Will an Oldsmobile 455 be a remove and replace with the current Olds 350?
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Will an Oldsmobile 455 be a remove and replace with the current Olds 350?

  1. #1
    Senior Member nikwho's Avatar
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    Default Will an Oldsmobile 455 be a remove and replace with the current Olds 350?

    Hello all,
    I'm trying to keep a boat in service for the next couple of months while I build a 468 BBC and source all of the parts to install a BBC into my '70 Cheetah.

    This boat is new to me. Has a Olds 350 in it. Yesterday morning my son and I took the boat out onto the lake. After setting the timing, it started to run well and we did a few laps, running around, having a blast. A small leak turned into a much bigger leak, with water spraying out of the bellhousing/flexplate cover. I figured that it was a freeze plug, so we put the boat back on the trailer, dragged it home and I yanked the engine out of the boat. Oddly, nothing looked to be leaking from behind the flexplate, which makes me wonder if I was looking at it wrong when I very briefly saw the water spraying. Perhaps it was coming from elsewhere. So, I was inspecting the block and it's got some pretty substantial cracks in it! One along the forward end of the drivers side, kind of along the #1 cylinder. Another crack between #4 & #6 cylinders, from the center block plug, up to the top of the block. Oddly, it was running well and has no water in the oil. But, I can't continue to run this engine as it is. So, I was thinking of trying to find another Olds engine, to keep the boat in service. Or, I've got a fresh 433" BBC that I just built for my '68 GMC that I COULD steal and drop in to boat. I'm worried about the piston to cylinder wall clearance, as this was built for a street vehicle. I forget the clearance, but it was machined to the specs that KB reccomended for the pistons.

    The 433" engine has a '71 4 bolt main block, forged 3.76" crank, factory rods with 7/16" ARP bolts, 9:1 KB hyperutectic pistons w/ -7cc domes (KB 360-030), 291 heads, (105.9cc chambers) Edlebrock Performer RPM AIR-GAP intake and Comp XE274 camshaft. It's far from ideal for this boat. I don't want to take this freshly built engine apart to have the piston to cylinder wall clearance changed. I'm assuming that this option is out, as the cooling characteristics of these boats could be problematic for street vehicle piston to cylinder wall clearances? But heck, I don't know.

    The other option was to source a cheap Olds 350 or 455 that'll keep this thing wet for the Spring/summer without rushing an engine build that I can't afford right now. If I were to throw money at it this way, would a 455 bolt right in place of the Olds 350? Same exhaust manifolds (Hardin logs with S pipes)?

    Im pretty bummed that this thing froze and broke the block. Just assessing my options to keep the boat usable for now.

    FWIW, I don't like the ideal of throwing good money at another Oldsmobile engine, unless I found a decent 455 that would use all of my current parts and bolt right in. If I found a decent 455, I wouldn't mind keeping it in there until it died. Perhaps I'll get lucky and find a good deal on some BBC Engine plates, oil pan, cooling components, headers, PTO, etc!

    So, to clarify my two main questions;
    1- Will a 455 bolt in place of my Olds 350 and use the same flexplate, PTO, cooling stuff, engine mounts, logs, etc?

    2- Would I be risking too much running my 433" BBC that wasn't built with boat piston to cylinder wall clearances?

    Thanks for any/all help!

    Nik

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    Senior Member jetboatperformance's Avatar
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    Default

    So, to clarify my two main questions;
    1- Will a 455 bolt in place of my Olds 350 and use the same flexplate, PTO, cooling stuff, engine mounts, logs, etc?

    Yes all perifierals should swap over , you need to compare the flywheels for balance weights however I recall them to be the same

    2- Would I be risking too much running my 433" BBC that wasn't built with boat piston to cylinder wall clearances? Is this a "seasoned" motor with time on it or fresh ? will you use thru hull exaust ? if so how big is the cam (lift , dur, [email protected] , centerline)

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    Senior Member nikwho's Avatar
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    Thanks for your reply! So, the engine has about 1000 miles on it in a '69 Camaro. The previous owner decided to go to a turbo'd LS7. So, I got it, pulled it apart, checked everything out, reassembled it and put it back together with this new cam and intake manifold. So, its got a little bit of time on the short block, but it's a new cam.

    Here's a link to the cam specs:
    11-246-3 - XTREME Energyâ„¢ Hydraulic Flat Tappet Camshafts

    ETA: Sorry, I'm undecided on exhaust. I like the thought of running a jacketed through transom exhaust, but open to running OTT headers, too. I imagine that lobe seperation angle will become an issue with most street cams with through transom exhaust?
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    Senior Member jetboatperformance's Avatar
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    Quote Originally Posted by nikwho View Post
    Thanks for your reply! So, the engine has about 1000 miles on it in a '69 Camaro. The previous owner decided to go to a turbo'd LS7. So, I got it, pulled it apart, checked everything out, reassembled it and put it back together with this new cam and intake manifold. So, its got a little bit of time on the short block, but it's a new cam.

    Here's a link to the cam specs:
    11-246-3 - XTREME Energyâ„¢ Hydraulic Flat Tappet Camshafts

    ETA: Sorry, I'm undecided on exhaust. I like the thought of running a jacketed through transom exhaust, but open to running OTT headers, too. I imagine that lobe seperation angle will become an issue with most street cams with through transom exhaust?
    The Exaust type will to some degree dictate cam specs and profile (choice)

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    Default Hyper pistons..

    Although some people swear by them, the hyper pistons are real picky when it comes to wall clearance AND top ring clearance..... I don't think I would use hyper pistons in a marine application. Again, some people swear by them but I just don't trust them in a very demanding application like a boat that never coasts.....
    Ray
    LOUD BOATS SAVE LIVES

  8. #6
    Senior Member nikwho's Avatar
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    Interesting. I appreciate that bit of info!

    Nik

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