Carb PVCR and Powervalve questions

[Stickshift1320]

Hi guys,

I have some questions on the secondary side of the typical Holley 4 barrel carbs. When you are in the idle / transition / light cruise modes, are the Secondary main jets in play at all? I understand that the fuel that goes to the idle discharge and transitional slots go through the main jets, but I am looking to know if when you are in the primaries only, are the secondary jets contributing to the fuel curve at all?

Also, My 950 HP carb came with both power valves installed. I removed the sec. and jetted up about 8 sizes. What is the point of having a secondary power valve when the secondaries come in, you are pretty much into the peddle, and vacuum drops anyway to open the valve. With no valve, and larger jets, you only really use them when your on the gas most of the way. What's the point of having it?

Thanks for any tips/info. I am adjusting the PVCRs with the adjustable jet set, and don't think I need to bother with the secondary side and run a sec. power valve. Am I correct to only calibrate the primary side, and block the sec.?

Thanks.

[jmarkaudio]

On a drag engine you NEVER want a PV in the secondary side. Not only do you not need it as you have figured out, but where are the fuel pickup extensions for it? On the launch, fuel runs away from the PV, why you have jet extensions on the jets. If you want to tune it well for the track, plug both and square the jets. Jet up and down to find optimum jet for the engine. Once you find it leave the secondary alone, put the primary PV back in and jet back down, size the jet for best cruise to save fuel if it's a street car, then adjust the PVCR as needed for best performance to get it back. Once you find the best baseline for your current weather, you can go up or down on jet as needed when the weather changes significantly.

[Stickshift1320]

Thanks for the information, Mark. Much appreciation. So it is as I thought. I am glad that I understand it correctly. Thanks for the tips for tuning at the track ... I will do that.

[John_Heard]

We need some pic's of that car in your avatar...

[Stickshift1320]

We need some pic's of that car in your avatar...

Ask and you shall receive:











This is my other '68 R/T that i am going to stop racing because I don't want to twist it (has no bar or cage) and I have owned it since I am 19yrs.old. .It is a street pump gas car that runs 11.37 @ 120 with a 1.49 best 60 with a 440 and Tremec 5 speed overdrive manual tranny. This new drag car will be raced and the other will get a full resto.



Thanks for the interest in my car.
Greg.