new aluminum sleeves for omc xflow v4 or v6. a project.

[Umassot50]

I have a v4 I have been working on off and on for a while. I have been going back and forth with myself as to whether I wanted to sleeve it or not. So I decided yes and they will be aluminum sleeves that will eventually be nikasil plated.
It will be stock 3.5" bore. I considered a big bore but I want to keep the sleeves thick and not have to take out too much of the existing aluminum casting around the current iron sleeves.
I have a lot of experience with this in snowmobile engines and the advantages of port design and cooling capacity of the al\nikasil is a great advantage. Having a shop I have done a lot of these and the boring and shrink fitting is the critical part. A bit trickier than putting in or pulling iron sleeves.
The goal is to fill the bottom edge of the transfer port windows square so they are flush with the piston top at bdc. Improvements in exhaust port shape will also be possible.
The top flange of the sleeve will be a much larger diameter. The top of the aluminum portion of the linner will need to be cut down to accommodate a flange. The flange diameter will also be large enough that it will extend out to and engage the cylinder head bolt bosses which will be cut to register the sleeve flange. Making it a semi closed deck design. The sleeves will be cut on the side of the flange to Siamese together with the other bore and sleeve. Installed two at a time will ensure perfect port and sleeve alignment. And also tie the whole top end together.

The transfer port will also be changed with some new cast parts. One being a new outer cover that will have a very curved arcing outer port wall and a corresponding curved inner port wall filler that will be welded or epoxied in. You have heard of "cross charge" mod... Think of this as the opposite of that. The idea being that the highest power two strokes in the world have very well shaped arced port tunnels that are smaller than you would think. Definitely not big gaping cavities...

I'm interested to hear any thoughts about cylinder boost ports. They would need to be fed through a hole in the side of the piston at the 3 and 9 o'clock positions. A port in the sleeve wall here would be easy to do but I'm usually against such ports due to such little port area to have any true effect...thoughts. I'll have to see how much port I can get in the casting between the bores too.

[Umassot50]

some models.

[patchesII]

Sounds very interesting

[racer]

I have done what you are talking about on the intake ports, filling to make the arc you mention and redone the covers. I however had to use epoxy to stay within the MODVP rules. What I found was a slight gain in low end power and mid range punch, on the boat about 50rpm at full throttle but understand we turning them a lot higher than most even for 30 minute races. Finger ports are the best gain.

[olboatman]

Scribed. Gary

[Umassot50]

Interesting. You must relieve the piston top deflector on the sides a bunch then? There is so little meat in those bore walls...on the top and bottom of the block the water jacket is right next to the area where the port would go... A little too deep and your in the water jacket.. Unless I cut open the water jacket to weld in more material from the back side?...
When do you open the boost port? Same time as the rest of the transfers?

[racer]

We were running 3.625 bore engines so had even less room for the fingers, what they allow is running the engine closer to the edge without burning the sharp edge on the piston thus power. Yes you need to cut the deflector toward the exhaust on the outer edge only. Yes same time.

[Umassot50]

like this

[71V153]

Hmm. Are you tryin to reinvent the Vega? Kidding! Subscribed.

[wanagofass]

Way cool project dude!

[Schramer]

I always wanted to do this lol but I had a different idea for the intake....curious on the rings/pistons you will use??

[Umassot50]

Vertex pistons most likely.

[wanagofass]

Just curious. Kinda........... What kind of equipment does it take to bore the block like you are planning?

[Umassot50]

An oversized mill with an nt30 spindle and a 3 inch boring head. Well that's what I have.

[Markus]

Great project!

Just checking: Are you aware that there are stock engines out there that already have Nikasil coated aluminum sleeves and in addition have more advanced loop charging?