Stock 1200 or Converted 883 to 1250/1275?

[GorilladaHun]

First post here, but this was the kind of thread I was looking for. I'll be doing a 1275 in mine this summer, for sure. Street light to street light, roll-on power, less rowing through the gears: Hell yeah!

[NGOT8R]

Welcome to the fun from Kansas!

[Turbo Sporty 48]

Would Hammer 570 cams work with 883 heads and a 1275 kit? ?
Would they fit? Any issues?
There is a very sweet, affordable 883 for sale nearby that could fill the bill...

[Tomcatt]

Originally Posted by Turbo Sporty 48

Would Hammer 570 cams work with 883 heads and a 1275 kit? ?
Would they fit? Any issues?

This is dealt with in the 570 cams thread here. The simple answer appears to be "there are clearance issues with stock 883 heads".

http://xlforum.net/forums/showthread.php?t=1780906

[Turbo Sporty 48]

Ok, are the piston to valve issues manageable?
Valve to piston clearance measurement required?

[flshovelhead]

All things being equal, how does an 883cc head sporty with a 1250 / 1275 kit compare to a 1200cc head sporty with a 1250 / 1275 kit in real-world riding?

Obviously the flow advantage above 6,500 rpm makes a huge difference at wide open throttle with the 1200 heads, but what about in the mid-range "day-to-day" riding area where most guys live?

[aswracing]

Originally Posted by flshovelhead

All things being equal, how does an 883cc head sporty with a 1250 / 1275 kit compare to a 1200cc head sporty with a 1250 / 1275 kit in real-world riding?

Obviously the flow advantage above 6,500 rpm makes a huge difference at wide open throttle with the 1200 heads, but what about in the mid-range "day-to-day" riding area where most guys live?

I can't comment on the "real-world riding" question, but I can show you the data:



Blue is stock EFI 1200 heads over a flat top 1275 kit.

Red is stock EFI 883 heads over a reverse dome conversion 1275 kit.

Same cams, same exhaust, same air cleaner, even the same bike for that matter, tested and tuned on the same dyno by the same person (me).

Compression ratio is very close to the same. About a quarter point advantage to the 1200 head motor.

[flshovelhead]

Wow. Not what I was expecting. Thanks for taking the time to post the results!

[JB in NC]

Any similar testing done with 883 heads that have been fitted with 1200 size valves? Old tech at this point, but I'm curious.

Jim