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402 Chevs

Discussion in 'The Hokey Ass Message Board' started by panhead_pete, Jul 26, 2007.

  1. panhead_pete
    Joined: Feb 22, 2006
    Posts: 3,487

    panhead_pete
    ALLIANCE MEMBER

    Hi guys in my recent tavels I have been offered a 402 chev motor and know nothing of these. Is there something I need to know prior to purchasing this? Here's a snap of the motor, thanks.

    [​IMG]
     
  2. nexxussian
    Joined: Mar 14, 2007
    Posts: 3,240

    nexxussian
    Member

    I'm no expert by any means, but I thought the 402 was one of the W head engines? To my decidedly untrained fryball that looks like a prettied up Mark IV Big Block Chevy. I don't know though.:confused:
     
  3. Wesley
    Joined: Aug 12, 2006
    Posts: 1,670

    Wesley
    Member

    basically it is just a overbored 396.
     
  4. nexxussian
    Joined: Mar 14, 2007
    Posts: 3,240

    nexxussian
    Member

    Duh-Hah! Makes more sense now.:D
     

  5. factory f up starting in 69 i think
    like they said above .030 over 396
    and 396 sounds cooler than 402 so they kept the badges( my guess)
    tk
     
  6. panhead_pete
    Joined: Feb 22, 2006
    Posts: 3,487

    panhead_pete
    ALLIANCE MEMBER

    Thanks. So not many were used back in the day in rods?
     
  7. F&J
    Joined: Apr 5, 2007
    Posts: 13,222

    F&J
    Member

    402 came out in 70, but it's the same look as 396 that came in 65 vettes & just 200 65 chevelles. I'm sure someone used one in a rod by the late 60s, but they need multiple carbs to look better. Multiple carb manifolds are too pricey, plus the rest of the rod would need the late 60s look.
     
  8. oktr6r
    Joined: Feb 14, 2006
    Posts: 724

    oktr6r
    Member
    from Tulsa

    If you use it, might want to make sure the oil pump pick-up tube isn't loose. I knew a guy that had one drop off, and toasted the bearings before he knew what happened. He rebuilt it and used a new oil pump, the pick-up tube came loose a few days after he got it running. He caught it in time, dropped the oil pan and tack welded the pick-up tube in place.

    Pretty strong stock engine, I heard rumors of 140+ mph in the '72 Chevy truck he was driving.
     
  9. nexxussian
    Joined: Mar 14, 2007
    Posts: 3,240

    nexxussian
    Member

    He could always put a blower on it.:D Or 4 Webbers, are Webbers any cheaper in Australia? I doubt it, but then I have never been, so:confused:

    What would a Big Block Chevy have had in a rod in the past in Australia?
     
  10. GM made a batch of 396's starting in about 67 that they had a high failure rate on. They all burned oil like mad, turns out the cylinder walls were out of spec. Instead of a recall they just overbored all motors out 0.030. and dropped them back in. They continued until they got caught on the track they left the 396 on the side of the cars.

    Late 69,70 they announced they had a new motor, they had pistons made that matched the .030 overbore without the .030 marking and called it a 402. Good motors. No major issues.

    Only negative of the motor is you are limited to another .060 on the walls. Basically treat them as a 396.
     
  11. tomslik
    Joined: Mar 3, 2001
    Posts: 2,161

    tomslik
    Member

    \

    supposedly, they came out in 69 as a replacement (crate) engine....
    just a .030 396.......
    btw, love the valve covers on that....
     
  12. Deuce Roadster
    Joined: Sep 8, 2002
    Posts: 9,519

    Deuce Roadster
    Member Emeritus

    Big Block Chevrolets came in two very different ways. The standard, everyday oval port head with 2 bolt mains ... and the High Performance square port head with 4 bolt mains. The square port main engines came with solid lifer camshafts ... :) better crankshafts and parts.

    [​IMG]

    [​IMG]

    [​IMG]

    Look at the engine number/VIN code ... to know what the engine originally came in and the horsepower it was rated at ... :)

    A BBC 402 makes a lot of torque ... and moves a medium to heavy car good. It moves a light car ... REAL GOOD ... :D
     
  13. RichFox
    Joined: Dec 3, 2006
    Posts: 10,020

    RichFox
    Member Emeritus

    My brother put one in his eariler Chevy pickup and that thing ran good. I liked it.
     
  14. enjenjo
    Joined: Mar 2, 2001
    Posts: 2,689

    enjenjo
    Member
    from swanton oh

    The reason they overbored the 396 to make a 402, they could use the same ring set as a 400 SBC. I have one in my truck, originally a 396. I bored it .030 over and used standard bore 402 pistons.
     
  15. Vance
    Joined: Jan 3, 2005
    Posts: 2,135

    Vance
    Member
    from N/A

    I was always told they were Canadian made 396 motor and went through a different casting process that allowed for a slower cool down period making them a more straight, (read as less warpage) motor and heads. Made sense to me.

    Either way, what you have is junk. Crate it up and ship it over here and I'll deal with it ;-)

    Vance
     
  16. Vance
    Joined: Jan 3, 2005
    Posts: 2,135

    Vance
    Member
    from N/A

    Wait for squirrel. He's the one to set us straight.

