Flathead Tuning & Maintenance

This web page is about restoring/resto-rodding a 1950 Ford F-1 pickup, and is one of a series of articles documenting the project. I am providing this in the hope that it is helpful to fellow Ford truck owners, but beware that there are many ways to accomplish the same goals... I have only shown one way. Also, keep in mind, that my comments are specific to this year, make and model, and should not be generalized. Feel free to drop me a line if you see mistakes or need more information, but please understand if it takes me a while to respond. To go back to the main project page click here.

This page is under construction, please try back later.

General

This article is about Flathead V8 tuning and maintenance. I created it mainly for my own reference purposes; I am sure some people will disagree with what is shown here, but it works for me. You are welcome to send advice and comments by sending me an email. Please keep in mind the part numbers and specs show here are specific to the equipment I used; I have tried to carefully identify items that are specific to the options I chose.

Tuning

Carburetor

Applies to: Holley 390 CFM, Vacuum Secondaries, Electric Choke, #0-8007.

For more information, see:

CARBURETOR SETTINGS SUMMARY
ITEM FACTORY SETTING MY SETTING NOTES
Altitude, above MSL Sea Level 4000 ft MSL = Mean Sea Level
Idle Speed - 650 RPM Throttle solenoid maintains idle speed when AC clutch engaged.
Main Jets 51 49 Hesitation started w/ Jet 47.
Power Valve 65 75? 15" vacuum at idle. For part number, prepend "125-".
Secondary Diaphragm Spring ? TBD -

Idle Adjustments

Idle mixture is set by adjusting the idle mixture screws to achieve the highest manifold vacuum. If you do not have a vacuum gauge, set the mixture using a tachometer to acheive the highest idle speed.
Once the idle mixture is set, its time to set the idle speed. Flatheads sound great at idle, and the slower the idle, the better they sound. In my case, I have lots of oil pressure, so I could safely set the idle very low, but I run an electric fan, fuel pump, and air conditioning, and the alternator needs about 650 rpm to work, so that's where the idle is set.

Jetting

This engine operates at 4000 ft MSL in a low humidity environment. The carburetor comes tuned for sea level operation, with #51 jets. Many people in the Forums report this is good jetting for sea level. At 4000 ft, this is a little rich. The generic recommendation from Holley is to reduce 1 jet size per 2000 ft above sea level. The Hot Rodder's rule is down jet 1 size, drive it, and if there is no hesitation (like when switching gears), down jet again. Once there is a hesitation, increase 2 jet sizes and you're done. In my case, the hesitation started at jet 47, so I increased to Jet 49, which also matches the Holley recommendation.

Power Valve

Holley ships most carbs with the single-stage, standard flow, power valve #65. The power valve number is stamped on the face of the power valve; divide the number by 10 and that's when the power valve starts to open. A "65" power valve means it starts to open at 6.5 inches of vacuum. The generic recommendation is to use a power valve that is half the value of your idle vacuum. The engine should be thoroughly warmed up, and in gear for an automatic transmission. Race engines with long duration cams and low manifold vacuum can use a power valve 1-2 sizes smaller than idle vacuum. Holley also makes "high flow" power valves for highly modified engines, and two-stage power valves for the economy minded.

Single-stage standard flow power valves part numbers are 125-[size], e.g. 125-65 is the part number for the 6.5" power valve.

Carburetor Notes

1. You cannot use the factory distributor with a Holley carb. The factory distributor requires venturi vacuum to operate the vacuum brake (often confused for a vacuum advance). Holley does not provide a venturi vacuum port!
2. On Holley carbs, the metering jets are not used at idle. Do not change jet sizes for idle problems; adjust the idle mixture screws.

Secondary Diaphragm Spring

TBD. Holley Recommendation.

Ignition

Distributor

Applies to: Mallory Dual Point #2527501

I am using the Mallory #2527501, which is a dual-point distributor with female socket cap terminals. It has mechanical advance but no vacuum advance. The coil is from NAPA and has an internal ballast resistor (P/N IC-14 or IC-64).


DISTRIBUTOR SETTINGS SUMMARY
ITEM FACTORY SETTING MY SETTING NOTES
Timing 2° BTDC Same -
Point Gap .022 nomimal Same -
Dwell 26° [S]
33±2° [T] 		33° [T] [S] = 1 point set connected.
[T] = total, both points connected.

DISTRIBUTOR PARTS
ITEM STD P/N OPT P/N NOTES
Cap & Rotor Kit 2091M - -
Points 25042 25042X Opt. P/N is heavy duty
Points & Condensor Kit 29320 - Standard Points
Cap Retention Hardware Kits 29318 - Female socket style dist
Advance Spring Kit 29014 Purlple and Grey springs, 18° limit Factory advance limit is 16°.

Electronic Ignition Conversion

Electronic ignition is also available. You can convert the dual point to electronic ignition, or buy a Unilite distributor (#3727501) or a magnetic pickup distributor (#5027501). If you want vacuum advance, look for the MSD ready-to-run distributor (#8573).

December 2011: After suffering 2 condensor failures in less than a month, I converted to electronic ignition using the Pertronix Ignitor III ignition module and coil. This kit is easier to install than the Mallory E-Spark kit (which requires removing the points cam). It is a magnetic pickup module that uses the points cam as the trigger. It requires no modification of the distributor, so you can convert back to points at any time (like carrying them as a spare). Furthermore, the Ignitor III kit has a built-in rev limiter, adaptive dwell, and (in my opionion) Pertronix has a better reputation for reliability than Mallory's Unilite-derived systems. Use the Pertronix Flame Thrower III coil with the Igniitor III module.

