'66 Skylark 300 2bl. change to 4bl.

Discussion in 'Small Block Tech' started by 71route66, Sep 7, 2017.

  1. 71route66

    71route66 New Member

    I have a 300 2 bl. and want to change to a 4 bl. From what I read, I can use a 4bl. intake manifold from 340. The 4 bl. 340 intake manifold I purchased is about 1" wider than the 2 bl. 11.75" vs. 10.75. Everything else looks the same. Not sure if getting two new 340 heads will allow it to fit the 300 block. Has anyone successfully tried this? If so, does anyone have a set of 340 heads for sale?
     
  2. alec296

    alec296 i need another buick

    No you can not use a 340 intake manifold. Even with 340 heads. It's a taller block. Only a 300 intake will fit and a 4 barrel intake for 300 is rare
     
  3. Gulfgears

    Gulfgears Gulfgears

    Nope, not gonna work.
    You need a 300 specific manifold. Your choices are the aluminum version or the one year only cast iron 65 model.
    The 340 is much larger and I've never heard of anybody modifying one to fit a 300.
    I believe the 340 and 300 heads are the same, but the 340 is a larger, wider block.
    I could be all wet here, but I believe this is good information.
    A good cast iron 300 four manifold can set you back north of $300.00, so be prepared.
    Spend your money on a good, razor sharp tuneup, make sure your transmission is working properly (two stage torque converter).
    Better outlay would be to get a lower rear end ratio to bring it alive.
     
    300sbb_overkill likes this.
  4. 67skylark27

    67skylark27 Brett Jaloszynski

    Completely agree with Gulfgears. The 300 and the 340 share heads but not intakes. 300 4bbl
    intakes are rare but some come around occasionally. Minumum gains to be had with that swap,
    mainly chewing through more fuel. The 300 2bbl I started with really perked up with
    the 2004r swap but then needed rear gears. You can gain a lot of snap by swapping
    out rear gears. I updated my engine to a 340-4,2004r then 3:36 posi gears-great combo.
    The 300-2,2004r and 3:55's would be a great combo also.
     
    300sbb_overkill likes this.
  5. philbquick

    philbquick Founders Club Member

    There are 2 4 barrel intakes for the 300, the 64 only aluminum and the 65 only cast iron. The ports are smaller on the aluminum and I'm not sure there's enough material to port match it to the cast iron heads so watch out for that. 66 and 67 300s did not have a 4 barrel option although the 65 manifold bolts on with no problem.

    I have has several cars with 300 2 barrels and I've been happy with them. A few months ago someone posted data saying that a 2 barrel with single exhaust has more torque from idle to 3,000 rpm than a 4 barrel with dual exhaust. From 3,500 rpm and above the 4 barrel wins but you normally drive in the idle to 3,000 range. Try putting a curve kit in the distributor, it the best $20 you'll ever spend, it will really wake-up your engine.
     
  6. James66Skylark

    James66Skylark Well-Known Member


    I'd gladly pay $300.00 for one. I found one in California and the guy wanted $750 for it.

    A friends dad who builds cars and races (non-pro) suggested a good 2bbl Holley 500 or 550. He said that wouldn't be as good as a 4bbl but it would be close.
     
  7. James66Skylark

    James66Skylark Well-Known Member


    I have a stock 66 300 with 2 bbl and stock 2;79 gears. When I drive it feel like the engine wants to go but the gears are holding it back if you get what I'm saying. I'm planning on doing the gears first, then if I still want more I'll do the tranny swap.
     
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  8. James66Skylark

    James66Skylark Well-Known Member

    Any idea where to buy a curve kit? I googled it but all I'm getting is links to ebay for an entire HEI distributor or a vacuum advance.
     
  9. alec296

    alec296 i need another buick

    Summit racing or jegs will have the recurve kit. I just got one myself with a Mallory point conversion kit.
     
