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| Jetting for power valve | Login/Join |
DRR Pro |
Consensus opinion shopping. How many jet numbers (std. Holley jets) to add or subtract for adding or deleting a primary power valve? Plain ol' 4150 Holley 850 I've heard and used everything from 6 to 10 over the years. Maybe with the advent of modern tuning devices someone has nailed down a close starting number? "Despite the high cost of living, it remains popular." Dave Cook N375 | ||
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DRR Pro |
I'll take 8 | |||
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| DRR S/Pro |
No magic needed, you just need the diameter of the main jet and the diameter of the hole in the metering plate behind the power valve. Calculate the areas of both and add them together then divide by 3.14 and then square root that number, that's the new radius of your new main jet, multiply by 2 to get the new main jet diameter. Use the holley jet chart to get you new holley jet number | |||
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DRR Pro |
If you believe your jetting to already be correct, then why would you not just square the jets? Or do you think the power valve is adding more fuel than squaring would give you? ____________________________ 2017 and 2018 Osage Casinos Tulsa Raceway Park No-Box Champion 2018 Div4 Goodguys Hammer award winner | |||
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DRR Pro |
Best answer is it depends on the size of the PV restrictions. 2 little holes under the PV are the PV "jets". Rarely are they the same size from metering block to metering block, especially if the blocks are aftermarket. Method Top38 describes is about the best starting point. Basically, compare the cross section area of the current jet vs. future jet (unknown) + PV "jet". Matt Ward | |||
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DRR Pro |
dont make it harder than it is, just a starting point,pick a number run it and check jetting by plugs and adjust accordingly.and top is correct honesty is the best policy,insanity is a better deffense 1.036, 6.16@ 224 | |||
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| DRR Trophy |
I have used 10 in the past on drag cars, and a few hotter street cars. Better to be a little fat than lean... good luck Ken KEGRACING - DOING IT THE POOR BOY WAY! PONTIAC with a BowTie... for now! 2017 TX Motorplex No E Track Champion | |||
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| DRR Pro |
I've always run it squared with no PV's, and on the fat side. It's a little dirty off idle (pit speed) now, so I'm thinking of running the PV to just keep things clean. I've also seen some data to suggest it might be better if I lean it out a touch. New intake and a 7/4 swap cam have slightly altered the tune quality of my old carburetor (?). It just had it's 20 year freshen up....  I think I'll take a gander at the PV orifices and start at about 6 numbers under. Thanks for the scientific methodology as well Gentlemen! "Despite the high cost of living, it remains popular." Dave Cook N375 | |||
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| DRR Pro |
Ah, I thought you were deleting, didn’t realize you were adding. ____________________________ 2017 and 2018 Osage Casinos Tulsa Raceway Park No-Box Champion 2018 Div4 Goodguys Hammer award winner | |||
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DRR Sportsman |
6-7 But do a plug check after a clean wot shutoff coast around the corner. Either carry 4 used replacement plugs in your pockets and remove 4 and replace them with the ones from your pocket or have someone tow you back so you can pull them all at the trailer. 50% of the cars out racing have too much fuel in the engine. | |||
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| DRR Trophy |
no need to change much just try a little larger idle air bleed size should clean it up without changing full throttle tuneup The difference between ignorance and stupidity. Ignorance is lack of knowledge. Stupidity is the inability to learn. Don't be stupid | |||
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| DRR Pro |
Roger on the idle air bleeds, I opened them up years ago. Trying to zero in on a little leaner all weather tune.... "Despite the high cost of living, it remains popular." Dave Cook N375 | |||
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DRR Pro |
The jet change depends on the PVCR size, but isn't a straight forward area calculation like suggested above. Restrictions in the passages thru the PV circuit cut down the actual fuel it supplies. A stock 850 had an 80 primary jet, typically 88 secondary. With a stock PVCR size figure 8 jets down to start. Jet the primary up first then down if needed to get/find best performance.  Mark Whitener RFD Heads FTI Converter Fab Shop Headers Home built 2 circuit Dominator :-) www.racingfuelsystems.com ____________ Good work isn't cheap and cheap work can't be good. | |||
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| DRR Sportsman |
Thank you. Good info. BG | |||
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DRR Top Comp |
True, if you are adding a power valve just look up the list number of the carb and go with original jetting to start. https://postimg.cc/gallery/np3zpruo/ "Dunning-Kruger Effect" -a type of Cognitive bias where people with little expertise or ability assume they have superior expertise or ability. This overestimation occurs as a result of the fact that they do not have enough knowledge to know they don't have enough knowledge. Before you argue with someone ask yourself, "Is this person mentally mature enough to grasp the concept of a different perspective?" If not there is no point to argue. 4X NE2 CHAMPION. 2020 TDRA NE2 Champion | |||
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