OMC 3 Cyl expansion Chambers

[Jeff Akers]

There are some that belive that the "up exit" is more beneficial to exhaust scavenging . There was some discussion on the subject in the original "Fast Fred's Secrets of the MOD 50 thread", I think the discussion starts around pages 9 to 11.

[Tim Kurcz]

Johnsonracer: 30 years ago I spent a month in Kiwi and happened to drive a race boat while visiting friends in Auckland (after touring the south island from Christchurch). It was a very good roughwater Chrysler powered 25 cu inch v-bottom runabout about 11 ft in length. I sent some Michigan Wheel 2-blade racing props back from the US to help the fellow out, but lost track of him years ago. NZ is a truly wonderful country. My dream is to visit again, and retire there a bush pilot. The possibilty of racing boats would be like foam on a fresh Lion's brew!

Anyway, the obvious advantages of top outlet exhaust are:

1) No interference with steering as with my earlier down outlet versions.
2) No hassles incorporating the Mod-50 exhaust inside a closed tower or under a "stick" style tower as through ducts are always challenging.
3) No uncontrolled water vapor contamination of the exhaust system from cooling water dumps, vacuum pockets at/near the hull, hosing from roostertails, etc; the meg points back away from the boat, not sideways.

Note there is a small sump and drain hole provided in case of rain or other accidental aft watering. I've thought of adding a John Deere style "rain cap" flapper just for grins, but didn't want to spend the engineering time or add weight/cost.

Basically, if you're tower is so short as to submerge the bottom cylinder upon launching, a piece of tape could be applied as a temporary measure, or the 1/16" hole could be plugged or welded shut.

There may be serious engineering reasons why a top outlet might work better than a bottom, but they don't matter. I built the best possible, reasonably priced copy of the highly effective factory developed Mod-50 racing exhaust system. It just plain works.

Tim

[Roy Hodges]

DON'T do it ! I had one on my Lincoln SA250 diesel welding machine ,and even as loud as the exhaust was, the cap drove me crazy ! I threw it AWAY !

[johnsonracer]

I am liking the idea more and more of the pulse tune. I guess you guys and omc have spent lots on hours designing / testing. If I were to pipe it I would be stating from scratch.

The blocks at the welders, so when I get it back I'll make sure its going to work before i order.....

Tim, if you ever planning a trip to Kiwi land I'm sure I could put you up, same goes for any other race guys wanting to visit N.Z.... As long as you not gun weilding wacko's!! :-)

[Fast Fred]

So,

Tim Kurcz

was thinkin maybe you could help me out, gots me one of them thare "Straight in" Modas, gots every thing i needs for it but she has a worn out liner. think you could share how you worked that out with yours . like if ya needed them, ware you got them, who put them in, and when thay were done how thay looked compared to the factorys, and how much about the cost. any help would be cool.
thanks
FF

[Tim Kurcz]

Hi Fred,

Nice looking 10-port. Try LA sleeve. They built replacement Mod-50 sleeves for years and still have the drawings. If no luck, let me know and I can machine/install them for you.

Tim

[johnsonracer]

I Have one of those motors too.. I have never assembled it because the exhaust exiting out the bottom doesnt fit my mid. Bot with that exhaust system of yours this will solve that.

I have all the parts, even 3 new rings. Which motor would be recomended for top speed? I cant help but think that more C.I's is always better.

[Tim Kurcz]

OK on the Kiwi trip, and I was only teasing about the exhaust flapper!

Otherwise, the 56 never saw development like the Mod-50. Rumour is the typical six-pack 56 will make 100 +/- HP, where the US-factory Mod 50's were 110 +/-, and the European F3 with it's reversed exhaust was supposed to go 120 +/-. Though delivering moree power, the Mod-50 is a known piston burner and less durable. My best FE racing engines are good for only 10-15 hours hard race time with the fishing blister sleeve design before they wear out (two-three years Mod racing). The pressed sleeve (factory) race engine has better piston support and durability. But be aware this engine is extremely sensitive to fuel quality and delivery and propping (don't lug it). I've got boxes of melted pistons to confirm it, all burning Avgas! That said, it's a tremendous rush of power on as light boat.

Let me know when you're ready for the exhaust. It will make your engine lighter and less complex, and is known to work.

Tim

[johnsonracer]

The engine I am building is for a Kilo run. So low down etc is not an issue. I need to get 103mph so the best suited engine is the one I'll be going for...

[Tim Kurcz]

Then the 50 will likely do better and is easier to build with up exhaust. Either will benefit from the Mod-50 exhaust system.