350 ho

Discussion in 'Small Block Tech' started by 70 Buick Gs, Aug 8, 2019.

  1. 70 Buick Gs

    70 Buick Gs Member

    i posted yesterday a bit about my car and I guess needed to have put more info about my engine it’s a 350 high octane I assume because it had to run on premium gas that’s what it says on the engine sticker it’s a original numbers matching engine I had it rebuilt to original valves , pistons, rocker arms the whole engine is got all the correct parts as it had before. basically had the block machined it has been done a little over I think but not sure .30 over I had it seaded so it can run on regular fuel it has original crank shaft it was mint so it was just polished and original carb 4 bbl quadrajet original tranny automatic power glide I no it has to do with the carb it was rebuilt but had the issue before engine was rebuilt the bogging
  2. 70 Buick Gs

    70 Buick Gs Member

    image.jpg image.jpg Here is a picture of the sti
  3. Brad Conley

    Brad Conley Super Moderator Staff Member

    315 horsepower GS 350 engine.
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  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    There were two 350 4bbl engines in 1970. The one that came standard in the GS350 was engine code SP. Specs were 10.25:1 compression (it wasn't), and 315 HP/410TQ. The other one was engine code SB. Specs were 9:1 compression and 285 HP/375 TQ.
  5. 70 Buick Gs

    70 Buick Gs Member

    Mine had the SP and a 4 but can’t read the other numbers looked like a 6 and a 0
    With some other numbers 1382201-L and not sure if it was a G or a 6 above the numbers
  6. Mart

    Mart Gold level member

    Numbers/ compression, doesn't matter. You saving it for someone? Make it the way you want it.
    Last edited: Aug 8, 2019
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  7. gstewart

    gstewart Well-Known Member

    I have a '72 GS 350 and I use Shell #1 gas in my engine - no alcohol. Yes, I pay 20 cents per litre but it is worth it to me. I added a little timing & the car runs great on it. When I had the head off the engine last year, the pistons were carbon free.
    MrSony likes this.
  8. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Hopefully your engine builder went with the 10:1 compression replacement pistons and not the cheap jobber 8:1 replacement pistons!? There is a big price difference between the 2 different piston sets, the turd pistons are around $80 and the machine shop can mark those up more than the correct replacement pistons that are around $350.:eek:

    The above is how sbb 350s get a bad reputation from people getting the $80 set of pistons and wonder why it runs worse than it did when it was tired!:mad:

    If they installed the cheap jobber 8:1 pistons and didn't machine the deck so your "SP" is still there, that thing is going to run like a turd because it won't even be at 8:1 compression more like 7.6:1 to 7.8:1 and possibly even less because of head gaskets? That high octane fuel won't be necessary @ 7.6:1 that's for sure if that's what happened.

    The pistons in the "SP" are what gives it the higher compression ratio which would be a night and day difference on how it will run, 315 HP vs around 165 HP and that's being generous. Hopefully your shop got the better pistons, that extra $260 for 150 more HP sounds like one hell of a deal to me.

    Make sure your shop installed the correct replacement pistons before you reinstall the engine in the car, if not have them correct that before you get the engine back. If you told them you want it back as close to factory as they can and they didn't install the better pistons then that should be on them to correct that situation before it goes back in the car.

    Ask them for the part number of the pistons and post here if you can't figure how to look them up before you go off on your shop though because they might of used the right ones? But if you didn't give them a part number to use then they probably more than likely used the wrong ones if they aren't a Buick specialist shop?
    Mark Demko likes this.
  9. MrSony

    MrSony Well-Known Member

    Also don't forget after 1971(?), they changed to net hp. so that 315 gross hp for the '70 SP in net hp is probably around what... 250? And a 165hp mid 70s 350 would be about 220 net hp. something like that.
  10. Mart

    Mart Gold level member

    My orig 71 SB (Dec. 70 build) code blk came with steel shim head gaskets.
  11. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    I wasn't quoting mid 70s HP, I quoted using the same standard as the '70 SP for both of them.

