User Tag List

Page 11 of 11 FirstFirst 1 2 3 4 5 6 7 8 9 10 11
Results 151 to 156 of 156
  1. #151
    Join Date
    May 2014
    Location
    Livingston, Louisiana
    Posts
    2,183
    Thanks (Given)
    76
    Thanks (Received)
    270
    Likes (Given)
    566
    Likes (Received)
    966
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by akuczera View Post
    So if it was covered already sorry. My question is at what point could the incoming charge over power the exhaust wave. By stuffing the crankcase. It seams like the returning exhaust wave could over power the incoming charge if you were to lower you crankcase volume to much. I would venture a guess that the engineer's at mercury would have calculated this in to the design of the 260's and 280's. Making stuffing only necessary to return the balance after working the rod slots and ports. Well just wondering if I'm to off based here or not?
    I feel you hit the nail on the head with merc getting it pretty much right. The way I look at it and do it is, depending on how much material I remove any where that would effect cc volume to improve flow/velocity I replace the material else where with epoxy. Also depending on porting I'll change volume. I fool mostly with bass boats, so I normally tighten em up a little to add the needed low end to mid range needed for the heavier boats when raising boost/ transfer timing that causes the ports to be larger and slowing down velocity. On the inlet side velocity is the most important factor, without it, you ain't got nuttin. You can have all the flow ya want, but if it's slow, it's a turd.

  2. Likes spybot, Mark75H, powerabout, Baker343 liked this post
  3. #152
    Join Date
    Feb 2015
    Location
    Ontario
    Posts
    8,091
    Thanks (Given)
    205
    Thanks (Received)
    321
    Likes (Given)
    1921
    Likes (Received)
    2005
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Nosubforcid View Post
    Well the theory that all cylinder filling is the result of piston displacement and pressure in the crankcase is pretty outdated. That theory held that cylinder filling is simply a one to one volume exchange. The problem is that theory doesn't allow for the time lag to get the charge moving, and since charge mass per stroke is essentially constant with rpm so is the time lag. This leads to progressively poorer performance as rpm increases and this time lag becomes proportionally larger with respect to the time available to fill the cylinder. Current two stroke theory holds that a properly evacuated cylinder is not just one that is blown down to ambient pressure but one that is pulled below ambient pressure by the momentum of the exhaust rushing out the port. This low pressure wave is what starts the fresh charge moving in the transfers(generic use meaning all intake ports) before any positive pressure in the crankcase could ever hope too. Similarly the columns of charge in the transfers have mass and correspondingly momentum so they do not stop flowing as soon as the cylinder is"full" or back to ambient pressure. The charges continue to stream from the transfers and collide with each other producing an area of localized high pressure while some flows out the exhaust port. This charge that flows out the exahust is to a great extent rammed back in to the cylinder by the rising pressure in the exhaust tract either from an adjacent cylinder blow down in our V6s or a reflected wave in the expansion chamber in other applications. This combination leaves the cylinder "overfull" or supercharged above ambient pressure something a high crankcase pressure design could never achieve due to lack of crankcase volume.
    G2 WOT 5500, PSIA through 360° 11-24 PSIA , not bad at all.

    13.75 - 20.5 at 2000rpm
    Last edited by FMP; 06-08-2020 at 03:02 PM.

  4. Likes dwilfong liked this post
  5. #153
    Join Date
    Mar 2018
    Location
    Michigan
    Posts
    15
    Thanks (Given)
    0
    Thanks (Received)
    0
    Likes (Given)
    0
    Likes (Received)
    1
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I background is around snowmobile race engines and have only been working on outboard motors for 15 years. The extent of outboard performance has been limited to jetting to get improved performance. In the snowmobile world, we look at horsepower per liter. The maximum horsepower per liter today (it has been creeping up over the years) is 300hp/liter. As I have not been involved with racing outboards, I have not heard of an outboard making anywhere need that. A 2.5 liter outboard would be around 750 hp. I had the idea of putting expansion chambers on a V6. After some searching, I saw it had already been tried with limited success, not making the HP/liter. I suspect that the reason is that the air flow is limited by having to go thru the crank/rod assembly to get into the transfers. Snowmobile engines get there air above the crank wheels. Arctic cat has figured out that tipping the cylinder away from the intake made for a mord direct flow into the bottom of the transfer tunnels increased torque. They call them laydown motors. If I didn't have anything else to do, I would like to build an outboard motor using the laydown engine platform. All outboards that I know of flow air thru the crank wheels which may required to produce the torque necessary to get a boat on plane. Just my observation.

  6. Likes Instigator liked this post
  7. #154
    Join Date
    Jun 2007
    Location
    Singapore/Melbourne/Italy
    Posts
    9,097
    Thanks (Given)
    1008
    Thanks (Received)
    354
    Likes (Given)
    4297
    Likes (Received)
    1951
    Mentioned
    7 Post(s)
    Tagged
    0 Thread(s)
    bore spacing is where an inline beats the Vee outboard, you just cant fit great porting into an outboard

  8. Likes Instigator liked this post
  9. #155
    Join Date
    Apr 2001
    Location
    Cardington Ohio
    Posts
    19,661
    Mentioned
    7 Post(s)
    Tagged
    1 Thread(s)
    Part of the questionable results of pipes on OBs is targeted RPM of the pipe.

    An OB does not have a centrifugal clutch/transmission to keep the motor “on the pipe” like a sled.

    In open class OB hydroplane racing they are allowed to run pipes/chambers and to make them work, they set them up to slide on the manifold, thereby adjusting their tuned length, allowing them to follow the power band.

    Last I heard, the best 500’s were at about 150 hp’s or, 300 per liter.

    Tuning, porting a two Stroke in an application w/no gear box changes everything.

    Take your baddest sled and replace the clutch w/a sprocket and chain and see how it does.


    Quote Originally Posted by Mel Winnie View Post
    I background is around snowmobile race engines and have only been working on outboard motors for 15 years. The extent of outboard performance has been limited to jetting to get improved performance. In the snowmobile world, we look at horsepower per liter. The maximum horsepower per liter today (it has been creeping up over the years) is 300hp/liter. As I have not been involved with racing outboards, I have not heard of an outboard making anywhere need that. A 2.5 liter outboard would be around 750 hp. I had the idea of putting expansion chambers on a V6. After some searching, I saw it had already been tried with limited success, not making the HP/liter. I suspect that the reason is that the air flow is limited by having to go thru the crank/rod assembly to get into the transfers. Snowmobile engines get there air above the crank wheels. Arctic cat has figured out that tipping the cylinder away from the intake made for a mord direct flow into the bottom of the transfer tunnels increased torque. They call them laydown motors. If I didn't have anything else to do, I would like to build an outboard motor using the laydown engine platform. All outboards that I know of flow air thru the crank wheels which may required to produce the torque necessary to get a boat on plane. Just my observation.
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.


    I refuse to allow common sense to interfere w/my boat buying decisions.


    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

  10. Likes powerabout, AZMIDLYF, Mark75H, Captain75 liked this post
  11. #156
    Join Date
    Aug 2001
    Location
    Annapolis, MD ragboat capital of the world
    Posts
    11,463
    Thanks (Given)
    591
    Thanks (Received)
    164
    Likes (Given)
    2428
    Likes (Received)
    445
    Mentioned
    2 Post(s)
    Tagged
    3 Thread(s)
    And then give it a second maximum torque demand at 30% rpm (getting the boat over plane).

  12. Likes Instigator liked this post
Page 11 of 11 FirstFirst 1 2 3 4 5 6 7 8 9 10 11

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Aeromarine Research