking them off and jetting up 3-4 sizes to compensate for the lean condition.
~Ty OK im a little confused on this. Im running a tunnel ram with 600 Holleys (1850's) and am using 8.5 pv's. I adjusted my idle with a vacume gauge and have 10-12 inches at idle and 15-17 at cruise, soon as I get on it the vacume drops off below 3 or 4. What would be the advantage (if any) if I ran a 2.5 pv or blocked it off? If your set-up is working fine, then don't change it. As a generalization for the boards this has been my experience on powervalves. There is nothing wrong with running 8.5 or even 4.5s. Just check you vacuum at idle and a cruise RPM, then enrichen your circuit accordingly.
Call me if ya need some guidance.
~Ty

[BK]

[/QUOTE]If your set-up is working fine, then don't change it. As a generalization for the boards this has been my experience on powervalves. There is nothing wrong with running 8.5 or even 4.5s. Just check you vacuum at idle and a cruise RPM, then enrichen your circuit accordingly.
Call me if ya need some guidance.
~Ty [/QB][/QUOTE]
Actually im real happy with the way my carbs are working, mostly due to the guidance I recieved in our conversation a couple months ago. Thanks again Ty!
Hey Bud, im am running a jet. Its a berkely with an A impeller, WOT is just under 5400 cruise is between 28-3200 and I have the idle set at 1200. If you want more info let me know. :)