reworking a holley 950HP carb

[chevy art]

im rebuilding my factory stock holley 950HP carb. its going on a healthy 377 cubic inch SBC, goes to 7800 rpms,(aprox 600HP) stock carb specs are 78-78 jets and 6.5-6.5 PVs with 30 cc pumps front and rear and >031 squirters and pink color cams. im going to use 3,5 PV in front with a #80 jet and keep the 30cc pump and .031 squirter. in the rear i will remove the PV and use an ,087 jet . my main question is should i leave the 30cc pump and ,031 squirter and pink cam in the rear of carb OR i was thinking of using a 50cc pump and an .035 or .037 squirter and changing the cam to a better one(dont know which color to use) to step up the fuel shot.should i leave the stock rear setup alone or go to the combo i just described. also, what color cam would i use in the rear if i go with the change? the car has 14 inch slicks and a glide with .561 ford gears and a tranny brake(launch at 5,000 rpms.) my gut feeling is that i am coming out high and both pumps are already past the squirt mode and i probably dont need the extra pump shot. sure would appreciate advice on my carb rebuild. PS i wasnt going to touch the low speed air bleeds, but will listen to adbice on those air bleeds . thanks art in NY

[statsystems]

im rebuilding my factory stock holley 950HP carb. its going on a healthy 377 cubic inch SBC, goes to 7800 rpms,(aprox 600HP) stock carb specs are 78-78 jets and 6.5-6.5 PVs with 30 cc pumps front and rear and >031 squirters and pink color cams. im going to use 3,5 PV in front with a #80 jet and keep the 30cc pump and .031 squirter. in the rear i will remove the PV and use an ,087 jet . my main question is should i leave the 30cc pump and ,031 squirter and pink cam in the rear of carb OR i was thinking of using a 50cc pump and an .035 or .037 squirter and changing the cam to a better one(dont know which color to use) to step up the fuel shot.should i leave the stock rear setup alone or go to the combo i just described. also, what color cam would i use in the rear if i go with the change? the car has 14 inch slicks and a glide with .561 ford gears and a tranny brake(launch at 5,000 rpms.) my gut feeling is that i am coming out high and both pumps are already past the squirt mode and i probably dont need the extra pump shot. sure would appreciate advice on my carb rebuild. PS i wasnt going to touch the low speed air bleeds, but will listen to adbice on those air bleeds . thanks art in NY

Why are you changing to a 3.5 power valve? That makes no sense to me.

[chevy art]

stat: the car is a drag car only and i use a power valve so i can drive around the pits without loading up. the car only registers about 5-51/2 inches of reading on a vacuum gauge and i use the rule of thumb(by most info ive seen) to go aprox 1 -2 sizes smaller number power valve than what the vacuum gauge reads. i could use a 4.5 pv if i had to. this is the way the carb on the car now is set up(830 cfm holleu). thanks for your reply. think im doing this right. maybe you can comment on this , art in ny

[gnicholson]

picking a power valve by idle vacuum is an old wives tale that wont go away. 3.5 is way to low for me on a drag car. if that thing opens under load and goes lean bad things are going to happen. i would put a 6.5 in it if you want to lean it up at part throttle for driving around in the pits

[chevy art]

thank you gnic that was one of my questions about using (or not)using a low number pv.i have heard the discussion about not using a low number pv as it may not open at WOT and cause a lean out. i have no problem using a 6.5 pv if it gets me around the pits , which what i am looking for. i would not want to chance a lean out. i used the 3.5 pv because i just didnt know the real answer for use of these valves. art

[In-Tech]

Hiya,
A vacuum gauge and a wideband will answer a lot of questions especially regarding tip-in as well as the "power enrichment" circuit activity. Mechanical stuff doesn't happen as fast as we would like sometimes. Even EFI doesn't react as fast as we would like.

