holley carb tune info

[grumpyvette]

I usually start at what ever point, (jets/power valves )the carb came with and let the plugs and a/f ratio and an IR temp gun on the headers tell me the necessary changes, if I had to guess Id start with 70 jets and 5.5 pvs front and rear, fuel pressure at 5 psi and set the floats to the bottom of the inspection ports and go from there!

read thru this stuff below while keeping in mind the basic goal is a 13.5-14.5:1 mid rpm cruise a/f ratio and about that same ratio at idle, with about 12.8:1-13.5:1 at wide open throttle, a vacuum gauge and a fuel pressure gauge,(I like to try for 5.0- 5.5 psi on the FP regulator) having your floats set correctly(just damp lower sight hole threads) and your ignition timing correct (all in at about 3200rpm at about 36-38 degrees total advance)and about 6-10 degrees BTDC at 900rpm idle)are mandatory
max power is usually at between 12.4-12.6:1 max mileage is usually at about 15:1
on a street car engine, 14.7:1 is where all the available fuel gets burned
I generally try to get about 13:1-13.5:1 at idle and part throttle, cruise at about 14:1 at 70mph in over drive and have it run at about 12.7-12.8:1 at wot
as a compromise, that gives decent mileage and keeps the plugs clean, that generally requires playing with the power valves and jets in a Holley so that your basically running a bit lean on the jets and having the accelerator pump, and power valves add fuel over most of the carbs flow range if the vacuum drops and have power valves richen the mix during transition, and wot phases
keep in mind this generally requires different jetting and power valves in the front/back
and consistent fuel pressure, and float levels
which a decent fuel pressure regulator and some basic tuning skills will help with.

LETS ASSUME YOU NEED A 4%-6% richer fuel ratio, how do you calculate the correct increased jet size?

I'll take a stab at the math behind this question...

https://www.summitracing.com/search...r=Ascending&keyword=holley air bleed jet sets

https://www.summitracing.com/search...r=Ascending&keyword=holley air bleed jet sets

https://www.summitracing.com/parts/hly-36-181

https://www.summitracing.com/parts/hly-36-201

• First you have to find a chart that lists or measure the hole size in the jets that you are currently running. (EX. Holley 83 jet has a 0.094" diameter hole through it)
• Next divide the diameter by 2 to get the radius. (EX. 0.094/2= 0.047")
• Then find the surface area of that circle SA = pi x r^2 (EX. 3.1415962 x (0.047^2) = 0.00693978 square inches
• Next add the surface area of all the jets in your carb together (EX. for a carb with 83 jets all the way around 0.00693978 x 4 = 0.02775912 square inches. Note if your carb has staggered jets then you would need to find the ratio of the surface area front to back to maintain the same ratio with the new jet size)
• Next take the surface area and add the percent you want to change it (EX. 0.02775912 x 104% = 0.0288694848 square inches)
• Then just work the math backwards at this point (EX. 0.0288694848 / 4 = 0.00721737712 square inches
• 0.00721737712 / pi = 0.00229735801
• square root of 0.00229735801 = 0.0479376269" radius
• 0.0479376269 x 2 = 0.09586152538" diameter
• Round that off to 0.096" and on the chart that falls between an 83 and 84 Jet so you would go up one size in this example to get yourself close.

posting.php?mode=edit&f=44&p=1123

viewtopic.php?f=55&t=1639

http://gottafishcarburetors.com/CFM Formula.html

http://wallaceracing.com/intakecfm.php

http://www.bob2000.com/carb.htm

http://www.mortec.com/carbtip1.htm

http://www.corvettefever.com/techarticl ... index.html

http://www.classictrucks.com/tech/0806c ... index.html

http://bgsoflex.com/holley.html

ID buy TWO of these

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-210230&N=700+4294861568+4294860208+115&autoview=sku

accellerator pump cams
http://store.summitracing.com/partdetai ... toview=sku

http://store.summitracing.com/partdetai ... toview=sku

keep in mind theres lots of small passages that can get clogged and theres several different fuel bowl gaskets, these vary by manufacturer and carb model, so be sure you use the correct gasket on the meter block and fuel bowl, if you leave debris in the fuel bowl or use the wrong gaskets they can block passages and the carb won,t function

AS ALWAYS YOUR GOING TO MISS A TON OF INFO IF YOU SKIP THE SUB LINKS

 

