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Thread: 1966 Buick Riviera GS : Wrong engine and carb ?

  1. #1
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    1966 Buick Riviera GS : Wrong engine and carb ?

    Hi , i live in France and i own a 1966 Buick Riviera GS , an export model sold new in France .
    After conducting research it seems that the original engine was replaced by another. Indeed one would have 425 MW code, or my engine code for MR , which specifies a 400 CI.
    Furthermore the carburetor should be a Q-Jet was replaced with a Carter AFB whose identification number ( 3923S ) , indicates that it was intended for 425 of 1965 ; but the air cleaner is a chrome plated one , wich came with the 66' Riviera Gs .
    I have no way of knowing if my engine is a 425 or 400, but I want to know the size of the carburetor i own (cfm) , if it is appropriate for a 400 CI , and if not, what type or size of carburetor replaced.
    If my engine would still be a 425 CI, what was the type of
    Q-Jet used with engines coded MW , or what was the type of Carter AFB carburetors used in mountings in 2x4BBL , on coded engine MZ ?
    Thank your for your help . Bertrand .

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    Is it a nailhead? The nailhead sizes are 401 and 425. Do you mean 401? If you mean 400, the 400 looks differnt and came around in 67 i dont know if this could be swaped in or what? Someone with more info will help you out more.
    Last edited by 30coupe1; 08-25-2009 at 04:55 PM.
    1930 ford 5 window coupe (401 Buick Nailhead)
    t5 trans

    1963 Buick Riviera (425 Nailhead)

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    The Q jet is very versatile and what would fit the 425 would also run fine on the 401

    There is a Buick carb list in the reference section here:
    http://www.teambuick.com/forums/view...uretor_numbers

    The '66 401 should have a 4GC on it, the 425 a 4 MC as shown in the shop manual:

    http://www.teambuick.com/reference/l...chassis/60.php


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    Hi , thank you for you answers , yesi think my engine is a Nailhead , because : 1 The buick engine identification chart gives for the code MR : a 1966 V8 400 ( known as Nailhead ) and GS 401 .
    The engine number chart says the MR code can be found also on a 400 CI 325 HP on Skylark Gran Sport with a 4BC carb .

    2 The engine code and the engine serial number are stamped on a machined surface located on the front side of the valley pan , behind the water manifold ; wich indicates a Nailhead ;

    The number of my carburetor :3923S , indicates a 63 - 65 425CI.

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    1n 1966, there was a production 400 cid nailhead. However, it had the exact same bore and stroke as the 401. In order to meet GM's mandate of 1966 that no intermediate sized GM vehicle could have an engine over 400 cubic inches, Buick just changed the numbers on paper to be a 400.

    There were quite a variety of nailheads produced in 1966.

    MR - "400" (Same as MT)
    MS - "400" but with 11:1 compression ratio rather than 10.25
    MU - "400" with a Q-jet carb
    All of the above were fitted in the Skylark series

    MT - 401 Carter AFB 4bbl, 10.25:1 compression
    MY - 401 Carter AFB 4bbl, 8.75:1 low compression - Export
    MW- 425 Rochester Q-jet, 10.25:1 compression - std. Riviera engine
    MZ - 425 Dual Carter AFB's, 10.25:1 compression - late production

    This is from from Dealer letter #66-106A sent to all dealers on March 18, 1966. It was issued to "...include engine with prefix "MS" to the 1966 engine usage.

    It's very simple to tell a "400" nailhead from a Big Block 400. The nailhead "400" has the distributor on the back of the engine, the BB 400 has it on the front. Starters on nailheads are on the drivers side, BB 400/430/455 have the starters on the passenger side.

    The Buick Service Manual for 1966 shows both Carter AFB and Rochester 4GC applications for "400"/401's.

