Cobra Intake and Holley 715 Carb Worth It?

  • Hi all,

    I was wondering about everyone's thought on doing what Shelby did for extra horsepower on a K code non GT350.

    I have been thinking about buying a reproduction Cobra aluminum intake and Holley 715 setup but for $1600 or so I don't know if it is justified for the modest horsepower gains.

    I do not have a trailer queen so being perfectly concourse correct is not super important but I am limiting my upgrades to items that were available in the 60's.

  • You will definitely receive differing opinions on this subject. Having done this same upgrade in the past, I did not experience any large gain. Keep in mind that another part of the upgrade on 65 and 66 Shelbys were the Tri-Y headers. I did not add those.

    -Fred-

    65 Koupe early San Jose Phoenician Yellow 4 speed
    66 GT Koupe Dearborn Blue 4 speed
    66 KGT San Jose fastback pony interior Silver Frost 4 speed
    64 Falcon sedan delivery 289 4 speed
    65 Ranchero 289 4 speed
    66 Corvette roadster 427/425 4 speed

  • I have the Shelby manifold S2MS 9424A with a Holley 4777 (650) manual choke, and FPA Tri-Y headers.

    I have the 4100 carb too but I’ve only owned the car a few weeks now so haven’t had the 4100 on it to compare.

    I do have a dyno sheet with this set-up if you’re interested.

    65 Koupe

  • You will definitely receive differing opinions on this subject. Having done this same upgrade in the past, I did not experience any large gain. Keep in mind that another part of the upgrade on 65 and 66 Shelbys were the Tri-Y headers. I did not add those.

    -Fred-

    +1 Fred


    Some comments.

    - I will add to Fred's MUSTANG GT350 comments. The 1965 cars also used straight through very low restriction glass pack mufflers and for most states very short side out exhaust pipes for free exhaust flow.


    - Larger volume intake manifold and larger volume carburetor normally means a little more sluggish low end while pushing the engine's power band up to a higher rpm range. Shelby American assumed buyers were competition minded and assumed they would be running up to 6,500 rpm frequently.


    - For testing Shelby American had super premium, usually highly leaded, fuels that users could also get somewhere close to where they lived. Their highest numbers used in advertising were obtained using special leaded race fuel, no alternator, no air cleaner, dynamometer room headers, and BF603 (very cold) racing spark plugs. If your engine block decks or cylinder head decks have ever been milled the static compression ratio went up unless something was done with pistons or head gaskets to prevent the increase and higher pressures make fuel choice more important.


    - Shelby American normally, based on their engine test reports, used a total ignition advance of 36°. Some users now find that too high these days; goes back to fuels available. Every engine, exhaust, and vehicle system is different and so are driving requirements and styles so one setting may not suit everybody.


    - The Ford 4100-A carburetors are generally regarded, some will disagree, the best 4V carburetor ever produced. Being a smaller carburetor than the GT350 one the velocity of air and then air/fuel mix will be faster and that is a good situation all around especially in the low and mid range. How many times does one run 5,500 rpm and above these days and for how long?


    There are lots of pros and cons about going to an aftermarket larger volume induction system. The whole topic is way too long to cover in little text boxes in forums.

    Dan

  • Thanks all for the comments. It is becoming apparent that the stock setup is the best bang for my buck in this case.

    The car runs nice and has adequate acceleration I guess. I am able to get a 6.5 s quarter mile and 14.7 s 1/4 mile on the street. Maybe I am expecting too much.

    I guess I could build a different engine with aluminum heads that flow better, a camshaft to match, a better flowing intake and carb, and exhaust system to really optimize the SBF.

    At that point though it would lose some of its 60’s authenticity and feel which is more important for me with this car.

  • Part of the original post was that it was going to cost him $1,600 and whether that justified the modest horsepower gain. Yes, it would run fine with a 4 speed but would probably not be justified for the expense involved.

    -Fred-

    65 Koupe early San Jose Phoenician Yellow 4 speed
    66 GT Koupe Dearborn Blue 4 speed
    66 KGT San Jose fastback pony interior Silver Frost 4 speed
    64 Falcon sedan delivery 289 4 speed
    65 Ranchero 289 4 speed
    66 Corvette roadster 427/425 4 speed

  • I have just done this modification to my Kar, just for the cool factor and being period correct, Cobra Pan from Branda, manifold is a genuine Offenhauser Cobra Hirise I sold to a mate 25 years ago, He agreed to sell it back to me as long as it went on my Kar , just had it Vapour blasted to clean it up and the carb is 69 date coded 3259 , 715cfm20210827_152853.jpg20220423_085552.jpg20220423_085624.jpg20220423_085710.jpg service replacement restored by Tom Zeman in East Islip. after bolting the carb on started it up,settled into a nice idle , only minor adjustment needed and happy to say was impressed how it runs noticeable improvement and pulls hard

    Edited 3 times, last by k kode (April 24, 2022 at 7:31 PM).

  • It sounds like everything worked out well for you and I am happy for you. This setup works well on 4 speed cars like yours.

    -Fred-

    65 Koupe early San Jose Phoenician Yellow 4 speed
    66 GT Koupe Dearborn Blue 4 speed
    66 KGT San Jose fastback pony interior Silver Frost 4 speed
    64 Falcon sedan delivery 289 4 speed
    65 Ranchero 289 4 speed
    66 Corvette roadster 427/425 4 speed

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