I cracked my 205 block sapp on about 370bhp, was running mls h/g and STD head bolts ( gen cosworth ones) . Also seen a mates 200 block crack on STD headgasket and bolts. I have NEVER seen a long-studded block crack or "twist" in ten years of being into cosworths..... I'm not a tuner, but I am an aircraft engineer, so have a good knowledge of stresses/moments etc, and I think the relativly small outlay to get your block longstudded is well worth it, and personally wouldn't build an engine over 400bhp without it being done if the option was there....

My saff is running T4/450bhp+ on a mls and STD bolts, but the engine was built before I bought the car, seems to be ok but when it gets rebuilt it WILL be longstudded.

That's my view, if you are spending 10k on an engine why risk the block for the price of a proven excellent mod? I'm with Danny on this one, I'm sure Karl has built lots of engines with STD head bolts with no ill effects, but IMHO longstudding is well worth doing.