70 GSX vs 70 Chevelle SS 396

Discussion in 'The Bench' started by 1969RIVI, Jan 8, 2020.

  1. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    I restored a `69 Chevelle SS396-375hp, 4 speed car 20 years ago and had the engine rebuilt stock with the exception of a hydraulic cam that was fairly close to the stock solid specs. The car was going to be a driver, which it still is, but the guy who owned it at the time knew nothing about cars so I didn't want him to have to worry about solid lifters. I also replaced the 4.10 gears with 3.73s. The engine dyno'd at 424hp with dyno headers. I figure with stock manifolds and exhaust it probably came in real close to the original 375hp rating. That car has never ran better than a 14.20 at the Pure Stock Drags.
     
    BUQUICK likes this.
  2. 70 GMuscle

    70 GMuscle Plan B

    Mine are just the opposite.
    Buick heavier.


    I love that GSX. Sexy ass hell.
     
  3. UNDERDOG350

    UNDERDOG350 350 Buick purestock racer

    The only real difference weight wise is the engines, providing both are bucket seat/auto trans equipped. Buick engine being lighter. This Chevelle is 4 speed so it could be lighter overall.
    Bill, not to disrespect your tuning abilities but if it was built to stock specs 14.2 still sounds a little off. If built and tuned to Pure stock allowed specs I would think 13.5 is possible from a 350 HP 396. A 375 HP should be 13 flat. My 350 GSX runs 13.40s all day but it didn't happen overnight. It's got about 2500 passes on it. Test, test, test. Air ratio meter. log books. etc.

    FYI Roberta's car has run 12's, but Roberta has not!
     
    300sbb_overkill likes this.
  4. 70 GMuscle

    70 GMuscle Plan B

    Buick is 1/2 foot or so longer.
    Same wheel base of course but longer over hangs front and back.
     
  5. Quick Buick

    Quick Buick Arlington Wa

    The 70 chevelle SS396 did Not have a 396 in it.. It had a POS 402 it. A low compression truck motor. it was show not go motor.
     
  6. 70 GMuscle

    70 GMuscle Plan B

    It’s just a .030 over 396 a 402.
    Semi open/closed chamber head.
    Pancake intake.
    Poor Chevelle getting all beat up here, lol.
     
  7. Quick Buick

    Quick Buick Arlington Wa

    Dont forget 8.5 comp ratio..
    SBC out ran it.
    true 69 396 cars beat the **** out of the 70 402
     
  8. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    The 402 engine as stated above is a .030" over 396. They had a bad production run of 396 blocks that the bores didn't clean up at the 396 bore size so instead of scrapping all those blocks they opened the bore up a bit larger and the 402 was born.

    I wonder if they got rid of the closed chamber style heads by '70 and only made one style fits all, which made the compression fall for the 402? I'll check;

    Well it looks like that the closed chambers were made up to '70 and there were 2 HP ratings for the 402, a 10.25:1 compression 350 HP and 11:1 compression 375 HP versions. The 396/402 wasn't neutered until '71 when there was only 1 version of it that was 8.5:1 compression. This is all according to my '96 Federal Mogul piston catalog and cross referenced with the '67 to '73 Motors Manual.

    Maybe you're remembering a '71 as the slow turd Chevelle?
     
  9. BUQUICK

    BUQUICK I'm your huckleberry.

    We've had many legit SS396 (402) Chevelles here and can speak from experience that they are not low compression nor a truck motor. They run as they should. No more, no less. All ran great.
     
  10. 1972Mach1

    1972Mach1 Just some M.M.O.G. guy.....

    As Derek and Gary stated. Same thing, just .030 over. There were truck 402s also, but they're not the same as an "375 hp 396" 402, just the same as a truck 454 isn't the same as an LS6 454.
     
  11. 70 GMuscle

    70 GMuscle Plan B

    8.5 to 1? That I never heard before.
    Closed chamber heads still in 69?
    I know it was for emission reasons they went to 402 I heard.
    69 had I believe better intake a high rise, lighter weight, not sure cam timing as there was a 325, 350 and 350 hp.
    what else are difference.
     
  12. 70 GMuscle

    70 GMuscle Plan B

    Regular 402 350 and 375 very different.
    Heads, cam intake carb among other upgrades.
     
  13. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    I agree, but I only restored the car for a guy 20 years ago. It has since been sold to another person who I do know but he doesn't race the car himself, I think his brother-in-law drives it and quite possibly is a little afraid of it. Anyway, I've never had a hand in tuning it. I always believed had it still had the solid lifter cam and 4.10 gears in it, it would be doing a lot better than it is. But like I said, the guy who I restored it for barely knew how to open the hood without help so I tamed it down a bit. I have no idea what has been done to it since.
     