[Grumpy]

as Im sure your aware the best torque will usually be with a ratio of about 12.5:1-13:1 and the most fuel efficient ratio will be closer to 14.7-15:1
carbs react to CHANGES in air flow rates, to change the fuel feed rates so theres always a delayed reaction, EFI generally uses sensors to detect BOTH changes in AIR/FUEL RATIOS in the exhaust and changes in vacuum and airflow rates
carbs generally cover up sudden increases in air flow such as stomping on the throttle to WOT from idle with a long shot of fuel from the accelerator pump and power valves adding extra fuel, neither one is a precisely metered response.
you can tell a good deal about the conditions in an engine if you know the vacuum readings (use a gauge), and know how to read spark plugs
now I use a vacuum gauge a timing light, and an IR temp gun on the headers along with the data from reading the plugs and the a/f ratio sensors, each adds to the indications of whats going on, yes you can achieve a 14.:1 ratio and get the engine to run decently, but in most cases it will tend to run better in the low 13:1 ratio range during transitions and about 14:1-14.7:1 during cruising simply because theres always a tendency to go lean during sudden transitions with most carbs.
Id keep in mind that going rich during rapid transitions is preferred over going lean and getting the a/f ratio stable and predictable at cruise and idle and during mild acceleration like on the freeway,where you'll spend 90% PLUS of your time is far more important than temp swings during throttle changes, or during WOT where running slightly richer, during high load high rpm conditions is preferred simply because it makes better power and has less tendency to run into detonation, especially since you'll spend far less time under those conditions
you won,t know the answer to how well any combo runs until you do some testing and tuning with that combo, but its very likely that it should function well with minor adjustments, if the parts you select match and are properly installed.
for some reason most guys think that, the constant addition of new parts solves most issues, and the truth is that the VAST majority of issues, are due to either mis-matched or improperly installed parts,or lack of tuning experience.
damn few guys ever get their car engines and drive trains functioning at near peak potential performance.

BTW (lots of links and sub links on carb tuning, spark plug reading, etc.)
if you do some searching on the hybridz site,
but heres a bunch

http://www.digitalcorvettes.com/forums/showthread.php?t=77602

BTW use a 190F T-stat and an extra electric fan that comes on at 200F to keep the engine coolant temp stable, try to keep the oil temp in the 215F-220F range if you can,to burn off moisture that can form acids over time in the oil, and the fuel pressure stabile at about 5 PSI,, have no more than 1-1.5 psi of back pressure in the exhaust at WOT, it makes tunning far easier, make sure the ignition timing curve is smooth & consistant, and do a leak/down test and adjust the valves, do a vacuum leak test, check the oil pressure,and fuel filter, to make sure your not working with mechanical problems.
if your tunning an n/a engine and the IR gun shows header temps over 1250F or under about 1100f once its up to temp, youll generally find vacuum leaks, ignition curve problems or a/f ratio problems

before you get crazy chasing some problem your sure is an intermittent fuel delivery issue
(1) Do a compression test!
(2) verify your ignition advance curve, and verify the ignition systems working correctly , the spark plugs are new, properly gaped and the ignition wires in excellent condition visually and with an OHMS meter.
(3) adjust your valves, correctly
(4) carefully verify theres no vacuum leaks, in lines or gaskets
(5)Check the fuel delivery system, WITH A GAUGE, while the engines under real operational inertial loads to verify you have a consistent 5-6 psi at the carburetor inlet port
(6) change out the fuel and air filters, especially if over 3-4 months old
(7) actually check your exhaust back-pressure levels
(8) verify your return style fuel pressure regulator and fuel lines function as intended
(9)verify your using FRESH FUEL WITHOUT MOISTURE OR PARTICULAR CONTAMINANTS
(10) actually look for and read installation instructions and rated flow and pressure limitations on fuel pumps and filters
(11) If ALL of the above are normal, only then start looking at the carburetor, and tuning issues

I think most guys would be amazed at how often, a high flow water separating fuel filter installed near the fuel tank that,s being checked and drained, with the filter medium changed regularly will cure or prevent a good many TUNING ISSUES
http://www.harborfreight.com/38-x-38-ba ... 68213.html

http://www.amazon.com/RACOR-320R-RAC-01 ... m_sbs_sg_2

http://www.amazon.com/Moeller-Separatin ... d_sbs_sg_1

fuel injection usually requires a 40psi plus fuel pressure, the line size and the fuel pressure regulator will have a big effect on your results, theres some threads and calculators above that will help,
generally a 110-150 gph pump and 3/8" / AN#6 lines minimum ,works fine up to about 550- maybe even 575hp, IN A FEW CASES with carbs BUT above that POWER LEVEL Id suggest a 1/2 AN#8 line

