OMC 3 Cyl expansion Chambers

[David Mason]

If you want to go fast with a 49 cuber, you must run a exhaust system that works. Fixed chambers will work great fo rmaybe a kilo run, if you get it right. For competition races, you need something like what Chenny and Kurcz are using. I have one of the original Mod 50 exhaust systems along with many other people that race in FEH. They work very well, however there is room for improvment today. One can take a stock exhaust system from that engine and do a little carving and achieve decent results. The engine I won the APBA and AOF Nationals with was using a stock exhaust system slightly modified.

There is no one magic pill for exhaust. A lot depends on other factors, such as porting, and some other measurments. The beauty of this class is the fact that there are so many blocks out there one can experiemnt for a very small amount of money. I can honestly say that all of my 49 CI blocks I have tossed in the trash with failed experiments would not even come close to the cost of a current DSH or Sidewinder.

Back to the topic of exhaust. You need to find what works on your own application, boat, weight, etc make a difference as well. You can adjust porting to accomodate some things, thus changing exhaust math.

Like Tim said, there are things done on his system that he does not disclose.

[johnsonracer]

Hey Tim,

Does your exhaust come with that megaphone and everything?

I think it would be easier to adapt that to fit than fabricate pipes.

Top end is what I am looking for. I would like to be pulling near 10,000 rpm if possible.

You have a rough idea on how much to air frieght it to NZ?

[Tim Kurcz]

Yes, the meg, springs, and fasteners are included. As you can't use the lower plate, I'll separate that out. The nickel plated manifold, cone, and springs is $400 US. This will easily adapt as bore centers are the same for the 49 and 56 cubers. Send your address and I can get shipping information.

Tim

[johnsonracer]

I'll PM you with address :-)

With there being one megaphone for three cyls, does it affect the top cylinder differently to the bottom one? Being such a different length?

How would 3 of your megaphones go one one motor for example.....

DO you have any idea in power increase that system might add? When people talk about race pipes on two stroke bikes for instance they talk like 50% power increase. Thats huge!

[Tim Kurcz]

No, the plugging pulse is the same for all because of the close interconnect. The top outlet merely inverts the factory Mod-50 system. Three individual megs would eliminate the pulse tuning and go slower. Finally, anybody talking 50% by just bolting in a pipe is smoking hooch. Now, if you increase port timing to match the pipe, tighten crankcase pressures and increase cranking compression, and bump carburetion to match, then you've got something.

So, do you run in lake Te Anau?

Tim

[johnsonracer]

No I havent run in that lake. I am in the North Island. Have been to 4 or so lakes down south but not that one.


Another mod I am trying is copying the mod 50 type porting in the 56er.

With the main transfer going beine the sleeve in the 56 I am making some sleeves and pistons with the square transfer. I will put the sleeve in and fill the bottom to try match as closely as possible. This should increase crankcase comppression massively. I also thought the aire going through the piston (and finger ports) would reduse the resistance on the piston...
You tried this?

[johnsonracer]

What I am trying at the moment.

[Mark75H]

Excellent pictures, worth more than a thousand words each!

[Roy Hodges]

[QUOTE=Tim Kurcz;68935]No, the plugging pulse is the same for all because of the close interconnect. The top outlet merely inverts the factory Mod-50 system. Three individual megs would eliminate the pulse tuning and go slower. Finally, anybody talking 50% by just bolting in a pipe is smoking hooch. Now, if you increase port timing to match the pipe, tighten crankcase pressures and increase cranking compression, and bump carburetion to match, then you've got something.

So, do you run in lake Te Anau?............................................. ..........................................
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I guess I'm very dense, having to ask this question. Is the reason for the outlet out the top , so that water don't enter the engine while launching the boat? Or since exhaust is hot & light , and rises ,i guess ,does aiming it up help scavenge the engine exhaust ?

- Roy Hodges

[johnsonracer]

I'll take agues Roy, I think its at the top so it doesn't foul on the midsection or steering etc... Let us know if i'm wrong Tim.......

No I don't run in Lafe Te Anau. I notn know if anyone else does. I havent seen it on a programme in the past few years.