  14. 1972Mach1

    1972Mach1 Just some M.M.O.G. guy.....

    Yessir, that's what I was getting at, just worded it badly. I was saying not all 402s are low compression truck engines, the ones that are supposed to be 375 hp versions are the same as a 375 hp 396, just .030 over.
     
  15. Quick Buick

    Quick Buick Arlington Wa

    I bought a one owner 70 ss396 for dirt cheap...The owner was pissed... He gave the car to his 17 yr old son. first thing the kid did to it was put a sun roof in it. Problem was he over cut the roof. so when I got it had kitchen linolium flooring duct taped to keep the rain out..

    The owner informed the itself was 100% original and seamed to be.. Motor was never abused. But it never ran like it should. HP wise.. It ran good but not like a 69 396.. It had about 80k on it. pulled the motor out thats when I found out it was a 402 bore not 396 bore. I got a hold of the owner and asked if he had the motor rebuilt? Answer No.

    Took it to the machinist forget his name that was back in 85 86. Thats when It was a 402 low compression truck motor as he called it.. Ended up putting a used low mile 396 or 427 in it. fixed the hole in the roof new headliner drove it for a year os so then sold it.
     
  16. UNDERDOG350

    UNDERDOG350 350 Buick purestock racer

    Derek is correct (for once, Just kidding). 70 402's were exactly the same as 69's just .030" over bore so should run as well. 71 brought on changes for emissions.
    Bill, sounds like it was wise to tame it down. World don't need another Kevin Hart.
     
    70 GMuscle likes this.
  17. 70 GMuscle

    70 GMuscle Plan B

    Lol. Keep Kevin on the mopar.
    Doesn’t matter truck or car block.
    Same thing except the tall deck 366 n 427.
    like Buick’s, head ccs and piston style n deck heights.

    we are blessed Gm made 4 different brand big and small blocks. All of which are pretty well supported to this day.
     
    1972Mach1 likes this.
  18. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    GM actually only made 2 different small blocks and they were sbb and sbc. Pontiac, Olds and Cadillac did NOT make a small block engine.

    The smaller displacement Pontiac and Olds engines were basically the same platform except with a shorter deck height than their bigger displacement engines. I would go as far to say that Olds and Pontiac engine can be call medium blocks because there bore spacing was bigger than the sbb and sbc but smaller than the rest of the GM's big blocks.

    sbb = 4.240" bore spacing.
    sbc = 4.400" bore spacing.
    BBB = 4.750" bore spacing.
    BBC = 4.840" bore spacing.
    BB Caddy = 5.00" bore spacing.

    And the medium block Pontiac = 4.620" bore spacing.
    Medium block Oldsmobile = 4.625" bore spacing.

    Much like the Mopar big blocks, Pontiac and Olds just changed the deck height on their smaller displacement engines while just about everything else is the same except for the intakes because the taller deck, the V is wider so the intake needed to be wider to be able to bolt on without having to use 1/2" thick gaskets!:eek: But if one wanted to use spacers then the smaller displacement short deck intake could be used on the taller deck engine if someone 100 years from now can't find the tall deck intake they can use the short deck one with spacers.:rolleyes:

    If you're going to argue that the smaller deck height makes them a small block then what would you call the small block Buick series of engines that have 3 different deck heights 215/300/340,350 but have the same bore spacing?:eek:

    That hits all three, small, medium and large(big).
     
  19. 70 GMuscle

    70 GMuscle Plan B

    Lol, yup.
    I know.
    And caddy never built a muscle car.
    You can get down to the nitty gritty points.
    But the fact is 350ish, 400ish and 455ish sized engines were available in 1970.
    Only Pontiac hid there’s completely well almost separating 455 from 350 or 400 inch.
    Glad I’ve owned them all in those variations
     
  20. 1972Mach1

    1972Mach1 Just some M.M.O.G. guy.....

    Yes Derek, we've all read your opinion on this many times. When the Olds guys call them a small block, I'm going with what the Olds guys call them. I've never heard one call his 350 a "short deck" and his 455 a "tall deck". Big and small block. The block is physically smaller or bigger is it not? Why would bore spacing be the determining factor of big vs small? Shouldn't they be called a "short block" and a "long block" by that thinking? And why does a real long block have heads and a short block doesn't if it doesn't actually make them shorter or longer? Why are they called motor mounts? Shouldn't the block or bellhousing be called the motor mount since the starter motor mounts to them?....all technicalities of terms that don't matter.
     
    Last edited: Jan 11, 2020
    70 GMuscle likes this.

Share This Page