I ran accrossed this chart that might prove useful as a rough guide, and don,t forget this thread, and ITS sub-links

http://forums.hybridz.org/showthread.php?t=131390&highlight=plugs

obviously theres a wide variation in quality and most modern cars with EFI use oxygen sensors used in the exhaust of cars to do this type of sensor work and NOTHING ELECTRONIC in nature lasts forever,but the sensors are used to feed constant data on remaining un-burnt oxygen in the exhaust back to the computer controlling the fuel injector pulse duration,yes in some cases its potentially possible to damage the sensors, sensors normally last 3-6 years in service, but in most cases its not critical if properly installed , and not all that expensive or time consuming to replace them on occasion,so its not a big deal to suggest a dash mounted fuel/air ratio gauge be used as a tuning tool on a carburetor equipped engine, there even several BUILD IT YOURSELF F/A RATIO GAUGES

http://www.scirocco.org/tech/misc/afgauge/af.html

http://www.aces.edu/~parmega/efi/temp/wb/guide.html

http://www.autospeed.com.au/cms/A_1716/ ... larArticle

http://www.autospeed.com.au/cms/A_0217/ ... larArticle

http://www.jaycar.com.au/productView.as ... BCATID=347

http://www.eagle-research.com/cms/store ... cer-manual

http://www.youtube.com/watch?v=sS6olf1o ... ure=fvwrel

http://www.youtube.com/watch?v=RizrDvP8 ... re=related

 

[grumpyvette]

BTW if you find the car runs better with the choke partly closed...
the (choke) is used to temporarily richen the f/a ratio, making the engine easier to start on cold conditions, restricting the flow rates , with the choke, typically increases the vacuum signal the venturies see and richens the effective f/a mixture ratio, as it tends to draw more fuel. if your running better with the choke partly closed richening the jets usually tends to solve that.
now obviously the type of jetting and the float settings, adding differant boosters, discharge nozzels,fuel pressure levels, accellerator pump settings,the type of carb, engine size, cam timing or other factors might come into this in some applications



http://www.2carpros.com/how_does_it_work/choke.htm
"Carburetor Choke Operation
A choke is used in conjunction with a carburetor. It is a valve that opens and closes and used to restrict air flow. The restriction enriches the fuel/air mixture to aid in the initial startup of the vehicle. The choke creates a stronger vacuum to pull more fuel from the jets and into the air/fuel mixture. When the engine warms up the choke slowly releases and stays in the wide open position."

http://www.carcraft.com/techarticles/116_0508_carburetor_showdown/index.html

IVE ("wasted" A ton OF CASH GAINING A GREAT DEAL OF EXPERIANCE)
I guess I would not know 1/100th of what I know without having done that though!

 

[grumpyvette]

Id start by checking for vacuum leaks and verifying the timing curve

Id start by dropping or raiseing the fuel pressure to 5.5 lbs and verifying your getting a minimum of a 1/2 gallon a minute unrestricted flow

Id start at all four jets #70

Id install a NEW power valve and ID buy several,if your carb uses them, so I could play/exchange/test


start here, theres no sence in guessing

http://www.themotorbookstore.com/holley ... etors.html

http://www.themotorbookstore.com/motuhocavo2.html

http://www.themotorbookstore.com/holley1.html

http://www.bob2000.com/carb.htm

http://www.mortec.com/carbtip1.htm

http://bgsoflex.com/holley.html

http://store.summitracing.com/partdetai ... toview=sku

http://www.professionalequipment.com/ex ... ermometer/

http://www.centuryperformance.com/vacuum.asp

http://www.carcraft.com/techarticles/carb_tuning/

heres where
a infared non-contact thermometer helps diagnose mixture problems very quickly, but youll need one that reads into the 1400F range for the headers for quick diagnoses

http://www.professionalequipment.com/xq/ASP/ProductID.3461/id.22/subID.177/qx/default.htm

temperature range from -58 to 1832°F

I use this one :grin: (above) and youll need to learn how to read plugs (this may help)

