Larger primary tubes

So I have both a Kerker 4-1 for a 650 and a 1000.  I understand the primaries are larger, but beyond the initial fab work required and the torque moving up in the RPMs what are the drawbacks to fitting this to my 810 kitted 650?  

before any one starts howling too much, this has already been fork swapped and monoshocked and everything else, just trying to get some insight.  There was a guy on here that had done it to his drag bike 650 and this is slowly becoming one.

thanks,

Brandon

wrote:

So I have both a Kerker 4-1 for a 650 and a 1000.  I understand the primaries are larger, but beyond the initial fab work required and the torque moving up in the RPMs what are the drawbacks to fitting this to my 810 kitted 650?  

before any one starts howling too much,
thanks,

Brandon

Howling about What exactly ?   Use the kerker for the 650....

Are you asking for opinions about using the 1000 exhaust on your 650?  If so, losing bottom end, and quite likely top end power as well, would be my reasons against.  

 but beyond the initial fab work required...

Isn't the bore spacing different between the two? So you'd cut the header pipes and change the angle/spread?

Also, are the exhaust port sizes the same? Will the 1000 header fit between the 650 exhaust studs and match up with the sealing surface?

Exhaust speed will go down. That may affect your cylinder scavenging.

You may have an extra reversion wave because of the port/primary size mismatch.

It will change the shape of your torque curve.

The 4 into 1 will have a bigger flatspot in your torque curve than a 4-2-1 exhaust setup.
 
All of this may not matter if you will be wide open throttle the entire time.

Easy answer... it's complicated.

Yes the bore spacing is different, but not too far off.  I can manually get them into the exhaust ports, but a little heat applied judiciously will make them a little easier to fit next time.  I assumed they would be too long in the tube where they tuck up under the bike.  But they still fit nicely up under the oil pan.  The difference in primary tube OD is only around .080” which kind of surprised me.  I would need the collars taken out a little and I would have to address the port mismatch.  May go ahead and get a new baseline dyno for the engine combo as is and then play around with it this coming winter.  

650 pipes are narrower overall.  The ports are smaller.  The collars are smaller.  I have a V&H manifold for a 1000 and thought about using it for my 650 build but decided against it.

wrote:

So I have both a Kerker 4-1 for a 650 and a 1000.  I understand the primaries are larger, but beyond the initial fab work required and the torque moving up in the RPMs what are the drawbacks to fitting this to my 810 kitted 650?  

before any one starts howling too much, this has already been fork swapped and monoshocked and everything else, just trying to get some insight.  There was a guy on here that had done it to his drag bike 650 and this is slowly becoming one.

thanks,

Brandon




 

If your talking about my drag bike I do not have a normal 650 head on it.

I did put some 1000 pipes on it only because I drastically up scaled everything else. If this bike is any way street driven you will not need it even with a 810 kit. Like others on here have suggested your going to loose performance especially at lower RPMs. Drag bike work at wide open throttle all the time so they really do not need any back pressure, you need that on a street bike. Most drag bike engines idle at 2K, take off at 3-5K depending on which clutch you use, sometimes as high as 7K.

The head tubes on a 1000 hang down longer so the pipes need to be sectioned in the middle then rejoined - you can see that on the picture.
The 1000 head pipe tubes are 1.50" the flange where it contacts the head is 1.62" the collector placement on a 1000 is also different and that is very important. On the 650 the head pipe tubes are 1.38" and the flange where they touch the head is 1.56"