Page 1 of 5 1234 ... LastLast
Results 1 to 15 of 74
  1. #1
    254RWHP boat anchor EVL253's Avatar
    Join Date
    Nov 2006
    Location
    bathurst
    Posts
    5,125

    Default Tuning a holley for economy

    So cause we drive a v8 piss poor economy is to be expected right? Not always. Ive had a few people ask how i do it after mentioning it here before. Will take a few replies to fit it all in but here is some basics i do.

    Back when carbs were standard fare a manufacturer didnt just grab a carb off the shelf & plonk it on & call it good. They were tuned in every way to suit that engine & emissions. Most are adept at changing jets for full power fuel mixing. But for most street engines they spend more time on the idle circuit. Which until last few years majority of holleys were fixed not easily adjustable.

    First & foremost. Timing has gotta be right. Trying to tune a big cammed engine with stock 6 deg idle advance aint gonna work.

    Transfer slot has gotta be usually set square on pri side. None showing or very little on secondary is ideal. As vac at cruise rises over idle it will pull harder & make it richer.

    Idle jet. Most holleys are to rich..rich covers up a lot of issues & warranty comebacks.

    First up i measure what its stock at. In the case of this 3310-3 750 vac its at 33 thou. Probably ok for a 400 cuber but not on 302 its on.


    So as its really hard to drill a hole smaller i drill it with a 2.7mm bit to tap for 6/32 set screws.


    Sometimes it leaves a thin sleeve of the original brass insert. One side came out easy..other side was a right mongrel & part wedged up in the drilled channel. Not having a compressor 900psi of nitrous blasted it back out so could use a pick to get it out.

    Then tapped it for 6/32. Good luck finding these set screws in oz cheap. Gotta come from the states


    To be continued
    11 second E85 bottle fed boat anchor

  2. #2
    254RWHP boat anchor EVL253's Avatar
    Join Date
    Nov 2006
    Location
    bathurst
    Posts
    5,125

    Default

    when tapping these holes best to take it slow want the set screws to sit flush. one side i went maybe 1/2 turn to far. dont want to sit down to far obstructing the channel.

    now i do the same to the pv jets. in most instances these will end up bigger than stock but for ease of tuning i drill these out with a 3.5mm drill then tap for 8/32 set screw..6/32 will generally only got mid 50 thou sizing without drilling the hex head out so 8/32 are good. you can do 10/32 but its tight for room. most petrol wont need that big. E85 & methanol will.


    same tap slowly. these 8/32 set screws are 1/8 long so not much. these you need them to sit slightly below flush as when flush wont screw pv in easily as they sit right at edge of thread



    once got it all tapped give the block a blast out & wash out to remove swarf. now comes the tedious part of drilling set screws. zok has these pre drilled for a couple bucks each if you want to go that way as i have before. i got bulk blank brass set screws so gotta drill. i do have a fixture i can screw them into but find this way better. set screw into drill set on reverse. hold drill bit with proper holder or pliers. with these tiny bits gotta be gentle. u will break some.


    bit of vaso works good i find on the bit same for the thread tap. a hole always comes out bigger than the bit so in this case select a bit a thou or 2 smaller than you want.


    to be continued
    11 second E85 bottle fed boat anchor

  3. #3
    254RWHP boat anchor EVL253's Avatar
    Join Date
    Nov 2006
    Location
    bathurst
    Posts
    5,125

    Default

    this carb is for a mate. he knows a little he will be doing most of the tuning with my input when needed. i have already checked the air bleeds in this carb & within a good range so left alone..some of the late model holley stuff like a 650 street hp i did the factory went wild with drill bits & really out to lunch!

    figure holley didnt have powerful ignitions way back when so couldnt choke them up to bad.

    this carb i shrunk the idle feed restrictor from 33 thou down to 28 thou. it doesnt sound like much but if you want to get mathematical the size reduction is lots.
    for now i left pv restrictor at stock 62 thou but needs to go bigger.

    so onto tuning. first up idle mixtures will need readjusting when hot. i usually adjust for best vac then a fraction more.

    on low speed level road cruise say 1500-2000rpm shrink idle feed restrictor down in size till it surges then go back up a thou or 2. the idle circuit feeds idle & transfer slots. ifr controls total fuel. mixture screws trim it again for idle. each change will need idle mixtures reset.