http://www.chevytalk.org/threads/showfla...rue#Post1448415

heres A/F

http://www.rbracing-rsr.com/rsrgauge.htm

http://www.mummbrothers.com/SRF_Stuff/Secrets/Driveline/Air_Fuel.htm

http://www.airfuelmeter.com/english/

http://www.innovatemotorsports.com/products/lm1.php

http://thedynoshop.net/prod01.htm

http://www.dawesdevices.com/airfuelmeter.html

http://fastrides.com/articles/DoItYourself_AirFuelRatio_Gauge.html

http://www.fuelairspark.com/Products/Information/AirFuelMeter.asp

http://www.3barracing.com/product_3.htm


a few places to look for plug/ignition info

http://auto.howstuffworks.com/ignition-system.htm

http://www.ngksparkplugs.com/techinfo/spark_plugs/techtips.asp?nav=31000&country=

http://www.gofastzone.com/techtips/sparkplugs/sparkplugs.htm

http://www.acdelco.com/html/pi_plugs_ident.htm

http://www.autolite.com/framer.cgi?page=http://www.autolite.com/products/racing.htm

http://members.uia.net/pkelley2/sparkplugreading.html

http://www.atlanticjetsports.com/_techtalk/00000005.htm

http://www.strappe.com/plugs.html

http://www.babcox.com/editorial/cm/cm59910.htm

http://www.ngksparkplugs.com/techinfo/spark_plugs/partnumberkey.pdf

http://www.nightrider.com/biketech/spkplghnbook.htm

http://www.tsrsoftware.com/sparkplug.htm

http://www.gnttype.org/techarea/engine/plugs.html

http://www.dansmc.com/sparkplugs1.htm

http://www.ngksparkplugs.com/techinfo/spark_plugs/overviewp2.asp

http://www.pajjakid.com/ubipa/sparkplugs.htm

http://www.edelbrock.com/automotive/sparkplugs.html

http://www.bullittarchive.com/Maintenance/Sparkplugoverview/

http://www.powerarc.com/sparkplug.htm

http://www.carcraft.com/techarticles/64378/

http://www.wakularacing.com/TechnicalInfo.htm

http://www.geocities.com/MotorCity/Flats/3877/spark.html


http://www.rmlautomotive.com/ignition.html

http://www.bgsoflex.com/auto.html

http://ourworld.compuserve.com/homepages/JET_AV8R/Vision/Ignition/CDI.HTML

http://www.howstuffworks.com/ignition-system.htm

http://auto.howstuffworks.com/ignition-system1.htm

http://www.familycar.com/Classroom/ignition.htm

http://www.motocross.com/motoprof/moto/secontent/seign/ignprin/ignprin.htm

http://www.northwestautorepair.com/ignitionsystem.htm

http://www.boyleworks.com/ta400/psp/distcurve.html

http://www.chevytalk.com/tech/index.html


heres other options

http://www.davessmallbodyheis.com/


http://www.msdignition.com/

http://www.proformparts.com/catalog/distributors_GM.html

http://www.atlanticspeed.com/store/MSD Chevrolet Distributors.asp

http://www.holley.com/HiOctn/ProdLine/Products/IS/ISD/ISD.html

http://www.performancedistributors.com/gmdui.htm


Spark plug /ignition info

http://www.edelbrock.com/automotive/sparkplugs.html

http://www.ngksparkplugs.com/apps/car_truck_suv/default.asp?nav=60000&country=US

http://www.strappe.com/plugs.html

http://www.applink.net/cct/tips/plugwires.html


http://www.acdelco.com/html/pi_plugs_ident.htm

http://www.atlanticjetsports.com/_techtalk/00000005.htm

http://www.ngkspark.com.au/spark_plug_cross_ref_chart_index3.htm


http://www.strappe.com/plugs.html

http://www.babcox.com/editorial/cm/cm59910.htm

http://www.ngksparkplugs.com/techinfo/spark_plugs/partnumberkey.pdf

http://www.eric-gorr.com/techarticles/sparkplugs.html

http://www.gnttype.org/techarea/engine/plugs.html


http://www.tsrsoftware.com/sparkplug.htm

http://www.racinghelp.com/read_spark_plugs.html

http://www.ngksparkplugs.com/techinfo/spark_plugs/overviewp2.asp

http://www.gofastzone.com/techtips/Spark...20Reference.htm

http://www.geocities.com/zgarage2001/adv...01/advance.html

http://www.hotrod.com/techarticles/43300...harticles/43300

http://www.centuryperformance.com/vacuum....com/vacuum.asp

http://www.custompistols.com/cars/articl...tion_timing.htm

