I am wondering about my hull shape speed wise

Discussion in 'Wooden Boat Building and Restoration' started by sdowney717, Jul 6, 2015.

  1. PAR
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    PAR Yacht Designer/Builder

    Most flow gains on mild porting jobs are had around the bosses and the exhaust side, assuming a good port match on the intake side.
     
  2. sdowney717
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    sdowney717 Senior Member

    The IH 392 heads are known to have flow issues on the exhaust, while the intakes are huge and good.
     
  3. PAR
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    PAR Yacht Designer/Builder

    I've ground on those heads before and the intake valve bosses need to be "faired" a bit and the top of the passage can use some work too. Relieve the shrouding on the valves, polish the piston, chamber and exhaust ports and you're good to go on a mild engine, with modest compression, running pump gas. Leave the intake side fairly rough for better mixture atomization.
     
  4. sdowney717
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    sdowney717 Senior Member

    I have some good results and some bad results.

    The engine no longer smokes any oil smoke, has no blowby, runs clean etc...
    But the engine has no more power than before I rebuilt it.

    It does run very nicely and also slowly goes the boat through the water. It can still not rev as high as the port motor.
    There is one thing I noticed, the cam lobes are off spec on the intake by maybe .010, I recall this number from memory. At the time I did notice ALL the intake were EXACTLY measuring the same slightly lower lift on the lobe. The rocker ratio is 1.6 to 1.
    At the time I was thinking such a small difference, and they really are measuring out all the same, how could that be the cause. Now I just wonder, maybe it is the cause of the lower power output.

    I can change the cam in the motor and don't have to pull motor up. Just have to drop trans, pull off drive damper assembly from crank nose and then the camshaft cover. Pull the lifters, they can be pulled without removing the intake manifold. And the cam will slide out.

    Since it is a higher rpm horse power issue, maybe the engine cant breathe like it should.
    A slipmate also has a wooden egg. He bought off ebay an old egg harbor sales brochure.
    In it egg harbor states the 37 cruises at 20 knots with a maximum speed of 25 knots.
    Trim tabs are not listed as an option.
    So in theory then it should be able to do this.

    If I get a cam, I would get an aftermarket cam like this here
    http://www.compcams.com/Company/CC/cam-specs/cam-search-results.aspx?sc=62&sm=By Engine Family

    I think the 252H grind is the one to use.
    Any ideas on this?

    268H grind is way too aggressive, 252H is closer to stock, has greater lift than stock. Stock was supposedly good enough back in 1970.

    Regardless, next haulout, tabs go back on. I am going to go from 42 by 9 to 42 by 12.
    And regardless of cam replacement, in a few years, I will haul the block to the machine shop and have block decked .040 so pistons are at zero deck height to set the combustion quench at .040
    With a 252H cam grin, that puts the DCR at 7.75 to 1 and the static ratio at 9.5 to 1. Which is why I lean to buying a 252H cam.

    And other thing is, this velvet drive has a very slow leak in the gasket between clutches and the gear reduction unit.
    So really I need to fix the leak anyway so just a little more effort to replace the cam.
     
  5. Stumble
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    Stumble Senior Member

    I really think you need to have your props looked at. If the engines are running good, and there is a history of hitting something, there is a real possibility one of the prop blades was knocked off true. Or while unlikely it's possible that somehow a yard installed someone else's prop on the boat.
     
  6. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    Sure is a mystery to me.
    Props are 22 by 20. And have been on here since I owned boat.
    There is another egg with 454 motors, so when they haulout, I will see what props it has.

    Anyone know, how much HP and torque required to drive a 22 by 20 prop?
    trans is velvet drive 2.57 to 1 gear reduction., shafts are 1 3/8

    [​IMG]

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    upload foto
     
  7. sdowney717
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    sdowney717 Senior Member

  8. PAR
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    PAR Yacht Designer/Builder

    I'd look at a "taller" cam instead of the 252. The 260 is a better choice, still having a fairly wide 110 degrees of separation, so she'll idle, but more duration and slightly more lift than the 252. It's operating range is better suited and a better torque curve for the MK4 block. Those particular heads respond well to a good valve seating and triple angle cut. A good machine shop can cut the seats, ensuing uniform concentricity to the stems. You can skip the hardened seats, if you toss some lead additive in every 3 tank fulls.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    lead additive ? Is that actually marketed ? I have heard of people adding proprietary brands of "upper cylinder lubricant" to fuel in small quantities, for use in older petrol engines running unleaded fuel, don't know the contents of it, but I'd be surprised if there was lead in it, though.
     
