If not for bad luck I'd have none....finally got boat working and Big block goes boom

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by WetPleasure, Sep 21, 2021.

  1. WetPleasure

    WetPleasure Member

    101
    Jan 30, 2021
    99 260 sundancer
    7.4 bravo3
    again not apples to apples as this is a newer boat but its a 5.7L rated at 300 horsepower and it's a 280 sundancer so its a BIGGER boat than mine and it's saying it hits 43mph
     
  2. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx 502 mag
    2005 Baja 242 islander 496
    502 mpi Bravo 1
    496 mag B1
    Can't see the video but the newer 280's are the same size as the boat you have.
     
  3. HawkX66

    HawkX66 Well-Known Member

    Jul 27, 2020
    SE Virginia and NH
    "Tread Knot"
    1997 Sea Ray Sundancer 290DA

    2020 F350 6.7L
    454 L29 Carb w/ Bravo III
    "I guess i'm expecting that if i increase the horsepower of a motor and keep the same drivetrain that i would see more rpm" My question as well and its where my knowledge of boats drops off.
    I hear you. Alot of this is a learning curve. Even for me that's been building cars and motorcycles for more than 40 years as a hobby. Be careful who you listen to on the net. Some guys will never admit they're wrong or admit they don't know what they think they do.
    If you have a Gen VI 454, you can't use domed pistons unless you use Mk4 heads. The easiest and cheapest way to bump compression in a safe way is 1. Zero deck the block. 2. Use 279 heads from an L29 454. That's what I did. I'm now at 9.3:1 which is still safe. It depends on cam lift and duration too. Lots to learn if you're doing it yourself. Even if you want to know what you're paying someone to do.
    In the end, yes, it's a 454 and has a ton of torque compared to a SBC.
     
    Last edited: Sep 23, 2021
  4. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx 502 mag
    2005 Baja 242 islander 496
    502 mpi Bravo 1
    496 mag B1
    Find out what your pkg. should do when it was new, maybe a stock rebuild will get you there.

    Merc customer support might have that info. 920-929-5040.
     
  5. Espos4

    Espos4 Well-Known Member

    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    4250 max rpm and engine destruction………. Both could be caused by running lean.
     
  6. WetPleasure

    WetPleasure Member

    101
    Jan 30, 2021
    99 260 sundancer
    7.4 bravo3
    Okay gang, I dont want to be that guy that posts a thread and then years later someone thinks they are going to find a gem of info when googling but they don't because it was never updated lol. So i'm about to head over to the engine shopt today, rebuilder should be finishing up the rebuild. I did a ton of research and watched a ton of youtube videos form Richard Holdener who is apparently a well known gearhead. He had several about peanut port 454s with loads of dyno testing to back everything up. I ended up going with a build very similar to one of his.

    First and foremost, the autopsy. I am posting this frim my computer and all my pics are on my phone, I'll try to come back and add some pics. Basically, in the cylinder with the lowest compression there was substantial rust inside the cylinder head. Water had gotten in this motor at some point and sat there. the machine shop bored the block to .30 over and you can still see a little evidence of rust in this cylinder head. They tell me that it will be fine to use moving forward and that they didn't need to go to 060 over. They theorize that the rust that had sat in there chewed up the rings and that caused the loss of compression. What blew my spark plug apart is still a bit of a mystery but there was no evidence of water in the cylinders when they took it apart, this just looked like past damage. Based on issues i had with rust that i found in the carb and in the mechanical fuel pump, it makes me wonder if this motor came out of a sunk boat. C'est la vie. I knew i was taking a chance buying a used motor off of ebay and i honestly can't even fully say the seller was trying to pull a fast one. Once we worked through a few things, we had this motor purring briefly. So if he had it purring he may not have known it was due to go kaboom! The good news is that everything else with the block was in pretty good shape. Rods, crank, and heads in good shape and will be reused.

    https://www.summitracing.com/parts/cca-k11-232-3 is the cam kit we are going with. Its a flat tappet cam which is what is in my gen 5 454. It has a 112* lobe separation angle which should rule out reversion issues. It's got a good bit more lift than the factory 330hp cam. This is a full kit so it comes with the upgraded springs and everything fits fine on the stock peanut port heads.

    https://www.summitracing.com/parts/uem-ic779-030/make/chevrolet Keith Black Icon Forged 18cc dome pistons. Going with these forged dome pistons is going to bump this very low compression motor up a good bit but it should still be able to run on plain ol pump gas just fine though i will definitely make it a point to run ethanol free 89 as it's plentiful here in Florida.

    One exhaust manifold did look a bit suspect. the other looked great. both the risers looked great and it turns out they are stainless steel risers. However, with the amount of money invested, we decided to go with brand new manifolds, spacers and risers. The measurements indicate we shouldn't need spacers and it's gonna be a bitch to fit them but we aren't going to take any chances here so we will use them.