http://chevyhiperformance.com/howto/4567...com/howto/45673

http://www.lmengines.com/Ignition_Timing...tion_Timing.htm

http://www.73-87.com/garage/hei.htm]http.../garage/hei.htm




http://www.bgsoflex.com/auto.html

OPTISPARK info

http://www.gmhightechperformance.com/tech/0310htp_optispark/

http://www.charm.net/~mchaney/optisprk/optisprk.htm

http://www.fierolt1.com/lt1_95_up_OptiReplace.htm

http://www.noid.org/~muttvette/opti.html

http://www.gulicks.com/vette/projects/opti/index.html

http://www.houston-f-body.org/tech/optispark/


http://www.dynotech-eng.com/dynaspark.htm

http://www.corvetteclinicinc.com

http://www.corvettefever.com/howto/16758

 

[grumpyvette]

are f/a meters useful?

thats a good question for this forum,
Ok Ive got one and have tested several of them.

http://www.modernperformance.com/product_info.php?manufacturers_id=&products_id=1149

http://www.3barracing.com/product_3.htm

http://www.rbracing-rsr.com/rsrgauge.htm

http://www.scirocco.org/tech/misc/afgauge/af.html

http://www.innovatemotorsports.com/products/lm1.php

http://www.autospeed.com/cms/A_0217/article.html?popularArticle

http://thedynoshop.net/prod01.htm

heres my take on them, short answer, they are a big help but a P.I.T.A. to set up and use if your not going to semi permenantly install them on your car.


IVE come to use reading spark plug condition,

http://www.digitalcorvettes.com/forums/showthread.php?t=80783

http://www.digitalcorvettes.com/forums/showthread.php?t=85537&highlight=plugs

use of a good timing light and vacuum gauge , a fuel pressure gauge, to verify your fuel pressure under load, and use of a GOOD HIGH TEMP INFARED THERMOMETER (THIS ONE)

http://www.professionalequipment.co...hermometer-501-ds-42545/infrared-thermometer/

as a very quick to use and accurate set of tools.

OK WHY???

well your main concern when tuning an engine is to keep the all the cylinders running aproximately the same ratio and at about 12.8:1 for max power up to about 14.7:1 for low emmissions and good mileage, AND WHILE A A/F GAUGE IS A GREAT ASSET, ITS EASY TO DAMAGE, AND ITS BEST INSTALLED IN YOUR CAR , NOT USED AS A SHOP TOOL.

so whats the advantage/disadvantages

a fuel air meter uses a o2 sensor, if you place it in the header collector it gives an AVERAGE of all the cylinders on that cylinder head,If theres an (X) installed close to the dual collectors reversion pulses can occasionally even give data from the other side of the engine, so in theory and in practice you can have two cylinders run lean and two rich and the AVERAGE tends to look RICH to the O2 sensor as it SEES unburnt fuel, if you place it in the individual primary header tubes you either need eight O2 sensors (VERY EXPENSIVE, and keeping the wires from burning or grounding outs a TOTAL P.I.T.A......IF you don,t succeed you destroy the O2 sensor and need to replace it.) or you need to be constantly swapping very hot and fragile O2 sensors and bung plugs constantly, but with the IR thermometer you can almost instantly see which cylinders are running hotter or cooler and adjust the jets or look for vacuum leaks, or other CAUSED for the TEMP DIFFERANCE, ETC, far faster too get all the cylinders running at approximately the same temp, indicating the same fuel air ratio, youll be amazed at how close the temp follows the fuel/air ratio, and you can confirm it with plug condition and the other test equipment. run any cylinder too lean and detonation can break rings or melt pistons, run it too rich and you can wash the oil off the cylinder walls and ruin rings/scuff pistons, you need to verify the fuel flow rates and pressure at the carb, or fuel rails the injectors are fed from,and you need to know whats going on in EACH CYLINDER not the AVERAGE of all cylinders.

