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Power Valve
https://slantsix.org/forum/viewtopic.php?t=19406		 Page 1 of 1
Author:  70valiant [ Tue Aug 29, 2006 8:05 am ]
Post subject:  Power Valve
OK. yesterday I finally got the front end put back together so the pusher doesn't hit the hood latch support any more (I rear ended someone over a year ago). It looks much better since I painted the argent parts silver and I blacked out the center. I will try and get comparison pics up soon.
I took it for a ride with the vacuum gage hooked to the vacuum advance port on the carb. On flat ground I am pulling 15-17", down hill any where from 18-23", and up hill 11-13", this is all at 65mph. with these numbers I am figuring on getting a "stock" power valve unless someone here tells me I did something wrong getting these numbers.
any advise is appreciated

Phil
Author:  Doctor Dodge [ Tue Aug 29, 2006 8:11 am ]
Post subject: 
As with most Slants, you are pulling a good strong vacuum signel.
Try a 10.5 PV, that is the highest rated single stage p-valve available.
DD
Author:  70valiant [ Tue Aug 29, 2006 9:17 am ]
Post subject: 
Thanks DD.
Author:  emsvitil [ Tue Aug 29, 2006 5:18 pm ]
Post subject: 
What kind of transmission (auto/ manual)


I find with my automatic that it will drop to 6" of vacuum with slight acceleration because it's already shifted to top gear at lower speeds. I know there isn't enough load on the engine to warrant the enrichment circuit so if you have an automatic you may want a lower rate PV.

With a manual, you can shift at higher rpms so it doesn't matter.


BTW, if I manually downshift, the vacuum rises with the same amount of accleration, so rpm is a factor in manifold vacuum
Author:  70valiant [ Tue Aug 29, 2006 6:29 pm ]
Post subject: 
it is an automatic trans.
the only time it goes below 9" is when it is floored then it drops to 2"
Author:  emsvitil [ Tue Aug 29, 2006 7:20 pm ]
Post subject: 
Quote:
it is an automatic trans.
the only time it goes below 9" is when it is floored then it drops to 2"

Then I'd say get a 8.5" valve so you're not running rich at part throttle (unless you think you need to...........)
Author:  Doctor Dodge [ Tue Aug 29, 2006 10:04 pm ]
Post subject: 
9.5 and 7.5 power valves are also available... :? :wink:

You are doing the right thing, drive around with a vacuum gauge and take your best shot on where you want the power enrichment to cut-in.

Just to review for others, the power valve will open when the manifold vacuum drops below it's rating. Manifold vacuum is high during closed or slightly opened throttle and drops as you open the throttle. You want to set the power circuit (power valve in a Holley carb) so the enrichment happens when you need it. If the power valve opens late (a low rating PV) you get a sag in power right when you are giving the engine throttle. If the PV open too early, you get bad fuel economy.

I install a power valve that is about 1 "step" higher rating then were I see (vacuum gauge) and feel a power 'sag' or hesatation as I open the throttle. Needless to say that I have a good selection of power valves in my Holley "jetting box", every PV from 10.5 down to 2.5
DD
Author:  70valiant [ Wed Aug 30, 2006 6:59 am ]
Post subject: 
Thank you gentlemen.
I think I am going to call the local speed shop and see if they stock an 8.5 for a 4160 holley. If not I'll just order one from summit.

Phil
Author:  70valiant [ Wed Aug 30, 2006 2:08 pm ]
Post subject: 
I got the 8.5 power valve and installed it. I backed the timing to 10* inital (18 mechanical) and it runs great again. I had it advanced 4* since I was running premium in Pittsburgh and it could handle it, but now I have regular in it. thanks for all of your help. now I have to get it to the strip and see what it is running.
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