The Doc is in

[GoBigBlue1984]

In all seriousness Scott that's some beautiful weld, much better than I could do.

 

[jake wells]

In all seriousness Scott that's some beautiful weld, much better than I could do.

im uploading some videos and made a thread to promote your bizznes.

 

[GoBigBlue1984]

Thanks Jake. That's very kind of you.

 

[Jimmy in NC]

Some time ago I sent a couple of Pistons to Al to tig up for me and a few weeks ago he sent them back.
First off Al does incredible work, he got excellent penetration and didn't burn through at all.
Great Job Al! I hope to do some more work with you in the near future.

Al roughed these down before sending them back. Here is the 395 piston when it showed up.
View attachment 25056
Here's the 395 piston in the lathe....
View attachment 25057
Finished product.......I may have to turn down the diameter a tad more but I'll check all that before this next 395 goes together.
View attachment 25058
View attachment 25059
Again, a great big thanks to Al, I owe ya one.
I'll add more to the thread once this build begins.

What is your target cylinder pressure? A 395 is pretty darn stout with out that much pop-up. I would worry about the bottom end longevity. If it is just a cookie cutter..please get videos.

 

[jake wells]

Thanks Jake. That's very kind of you.

 

[GoBigBlue1984]

That's a different 395 Jake. The one in the video that Ben is reassembling has a flat top piston.

 

[T.Roller]

What is your target cylinder pressure? A 395 is pretty darn stout with out that much pop-up. I would worry about the bottom end longevity. If it is just a cookie cutter..please get videos.

My 395 has been blowing 225 for years now. But not many hours on it. 18 hours I believe

 

[jmssaws]

A 395 can't take big compression for long but nothing fast lives forever.

 

[Scotts_4x]

I wasn't trying to say anyone didn't do a good job, my point was if you're going to say someone did an incredible weld I want to see the beads that's all lol. I've been in the welding business since I was 18, so it's taken a while (and lots of practice) to get where I am today. I'm taking nothing away from Al, he did a job most would struggle with. cast aluminum lends itself very well to porous welds, even more so after its been soaked in petroleum products for years.

-scott

 

[Lightning Performance]

You guys using popups might be adding weight but the gains can be huge on certain transfers and chamber shapes. They didn't use those outrageous popups in old outboard motors for no reason. They really do help complete "the loop" when poor transfer shot angles was all that could be had back then. Short ports also hindered the loop.

 

[paragonbuilder]

You guys using popups might be adding weight but the gains can be huge on certain transfers and chamber shapes. They didn't use those outrageous popups in old outboard motors for no reason. They really do help complete "the loop" when poor transfer shot angles was all that could be had back then. Short ports also hindered the loop.

Can you elaborate on this relationship between port shapes and pop ups.


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[Lightning Performance]

Sure.
If you can aim the charge at the plug it helps the mix to go evenly around the chamber. Also helps the charge shot to cool the pocket, the plug and better evaporates or atomizes the mix. The fresh cool shot eats the heat. The improve angle pushes the loop around to help dump spent gasses out. The popup becomes and extension of the port in some respects. Hope that helps some.

 

[paragonbuilder]

Sure.
If you can aim the charge at the plug it helps the mix to go evenly around the chamber. Also helps the charge shot to cool the pocket, the plug and better evaporates or atomizes the mix. The fresh cool shot eats the heat. The improve angle pushes the loop around to help dump spent gasses out. The popup becomes and extension of the port in some respects. Hope that helps some.

I see. So would a domed piston be better suited to this, like an 026? Or does the step in a pop up actually help as well?


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[Lightning Performance]

I think the step helps more in small diameter bores. That is just my 2cts.

Do most small bore saws come with a factory domed piston? If so, why? It ain't just surface area they were looking to gain. They were surely not looking to add weight.

 

[Mattyo]

so.... just to thread jack here... why are transfer angles, such as on a 372 or 346xp so flat? just looking at the transfers it looks like they shoot parallel to the top of the piston..not at the dome of the cylinder head

 

[paragonbuilder]

I think the step helps more in small diameter bores. That is just my 2cts.

Do most small bore saws come with a factory domed piston? If so, why? It ain't just surface area they were looking to gain. They were surely not looking to add weight.

I don't believe most do. Most I've seen are flat. But I know these engineers weren't shooting from the hip in there designs, and I'm trying to understand.


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[Lightning Performance]

Understand... we will all go down trying to. Flow bench is the next step for me. Of course that will preset more questions than answers.

 

[drf256]

so.... just to thread jack here... why are transfer angles, such as on a 372 or 346xp so flat? just looking at the transfers it looks like they shoot parallel to the top of the piston..not at the dome of the cylinder head

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.

 

[drf256]

The right side of the dome is the intake side. I learned this the hard way after putting in backwards a few times.

 

[paragonbuilder]

The right side of the dome is the intake side. I learned this the hard way after putting in backwards a few times.

View attachment 63309

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


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