SO, if your going to install a decent wide band fuel air ratio meter on your car thats fine, its going to be an asset to your tunning skills, if you install the indicator/gauge inside the car and weld in a couple extra bungs in the collectors for tunning and wide band O2 sensors which are a big help, but you will quickly find that its a P.I.T.A. to use it for tune ups on all your buddies cars with the welding collector bungs and installing plugs and O2 sensors while the IR thermometer route is fast and very simple and you can confirm with oplug reading the condition of the engine.

YEAH! theres meters that you can stick in a tail pipe, but they read THE AVERAGE, not the individual cylinders ,
think about AVERAGEs
AS my old physics proffesor once said,
IF, I pour molten lead in your front slacks pockets and pack your butt in solid with DRY ICE,.... ON AVERAGE your comfortable


BTW
http://www.digitalcorvettes.com/forums/showthread.php?t=79676


bits of useful info on these

http://www.thirdgen.org/o2tuning

http://www.thirdgen.org/fuelgauge

http://www.thirdgen.org/tpimod2

http://www.thirdgen.org/injectorswap

http://www.thirdgen.org/coolantbypass

http://www.mummbrothers.com/SRF_Stuff/Secrets/Driveline/Air_Fuel.htm

http://www.ws6.com/mycar.htm

 

[grumpyvette]

--------------------------------------------------------------------------------

HOLLEY and DEMON carbs are generally much easier to tune, trouble shoot and adjust than most of the others, the demon carbs have a small advantage in that they offer more adjustments and finer mettering, now thats a two edge sword, if your a clutz it means your options allow more areas to screw up, but once youve got the basics down , the HOLLEY and DEMON carbs are generally much easier to tune correctly REMEMBER WERE TALKING A STREET STRIP APPLICATION HERE

let me say this, if you can follow dirrections and read plugs and do basic carb adjustments the HOLLEY and DEMON carbs make tunning the engine correctly far easier than something like a carter, quadrajet or edelbrock carb that, has less flexibility ID ALSO POINT OUT
that many "carb" problems are really related too or caused by ignition or cam sellection or intake manifold sellection choices, or matching those parts to the wrong compression ratio, rear gearing, or stall speed

its hardly the carbs fault if you sellect a great holley or demon carb in the 700cfm-850 range and stick it on an engine combo thats basically a collection of mismatched components and then find its difficult to get it running correctly

as an example,
I had a neighbor who constantly played with his classic mustang 390 ford engine, claiming his carb was nearly un-adjustable, I quickly found the problem, his fuel presure was 3 psi , his fuel filter was mostly clogged,and his ignition didn,t advance smoothly, as the rpms increased yet he cussed that carb for months, be fore calling me over to look at his car after swearing to everyone who could hear , his carb sucked!


The Rated Cfm Is Almost Meaningless Between 750cfm-825 -850 Cfm.(the range many performance carbs from HOLLEY and DEMON fall into) The Important Factor Here Is The Ease Of Tunning And The Quality Of The Fuel Metering