  10. PAR
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    PAR Yacht Designer/Builder

    Yes, lots of old cars without hardened valve seats exist, so an additive can be used to prevent the seats from getting pounded into the head.
     
  11. Barry
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    Barry Senior Member

    I think that Mr E was referring to your comment about being able to buy a lead additive. There are lead additive substitutes, but I thought the EPA banned all lead for automotive use
     
  12. Barry
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    Barry Senior Member

  13. PAR
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    PAR Yacht Designer/Builder

    I'm not sure what's in it, but it's an additive that keeps the seats from getting pounded to death, from unleaded fuel. Persoanlly I always have the hardened seats added, anytime a head has to get cut, decked, etc. It's simpler to know you can run any fuel grade.
     
  14. sdowney717
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    sdowney717 Senior Member

    All the seats were replaced by a rebuilder years ago, and I think they used stellite, if true they dont need any help.. They all looked really beautiful.

    And your right about the cam. I do think I will get the 260 grind.

    Years ago, I had the heads shaved .050, but that caused a massive amount of detonation on regular non E10 fuel which may be due to the stock OEM emissions style cam, the intake close degree is very low, so the cylinder fills a lot with air-fuel mix.

    So I doubled up the head gaskets, each one is .040 thick, so a net .010 difference.

    What I am thinking now is, get the 260H grind cam. The valve lift goes up from 0.4 to 0.45, the intake valve later closing degrees wont fill the cylinder as much as OEM, and also go back to using just one head gasket.

    That would put the SCR at 9 to 1, and the DCR in the low 7's.

    If that is not enough, someday I will take block to machine shop and have the deck shaved .040, which will put pistons even with deck at TDC. Right now they are .040 in the hole.
    That will also put the quench at .040 which is perfect to reduce detonation. SCR goes to 9.5 to 1, the DCR goes to 7.5 to 1.

    Part of this power problem in the engine is a prior owner had the engine replaced with a totally stock IH 392 emissions style motor meant for a truck. So the higher performance cam, solid lifters were gone.
    I have had both motors apart, and the other parts are not specialized from what I can tell, they are standard parts.
    Many rebuilders use destroked pistons, so the compression numbers fall. I suppose this could be justified by rebuilders shaving heads down, so a destroked piston brings compression closer to factory specs. and with crappy gas of today, less likely to detonate and blow up the rebuilt motors.

    But I just dont like the whole idea of destroked pistons, you then have to compensate for if you want compression pressures to be higher, closer to factory specs, you need machine work done.
     

  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Good to see other gearheads around. You can do the math as well as anyone else, but your going back to the single gasket and better set of parts, with the new cam will probably do fine. Getting the deck cut is a good idea, assuming your pistons have stock wrist pin heights. I'd hate so see you fly cut and not have enough hole for the stock height slugs.

    The 260 will make the power you want and you'll have to play with timing a bit to get rid of pre-ignition, if fuel quality is a problem. I've long ago given up on solid lifters on mild engine builds. You just don't need them. Good hydraulics (not stock replacements, but good ones) or better yet conversion to rollers offer a lot more on mildly modified engines. Cam profiles can be much more aggressive, while retaining good idle, emissions and reliability. You also get less friction, which is just free power, which is why I usually couple rollers with rollers at the top end too. Just more free power. A stock MK-IV with stock lifters and stamped rockers will kiss off 30- 40 HP at WOT over a roller/roller setup, just from friction. Coupled with better lobe profiles, bigger gains can be had. The old school stuff still applies, but some of this new school gear, really makes huge improvements.

    I took a 1st gen SBC, rated at 230 HP (older Crusader) and just the roller cam of the same basic grind produced nearly 260 HP at 5,500 on a flywheel dyno. The addition of rockers (double roller) bumped it to 270 at 5,500 and 275 HP at 6,000 RPM. Toss in better flow rates on the runners, with 8 to 10 hours of grinder work and a cam profile that can take advantage of the improved CFM, you'll add an easy 25 more HP.
     
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