exhaust manifold trick

[jetski9010]

so I was talking to a guy that use to build race snowmobile motors in the 80's. He was telling me about a trick they use to do before power valves came out. He said he would blueprint the exhaust manifold to the cylinder but then at the bottom he would cut the manifold down 4-6mm lower so when the sound wave came back it would hip this lip and be forced upward to help block in the fresh charge as much as possiable. He said this mod helped out with torque. Is this already a well know mod out there? Would this work the same on a jet ski engine?

 

[DAG]

wammer mod port matches... not sure about the lip?

 

[Polish jet pilot]

V.interesting - picture or drawing??

 

[jetski9010]

Now after hearing this I was looking at the exhaust ports of some 62T cylinders and it looks like they have a very small 1mm lip on the bottom. I wonder if this is the same theory behind this.

 

[Polish jet pilot]

what about 61X?

 

[jetski9010]

not sure I dont have an extra set of them around to look at.

 

[SUPERTUNE]

If you use unported 61x cylinders and a unported Factory B pipe manifold, you would almost have the same thing as they don't match up very well stock.

 

[Roo]

If you use unported 61x cylinders and a unported Factory B pipe manifold, you would almost have the same thing as they don't match up very well stock.

So on a setup such as this...

don't port match the manifold to the cylinder?

just *perhaps* open up the exhaust manifold outlet and head pipe (factory b pipe?)

 

[GIL]

hmmmmmmmmmmmm

 

[jetski9010]

So on a setup such as this...

don't port match the manifold to the cylinder?

just *perhaps* open up the exhaust manifold outlet and head pipe (factory b pipe?)

I think you would want to port match it everywhere eles just leave a lip at the bottom.

 

[GIL]

I think you would want to port match it everywhere eles just leave a lip at the bottom.

Dan has my 'lips' at the leading edge of both exhaust ports. He says it is to help w/exhaust reversion. If you do a search on posts started by me there is pics of it somewhere on here.

 

[Matt_E]

I smell a bandwagon coming.

 

[QJS]

I smell a bandwagon coming.

Me too, gonna start making exhaust port scuppers, think it would work?

 

[WaveDemon]

hmmm, I've got a manifold on the bench that I was going to port...

 

[Matt_E]

Hang on to it until the bandwagon is in full swing, then sell it at the apex.

 

[Matt_E]

Me too, gonna start making exhaust port scuppers, think it would work?

It doesn't have to.
People just have to think it works.

 

[waxhead]

Ok not some thing i have done
But when you consider that that the exhaust gases and fresh air goes out of the engine and into the exhaust
not only will you be blocking new air in but also new air out

 

[Mark44]

i

It doesn't have to.
People just have to think it works.

LOL so true!

 

[GIL]

It doesn't have to.
People just have to think it works.

I am pretty dam sure my 'lips' are due to mis-alignment during the casting process. Why in the hell would you get the port alignment that far off? We are talkin a 1/4" on one hole and 1/8 on the other. I am pretty sure I was fed a line of B.S.

 

[Dustin Mustangs]

Interesting idea, but I really doubt it works. The idea of a tuned pipe on a two stroke is to push some of the fresh air charge that sneaks through to the exhaust back into the combustion chamber before the ex port closes. The only way this will happen is if the positive pressure returned by the pipe is greater than that in the combustion chamber (and that it's timed right). Well, putting a sudden contraction in the exhaust on the way back into the combustion chamber is going to rob you of some positive pressure produced by the pipe, not add to it. It may not sound like it, but this is pretty simple fluid mechanics.