    on highway same again higher rpm say 2500-3000 level road cruise reduce pri main jet down until you get a surge the go up 1 or 2 sizes.

    for purposes of testing this small bit of leanness wont hurt anything.

    now as you have reduced pri main jet at full throttle it will be leaner. in the case of this one the pvcr will need to go out to around .075 to get back to roughly stock fuel flow adding main jet & pvcr together.

    also for part throttle up hills will need need an earlier opening pv like 7.5 8.5 or even 10.5

    need to test with a vacuum guage to see what vac it surges with & adjust pv to suit.

    a pv being open at idle will NOT affect idle fueling. boosters aernt active.

    the mixture screws ended up at 1.5 turns out. from what ive found this usually means cruise mixture is close. no wideband in this falcon.

    a lean mixture at cruuse needs more advance hence vacuum advance. discarding emssions with time spent can get decent economy. on petrol scale i had my 253 on E85 out to 17:1 air fuel ratio on cruise. a 5 thou increase in idle jets no other changes on same trip to orange & back from bathurst used near 10 litres more fuel. that adds up real quick!
    probably left a lot out but its some basics of what can be done to stop that old holley guzzling the juice
    11 second E85 bottle fed boat anchor

  4. #4
    254RWHP boat anchor EVL253's Avatar
    Join Date
    Nov 2006
    Location
    bathurst
    Posts
    5,125

    Default

    so far from what he has told me the idle & cruise is much improved with the reduction in idle jet. pri main jet has gone from 72 to 66 being as lean as itll tolerate at highway speed. it has a flat spot under load up hills. back off or put your foot down a little goes away. a powervalve is not on or off they open gradually. it still needs work in that area.
    11 second E85 bottle fed boat anchor

  5. #5
    254RWHP boat anchor EVL253's Avatar
    Join Date
    Nov 2006
    Location
    bathurst
    Posts
    5,125

    Default

    just for shits n giggles here is the "950" E85 i built for my new baby stroker waiting to be assembled.
    i started off with a chinese carb of that junk brand we aint allowed to mention here. only cause i wanted a cheap main body to learn with. anyone who thinks these are good needs to buy a prius. rough cast boosters on a drunk angle jets n shooters no numbers on em casting flash in venturi sec idle adjuster catching. pure junk! i stripped it completely. knocked boosters out of it. smoothed off casting flash.
    it has custom from the states 24 hole annular boosters..i have the proper booster tool you need to install these. i sized up air bleeds for it. metering blocks are zoks ones off my 650 with my own calibration. fuel bowls as well off my 650. its only black paint for now. if it works good on dyno on stroker in new year ill either get better main body or powdercoat it. this is 750 main body with 850 base so somewhere around 800cfm. even getting throttle blades to sit right in the throttle bores to slow idle enough took several goes & persuasion.
    rolling a turd in glitter & turned a hunk of shit into something presentable. its on the 253 currently..havent spent much time tuning it. enough to drive ok. 253 is a bit hurt so only cruising it for now
    11 second E85 bottle fed boat anchor

  6. #6
    casual poster
    Join Date
    Feb 2013
    Location
    lurking in the shadows
    Posts
    344

    Default

    It's worth noting that the power valve diaphragm hardens over time and can alter the open point and rate due to tension against the spring, not really important on typically rich holleys but gets interesting if it tuned properly for the street.

    Nice writeup, add something about main body restrictors and when they are useful.

  7. #7
    254RWHP boat anchor EVL253's Avatar
    Join Date
    Nov 2006
    Location
    bathurst
    Posts
    5,125

    Default

    yes that is true. all the powervalves i have are used so already hardened but yes will happen if u start with new.
    i havent had to use a transfer slot restrictor yet but from what i know using them in dominators & lots of these newer carbs & billet ones where transfer slot is to wide or long is most common. due to oversize slot cant trim cruise fuel mixture properly
    11 second E85 bottle fed boat anchor

  8. #8
    casual poster
    Join Date
    Mar 2014
    Location
    Vic
    Posts
    370

    Default

    All very good. Good write up.
    Will you tackle emulsion set ups do you think?