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    Hi Nailheadnut , thank you for your reply , it confirms that my engine is a "nailhead" , because the distributor is on the back iof the engine !
    I wonder what the original carburetor on my car, because in an article published on the Net, see the website "Hemmings.Com" he says, "The dual four-barrel, 600cfm Carter AFB carburetor setup that Had been part of the 1965 GS package Became a factory option in March of 1966 and just 179 of these cars were MZ code produced "
    This leads me to wonder Thequestion following: "knowing that my car was registered for the first time on 27.12.1965, and it is a" 1966 Buick Riviera GS ", it is possible whether exit off the assembly with the pack 2x4BBl? "

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    Bertrand,

    With the GS option in '66 (remember, GS was an option just like air condtioning), the only engine offered originally in '66 was the 425cid (code MW) with a single Quadrajet carburetor. If the GS option was ordered, the standard black air cleaner was replaced with a large single snorkel chrome "pancake" air cleaner and the stamped steel valve covers were replaced with the finned aluminum valve covers with "Buick" in raised letters. If the buyer wanted the dual 4 bbl option it could be ordered from the dealer, but the engine would still have the "MW" code. If you orderd the 2x4 option, it was shipped in the trunk of the car and installed at the dealership. Starting in March of '66 the dual 4 bbl setup was available installed at the factory. If it was ordered that way, the engine was stamped with an "MZ" code. (MX was used on a 340 engine in '66.) As you said, only 179 Rivieras were ordered with the "MZ" code, but no one knows how many 2x4 setups were dealer installed on the early models. The vast majority of '66 GS's are Q-jet equipped cars. The transmission was the same as the modified option offered in 1965, with a "BS" code on the I.D. plate (firmer shifts and higher shift points.) All 66 GS models had a positive traction differential and heavy-duty suspension (spring rates and shock ratings.) The 3.42:1 axle ratio was once again standard on the GS cars. Buyers of the '66 GS had the choice of either white wall or red line 8:45x15-2 ply tires with a 4-ply rating. Starting in '66, the faster steering ratio was now a separate option (C-5) with a 15:1 ratio, and available at extra cost.

    From your description, it sounds to me like you have a true 1966 Riviera GS, but somewhere along the way, the engine may have been swapped. I say "may have been" because not much is known about what engine option was put into exported Rivieras. Another thing you should look for is the VIN number on your block. It's on the same surface as the engine code, but on the driver's side. Who knows, the export engine for '66 might have been the MR 401, rather than the MW 425. Is your speedometer calibrated in miles or kilometers per hour? What engine designation is on your air cleaner, Wildcat 445 or Wildcat 465? Your findings on the VIN will tell you a lot about what you have. Elsewhere on this site you can find the SHOP link. Scroll down in that link and you'll find some additonal information and illustrations on where to locate the engine code and the VIN on the nailhead.

    The Rochester Quadrajet carb (750 cfm) used on the 425 in '66 was a model 4MC, number 7026240 (unless it was a California car, then the number was 7036240.) There is an abundant amount of information on the internet to help you ID your carburetor by its number. The number is roll stamped vertically on the rear driver's side of the carb body. The Quadrajet is not too big of a carb for your 401. It was used by GM for many years on cars with much smaller engines (I had an '84 El Camino, 305 cid with a Q-jet) Q-jets are an "on demand" carburetors and will only give you the gas you need. Fuel delivery is controlled by a stepped metering rod that is positioned by engine vacuum. You floor the accelerator pedal and no gas is delivered until the vacuum signal moves the stepped metering rod. In most peoples' opinions, the Q-jet will out perform the 2x4 setup in all aspects except at top end, then the additional cfm's from the two four barrels (1250 = 625 X2) will give a better top end. A friend of mine in Denver, Colorado has two '66 GS's. One is a dealer installed 2x4 car, the other is a Q-jet car. The car with the Q-jet runs faster and quicker in the quarter mile, but the 2x4 car will top out faster out on the highway.

    Keep us posted as to what else you find.

    Ed

    PS Here's a link for ordering carburetor kits that will tell you the carburetor numbers for Buick engines in and around 1966.

    http://www.thecarburetorshop.com/Kbuick3.htm
    Last edited by nailheadnut; 08-30-2009 at 11:19 AM.

