The Doc is in

[drf256]

The dead space at BDC is what guys try to eliminate with intake finger ports.

The problem is that the can force the entire plume away from the intake wall and create more dead space.

I see exhaust fingers clearing the area between the rear of the upper transfers and the exhaust wall to be a possible performance enhancer. The roof angle will be super critical here though.

 

[drf256]

I've never seen inside an outboard before. Pretty cool!


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The cylinder wall has openings that are multiple small circumfiremtially placed individual holes around the intake side. The charge gets forced up by that wacky dome.

 

[mdavlee]

372 has the primary flat and secondary is aimed up.

Exhaust side fingers are going to cause more turbulence and mixing of burnt and fresh. If you get the exhaust side of the primary open too much a lot of the fresh charge is lost right out the exhaust.

 

[Mattyo]

Good Morning Matty.

Think about the design of the motor. It's loop scavenged.

As a side note, old outboards were cross scavenged. The transfer charge shot at a nearly flat piston dome and got pushed up into the chamber, forcing the spent gasses away from the chamber and down a sloped piston dome on the contralateral side.

On the 372, the piston comes down, the transfers crack open. The charge sweeps the top of the piston first. As the transfer opens more, the charge is pushed towards the intake wall and more of the transfer is revealed. As more transfer opens, the flow that comes out won't be fully flat. The roof simply changes the shape of the plume. I bet if you look at the set of transfers closer to the intake wall, there is more roof angle to them.

The name of the game is to avoid as much charge dilution from spent gasses as possible without losing unburned fuel out the exhaust port. The flat initial open angle helps to sweep the dome clean and eliminate the dead space between the piston at BDC and the intake wall.

so, would it make sense to open the mains 2 degrees early.... flat angle to clear the piston, and then open the 2ndary with some angle?

 

[drf256]

so, would it make sense to open the mains 2 degrees early.... flat angle to clear the piston, and then open the 2ndary with some angle?

That's what the Swedish and German engineers seem to think. I'll take the bet they are correct.

 

[drf256]

372 has the primary flat and secondary is aimed up.

Exhaust side fingers are going to cause more turbulence and mixing of burnt and fresh. If you get the exhaust side of the primary open too much a lot of the fresh charge is lost right out the exhaust.

Ya think exhaust venturi effect will pull it out Mike?

 

[mdavlee]

It sure will. I've seen swirl marks in exhaust ports. @rattler

 

[rattler]

You talking about the 288 a couple years back?

 

[Mattyo]

i'm building a 372 clone ....doing a vid series... going to include this principle if possible.

 

[mdavlee]

You talking about the 288 a couple years back?

Yes

 

[rattler]

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[TJ the Chainsaw Mechanic]

 

[mdavlee]

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Thanks Mike. Sometimes they'll be some of that on a piston crown showing up til they carbon over real good

 

[rattler]

Thanks Mike. Sometimes they'll be some of that on a piston crown showing up til they carbon over real good

Welcome Mike

 

[drf256]

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Any inside shots?

Where were they placed?

 

[rattler]

No Al that's all I got left

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[mdavlee]

One of the 46s I did had something similar on the piston. It was one with finger ports so I guess they were working pretty good.

 

[srcarr52]

we'd need to see pictures of the beads before they got "roughed down" to truely judge if theyou were "incredible. " most weld jobs that go back to the customer ground off after welding when it's not asked for usually means it wasn't super nice before grinding. it does look like there's no porosity so the job was at least good enough for machining.

-scott

I've done some welded pop-up for people and I always rough machine them after welding to check for any porosity. I still am yet to find any but I'd rather take the time to do it then have to have them send it back to be re-welded.

 

[Lightning Performance]

My mistake saying it was an early "popup motor." I should have said an outboard domed "looper piston". I can not copy and paste with my current TV internet link. Someone will chime in with a pic.

Check out specs about cylinder pressure on a piston. Domed or popup vs a flat top. The increase is minimal but the pressure is exerted from ALL directions to the piston top. The piston is forced down by the pressure. No such thing as "down pressure." The pressure comes from all angles.

 

[dustinwilt68]

Al is a top notch guy, done deals with him a few times, always good results. I was a welder myself and I would have taken offense if someone would have questioned my ability. I am sure Al would have said he couldn't do the job if he felt it was beyond his ability, obviously it was not.