Quick Fuel 950 jetting

Discussion in 'Holley' started by sailbrd, Jul 2, 2007.

  1. sailbrd

    sailbrd Well-Known Member

    Working on jetting a Quick Fuel 950 HP. Motor is 462, 10:1, sp-1, 3 inch x-pipe, ported Stage 1 heads, 3:73 gears, crane ignition. Cam is a TA 413.

    Carb started out with 85's on all corners, plugs were dark brown, clearly rich and ran rich. Switched to 80's for the secondary, 78 primaries. Has power valves. A short drive cleaned the plugs up and now look lean. Drivability is very good with new jets.

    Should I try 80's squared or 80/82 primary/secondary?
     
  2. 70 gsconvt

    70 gsconvt Silver Level contributor

    I have the same carb and similar engine combo. I have 82's up front and 86's in the back with jet extensions. Car runs great.
     
  3. sailbrd

    sailbrd Well-Known Member

    Thanks Phil,
    I know how good you car runs. The performance of your car has been my model. I think I am getting close. I see you run a lot of split between front and rear. Always good to see what works. I am going to have access to a wideband O2 meter and will race this weekend. Hope to get into the low 12's.
     
  4. Jeff Kitchen

    Jeff Kitchen Well-Known Member

    Maybe you knew this, but, looking at your combo, if you go the track much and your car hooks pretty good, you shouldn't run a power valve in the back. For the same reason you put jet extensions on the back. When the fuel runs to the back of the bowl, it can't get to the power valve openings.

    Have fun.
     
  5. 70 gsconvt

    70 gsconvt Silver Level contributor

    Good point Jeff. I also do not run one in the back. I'm trying to remember, but for some reason the one up front, I think, is a 4.5.
     
  6. sailbrd

    sailbrd Well-Known Member

    Jeff, Phil,
    Thanks again for the info. I am new to running Holleys so on a new learning curve.

    Did some O2 tuning with the 78/80 jets and had 12.75's AFR on the street at WOT. Plugs looked good. Pulled good all the way through 6000 rpm.

    Went to track yesterday. Finally figured out how to get an OK launch for 1.7's 60 fts. But started to get a little lean miss after 5000. Pulled the plugs and looked lean. To finish the day I added a half turn to the idle screws and short shifted at 5000. Could turn 12.75 et's very consistently and that is .45 better than first race this year. Also set new best at 12.66.

    A few questions.
    1. You both advise dropping the power valve and go with jet extensions. How many jet sizes up is needed for the power valve.

    2. Is it common to need to jet up for the track vs street?
     
  7. 70 gsconvt

    70 gsconvt Silver Level contributor

    Hi, I just wanted to let you know that I checked my Holley kit and the 88's are missing. So I guess that's what I have for my secondaries.

    I forget the reason for elminating the rear power valve, but it is a pretty common practice for performance oriented cars/engines.

    Here are a couple of threads with good jetting/power valve advice:

    http://www.chevelles.com/forums/printthread.php?t=19938

    http://chevelles.com/forums/showthread.php?t=165630

    http://www.camaros.net/forums/showthread.php?t=15513
     
  8. 7 skylark 1

    7 skylark 1 Well-Known Member

    When i broke into the 12s i started getting a lean miss(pop) at the top of 1st and 2nd gear. A wideband O2 sensor comfirmed a huge lean spot. Plugging the rear power valve and adding jet extensions cured the problem. I ended up 11 jet sizes more in the secondaries. The size of your powervalve channel restrictions will determine how much you will have to increase the jet size. http://www.netwelding.com/double_pumper.htm
     
  9. Jeff Kitchen

    Jeff Kitchen Well-Known Member

    Usually the difference between power valve vs. no power valve is 6-8 jets, but every carb is different. I had a carb once that needed 10 sizes difference.

    The reason for no rear power valve is that the PV is mounted on the metering block, which is the FRONT of the rear float bowl. When the car launches, the fuel runs to the back, so it uncovers the PV fuel inlets, creating a lean spot. Same thing with the jets. Fuel runs to the back uncovering the jets. You need jet extensions on a car that 60's in the 1.7x. I think anything below about 2.00 should get 'em.

    Have fun.
     
  10. sgrant2

    sgrant2 Well-Known Member

    :beers2: :beers2:

    Don't forget to look at the air bleeds.

    If they are not correct you will never get the carb right.

    Smaller bleeds bring the fuel in sooner.

    If you bleeds are to big 99 jets will be to lean.

    The three circut dominators are really easy to tune using air bleeds.

    :Smarty:
     
  11. sailbrd

    sailbrd Well-Known Member

    The history of this carb is that it came off of a half mile super stock car. These are small block chevies that run 700 plus HP. They accelerate from 80 mph to 140 in less than an 1/8, brake and corner at well over 1 G. The carb was custom built by QuickFuel for that car.

    The fuel system on my car has a stage1 pump with a mallory pusher. It has the glass sight windows so I can adjust the float level so that it is just below the top of the sight window. That sets the float about 3/8 of an inch higher than the old way of adjusting a holley style carb.

    It does not seem that my car should have any fuel problems but it may be the sustained acceleration over a longer period of time is pulling the fuel away. I see that Jeff's car is performing at the same level mine is. I usually have a good pull through 1st and do not run into problems until 2nd and 3rd so everything you guys are telling me makes sense.

    It looks like I need to go to the track with all the parts and spend all day tuning.

    Thanks for all the input.
     
  12. Johnny Angel

    Johnny Angel Well-Known Member

    My Holley 1000HP, has 77p and 88s. Ran great, before I ran into some other issues.

    Regards, John.
     

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