ELECTRONIC IGNITION CONVERSION KITS
BRAND MODEL MODULE PART NO. PICKUP TYPE COIL NOTES
Mallory E-Spark 61004M Optical Mallory 29219 Requires removal of points cam.
Pertronix Ignitor ML-181 Optical Flame Thrower or Factory Use with 3.0Ω resistance coil, or ballast resistor. Do not use "high energy" coil with this module.
Pertronix Ignitor II 9ML-181 Optical Flame Thrower II or Flame Thrower III. Uses hotter coil than Ignitor.
Pertronix Ignitor III 7ML-181 Magnetic Flame Thrower III #44001 Multiple spark module. Built-in rev limiter. Use low resistance coil. Uses points cam for trigger.

Timing

Flatheads do not run much initial timing. The factory recommendation for the 8BA is 2° BTDC. Flatheads are internally balanced, so there is no harmonic balancer. A single timing mark, a dimple, is on the crank drive pulley. This mark identifies the factory recommended timing. Aftermarket pulleys are available with timing scales if you are interested.

Maintenance

Oil, Filters and Fluids

OIL, FILTERS AND FLUIDS
ITEM PREFERRED ALTERNATES NOTES
Motor Oil Joe Gibbs HR-1 15W50 Conventional
  • Valvoline Specialty Racing Oil ("Not Street Legal")
  • Amsoil Z-Rod 20W50 #ZRFQT-EA
    		• Zinc Levels
  • Joe Gibbs HR-1: .127%
  • Valvoline NSL: .14%
  • Amsoil Z-Rod: ?
    • Oil Filter NAPA 1515
  • Motorcraft FL-1A
  • Fram PH-8A
    		• Purolator makes Motorcraft filter. Wix makes NAPA filters. More info
    Transmission Fluid MTL - For Borg Warner T-5 NWC!
    Coolant (Antifreeze) Dexcool - Dexcool is supposed to be good for dissimilar metals.
    Coolant Additive AMSOIL Dominator Coolant Boost - Lowers surface tension of water, improves cooling. Buy
    Fuel Prefilter Spectre 6931 - Inline filter before pump. Available at Pep Boys.
    Fuel Filter Summit SUM-G1501-SK - Cartridge type.

    Ignition

    Spark Plugs

    Flatheads came with non-resistor spark plugs with a 7/16" reach. Unless you are running fancy electronics, meaning computers or ECUs (perhaps for fuel injection), you probably want to stick with non-resistor plugs, however, they may cause a "whine" in the radio. I don't even think the MSD or Mallory ready-to-run electronic ignition systems call for resistor plugs; drop me a note if you know otherwise. Resistor plugs reduce electromagnetic interference, and are therefore needed if computers are in use, but they also reduce spark intensity, so don't use them unless you really need to. Early flatheads used different plugs than described here.

    SPARK PLUG SPECIFICATION - LATE FLATHEAD
    NOTES
    Type Non-resistor -
    Reach 7/16" *Some* alum. heads: 1/2"
    Thread 14mm -
    Seat Gasket -


    Proper spark plug gap depends on many things. In factory condition with a 6V electrical system, the gap must be kept small because the spark energy is low. The larger the plug gap, the more voltage is needed to drive the spark across the gap, hence a higher output coil is needed. Higher compression also requires more voltage. The leaner the fuel mixture, the wider the plug gap needs to be for proper flame initiation. In general, the spark plug gap should be as large as possible without causing a misfire, because fuel mixtures are a little leaner at the cruise condition. Most rebuilt flatheads converted to 12V can easily run a .035 plug gap; with electronic ignition perhaps even .045.

    SPARK PLUG GAP (INCHES)
    CONDITION GAP (INCH) NOTES
    Factory, 6V .025 - .028 From Operators Manual.
    Converted to 12V .035 - .045 With standard coil. I run .040.
    Electronic Ignition ~ .045 High output coil.


    If you have aluminum heads, always use anti-sieze on the spark plug threads!

    Many people complain that Champion plugs do not last - they foul easily; most recommend NGK or Autolite. I have had good experience with both NGK and Autolite. I run the "Hotter" heat range.

    The table below applies to later flatheads. You can also use this link to cross reference almost any plug, but be careful, most cross-references will find any plug that fits, without regard to heat range and whether its resistor or non-resistor.

    SPARK PLUG CROSS-REFERENCE
    BRAND NORMAL PLUG HOTTER PLUG NOTES
    Autolite 216 437 Heat Ranges
  • 216: A8
  • 437: C8
    • NGK B6L B4L
    B5HS*     		NGK numbers are backwards, lower is hotter. *B5HS is a longer (1/2") plug for use with alum. heads and has a heat range between B4L and B6L.
    Champion H8C (587) H10C (844) Not recommended
    Motorcraft ATL4 AL7C Unverified!
    AC Delco C43L M44L Unverified!
    Splitfire - SM021F Unverified!
    Accel 166 168 Unverified!


    Last Updated: Saturday January 07, 2012 Valid HTML 4.01 Transitional Powered by Powered by Sun