This may have been addressed somewhere but what is the practical safe maximum rpm with the 351 big bore kit? Reason I ask is that I really like my low gearing, 13/47, especially for it's downhill engine braking. That also means running at 8000+ rpm on the freeway with a practical speed limit around 65 MPH, or thereabouts. The 250 does fine at 8K but how about the big bores? I know a big bore kit will give me more power and I could gear up a bit but wouldn't I then loose some of that low gear engine braking? So what's the word, how does the something like the 351 kit handle sustained high RPMs?

 

Just fine.

 

the 351 stops making power at about 7.5K.
maybe it will run at 8K but it won't be puttin' out HP.
you most likely will feel it fall off around 7-8K.
look here.http://bandbcyclerestorations.com/page_2.html

 

OK, so sort of a corollary question: will a bigger bore engine (the 351) provide more engine braking at a given rpm than a smaller bore engine (the 250)?

 

I believe it does. Mine seemed to more than the stock 09 I rode a few days ago. It's pretty heavy.

 

I have to believe you will be changing out your gearing when and if you go 351.
I put a 15T on the front and am looking to go smaller on the rear as well.
The 351 has a considerable amount of torque. I can roll on the throttle and wheelie in 2nd gear with the 15T no problem.