[cjperformance]

PV for your use depends on how much throttle you use in the pits. If its idling around or "just" above and NOT on the main circuit the PV is best left at a higher value. (Bar other runing oddities)
If you drive back up the return road and are getting on the main circuit at all then this is where the PV will help keep it from being over rich with the correct PV setting. Check your return road "cruising" vac and have the PV just below this reading.
'Personally' i like to use a PV in the primary side of anything that sees any driving between throttle closed and WOT.

[chevy art]

thanks for replies. hey craig. i like your your advice of PV choice for driving around the pits. i basically put-put around the pits and i am always in high gear(561 gears and glide), so i will use a 6.5 pv up front (is that the right way as you suggested)?, also, i had asked the question about changing to a bigger accelerator pump but that question got lost in the PV discussion. i sure appreciate all the help you guys are giving me in this matter. trhanks art

[Ks Fats]

One factor in secondary cam choice is pri/sec linkage; 1 to 1 or 40%? How far are you into the secondary on launch? There are several charts available that address this issue, although there are some discrepancies between them. The one included has become my standard as it seems to represent what I see at the track. With a 950 on a 377 I doubt you'll see high enough vacuum at w.o.t. to worry about p.v. closing. Plenum volume , spacer, runner volume etc. affect pump and nozzle choice.

[Ks Fats]

Two more.

[novadude]

As CJ performance said above, why are we even talking about power valve for idling and driving around the pits? Under these conditions you are running on the idle circuit and not the mains. The PV has zero effect on the idle circuit. Lower number PV, higher number PV - it just wont matter for idle and just off-idle low rpm cruising around the pits. I wouldn't even think you'd be into the mains on the return road.

[6.50camaro]

chevy art, I am have used a holley 850HP on my 377 and 422 sbc . Used it first on the 377 it then on the 422 after swapping motors . It had a terrible hesitation at the hit off the line .I went from the stock 31 squirters to 35s front and back .It was still not quite right , it would jump off the line then a very slight for lack of a better word "pause" then recover and take off again , went to 37s on the secondaries problem totally gone . I tried a 50cc pump on the secondaries and did not notice an difference in the feel of the launch. I am using the hollow hi flow screws on the squirters . Pump cams are both stock pinks the primaries i have the screw in hole two on the carb and hole two in the cam .this is so I don't use up pump shot staging the car at 3000 to 3500 rpm's. The secondaries 1 and 1 on the holes . No changes made other than a little more secondaries main jet on the 422. Hope this helps as you have a 950HP but it might point you in the right direction . Dan

[cjperformance]

thanks for replies. hey craig. i like your your advice of PV choice for driving around the pits. i basically put-put around the pits and i am always in high gear(561 gears and glide), so i will use a 6.5 pv up front (is that the right way as you suggested)?, also, i had asked the question about changing to a bigger accelerator pump but that question got lost in the PV discussion. i sure appreciate all the help you guys are giving me in this matter. trhanks art

Yes if its just idle, maybe just a little squeek off idle around the pits then keep the 6.5 PV.

So you trans brake it to 5000 at the lights, no 2 step rpm limiter? So you are NOT at WOT at the lights? Just enough throttle to hold 5000? Just want to get that straight. If so then what the acel pump is doing under this "staged at 5000" throttle position is not the major importance. So long as it shoots enough fuel to not stumble off idle and get into a burnout and up on the convertor the low end of pump shoot is ok.

It would be great for you to know your "at stage throttle position", tons of ways to do that. One real quick way at the track or at home, just attach a length of wire to the throttle arm and zip tie the wire firmly around a return spring bracket or something that wont move. Bring it up on the convertor/transbrake to the stage/stall rpm you use and back off the throttle. The wire pulls thru the zip tie to the distance you opened the throttle. (Basic demo in the pic below). Now you know from what throttle opening you need to work on acel pump from. As has been indicated so far you may just be needing more pump shot BUT up in that staged throttle position thru to WOT.

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