    Vance
     
  17. I own one. As said, essentially it is just a .030 396 BBC. A couple of quirks to keep in mind about them:

    1) There are very few off-the-shelf performance pistons available specifically for the 402...TRW has dropped all but two part numbers. The first is a stock-style replacement piston that has a very small dome. Most 402s were either the "396/325 hp" baseline big block, or, installed in light trucks as a 396/265hp upscale option. The trucks & the late car 402s ('71-'72) used open chamber heads....with the TRWs, it is extremely difficult to get over 8.5:1 compression without severely milling the heads.

    The other TRW number has a gigantic dome & is intended as a replacement for the "396/375 hp" engines...the dome has to be milled quite a bit to be workable on the street. SOME of these pistons have been known to have thin domes & can't be milled much or at all. In addition, these pistons are over $560 US.

    It is possible to use 396 pistons, basically using (for example) .060 pistons if you have a .030 402.....the off-the-shelf offerings are slightly better for the 396, but not much. The dome sizes are different for a 402 vs. a 396, comparing equivalent pistons....basically what that means is that the listed compression figures for a 396 are completely wrong when used in a 402...so measure everything carefully. Again, it is difficult to either make compression, or reduce it, depending on the piston in question....

    Diamond, Ross, etc. can all make pistons for the 402....$$$$. Also, their pistons are mostly designed to be NHRA qualified replacements for Stock classes & as such may not be what's needed. Want something custom??? Step on up & pay the money.

    2) Most 402s cannot be bored to 4.250 to get a 427/454 bore size, regardless of what the junkyard guy tells you. :) If anybody is considering it, it MUST be sonic checked.

    3) The best part about the 396/402s is that they generally go for low bucks, compared to a 427/454. That's groovy, as long as you don't start plowing big $$$ into custom pistoms, aluminum heads, & so on. At the end of the day, you will have an overpriced turd that will be down 40-60 hp from an equivalent build 454. It will also have little resale value. Look at them as healthy street engines only & you'll be happy.

    I have a 402 that dynoed over 550 hp with moderately worked OC oval port heads & a Crane roller cam. Very streetable & cheap to build...(got a sale on the cam & lifters :)). Only disadvantage was that it was hard on springs...I'll go with a little less lift next time around.
     
  18. squirrel
    Joined: Sep 23, 2004
    Posts: 55,941

    squirrel
    Member

    I'm just kicking back, enjoying the stories.....

    Just about all the 402s were low perf motors, just give them a clean up head porting job, .550 lift hydrualic cam, and headers, and they wake right up. I haven't tried to buy one lately, but in the past they sold cheap because it was usually worth it to spend a few more bucks and get a 454. and there's no romance associated with the 402 number like there is the 396 and 427.

    buy it to use in some type of hot rod, or in a truck, or boat, or just to hang on and resell.

    I dig the Ford toploader to Chevy block adapter bellhousing :) clutch fork is on the Aussie side also
     
  19. Squirrel, not gonna debunk all those myths about the 402? I was counting on you!

    Actually guys, I've heard a lot of stories in the past, now I've heard a few more. The truth is; in '70, Chevy enlarged the 396 with a .030" overbore, the very first ones even had the oversize stamped in the piston top, then they made up some pistons, and actually were a thousanth or so larger, so 30-over rings aren't the same. They called them 396 in the SS Chevelle, in everthing else they called it a 400. In the truck, for instance, if you wanted the big block instead of the 400 small block you had to order the 400 4bbl.


    The early motors (don't know the cut-off) used closed chambered heads and had 10.25 compression, a bit much for pump regular, but open chamber heads drop it about a point.
     
  20. 6t5frlane
    Joined: Dec 8, 2004
    Posts: 2,399

    6t5frlane
    Member
    from New York

    Squirrel, I had a L-78 402 that came in my 70 SS Nova. Stock rated @ 375HP. Soild Lifters That car ran like a raped ape man. Scary fast
     
  21. squirrel
    Joined: Sep 23, 2004
    Posts: 55,941

    squirrel
    Member

    There were a few hi perf 402s made, but a whole lot more of them were low perf engines in pickups, Caprices, station wagons, etc. The high perf motors were indeed a handful! chevy rated the 65 vette high perf 396 at 425 hp, and it was pretty much identical to that L-78
     
  22. arkiehotrods
    Joined: Mar 9, 2006
    Posts: 6,803

    arkiehotrods
    Member

    From the American V-8 Engine Data Book, page 55:

    "By increasing the 396's bore to 4.125 in., the 402 cid engine was created. This was done during the 1969 model year, so both 396 and 402 cid big-blocks were fitted that year. Option numbers (LS3, L34, L35, and L78) and power ratings were unchanged from those of the 396.

    The L34, L35, and L78 continued to be available in 1970. There was also a limited run of the L78 equipped with aluminum cylinder heads; these were designated L89.

    The 300 hp LS3 was also carried over into 1970 and made available on other Chevrolet car lines, including Chevelle. It was marketed as the Turbo-Jet 400. After the L34, L35, and L78 were dropped at the end of the 1970 model year, the LS3 was the only 402 cid engine left. It was dropped after the end of the 1972 model year."

