Any Difference Between 256 and 447 Heads?

[pa-powerstroke]

I have a 447 that Im planning on rebuilding and hopping up a little bit. Was planning on porting and polishing the head too, I have some 256 stuff laying around like a head and rocker box and was wondering if there was any advantage to porting it and running it on my 447 motor?

 

[Jack]

The XS1 heads are have different intake ports and combustion chamber from the later 256 and 477 heads.

 

[650performance]

With reshaping that is properly done both can be made to perform well, but both also have the same impediments that relate back to Yamaha's fundamental decision to design the head for ease of manufacture and not with an eye to ultimate performance like, for example, they do with a modern R1 or R6.
If you are going to attempt to port it yourself just remember that the ports are already too large for a 42 horsepower 650, so making them bigger will actually decrease their flow. Just remove the casting flash and do a three angle race valve job or, if you want to get further into it, read the extensive threads on this site about porting XS heads before you go any further.

 

[pa-powerstroke]

My plan is to go 700cc, raise the compression a little bit, run a shell #1 cam, already running free flowing exhaust and vm34s. From everything I have read, once you go with bigger displacement and especially a cam, porting is needed to get the most out of it. I was actually thinking about sending it to Hoos Racing to get new valve seats cut, new valve guides, and a port and polish.

 

[Jack]

Porting should be on the dinner plate before any icing is added to the cake,the head is the key factor where the real power is produced. You'll be in good hands with Hoo's.

 

[pa-powerstroke]

Sooooo just stick with my head? No real advantage with a 256?

 

[650performance]

The CNC program we use to replicate the Harry Lillie porting scheme is equally effective on both 447 and 256 heads. The flow rates are the same, so, yes, you are OK with either head if the porting is done correctly.

 

[pa-powerstroke]

So you do head work? How much to do new guides, install valves and porting if I supplied valves, springs, guides, seals, ect...?

 

[pa-powerstroke]

The CNC program we use to replicate the Harry Lillie porting scheme is equally effective on both 447 and 256 heads. The flow rates are the same, so, yes, you are OK with either head if the porting is done correctly.

Read the above post

 

[650performance]

Michael Morse at 650 Central can explain the details about the CNC head. There are also other options you may want to consider, among them Hoos Racing, Engine Dynamics in Petaluma, CA etc.