Results 1 to 7 of 7

Thread: IFRs vs LSABs

Hybrid View

Previous Post Previous Post   Next Post Next Post
  1. #1

    Default IFRs vs LSABs

    Hi. I have a blow thru carb with .052 IFRs with no LSABs. Would replacing them with let's say .045 IFRs and .080 LSABs equal close to the same? I just want some adjustability. Thanks.

  2. #2

    Default

    I could be wrong here, but I think you would end up super LEAN at idle and light throttle. By going to a .045 idle feed restriction, you're removing fuel from the idle circuit. Readjust your idle mixture control, but still, a smaller hole will require a little more negative/positive pressure to pull/push the same amount of fuel out. So naturally, this is going to be a leaner situation. Then your going to introduce air into the IDLE circuit, to be mixed with the idle circuit fuel that just got leaner as well.

    What are you trying to accomplish? Think of the two like this: Changing the idle feed restriction is like a very COURSE adjustment. Little change with IFR will cause lots of rich/lean change in the idle/transfer circuit. The air bleeds are for FINE tuning once you get the IFRs close to the what you want. Also the two have opposite effects.

    Bigger IFR = richer
    Bigger air bleed = leaner

    If you're just looking for adjustability to your idle/transfer circuit, you would have to go opposite on IFR. Increase your IFR to .055 or .056, and then try a .050 LSAB. I would rather be rich initially, then too lean. Do you have a wideband AFR gauge to monitor the affects of your changes?

    Are you having a specific problem?
    Last edited by 69cam; 08-07-2014 at 11:19 AM.

  3. #3
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    23,099

    Default

    For the benefit of others reading this:
    IFR = Idle Feed Restriction
    IAB = Idle Air Bleed
    LSAB = Low Speed Air Bleed
    HSAB = High Speed Air Bleed

    http://www.theturboforums.com/thread...6-IFRS-VS-LSAB (Same Thread Here)
    http://www.innovatemotorsports.com/r...FI_mileage.php (Mileage Tuning)
    http://www.innovatemotorsports.com/r...uning-hero.php (Carburetor Tuning)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  4. #4

    Default

    Wow, nice catch there Danny. I naturally just assumed he had a PLUG in the idle air bleed not just a remove the idle air bleed out all together. Any reason you would have removed the idle air bleed? What size is this carburetor?

    If that is the case, and you didn't have an idle air bleed at all, putting in an .080 would richen the idle/transfer circuit up quite a bit. More like a lot. Your going from at least a .187 size hole, down to a .080. The area of the .187 hole is close to 500% bigger than the area of a .080 hole. To figure this our properly you have to do the formula to find the area of a circle on both of those numbers and then that would tell how much your are truly shrinking the LSAB.

    I think you should go back to the "way you got the carb " setting, and work from there.

    If you don't have those. I personally would put in a .070 IAB, and about a .032 - .035 idle feed restrictor. Get it to where your idle mixture screw are about 1 - 1.5 turns out from fully seated. If you find that with an .032 IFR, your idle mixture screws are best set at only a half turn out, then your IFR is too big and will need to go down to maybe a .030 IFR. If you put in a .030, and notice that your idle mixture screw require 2 full turns out or more, then your IFR is to small and will need to be increased.
    Last edited by 69cam; 08-07-2014 at 02:48 PM.

  5. #5
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    23,099

    Default

    Quote Originally Posted by 69cam View Post
    Wow, nice catch there Danny. I naturally just assumed he had a PLUG in the idle air bleed not just a remove the idle air bleed out all together.
    I thought you'd like that.

    To figure this our properly you have to do the formula to find the area of a circle on both of those numbers, and then that would tell how much your are truly shrinking the LSAB.
    http://www.math.com/students/calcula...cle-solver.htm (Circle Calculator - Area Of A Circle)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  6. #6

    Default

    I found an online calculator for area, but I just didn't believe my eyes. It was actually over 500% decrease in area size. I was using a 3/16" hole (without an air bleed) vs an .080" hole. Math was showing the area to be .0274" vs .005". I just wasn't believing it. Ha ha... That's why I didn't post the actual numbers, and only quoted a percentage of decrease.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
About us
Holley has been the undisputed leader in fuel systems for over 100 years. Holley carburetors have powered every NASCAR® Sprint® Cup team and nearly every NHRA® Pro–Stock champion for four decades. Now, Holley EFI is dominating the performance world as well as our products for GM's LS engine. Holley's products also include performance fuel pumps, intake manifolds & engine dress–up products for street performance, race and marine applications. As a single solution, or partnered with products from other Holley companies - Hooker Headers, Flowtech Headers, NOS Nitrous, Weiand, Earl's Performance Plumbing, or Diablosport - Holley products can give you the edge you need over the competition.
Join us