    The L78 was rated at 375 hp, L34 at 350 hp, L35 at 325 hp, and LS3 at 300 hp. The LS3 remained at 300 hp in 1971, but in '72, horsepower choices were 210 and 240.

    Interesting to me is the fact that there were no 396 engines in 1970 and 1971, even though Chevrolet badged cars (Chevelle SS 396 for one) as 396 when they were actually 402 engines. From the Encyclopedia of American Cars, 1930-1990, under both 1970 and 1971 engine specs, there is a footnote which reads, "Commonly known as '396,' actual displacement 402 cid."



    The American V-8 Engine Data Book also shows no 396 engines for 1970, and shows some suffix codes for 402 engines in 1969, which tomslik mentioned above.

    If you have the suffix code for the 402 you're looking at, I'll look it up in my reference material and let you know what it came out of.

    My first car was a 66 Caprice 2 dr with a 325 horse 396, and I've also owned a 71 Impala 2 dr with a 300 hp 402 (badged as a 400) and they were both decent street engines, though the 66 felt a lot stronger from the driver's seat. I like rat motors.
     
  23. overspray
    Joined: Jan 14, 2003
    Posts: 1,417

    overspray
    ALLIANCE MEMBER

    The "REAL" reason that GM produced the 402 cu. in. motor was due to new federal emissions regulations that exempted larger displacement engines (400 cu. in. or larger) from having to comply to certain "smog" laws. These began in 1970 and the cheapest route for GM was to bore the "396" .030. All production cars with a "396" in 1970 actually came as a "402" even though the flags remained on the fender and grille as "396". In 1971-2 the Chevy cars with the "402" were usually badged with a 400 emblem. I used to pick up Impalas with the BB 402 for "donor cars" and got some good deals on some cheap torque. Chevy parts guys who worked back then (1970) went nuts when they would order stock "396" pistons and rings which, course were .030 smaller. They kept the compression up in 1970, but it dropped due to more federal emission restrictions in effect for the 1971 model year. Along with the compression drop, intake manifolds were "low profile" and most had smog pumps.

    overspray
     
  24. also the 400 was a small block (which everyone knows)
    and insurance companys gave a reduced premium on small block cars compared to big block cars
    so if your car was labled as a 400 like the 70 capri and imp you got the lower rate
    this could be an old wives tale since i wasnt born untill 78 but thats what i was told
     
  25. arkiehotrods
    Joined: Mar 9, 2006
    Posts: 6,803

    arkiehotrods
    Member

    Plus, Chevrolet saved thousands in tooling costs by having one "400" emblem for both 402 big blocks and 400 small blocks!
     
  26. Sander
    Joined: Oct 31, 2006
    Posts: 134

    Sander
    Member

    Squirrel called it. The reason they didn't have "SS 402's" was because there was so much advertisement investment with the 396 and billing it as a legendary motor, they decided just to stick with it to keep the "romance," as squirrel said, alive. 396's sold cars.

    But at the end of the day, the bigger, the better.

    Sander
     
  27. I've heard a lot of stories about the 402, but this one has seemed the most likely to me. There were a lot of tactics used by Detroit to fend off the '70s freight train of emissions/economy regulations....Ford slightly uprated the F-100 load capacity & GVWR to avoid emissions standards (temporarily) for a few years...thereby naming it the F-150...offering both for a few years & dropping the F100 right before the standards went into effect...IH did something similar with the Scout II...& the list goes on. :)
     
  28. My father-in-law liked rat motored pickups and bought a '72 new with the 402. His older truck had a 427 in it so he expected the new one to have a little less in the power department but get better gas milage. Wrong on both presumptions! The 402 was gutless next to the older truck and liked gas even more than the 427. He kept the truck about 2 years and dumped it in favor of a new "350" equiped pickup. From driving both I found that the low end torque on the 400 was a little better than the 350 but other than that the 350 came in tops. He later traded for a '77 Silverado "Heavy Half Ton" pick up which was the last regular gas model chevy offered. It came with a 454 in it and he liked it so much he kept it until 2 years ago when he passed it on to me. It hasn't been started in about 8 years but I bet we could get it going if I tried.

    End result is I have a nice stock bore 454 to start with for my '50 GMC project.
     
  29. squirrel
    Joined: Sep 23, 2004
    Posts: 55,941

    squirrel
    Member

    the 400 cubes smog rule reason sounds reasonable to me too....fits in with corporate thinking better than any of the other stories presented. I've really never worried about why they did it.

    lotsa parts catalogs specified either a "400 2bbl" or a "400 4bbl" for early 70s parts applications, the 2bbl was the small block, 4bbl was the big block.
     
  30. 34toddster
    Joined: Mar 28, 2006
    Posts: 1,482

    34toddster
    Member
    from Missouri

    Strange thing happen to me I bought 6 BBC from a scrapper a few years back and found a 402 2 BBL in a 70 Caprice wagon, still have the intake along with around 20 or so 396 to 454 motors and parts, there were 2 bbl big blocks can't image the gas millage to be any different...still 10 MPG
     

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