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  10. FJM568

    FJM568 Well-Known Member

    I've ran the 64 aluminum intake on my 66 for years before something in the rotating assembly let go and poked a pinhole in my oilpan. Went to a 455 after that. Can someone say exactly what and why you "can't" run that intake on the cast iron block/headed motor? All I keep hearing over the years is you can't, when I did. I didn't have coolant in the oil or oil in the coolant. The only thing different I had to do was run one of the heater core hoses to the rear port of the intake, which was the only difference I noticed going from the 2bbl to the 4bbl. Was there a port mismatch? Probably. Did it keep the motor from running, not a bit. Maybe it didn't run as well as it could've, but it ran a helluva lot better with it than it did with the 2bbl. If that is the reason people keep saying you can't run the intake, then it's a pretty poor reason sending people on a wild goose chase to find a rare, one year only cast iron 4bbl intake, when the 64 aluminum 4bbl intake worked, in my case.

    I put a Carter AFB 500cfm on it and it woke that motor up.

    As a matter of fact, that intake is still on that motor in my garage. Never disassembled it after it came apart internally. That motor had good vacuum and flat out ran good with that intake/carb on it. Bought that intake from Dave Johnson from NW Buick Performance out of Bellingham, WA back in the late 80s-early 90s.
     
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  11. James66Skylark

    James66Skylark Well-Known Member

  12. alec296

    alec296 i need another buick

    Yes. Should work fine.
     
  13. James66Skylark

    James66Skylark Well-Known Member

    Ok thanks. I might try to install myself, even thou I've never done it before. Will I need anything else? Thanks.
     
  14. alec296

    alec296 i need another buick

    Timing light with a dial back .
     
    James66Skylark likes this.
  15. wkillgs

    wkillgs Gold Level Contributor

    I'm one of the few that have done it, and have been spreading the word that it's possible for years!
    Did it almost 20 years ago, bought the alum intake for $35. Opened up the intake ports to match, or almost match the heads.
    The iron intake is heated by exhaust gas, alum is heated by coolant. The exhaust heat port in the head is blocked off by the intake flange. I sorta recall plugging it with a freeze plug or something but could be mistaken. The 64 intake gasket is different than the 65. Only one of them will work....don't recall which one tho.
    Best mod I did to the car was to take out the 2 speed auto and put in a 5 speed manual! Fun car to drive!
     
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  16. wkillgs

    wkillgs Gold Level Contributor

  17. James66Skylark

    James66Skylark Well-Known Member

  18. FJM568

    FJM568 Well-Known Member

    I just used the gasket for the 66 300. I didn't plug any holes or anything like that.

    There was no internet back then to get info on these swaps. You just did them. Over the years, when the 4 bbl swap came up, and a few keep saying you can't run the aluminum intake, and I've brought up that it's been done, those same few kept repeating to find the cast iron intake over and over. I just quit responding to those threads. Nobody wanted to listen. Plain and simple, it does work.

    The price may have just dropped on the cast iron intake now, and maybe went up some on the aluminum intakes. :rolleyes: :D
     
    300sbb_overkill likes this.
  19. philbquick

    philbquick Founders Club Member

    It's kinda funny that there's 2 threads going now, one putting aluminum heads on cast iron manifold, the other putting aluminum manifold on cast iron heads. It will work with or without port matching but it's much better if you match the ports since there there would be a 1/8"step on all 4 sides of the port, and of course, use the 65/6/7 gaskets. Also, the 300 aluminum heads have smaller valves, the 215 aluminum heads valves are even smaller.
     
  20. Dan Jones

    Dan Jones Well-Known Member

    I've got a near perfect 1964 Buick 300 aluminum 4 barrel intake manifold that I'd sell for $325 if anyone is interested. I probably have the matching Rochester 4GC carb too. Also have several sets for aluminum Buick 300 heads including cores needing rebuilt, stock rebuilt heads and professionally ported heads with larger stainless steel valves, new seats, guides, flow sheets, etc.

    Dan Jones
     

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