    Sent from my SM-G930F using Tapatalk

  9. #9
    254RWHP boat anchor EVL253's Avatar
    Join Date
    Nov 2006
    Location
    bathurst
    Posts
    5,125

    Default

    i have on my own stuff. some good some not. was out of necessity to get rid of that mongrel bog. i managed to band aid it but was never right.
    in the case of this carb & many other old holleys the 2 .026 emulsions they have drilled factory works great to me.
    the 650hp street carb i done the emulsions were 2 .026 but things like hsab was around .040 from memory. changed that to i think .028 from memory. idle feed ended up around .026 on that. tuned it same for falcon 250 6 cylinder that was plenty cranky. owner was wrapped. used stuff all fuel idled full power better than it did stock owner reckons.
    case of tuning for the engine its on. it was borrowed to try on this particular 302. could get it to idle but transition was to lean to work on bigger engine it just surged
    11 second E85 bottle fed boat anchor

  10. #10
    Not the Kingswood! hq308's Avatar
    Join Date
    May 2010
    Location
    The Riff
    Posts
    1,908

    Default

    I havenít played with a carb for a while but when I was tuning my 750 DP I turned up a piece of aluminium and drilled and tapped it to hold a blank screw.


    Which I chuck up in my cordless drill and then I use a drill bit a few thou smaller than what I need in a pin vice to drill the first hole. I drill it by hand afterwards to the correct size.

  11. #11
    casual poster
    Join Date
    Mar 2014
    Location
    Vic
    Posts
    370

    Default

    Quote Originally Posted by hq308 View Post
    I havenít played with a carb for a while but when I was tuning my 750 DP I turned up a piece of aluminium and drilled and tapped it to hold a blank screw.


    Which I chuck up in my cordless drill and then I use a drill bit a few thou smaller than what I need in a pin vice to drill the first hole. I drill it by hand afterwards to the correct size.
    I like that. I have worked all skin off my fingers with the pin vice. Can rarely get spot on. Really need something mounted like that. Or drill press.

    Sent from my SM-G930F using Tapatalk

  12. #12
    254RWHP boat anchor EVL253's Avatar
    Join Date
    Nov 2006
    Location
    bathurst
    Posts
    5,125

    Default

    my pin vise wont hold the tiny bits tight so pliers for me till i get a decent pin vise. tried hand drilling em. got tired of that real quick!
    11 second E85 bottle fed boat anchor

  13. #13
    Part of the furniture
    Join Date
    Oct 2012
    Location
    qld
    Posts
    1,031

    Default

    awesome stuff EVL253..........


    VOTE +1! Smitty to make this a sticky..............
    HOLDENS don't leak oil, they simply mark there territory! like a dog p!ssing on a tree

  14. #14
    casual poster
    Join Date
    Feb 2013
    Location
    lurking in the shadows
    Posts
    344

    Default

    I just drilled and tapped a block of ally to hold the set screws, then used the dremel with the depth attachment to punch the pilot hole, then hand drill to size.

  15. #15
    Do you ever leave?
    Join Date
    Jan 2008
    Location
    Just outside the A.C.T.
    Posts
    1,546

    Default

    Great write up, well done !

    I have been a student of Tuner/Yeti for a while now and have picked up heaps, the idle restriction size and location really makes a difference to street car driveability.

    The other tuning orifice I find that makes a real difference is the siphon break or kill bleed (as the Americans call it !). Delaying the main circuit activation affects cruise AFR, particularly if you have a heap of stall speed and use more throttle opening than you would with less stall.

    I too am amazed by how far out a lot of the new carbs are as delivered.

    As for the pin vice, the best one I have came from Amazon, eBay also supplied a cool little one that fits in a regular chuck but will hold tiny bits.

    I buy the set screws already drilled to 0.025" and drill up from there, eBay again....

    As above, I tapped a chunk of aluminium and use it to support the screw while I drill it.

Page 1 of 5 1234 ... LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Tuning a holley 750 Carby
    By bfhoon in forum Holden V8's
    Replies: 31
    Last Post: 11-02-2017, 12:21 PM
  2. SBC and Holley tuning question
    By Cristian G in forum V8 Boats
    Replies: 15
    Last Post: 28-12-2016, 07:18 AM
  3. Holley tuning
    By vhg304 in forum Holden V8's
    Replies: 0
    Last Post: 06-03-2011, 08:51 PM
  4. Tuning a Holley 600
    By 73Q in forum Holden V8's
    Replies: 7
    Last Post: 24-12-2005, 11:52 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •