How to modify your Holley Power Valve Circuit
Here are some pictures on how to modify your Power Valve Channel Restriction (PVCR) circuit on your Holley carb. It is not very difficult and can make an incredible difference on how your car drives. To tune this circuit you will need a wide band O2 sensor.
Step #1: Drilling out your PVCR http://www.clubcobra.com/photopost/data/500/PV_1.JPG Step #2: tap out the PVCR, We like to use 6-32, some prefer 8-32. http://www.clubcobra.com/photopost/data/500/PV_2.jpg Step #3: I like to use a cordless drill to hold the set screw while I drill out the center. http://www.clubcobra.com/photopost/data/500/PV_3.jpg Step #4: Here you can see the jet we are about to install into the PVCR http://www.clubcobra.com/photopost/data/500/PV_4.jpg Step #5: The completed PVCR mod http://www.clubcobra.com/photopost/data/500/PV_5.jpg |
Great tech tip Tom. Jeremy did this on my carb.
:) |
Any tips or rule of thumb on determining a starting size for the new jet? I ass/u/me you want to start some significant size smaller than stock and increase one drill size at a time.
Should the inserts be removed from the metering block for redrilling? |
Great Tip!!!
If you use the 8-32 screws, you can have a wider range of sizes. I would recommend a small amount of loctite blue if the set screws are easy to turn. Thanks for the tip! :D |
is this done on the primary metering block only ? or do you do both ?.
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In the stock Holley metering block I am not aware of any inserts in the PVCR. Of course in the idle circuit their typically is a brass insert. |
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Thanks Tom,
Great Post, the photos make it so much easier to follow & understand. Craig |
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Thanks, |
Wide band o2 sensor
Does anyone make a reasonably priced wide band O2 sensor (and meter) that fits within the exhaust pipe? I really do not desire to weld O2 sensor bungs in my exhaust pipes.
Thanks |
pvcr are sometimes too small also. in this scenario you can enlarge the pvcr one drill bit size at a time. these channels are very sensitive. then if you go too big you can drill and tap for the bleed as tom has shown. fyi
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Sorry I did not include this picture earlier. It might have cleared up some confusion. This is a picture of an unmodifed metering block. The two little holes inside the black ring are the PVCR.
http://www.clubcobra.com/photopost/d...589_Large_.JPG |
Just curious
Are you doing this modification to decrease or increase fuel volume while still retaining the original PV vac setting ie. 6.5 etc. Or,is this for track use such as where performance suffers coming out of corners and a boost from more fuel is required. Or,are you just seeking better overall street driving. I realize many Cobra engine combos out there have cams that provide poor at best vaccum and wonder what PV's are being used,how low of a setting? The reason for the questions is the 2 -715 Holleys on my Boss 429 run pretty well and the engine produces 10 in of vac at idle with 6.5 PV's in both carbs. However,when I accelerate at full throttle I look like I'm leaving a vapor trail out of the exhaust. No hesitation,just acceleration,but adding insult to injury as I bested a ZO6 and washed him with the vapor trail at the same time.He was peeved,I might say I was embarassed ,or not.:3DSMILE: I also realize that the sewer size ports combined with dumping all that fuel at WOT may not be a cureable situation but am exploring all options. Anyone else with 2X4's experiance this? Carbs are from Carl's,and overall I'm very happy with the performance. |
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The availability of the billet metering blocks,make this and other metering block mods easy,but you need a good wide band A/F meter,like an INNOVATE LM-1,to verify results on the track or street.
What you try to do,with the Power Valve Restriction, is use the smallest main jet size,for best cruise performance,and then adjust the PVR, for best performance at heavier throttle loads,before secondaries start to open. I've been tuning with the LM-1 for 4 1/2 years,and it can be addictive,chasing the ultimate combo! Wait till you start tuning the emulsion bleeds/jets! You do that to straighten out the fuel curve. |
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"At cruise I'm in reality running a 2 barrel and the power band is very steady as I accelerate with no stumbling or hesitation. " "Yes,I'm sure it's running rich when I floor it and everything opens up,but the secondaries are vaccum and I'm thinking maybe the power valves are dumping to much fuel all at once at initial WOT,after the initial blast out the pipes everything is clear as a bell.The plugs and tailpipes both have the same coffee with cream coloring and driveability is actually fantastic. " "I'm sure the 482 FE is cammed differently.I can drive off idle with no issues,and if and when I've achieved 1/2 throttle I'd be exceeding the speed limit in any gear including first.And if I was any happier when driving it I'd likely get arrested Thanks for your thoughts,I may try closing down those holes a bit" |
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can you envision just using the air bleed jets instead of a brass set screw ? Is there enough material in the metering block to set the bleed jets in deep enough to clear the power valve ? Z. Ray |
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