    My biggest fear that i stumbled across was some data that talks about the 454 being a flawed motor prone to reversion not because of the lobe separation angle on the cam but rather becasue of exhaust pulses that make small amounts of water work their way back up and then a change to the riser design that doesn't have what is known as a "vaccumn break" to prevent this water going all the way back. The older style 3" risers have a hook cast into them that creats a vaccumn break and doesn't allow water to drip down into the manifold at low rpms. Note that this has been notated to be a huge issue at idle rpms. reccomendation for 454s is prior to shutting them down, engine the throttle only button and run the motor at 2000 rpm for a minute or so to absolutely make sure all water gets pushed out and no residual can sit and drip back down into the heads and then shut the boat down from that high rpm. Crazy that mercuriser has simply never bothered to try and properly fix this issue. A dry joint exhaust system would rectify it but they never committed to making one for the 454, only for the 350.

    The good news is that rebuilding this motor, i would have needed new pistons anyways because we bored it 30 over. I could have stayed with some cheap flat head Hypereutectics but these forged domes are only about $250 more so that is a small additional expense for more horsepower. Same thing with the camshaft. Flat tappet rebuild would have meant buying a new camshaft anyways. So only paying about another $200 for the upgraded cam. The boat already had the chevy aluminum intake manifold which is actually a good flowing option and has the brass inserts in it so no point in buying a new intake manifold and the carb was just rebuilt already. 750 cfm carb is spot on for this type of build. The dyno chart of a similar build on richard holdeners youtube put this build at about 450hp and torque at 550. Most importantly the torque curve is a beast. puts out 500 lb/ft starting down at 2500 or so rpm and stays above 500 pretty much the whole way out. Oh yeah, the forged pistons are easily capable of revving up to 5500 or even 6000rpm but it looks like the cam stops making power at about 5000rpm. Boat was getting to 4250 rpm loaded up before she blew last time with the 24p bravo 3 props so i'm hoping the added power wont need a reprop, just hoping we get this motor up to 5000rpm or so spinning those bad boys.

    Stay tuned! hope to have her out on the water early next week!
     
    Last edited: Nov 30, 2021
    OllieC likes this.
  7. WetPleasure

    WetPleasure Member

    101
    Jan 30, 2021
    99 260 sundancer
    7.4 bravo3


    That is the link to a good youtube vid on peanut port upgrades with dyno supported data
     
  8. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx 502 mag
    2005 Baja 242 islander 496
    502 mpi Bravo 1
    496 mag B1
    All your missing is the long tube headers with no mufflers, Did you upgrade your exhaust?
     
  9. ttmott

    ttmott PhD in OCD TECHNICAL Contributor GOLD Sponsor

    Apr 3, 2012
    Space Coast Florida
    2006 52 Sedan Bridge
    Cummins QSM11
    The 454 block is an excellent starting point especially if it is a 4 bolt main bearing cap engine. Someone said there are a lot of issues with the BBC; I'd like to know exactly what those are; I've built my share and really like them. The 383 SBC is a good engine but really doesn't develop the torque that the BBC does and tends to wear the piston skirts due to the thrust angles.
    My opinion - For a boat, horsepower really is not the relevant factor it is the torque and where that torque is at it's maximum. It is optimal to have the gear ratio in the drive and propeller configuration (diameter, pitch, cup, etc) to hold that engine at full throttle at it's maximum torque/peak HP. So before selecting camshafts and cylinder heads and pistons you need to know where that engine is to be operated at maximum throttle. The other way to do it is to develop an engine's configuration to a maximum torque at a given RPM and give those numbers to Mercury with your outdrive's gear ratio and have them spec and lab a propeller for that combination.
    Forged pistons wouldn't be my first choice for the simple reason they are fit very loose and must be up to temperature before the engine is run under load; they have to expand to the bore. I would have gone with hypereutectic cast pistons (Mahle) which avoid the loose fit and are almost as robust as the forged.
    Big cam's are a no no for pleasure boats; you trade bottom end power for a top end power gain. So unless you are going to have that throttle buried all of the time keep the cam mild and the overlap minimum. Overlap = Reversion.
     
    Last edited: Nov 30, 2021
  10. Pirate Lady

    Pirate Lady Well-Known Member

    Jun 2, 2020
    Chesapeake Bay, Middle River
    '91 250 Sundancer
    7.4 Bravo 1
    Interesting thread. Got a 250 / 7.4 basically same boat motor. “5000 rpm”.
    Missing something. Why? I try not go over 3400 cause the 4bbl open. Then fuel cost is crazy. I not in that big hurry.
    5k rpm. Do you own a refinery?
    Its a cruiser. What am I missing?
     
  11. WetPleasure

    WetPleasure Member

    101
    Jan 30, 2021
    99 260 sundancer
    7.4 bravo3
    Ha, I wish. This is going in a 260 sundancer. I wish I had some options to avoid dreaded reversion
     
  12. WetPleasure

    WetPleasure Member

    101
    Jan 30, 2021
    99 260 sundancer
    7.4 bravo3
    What you are missing is that when you have a more powerful motor you don't need to run it as hard to get desired results and thus you save on fuel. In my case, this 260 sundancer was maxing out at 35mph at 4250 rpm. That's ridiculous to me, cruiser or not, it's only a 28' boat. It should be able to go 50 mph at top end but allow me to cruise comfortably at 30mph around 3000 rpm.