    If I used the newer SAE HP standard for the low comp. engine I would of guessed it as around 125 HP, which would truly make it a turd.:eek:;)

    This is why piston choice is so important when building an engine, with the right pistons the end result will be night and day. For the extra $260 that only makes the extra 130 HP cost only $2.00 per HP, would be the biggest bang for a one time charge when building an engine like in the OP.:cool: I don't even think they sell a nitrous kit that can add that much power that cheap!
    MrSony likes this.
  12. If I used the newer SAE HP standard for the low comp. engine I would of guessed it as around 125 HP

    1971 was the first year of low compression engines and 1972 was the first year of SAE Net ratings.

    so you can see the impact of the compression drop in the difference in engine ratings between 1970 ( 315 ) and 71 ( 260 ), as both were rated in SAE Gross HP.

    likewise, you can compare the 'loss' from the Gross vs Net conversion by comparing the ratings between 1971 ( 260 Gross ) and 1972 ( 175, 180 or 190 Net, depending on which exhaust your 4 barrel had ).

    155 was the 8.5:1 low compression 2 barrel, single exhaust in SAE Net.
    MrSony likes this.
  13. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Here's the deal that I thought was obvious but it doesn't look like its clicking with anyone;

    We're not talking about a fresh off the assembly line engine, we're talking about a rebuilt engine. Those cheap crappy jobber "8:1" replacement pistons would be closer to 7.5:1 than to 8.5:1 if the deck isn't milled when the block machining is done because those kind of pistons are destroked. That means they will sit in the hole an extra .020" than the crappy 8:1 factory sbb pistons that were probably in the later model sbb 350s? At 8:1 the engine would be bad enough but under that would be even worse!

    They didn't change the chamber size in the heads for the entire run of the sbb 350 and the bore and stroke and rod lenght also stayed the same. So the only way to increase the compression ratio in a sbb 350 without any machining is to use pistons with a higher compression distance(pin height) and/or a smaller dish.

    None of the HP book numbers are relevant in this case unless the block is blueprinted, meaning deck to the 10.188" specs. The older blocks were closer but still were .030" taller than they were supposed to be. When you measure the later blocks they were even taller than the extra .030", some of them were even .060" taller than they were suppose to be!:eek:

    With an extra .060" of block deck height even the later model HP book numbers will be over stated! That extra .060" can be close to a whole point lower in compression ratio which would kill the power output. So the book numbers are for engines that are blueprinted to the written specs, not the allowed production tolerances. This is why an "SP" engine that is rated at 10.25:1 is only actually around 9.75:1. That is a 1/2 point lower than listed with .030" extra deck height typically found on the earlier blocks and the reason the later model engines were a lot worse than they should of been.:(
  14. Fox's Den

    Fox's Den 27 years of racing the same 355 Buick motor

    what knowledge you should write a book
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  15. UNDERDOG350

    UNDERDOG350 350 Buick purestock racer

    He is.
    It will be out 1 week before Sean's is.

    patwhac, 72gs4spd, alec296 and 2 others like this.
  16. Mark Demko

    Mark Demko Well-Known Member

    Cram as much compression in as you can:D
    I shoulda went 12 to 1:cool:
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  17. Mart

    Mart Gold level member

    Steel .020 gaskets.......abt .5 increase.
    Mark Demko likes this.
  18. TXGS

    TXGS Paint by numbers 70 GS 455 4spd

    When I tore down my 70 SP Motor it had steel shim head gaskets also.
  19. patwhac

    patwhac Well-Known Member

  20. sriley531

    sriley531 M.M.O.G.

    I just to point out as i dont think it was explicitly mentioned in any other posts, but there is no such thing as a Buick 350 "HO" engine (high octane, high output, whatever you want to dream up for the HO acronym). One of 2 models is it.
    patwhac and LARRY70GS like this.

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