Intake porting?

[rvbent]

Just finished rebuilding carbs on my '80 gs850. many thanks to John Bloemer and Robert Barr. Noticed how rough Susie Q's intake passages
were-any tips on porting/polishing would be greatly appreciated.

 

[Nessism]

Is the head off the bike?

 

[duaneage]

Rough passages are not a bad thing. The roughness helps with fuel atomization. If you are inclined to do anything raise the floor a bit on the ports and open the valve pocket area a bit.

Porting is a science and requires some skill and experience. Unless you have an established example to follow just ride the 850 as is and enjoy it.

 

[trippivot]

60 or 80 grit is perfect for the intake side. just cleaning up the casting flaws is ok to do if you not have any clue what you are doing. the rough surface helps for turbulence. don't cut off the guides. polished and smooth is for the exhaust side and compression dome.

 

[Nessism]

I "ported" the head on my 1000 using a rat tail file. Worked great to smooth out the sharp edge transition on the short side radius between the port casting and Suzuki's machining work when they installed the valve seats. Key thing for people that don't know what they are doing (like me) is to minimize how much monkeying around you do with the port shape. Smoothing out sharp edges and casting imperfections is fair game but stay clear of shape changes. Oh, and only do this kind of thing with the head off the bike.

 

[rapidray]

Jeff, I use 40 grit on the intake side AND I cut the guides off! I've seen a 3-5 cfm gain on some heads just in cutting the guides off. Ray.

 

[beingblueeyes]

Just wondering how much "meat" you could take off of the intake port before you hit something like a oil jacket in the head casting if you wanted to change the shape of the port? has anyone cut a head in 2 with a metal band saw to see how much space you have for porting?

 

[headsbikesmopars]

Jeff, I use 40 grit on the intake side AND I cut the guides off! I've seen a 3-5 cfm gain on some heads just in cutting the guides off. Ray.

Ray is correct about the guides. On my flow bench, flushing the guides with the port roof is 4 cfm. I do that even on my street bikes. Plenty of guide left for valve stem support, so it doesn't effect the longevity of the seats. To remove the 'edge-corner' left behind by the factory machining. on the port floor (short side) as it turns down toward the seat. Try using 1/4" - 3/8" strips torn from a 1" roll of 180 grit emery cloth, about 24" long. With chamber side up and valves removed, pull it thru the port in a back and forth motion to quickly and easily remove the 'corner' edge and radius the short side turn. This is easy and safe just stay away fron the seats. Good luck.

Terry

 

[posplayr]

A recent thread for 1100's but general principles apply.

http://www.thegsresources.com/_forum/showthread.php?t=137631

The head Terry did for me shows valve guides cut.

http://www.thegsresources.com/_forum/showpost.php?p=999223&postcount=29

 

[Nessism]

Grinding down the valve guide may be good for performance, but I wouldn't do it if durability is important. I went though three different cylinder heads before finding one with decent guides during my 8V 1000 rebuild. My "good" head has 26k miles on it and the guides are pretty good but do show some wear.

 

[headsbikesmopars]

Ed, the 16 valve engines are not as hard on the guides as the 8 valve motors. The valves are much smaller and lighter. Also if you study the 16 valve ports, you will see that the guides are tapered at the port roof end. When flushing the guide, you are removing mostly this tapered part. I really don't feel there is any loss of durability..JMHO.

Terry

 

[rapidray]

I actually get better life out of the bronze guides, even cut down, than the stock iron guides because of the "natural" lubricating qualities of the bronze. Fact is, I replace LOTS of iron guides but NOT many bronze guides! Ray.