but this may help you

http://users.erols.com/srweiss/calcdchg.htm

http://users.erols.com/srweiss/calccarb.htm

http://users.erols.com/srweiss/calcafhp.htm

http://www.rbracing-rsr.com/runnertorquecalc.html

http://www.engr.colostate.edu/~allan...a/effarea.html

http://www.newcovenant.com/speedcraf...runnerarea.htm

http://www.newcovenant.com/speedcrafter/toc.htm

http://victorylibrary.com/mopar/intake-tech-c.htm

http://www.geocities.com/MotorCity/T...92/vizard.html

http://www.bob2000.com/carb.htm

http://www.mortec.com/carbtip1.htm

http://www.rbracing-rsr.com/runnertorquecalc.html

http://www.centuryperformance.com/vacuum.asp

the question usually goes " what size carb do I need," or something similar,
4v carbs are rated at a flow rate determined with a vacume or pressure drop of 1.5" of mercury, your best power AT WIDE OPEN THROTTLE AT MAX RPMS will generally be found with a carb that lowers the presure drop or vacume to between 0.5" and 1.0" of vacume, not 1.5" at full throttle,more vacume at full throttle indicates a slight restriction to flow, now on a street car thats not going to be much if any problem, but on a race cars engine, its a sign that your potentially giving away some potential power.
lets look at your comon 600cfm carb some of you guys use, a 0.5 inches of vacume it flows only about 350cfm, at 1.0" it flows about 500cfm, at 1.5" it flows about 600 cfm , rated like a two barrel at 3.0" of vacume it flows close to 780cfm, and if you stuck it on a 600 cubic inch big block spinning 6000rpm youll pull about 6" of vacume and it would flow about 1000cfm plus!
now remember youll try to stay in the .5" to 1.5" range at full throttle, to make good power.
now some of you might notice that the flow dropped NOTICABLY once the vacume dropped and dropping the vacume at wide open throttle tends to help power, provided the a/f ratio is kept near 12.7-13.0:1,AND the engine is set up to USE the flow available to it.
VOLUMETRIC EFFICIENCY
in theory a cylinder fills to 100% full, but the limited time the valves are open and the ports restrictive flow will only allow that to happen at a narrow rpm range
your engines torque curve on an rpm scale closely mirrors the engines efficincy at filling the cylinders, on that same scale, once the cam timing and port flow become a restriction power falls off because theres less fuel /air mix burnt per power stroke, the power tends to keep going up for alittle further in the rpm band simply because theres MORE ,thou slightly less effective power strokes per minute.
at 1000rpm theres 500 intake strokes per minute thats 8 per second times the intake valve opens and closes, at 6500rpm thats 54 times a second, not much time when you think about what needs to flow thru that port in the limited time....especially if you remember that of that 720 degrees in the cycle only about 240 degrees have any useful flow potential, so you just cut even that time by 2/3rds

some of you may have figgured out that to get the lower vacume or restriction, youll want a larger carb or perhaps two carbs, remember were trying to get that .5"-1.0" of vacume at full throttle, and that 600cfm carb is not going to flow 600cfm, at that vacume reading but between about 350-500cfm, so if you have an engine that can take full advantage of the flow it may, and usually does require a larger carb to make max power,that 383 might require an 800-850cfm carb or two 600 cfm carbs (since you double the venturie cross sectional area with two carbs the vacume reading is generally cut to about 1/2 what it was and the two 600 cfm carbs now flow about 350cfm each or 700cfm per pair) yet the carb size is just NOT all that critical,to making fairly decent (NOT MAXIMUM POWER) simply because as the vacume signal goes up, so does the carbs flow rate, and as the vacume signal strength goes down so does the flow
RESPONCE!
up till now we are talking only FULL THROTTLE POWER, but you operate under a wide range of rpms and loads, put that larger carb on a small engine and it makes good power at wide open throttle, but it also tends to have a weak vacume signal at off idle rpm ranges and it may run like crap! so a ballance must be accepted. smaller carbs are generally more responsive, but slightly more restrictive with thier smaller venturies.

http://www.carcraft.com/techarticles/0304_intake_manifolds_contrast/index.html

http://www.superchevy.com/technical...p_0612_big_block_tunnel_ram_intake/index.html

 

[grumpyvette]

tracking down a MISS/STUMBLE

viewtopic.php?f=70&t=270&p=1289#p1289

viewtopic.php?f=50&t=609&p=1298#p1298

viewtopic.php?f=50&t=821

viewtopic.php?f=50&t=817

viewtopic.php?f=50&t=383

viewtopic.php?f=50&t=268

viewtopic.php?f=50&t=477

viewtopic.php?f=50&t=46


more info

ignition timing thats a bit to retarded will tend to make the plugs run cold and foul, setting your float levels and making 100% sure the linkage functions correctly is mandatory, before you start chasing problems

http://www.barrygrant.com/bgfuel/default.aspx?page=83

http://www.stockcarracing.com/techartic ... index.html

http://www.holley.com/data/TechService/ ... uretor.pdf

unscrew the site plugs and adjust the floats until the fuel level just prevents fuel flow from the site holes at idle, youll need a flat blade screw driver and a 5/8" wrench


QUESTION How do I adjust the fuel level on my carburetor?
ANSWER Setting the fuel level should be the first thing you do before attempting to make any further adjustments.The float level should put the fuel level just below the bottom of sight plug hole. You will make the adjustment with the vehicle on a level surface and the engine idling. You will first remove the sight plug, then to make your adjustment you will need to loosen the lock screw on the needle and seat. This will allow you to turn the adjusting nut to raise or lower the float level. Each hex flat on the nut will change the float level approximately 1/32". When you have the fuel level just below sight plug hole you will then tighten the lock screw and reinstall the sight hole plug. Make sure you have a shop towel handy in case you have any fuel leaks from the Sight plug or needle and seat adjusting nut.

if the fuel level won,t adjust, it
sounds like a needle valve needs replacement, or a carb floats defective

SIMILAR TO THIS

http://www.summitracing.com/parts/HLY-6-513/

http://www.summitracing.com/parts/HLY-6-519-2/

http://www.summitracing.com/parts/HLY-116-10/

sofakingdom POSTED THIS AND I AGREE WITH MOST OF IT
On a Holley, 1 jet size is an imperceptibly small step. 2 jet sizes is a tiny but noticeable step. 3 jet sizes is a standard adjustment. 4-5 jet sizes is a big step.

