these posts are very hard to understand, but since i'm in the process of building a B20VTEC myself (nowhere near stock, though) I'll try my best to help.
On a STOCK bottom end, I wouldn't rev any higher than 7100rpms or so.
There isn't anything wrong with the stock bottom end, as it is balanced enough to run to around 8000+.
The problem isn't in the crank or the rods, to be honest.
The problem (that makes people worry about high revving B20 motors) are the Rod Bolts, Main Cap bolts (to a lesser extent), Rod Bearings, and Main Cap bearings (CRANK BEARINGS, as i've read some people calling them. They are MAINS)
The bearings aren't really too much of a problem, unless you are revving really high (anything over 8000) with stock rod and main bolts. They will be prone to being spun or warped, which will result in a useless B20 block, which is never fun.
Even if the bolts are torqued to spec, the OEM bolts aren't meant to support the kind of load that high rpms place on them. I haven't seen many BREAK, but I have seen some that were bent and warped due to the added stress. B16 bolts etc. would be a better bet, but if you're rebuilding the bottom end for high performance, go with ARP bolts. Much higher tensile strength, and are just an overall stronger bolt. And considering they are same price, or cheaper than OEM Honda bolts, you'd be crazy NOT to use them. When its time to assemble my motor, there won't be any OEM bolts on the bottom end. They will all be ARP
Putting in lighter rods will help take some of the load off of the rod bolts, but if you're going through the trouble of replacing rods, why wouldn't you replace the bolts as well. Especially, since mixing aftermarket rods, with bolts that are meant for an OEM honda part, isn't a good idea.
My setup is pretty hush hush, for the time being. But if you want a GOOD performing B20VTEC, and one that will last for a while (to be just as dependable as a stock Honda motor) you'll definitely have to crack the bottom end open and reinforce it a bit.
Here is a "general" checklist of things to take do when you are building a B20VTEC (which isn't any different than an LS/VTEC.
*Replace all bearings (rod and mains) with BRAND NEW OEM or ACL (ACL makes great bearings)
**When replacing them, make sure all of them are machined to the exact clearances and tolerances. Any RESPECTABLE shop can handle this, if they can't, or seem questionable, do not let them touch your block.
*Replace AT LEAST your Rod bolts with aftermarket ARP bolts (google them, you WON'T be disappointed) Good prices for AMAZING products. THIS WILL BE THE BEST MONEY SPENT.
*Hone the cylinders (this is NOT OPTIONAL, in my opinion)
*Replace piston rings
*Have the bottom end balance checked, or improved to a higher RPM for peace of mind.
THAT IS MINIMAL WORK. If you want it to last, you will need to AT LEAST do those things. Without performing those, the motor isn't "done" and won't handle too much abuse before becoming unstrung.
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Kuchta,
for the record, B20 crankshafts are the same as LS cranks
same part numbers and all. The only difference between a B18A/B18B and a B20(b/z etc.) block is the cylinder bore. Otherwise, they are the same block.
