ok, a rotary pumped 6bt turned up to 300hp 900tq, imo will not equate to a 200hp 600tq 4bt. the motor isnt as "smooth" and doest rev as high. i know you can adjust the gov, but 3200 was MAX on a marine motor iirc.
its just my opinion. and i havent seen anyone running one at rediculous levels for any length of time.
i think due to the fact 3200rpm is pretty high for a 4bt, and no one is running a high hp 4bt there has to be issues somewhere.
i have seen a few marine mechanics complain on other boards about the 250hp marine 4bt being unreliable and NOT durable. they use seawater coolers, and seawater for coolant. but again, its all supposition on my part.
as far as balance, i have always understood that a 6cyl is the smoothest engine, and a v12 is just 2 inline 6's
now again, im not an engineer, but i can see that my 4bt is not as smooth as my 6bt.
I have always understood it as harmonics. In an inline 6 as one piston moves down, another moves up, as one piston rod swings left, another swings right. So they cancel each other out there by makeing a smother running engine.
Also don't forget that an inline 6 has 7 main bearings, where a V8 only has 5. So from a durability stand point a inline 6 will out live a V8. A 4cyl only has 5 main bearings and it does not have the harmonics that an I6 has. I see no reason why you can't get 200+ HP out of a 4BT, but I don't see it lasting as long as a 300+ HP 6BT
I cann't see 6000rpms out of a stock bottom end. PDR stated thet over 4500 you must ballance and run lighter pistons. The ho marine pistons are lighter than the truck pistons, They also use a different wrist pin. 250hp should not be a problem. In a pickup how long can you run it at 250hp? after a short bit you have to let you foot off or crash. Marine duty is constent load. It could see an hour at 250hp. All long as egt is in check and boost is bellow about 40psi, good clean oil and air, these engines do not brake. Early engines have bad heads and head gaskets, so this is a weak link. The more I run my truck the more I think my power is around 230hp and 500tq. Just the way it pulls compared to other diesel trucks, dodges fords gm. With the Super Chip pulled out of my 99 super duty. My 4BTA trailers as well as my 99 7.3 Power joke.