Holley Carb Testing - More than just CFM's.

Discussion in 'High Performance Modifications' started by G72Zed, Sep 10, 2021.

  1. G72Zed

    G72Zed Veteran Member

    Messages:
    3,322
    Likes Received:
    1,763
    Joined:
    Sep 8, 2015
    Location:
    Canada
    To those interested in carb testing and some surprising results.

    So, got called in to "do my thing" on the dyno for some final test & tune detail stuff, and a bit of a "carb" shoot out came about.

    Engine is a mild BBM stroker, 522 cube 9.6 ish cr pump gas deal, mild Hyd cam, open plenum, nice headers. My partner built it, all expertly machined/flowed/built in house with off the shelf parts, mostly used and refurbished, nothing exotic.

    I built a nice Holley 1000HP for another build, so it was available to use to test, and set the baseline, after all, it's not like it's going to hold the engine back.

    All typical dyno procedures followed to find best timing, plugs, spacer, jetting/bleeds with best average TQ and HP with correct AFR's with the same oil/water temps and test sweeps.

    After everything was said and done, I tossed on the old Holley 750 "Franken'Carb" that the customer gave me to see what I could do with it, all beat up, used, cracked ears and all, including the wrong metering blocks, both primaries of of who knows what. Did my thing, changed out the base plate for a used billet piece I had on my bench and tossed it on.

    Much to the customers surprise, he was taken back on how a 250 cfm smaller carb, with only the "down leg" boosters could not only hold on to the 1,000 cfm on the upper end, but beat it below 4,500, just where the Annulars shine, happy with the averages, but very surprised by the results.

    I said there is more to carbs then just the cfm, and just like cylinder heads, there is a thing as too much cfm's.....can't use what you have, and the combo can't get to the point of needing them, so it's almost a loose-loose situation...seen this so many times, people buy to much cfm's.....
    1000-750.png Franken'Carb 750.jpg InkedInkedHolley HP 1,000 vs 750_LI.jpg
     
  2. MChamp

    MChamp Veteran Member

    Messages:
    405
    Likes Received:
    110
    Joined:
    Jun 6, 2021
    Location:
    north carolina
    good read. thnx!
     
    G72Zed likes this.
  3. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

    Messages:
    11,434
    Likes Received:
    935
    Joined:
    Nov 4, 2004
    Location:
    Ringgold, GA
    Bigger is not always better, at least in carburetors. :eek:

    I think it was Tony Mamo; it's not about the quantity of air you put in an engine, it's the quality of air.
     
    G72Zed likes this.
  4. G72Zed

    G72Zed Veteran Member

    Messages:
    3,322
    Likes Received:
    1,763
    Joined:
    Sep 8, 2015
    Location:
    Canada
    X2 ^^^ absolutely correct CorkyE, you want the "quality" first, then the "quantity" to hit the hp/tq goals, nothing less, and more importantly (many don't see this) nothing MORE....

    I use the typical formula of cid x rpm / 3456 to start, gives me my baseline @ 100% VE, then I take in the whole engine package with head inlet tract design/specs and cam and build from there.

    I was informed that the "target HP" was going to be around 550 hp, knowing that most engines need/move/use 1.3 to 1.4 cfm per hp, it gave me a 715-770 cfm target, so the modded 750cfm fit the bill.

    This engine actually hit 564.2 hp @ 5,100, but only moved 696 cfm through the hat due to it's small cam profile, so not surprised by the 1.23 cfm per hp result.

    Max VE of 101.6% occured at peak TQ, my partners insight and talent let's me hone in on what's needed real quickly in the carb dept. that's for sure.
     
    MChamp likes this.
  5. 1980RS

    1980RS Veteran Member

    Messages:
    5,650
    Likes Received:
    1,903
    Joined:
    Jun 17, 2006
    Location:
    MN
    Hey, you stole my carb name Franken Carb, LOL. I am not surprised one bit by this as when I built my 1850 600 VS it was neck and neck with my 850 A/D Mighty Demon at the track. The little carb was .003 slower but the 60ft and 1/8 times were quicker and faster. I wonder if a different intake might have made a difference on that BBM? bet the newer Mopar single plane might like that 1000 better. Great test, thanks for sharing it with us. I will have some new carb tests this weekend brought a bunch to try out on the 358, starting the day with a 750hp vs model.
     
  6. Chevyforever

    Chevyforever Veteran Member

    Messages:
    1,183
    Likes Received:
    531
    Joined:
    Jan 4, 2011
    Location:
    Ontario, Canada
    The main body on that "old" 750 looks to be an HP series. They are so much smoother than say a regular old "4779."
     
  7. G72Zed

    G72Zed Veteran Member

    Messages:
    3,322
    Likes Received:
    1,763
    Joined:
    Sep 8, 2015
    Location:
    Canada
    LOL, it was my partner that actually called it that, and it stuck...the 1000 HP AN is called C-3PO.

    I'm not a Mopar guy, but the intake on that works well, and was ported by my buddy, and knows what to do and where to go get the stuff that makes a difference. Again, mostly used refurbished parts. There's enough TQ there he will be frying the tires mostly anyway.

    As far as a better intake, yes, I agree with you on that, you would be right.

    My buddy tested another one of my carbs that came back for recalibration (custom 875cfm) just to make sure it's balanced, 450 cubed Mopar with some nice Twisted Wedge heads and tall open intake as well, it's going to be forced induction, so in the mid 8's for CR, pump gas only, made 545 TQ and 612hp N/A, very good considering it was NA. Can't wait to get the twin screw superchargers on it...will be fun, might get 850-900hp out of it.
     
    1980RS likes this.
  8. G72Zed

    G72Zed Veteran Member

    Messages:
    3,322
    Likes Received:
    1,763
    Joined:
    Sep 8, 2015
    Location:
    Canada
    Yes, you are correct Chevyforever, it's an HP center section, and no model or serial numbers on the pads to be seen, all blank with no stampings......mmm, wonder why. But it measures out at 1.375 venturii and 1-11/16 on the exit, so it's a "750" cfm.
     
    1980RS likes this.
  9. 1980RS

    1980RS Veteran Member

    Messages:
    5,650
    Likes Received:
    1,903
    Joined:
    Jun 17, 2006
    Location:
    MN
    I have 2 of the 950 style HP carbs one FST and the other a rebadged Summit FST (says that under their sticker) and have crap calibrations. I am going to try them out again Sunday when I go out as I have changed the HSAB's to a smaller size, both are lean going down the track. If that does not work I will change the metering blocks to some Holley ones as I am not going to mess with something that should work right out of the box. So far the best have been the Demons but they are lean at WOT and fat at idle so you have to jet them up about 6-8 jet sizes to fix one issue then move to fix the other issue.
     
  10. G72Zed

    G72Zed Veteran Member

    Messages:
    3,322
    Likes Received:
    1,763
    Joined:
    Sep 8, 2015
    Location:
    Canada
    Are they "950" part #'s or true 950 cfm's..., sounds like it might be a lack of booster signal if the latter.

    What does the metering blocks look like ? issue could be in the blocks more so than the bleeds.

    I have worked/corrected some carbs that were just horrible out of the box, and even some high dollar models as well.

    I have found some carbs just need some staggered setups, left to right, front to rear needs balancing.

    I like to use the pvcr's to fine tune the WOT, does not effect the lower rpm's that way
     

Share This Page