I've thought about posting this since I read Kevin Cameron's "Classic Motorcycle Race Engines" a few years ago. I decided to re-read the book so this post is basically the result of information in the wrong hands!
We here in the HIPO section are a horsepower and torque based group and that's fine, but I think we can expand on this a bit. Considering we are enamored with 60's dumbed down street bike technology, I think we can be proud of our accomplishments. Now don't flame me, I dig these old machines too.
Consider that in the mid to late sixties Honda (one example) was producing race engines capable of nearly 200hp per litre, our 130 hp or so seems rather tame. Then when we realize Honda had teams of engineers and seemingly bottomless budgets, maybe our attempts with old single cam lumps aren't so bad after all!
To the point... Brake Means Effective Pressure is basically a means of comparing engine performance and efficiency ...simply that. I include this link with a simple formula that anyone can use. A few years back I spent time trying to follow more complicated formulas and in the end came to a nearly identical result to this. BMEP (PSI) = 150.8 x torque (lb.ft) / displacement (cu.inch) Read for fun. Some will have much better information I imagine.
In each of his engine descriptions Mr. Cameron always listed BMEP. More telling that HP alone. In most cases where an engine was being developed throughout a certain period the BMEP increased. So now where should one of our SOHC4's rate in BMEP? Just as an example from dyno graph's one stock used CB550 was 113PSI. Well over 200PSI is possible in F1 car engines.
http://www.epi-eng.com/piston_engine_technology/bmep_performance_yardstick.htm