Dan Case Student

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  • from Montana
  • Member since Mar 20th 2019
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  • Thanks Dan!

  • Hi Dan,


    If you can spare a few minutes I would like to get your opinion on a carb / intake for my 66 K code. I’m currently running a 4100 clone (didn’t realize what it was when I bought the car), stock engine that was bored 40 over (per the engine guy / previous owner). I’ve stumbled onto a Holley LeMans carb and I’m currently having it rebuilt with the intent of installing it on my car. My question or questions are around this carb and possible manifolds for use with it. 1. Is there a special “way” this carb should be set up to work optimally (jets, secondaries)?

    2. I am also considering a Cobra intake (Blue Thunder) and was curious if this is considered a “good” intake, as well as should the carb be set up any differently than for the original type manifold?

    My car not is not super original, hence the “day 2” type of mods.

    Thanks,

    Damon

    BiffF15@gmail.com

    • BiffF15 3 hours ago



      Hi Dan,


      DC: Hello Damon,



      If you can spare a few minutes I would like to get your opinion on a carb / intake for my 66 K code. I’m currently running a 4100 clone (didn’t realize what it was when I bought the car), stock engine that was bored 40 over (per the engine guy / previous owner). I’ve stumbled onto a Holley LeMans carb and I’m currently having it rebuilt with the intent of installing it on my car.


      DC: Specifically what do you have in a Holley® carburetor. There were at least twelve (12) Ford factory carburetors, and maybe more, that used the “center inlet” racing fuel bowls released in 1963. (The alias “Le Mans” bowls came out after a Ford-Shelby GT40MKII won the Le Mans race in mid 1966. The original factory bowls name was “center inlet” bowls.) There were Ford models between rated between 700 c.f.m. and 850 c.f.m. at sea level. The MUSTANG GT350 carburetors were rated between 700 and 713 c.f.m. depending on the exact version; people call them all “715s”. Chrysler also had some 426 HEMI® racing carburetors that used the center inlet bowls.


      Then there were/are the resissues and reproductions. Reissues started being made in the 1970s by Holley. As far as I know nothing was wrong with them other than they were not made for Ford Motor Company and they are not 100% like originals 1964-67. The reproductions started later and they often, not always, have some serious manufacturing errors that cause problems in use. Just rebuilding a reproduction with poor build quality will not solve the manufacturing problems.


      Then one must be concerned that somebody has modified any used carburetor. That can mean wrong calibrated parts or somebody took drills to orifices they should not have.


      Unless Drew in Georgia is doing the work on the Holley, I would be concerned any engine may suffer performance issues. I occasionally correct freshly “restored” GT350 carburetors for friends after they find operational problems. One is quite serious and only a few people in the world even inspect for it.


      Most individuals and commercial shops do not set them up and adjust any carburetor correctly much less a Ford performance Holley made unit.





      My question or questions are around this carb and possible manifolds for use with it. 1. Is there a special “way” this carb should be set up to work optimally (jets, secondaries)?


      DC: The GT350 carburetors work quite well on any good dual plane intake manifold provided they are not too large for the engine they sit on. The stock cast iron intake and spacer do better than most people realize.


      The secondaries on a GT350 carburetor will never / should never fully open the secondaries on any 289/302 c.i.d. engine. Most individuals and most shops fail right here. (Of course they fail on Ford 4100-A carburetors also.) 1965-66 MUSTANG GT350 could stand opening the secondaries sooner and further (but not all the way) because they had transmissions that allowed rapid engine rpm increases and they had 3.89:1 differential gears. A carburetor tuned perfectly for a 1966 GT350 that gets some aggressive play would be a disappointment to a 1966 Mustang with low number differential gears, maybe 2.80:1 or 3.00:1. 3.50:1 would feel better but still not 3.89:1 or bigger numbers.


      When, how fast, and how far secondaries open is highly tunable. Great carburetor shop knows these things and can better fit tuning to the end use. Before I even think about recommending a carburetor I have to know the engine size, camshaft type (mild to wild), intake manifold, static compression ratio, ignition, full advanced timing, exhaust system, type of car (weight is the real question), transmission type, differential gearing, rear tire diameter, altitude the vehicle will be used most at, type of use (cruising in town 90% of the time or open track car for example) and fuel type.



      2. I am also considering a Cobra intake (Blue Thunder) and was curious if this is considered a “good” intake, as well as should the carb be set up any differently than for the original type manifold?


      DC: I have never used a Blue Thunder® intake. Based on Internet postings most users believe that the cylinder to cylinder distribution is better balanced than any of the many factory COBRA intakes.


      Assume a manual choke carburetor, the normally adjustable details include


      Main fuel jets


      Power valve rating (a.k.a. economy valve)


      Idle air flow (idle speed)


      When secondaries start opening


      How fast secondaries open


      How far secondaries open


      Choke pull down clearance


      Cold fast air flow (fast idle speed)


      Idle air fuel ratio


      Where the primary throttle plates open to; 90° by design but can fall short or go too far.


      Where the secondary throttle plates open to; 90° by design but can fall short or go too far.


      Technically you can change secondary stop position but it should not be changed.



      Genuine carburetor experts can start changing calibrated orifice sizes. This is very tricky and should not be done on a carburetor unless full engineering support and testing is available.



      My car not is not super original, hence the “day 2” type of mods.


      DC: It is hard to beat the factory equipment for great all around performance. Stock does not mean slow or hard to live with. It is far easier to make an engine package’s performance over all go down than up. Great performance is not just one or two parts but all the parts working together. Even brand of ignition points can make or break a car’s performance. (Example: Brand X points start floating around 4,500 rpm while Brand Y points are doing exceptionally well at 9,000 crankshaft rpm.)



      Fuel quality makes a lot of difference. 87 octane E10 engine misfiring at 4,000 rpm or swap in 110 gasoline and run up to 8,000 rpm with no problem.



      Altitude is a big factor most people ignore. For example a 1966 Mustang with 3.20:1 differential and manual transmission might get by with a 600 c.f.m. carburetor between 0 and 700 feet above sea level. A 400 c.f.m. carburetor would be better and the closest Ford units were the 1.08 size 4100-As with an average flow at sea level around 440 c.f.m. at best. If a 600 c.f.m. carburetor did okay at 700 feet the engine would be sluggish, even retuned, at 5,000 feet above sea level. At 5,000 feet above sea level the engine might only get 350ish c.f.m. pulled into it.


      A well tuned 289 engine using a 1.08 size 4100-A will perform better at all altitudes (once tuned) than anything bigger carburetor wise unless it is a seriously hopped up car all over.

    • I forgot to mention but I have read that the Blue Thunder® intakes are aimed at users with significantly modified engines including high flow modern aluminum aftermarket cylinder heads.


      The FORD C9OX prefix intake was intended for users installing 351W cylinder heads on 289/non-Boss 302 short blocks and work best with heads with more flow capacity than modified stock heads. Can be used with modified stock heads.

  • Hi Dan, im also looking for BA & M boosters for my C4OF-AL K carb, if you have any extras contact me jjz109@msn.com thanks. chuck.