Look at your primary jets. Whatever size they are, buy some that are 2 sizes, 4 sizes, 5 sizes, and 6 sizes smaller; and 2 sizes larger. You'll be needing them.

First, set the fuel level. If it has sight plugs, set the primary one to where gas dribbles out while the engine is idling, when you just bump the fender; and set the sec one to where you have to jiggle the car pretty good to get it to come out.

Lean the primary jets (using the "step size" description above) until the car just barely starts to surge while cruising (55-60 mph) at a steady speed on a level highway and it starts going up a hill. Ignore all other misbehavior of any kind for the time being. Once you find that point, go back up 2 jet sizes.

Once you get it to do that, look at the primary side power valve. If it's stock, it's probably a 65. Stupid. Raise the value until the flat spot goes away when you're in high gear and driving along at about 35 mph (basically, as slow as you can possibly go in high gear), and you give it gas. It'll take a MUCH higher number power valve.... probably a 105 or a 125. If it starts giving you the burn-your-eyes idle, go back down one step.

When you get that right, set the idle speed right (800 RPM out of gear, say); then get the idle mixture right by turning each pimary idle screw in until the RPM drops, then back it back out 1/8 turn. Shut the motor off, and average the 2 screws (like, if one is 5/8 turn out, and one is 7/8 turn out, set them both to 3/4 turn out), and restart the motor, and check them again. Repeat until they're equal, or until you have determined that they absolutely CANNOT be made equal. In no case should they be more than 1/8 turn different.

Take the carb off, flip it over, and look at the transition slot. You want less than .050" of it exposed below the pri throtle blades. If more of it is exposed than that (it will be), open the sec throttles with their idle screw, 1/8 turn; put the carb back on; re-set the idle speed and mixture; then pop the carb back off and look at it. Repeat until you have between .030" and .050" of the transition slot showing.

At this point, the thing should run like a bat outta hell, on the primaries. The secondaries could be just about anywhere. Put a 65 power valve in them, if they don't already have that; and select jets for max ¼ mile mph.

At that point, you'll have your Holley set up better than about 95% of all other Holley owners. You'll be getting nearly the same gas mileage as you would with a Q-jet, and you'll be making 20% more power than most cars with the same cam & heads, and FI.


its the little stuff that usually hangs up a projects completion, and if your like most guys you tend to change your mind several times during a built, resulting in at least some minor changes in whats required, but thats one reason project usually turn out to be both unique and rather difficult for some guy that was not in on the construction phase to figure out in many cases booth what the builder had in mind or how he accomplished it, and it also tends to show up in some rather innovative and at times pathetically in-adequate engineering..
As an example,
.I especially remember my late friend LARRY having forgotten to purchase or fabricate the correct carburetor linkage on his 1963 chevy with a 409 using a few components, snapped together to form a chain between the carburetor and throttle lever from his tackle box in one case....(A+ on creativity....F- minus on safety) as in about 5 ove these and a spring vs

something like these components below

thoughts guys?
thoughts guys?

 

[grumpyvette]

if your going to do much HOLLEY carb tuning having a jet assortment, and a jet removal tool, and a PV tester and an assortment of POWER VALVES is damn near mandatory

http://www.summitracing.com/parts/sum-g1360/overview/
http://www.summitracing.com/parts/mor-62295/overview/

http://www.mityvac.com/pages/products_hvp.asp

http://www.summitracing.com/parts/hly-36-181

New
.
INDYCARS, did a search and didn't find this info anywhere on the forum. I got the info off the
Pipemax forum. Hope someone finds it useful!

http://maxracesoftware.com/bulletinboard/viewtopic.php?f=64&t=45

The creator of the chart used Plug Gage Set accurate to .0002" to measure the jet diameters.
https://www.mscdirect.com/product/details/86463015

http://www.summitracing.com/parts/hly-26-68