    I own this boat free and clear, not really concerned about fuel costs to be honest. Not trying to sound like a stuck up rich guy but if I keep this boat, I know where I'll be using it and it won't be making long runs anyhow so fuel cost is minor consequence.
     
  13. WetPleasure

    WetPleasure Member

    101
    Jan 30, 2021
    99 260 sundancer
    7.4 bravo3
    I'll tell you exactly what they are. It's issues with exhaust pulses at low rpm that makes water work it's way back up and drip down into the cylinders. I need to do some digging but there was a research study down showing that the lack of a vaccumn break allows this to happen. By all other accounts I agree with you fully, 454 is a torque is monster! Mercury decided NOT to make an exhaust system to fix this problem. Dry joint exhaust solves it on the 5.7l Engines.

    As for my build, what's done is done, forged Pistons are in. I think the issue of forged Pistons expanding is a non issue and if it really is, it's not that hard to let a motor warm up a bit where I boat.

    As for cam, I didn't out a big cam in it. I posted the link to the cam kit. It's an upgrade from the stock cam which is super mild but it's still very far from being a crazy big drag car cam. It's a marine specific cam made for the 454 by comp cams. I'm confident in that decision.
     
    Last edited: Nov 30, 2021
    Nater Potater likes this.
  14. WetPleasure

    WetPleasure Member

    101
    Jan 30, 2021
    99 260 sundancer
    7.4 bravo3
    PXL_20211004_180612500.MP.jpg PXL_20211004_180652861.MP.jpg PXL_20211004_180500852.MP.jpg Motor pulled apart, you can see the severity of rust in the cylinder bore.
     
    Last edited: Nov 30, 2021
  15. Phil S

    Phil S Well-Known Member

    Oct 16, 2020
    Taxachusetts
    2004 300DA
    5.0 Merc MPI
    Bravo III
    Another one for the quotes thread: There's no replacement for displacement
     
  16. WetPleasure

    WetPleasure Member

    101
    Jan 30, 2021
    99 260 sundancer
    7.4 bravo3
    Pistons, rings and cleaned up heads PXL_20211116_171954607.MP.jpg PXL_20211116_173619887.MP.jpg PXL_20211026_143051466.MP.jpg PXL_20211116_172003806.MP.jpg PXL_20211116_173615644.MP.jpg PXL_20211116_173600071.MP.jpg PXL_20211116_172056761.jpg
     
    Mauler34Rod and Nater Potater like this.
  17. WetPleasure

    WetPleasure Member

    101
    Jan 30, 2021
    99 260 sundancer
    7.4 bravo3
    Added a drive shower to the Bravo 3 to assist with cooling. Preventative measure based on the increased horsepower and the fact that we added thru hull cooling.

    Motor is all back together. One more coat of paint then back to th mechanic for install into the boat! PXL_20211116_180439140.MP.jpg PXL_20211119_145406080.MP.jpg PXL_20211129_154844852.jpg PXL_20211130_204843571.MP.jpg
     
  18. Thornton69

    Thornton69 Well-Known Member

    943
    Sep 15, 2014
    Northern BC
    1981 245 SDC
    2021 Solar 420
    '97 5.7 Bravo 2
    '20 Merc 25 EFI Jet
    Would think revision would effect the center or rear cylinders the most? Looks like the front were the worst in yours. Is that where the idea of a possible sinking comes from?
    Have a 5.7 donor block out of the scrap yard for a build over the winter. It has a couple holes that are stained but believe it is just from sitting for a long time without being turned over.
     
  19. Pirate Lady

    Pirate Lady Well-Known Member

    Jun 2, 2020
    Chesapeake Bay, Middle River
    '91 250 Sundancer
    7.4 Bravo 1
    Hey, cool, what I know. On original 30yo Merc. You on 3rd engine but what do I know. Good luck.
     
  20. ttmott

    ttmott PhD in OCD TECHNICAL Contributor GOLD Sponsor

    Apr 3, 2012
    Space Coast Florida
    2006 52 Sedan Bridge
    Cummins QSM11
    That is "Reversion" and specifically caused by the lobe overlap in a camshaft. Overlap is that ramp down on the exhaust cam lobe and ramp up on the intake lobe creating a situation where both the intake and exhaust valves are open in a cylinder. The piston has already started it's downward stroke to pull fresh air in from the intake but as the exhaust valve is also open it also draws from the exhaust system. The loping chopity chop sound of an engine at idle with high lift / duration cams is actually caused by exhaust gas contamination in the intake charge. Another down side for street cars and pleasure boats is the intake vacuum is closer to atmospheric pressure and will cause havoc with the MAP sensors in a fuel injected engine making the ECM think there is a demand for power when the engine is really only idling and consequently the engine gets excessive fuel. But to the water intrusion, that very draw from both valves being open can draw water over the riser and the end result may be water in the cylinder head exhaust port and cylinders.
     
    cod, hottoddie and techmitch like this.

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