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What do you think of this exhaust port

RacingJake

RacingJake

Forum Sage
Take a look at my GS1100E exhaust port at my WWW button below. I think alot of grinding is needed to match my V&H Pro Pipe. The exhaust pipe is the same thickness as the gasket that's in there. You can see the gasket in there and about 1/4 inch of aluminum is still blocking the exhaust pipe. And what about the floor in there what is that suppose to do.

Jake
 
Be carefull what you do or it might hurt preformance by removing too much material? There needs to be some back pressure to help the engine scavange the ex gases out. You need to talk to someone who does porting work
 
Be wary. As well as flow, you need gas velocity to get HP, along with matching exhaust and intake tuning. Hogging out the ports may lead to less performance or very narrpw bands of gains.
 
The flat port floor keeps the short side of the port the same apparent length as the long side. Adding an obstruction to the inside of the turn makes the gasses take as long going around the bend as the far side has to go. (did that make any sense???) Anyway it keeps the port velocity high.
 
In the Honda CBR900 series they have had it for awhile. They call it their "D" port.
 
Take a look at my GS1100E exhaust port at my WWW button below. I think alot of grinding is needed to match my V&H Pro Pipe.
Click to expand...

Be careful with a grinder in there, Jake. Porting is a black art and takes a LOT of time and effort trying things and testing to get it right. If you really want results the only way to go is to take your head to a respected tuner who knows your engine well and tell them what you want. Bob Bertaut (site mentioned elsewhere here) has a good reputation for the GS motors. If you only want to smooth things out, it is not too hard. Just remove casting marks and rough spots, but do not change the shape of the port. As a general rule, intake ports like a slightly rough, matte finish and exhaust ports like a shiny smooth finish.

As for your port not matching the pipe, you don't necessarily want it to. That step into the pipe helps stop negative pressure pulses from coming back into the cylinder and causing a big hole in the torque curve. You can also do this with anti-reversion cones incorporated into the head pipes. Jim Feuling has a patent on some that I am using to design a set for my ZX-9. Look at http://www.uspto.gov/patft/index.html and search for patent #4,206,600. It explains the design considerations and the layout for the cones if you are interested.


Mark
 
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