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    Hi ED , thank you for all these details , so I will bring them closer to what is on my car, in the order you gave them to me : 1 My carburetor is a Carter AFB 3923S ( Table ID indicates a "AT 1965 425 ) .

    2 Air cleaner is " a large single snorkel chrome " pancake " air cleaner " .

    3 Valve covers are " finned aluminium valve covers with " BUICK " in raised letters .

    4 The engine code and serial number of the engine appear as shown below, between the two there are two numbers or characters partially erased, I can not identify


    MR 418 2 ? 5 or 0 ? 6H259417

    5 The transmission has a Posi-traction differential , as evidenced by the label aluminum where it is written: " Limited Slip lube Only " .

    6 The VIN on the block is different from that found on the VIN plate attached under the hood, on the passenger side . This plate is as shown below :


    GENERAL MOTOR FRANCE
    ( Adress)

    TYPE ( Model) RIVIERA

    MARQUE ( Make ) BUICK

    CHASSIS N ( Serial number ) 494876H911277



















    7 The speedometer is calibrated in kilometers per hour .

    8 The engine designation on the air cleaner is missing .

    9 The body plate is as shown below , do not know what some numbers and characters, I have not found their service on this site .



    GENERAL MOTOR CORPORATION

    10B F

    ST 66-49487 EUC 20780 BODY

    TR 658-B WW PAINT

    XTSM 2R3B

    50

    BODY BY FISHER





















    10 In reference to a section of this site, called "425 identification" which explained the case of engines whose code is false (MT instead of MW ) , i looked at the block and it has a casting rectangle next to the transmision housing , on the driver side , towards the top of the engine ; rectangle, it says it is unique to 425 blocks . Is my engine a mismarked 425 ?

    11 There are other numbers on the block behind the distributor and near the transmission housing , as i can see on the site , but i can't read them and I did not really understand if they identify a 425 or if they are something else

    That is the information I collected, tell me what you think ; best regards . Bertrand .

  9. #9
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    It seems your original engine was replaced with a 66 GS 400 engine (MR). The 8 digit code on the block (6H259417) should match the last 8 digit of the vehicle vin (494876H911277). Your original block would have been stamped 6H911277: 6 is for 1966, H is for Flint, MI assembly plant and 911277 is the production # of the vehicle. The production # for the Riviera started with 9 (like your vin). My guess it that the original 425 had problems and was replaced with a 400 from a GS. Then it seems it was topped with a carter from a 65 425 at some point.
    Last edited by Dr. Frankenbuick; 09-01-2009 at 03:16 PM.
    Steve B.



    67 GS 525 Buick Stage IV
    66 GS Convertible
    65 GS HT
    63 Riv
    02 Subaru WRX Turbo
    03 Ford Cobra Convertible (Factory Supercharged)

  10. #10
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    Bertrand,


    I agree with Dr. FB on what your engine is. I have another question for you. What color is your engine? In '66 all of the nailheads in Rivieras were painted red; every other nailhead for '66 was painted Buick Green (it's really a teal color.)

    I'm using the '65 codes to tell you how part of your trim tag decodes, but I can't guarantee that they're the same for '66. See how close they might be.

    10B - 10 = 10th month, October; B = 2nd week

    F = Flint, MI assembly plant

    TR-658 Black Vinyl Bucket Seats

    WW - Riviera Fawn (Riviera only color)

    Here's where I'm not sure

    X = Power windows

    T = Power bucket seat

    S = Auto trunk release

    M = Vacuum door locks

    2R = Rear Speaker

    3B = ???? wasn't listed

    Is this anywhere close?

    One thing that has me puzzled. Your aircleaner is the chromed pancake style. BUT, those air cleaners only came on Q-jet carburetors. Q-jets and AFB have different diameter air horns them. How is this Q-jet air cleaner mounted on the smaller AFB carb?

    I'll do some more research, and see what else, if anything, I can come up with.

    Ed
    Last edited by nailheadnut; 08-31-2009 at 10:43 PM.

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