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Thread: 557 short block

  1. #1
    Senior Member
    Join Date
    Feb 2009
    Posts
    250
    What I have to work with is a 557cid chevy. Bowtie block tall deck, crower rotating assembly, enternally balanced. Initially it was set up to run a blower on alcohol. With a zero deckheight, 4.5 bore and 4.375 stroke would it be possible to run the blower deal on gas? Even with 130cc heads and .040 gasket the compression ratio is about 8.9:1. Are larger combustion chambers an option? The pistons are Ross blower with a single valve relief aprox 3cc's. I want to be able to run some respectable boost on gas, not limited to a narrow window. I do'nt want to change pistons. At this point alcohol seems like a pain in the ass with a lake boat, but may be what I will end up doing. I'm by no means an engine expert. All opinions and suggestions welcome.

  2. #2
    Fiat48
    I'll try here. Most alcohol deals are about 11 to 1. I have run 12.5 to 1. Alcohol doesen't care and you can run clear down to 7 to 1, maybe lower. But you do get some oil dilution at lower ratio's like that. I wouldn't consider blown alcohol carbureation so that means injected and yes it is a little pain in the ass for the lake. But, you'll never go back to gas!
    That said, most guys like 8 to 1 or lower for blown gas. Several ways you can approach lowering this Cr. One way is thicker head gaskets and larger bore diameter head gaskets. Another way is to have a machinest offset bush the pin end of the rod to move the piston in the hole, thus lowering your compression ratio. Are you sure your heads are 130CC's? I have formulas and can caculate your compression ratio options of head gaskets or lowering the piston in the bore. I need to know your present deck height and actual combustion chamber cc's.
    Other's here will have to chime in on Blown gas and what you can get away with on pump gas as far as boost and compression are concerned. My only experience with blown gas was racing in the 80's in which we ran 29% over in a 6/71 on racing gas. We have no idea how much boost it was, only that 32% over didn't go any faster (end of the blower efficency we had).

  3. #3
    blowngas
    Sounds like you have regular flattop pistons with some valve relief---I've run some wiseco pistons just like that in a 468 and only busted them up after going way up on the boost----some of the local guys down here in the badlands are running pretty much of the same stuff but not putting in much boost, and keeping the timing down, and are keeping them together---some are running pump premium with a little octane booster, some are adding av gas to pump premium---whatever u run, keep the timing down to keep it from detonating---fiat 48 has listed the alternatives---you can also use a thicker head gasket----.060-.080---I'm building the same cu. in combination as yours but it's a all aluminum rodeck, but will be an all out race motor with some dished JE pistons-----you should be ok on the lake with what you have as long as you limit it to short runs, keep it cool, and keep the timing in check-----if you want to sure about it not banging, install a knock sensor----be safe and keep the shiny side up---

  4. #4
    Infomaniac
    Just run race gas in it and have a blast.
    As long as the bottom end can handle it.
    Either that or just go for methanol.
    I always run 7.5 -7.75:1 on gas blown engines.
    Intercooled they will handle 10 -12 lb no problem on pump gas with 34 degrees of timing. No boost timing retard.

  5. #5
    Senior Member
    Join Date
    Feb 2009
    Posts
    250
    The bottom end should handle some decent power. Crower crank with the double key cut for blower, billet crower rods, the pistons are not dished but have a single valve relief....... Decent parts for a lake hot rod. I guess the question is how much boost could I run with 9:1 compression on race gas with intercooler? Yes the heads are 130cc. Victor cnc edelbrock. Zero deck height. What would be the HP difference between the gas and alky?

  6. #6
    blownalky557
    This is my Blown Alcohol 557 combo:
    Gen VI race block 4.50 bore
    Dart 360 heads done by Gromm Racing
    Fererra race valves 2.30 intake 1.90 exhaust
    K-Motion K-1000 valve springs
    Lunati Roller camshaft .786 lift 335 duration
    Crower stainless steel roller rockers
    Comp Cams guide plates for .4375 dia. push rods
    Dart stud girdles
    Blower Shop retro hi helix 1471 supercharger overdriven 18%
    Enderle Bird catcher w/ K style barrel valve also with port injection
    Enderle 990 fuel pump
    Venolia 13:1 static compression blown alcohol pistons
    Fowler Racing aluminum rods
    Callies 4340 steel 4.375 stroke crankshaft
    Keith Black gear drive
    Fowler Racing front mag drive
    MSD Pro Mag 20
    Rewarder 2.5 inch zoomies

  7. #7
    Senior Member
    Join Date
    Feb 2009
    Posts
    250
    Nice combo.

  8. #8
    Fiat48
    Compression would be 8.95 to 1 with .040 gasket (O deck) 130cc head. If you use a .062 gasket with a bore size of 4.625 you can get it down to 8.6. If you move the piston .025 in the hole, then you get 8.28 to 1. That will give you some idea of what does what.
    Roughly alcohol gives 15% more power for putting it in the tank, more if you optimize compression and camshaft for alcohol.

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