by blacksea7 » Sun Jan 03, 2010 7:30 pm
Guess I should add something to this.
Inline 6 has six independent throws thereby making it inherently balanced without the need for balance shafts... as perfect as it gets.
Flat 6 will use a 3 throw counter weighted crank. 6 throw shafts exist as well and are incredibly balanced (again, six throws, not 3) Three throw cranks are not inherently balanced however they can be engineered to do the job without being offensive. Balance shafts are a great solution.
V-6, with a 60 degree bank isn't a balanced engine. They need balance shafts to quell the frequencies that'd bother you however internally the engine is literally thrashing. When they break they usually do on the number 5 journal.
V-6 with a 90 degree bank isn't balanced and makes for a rough running engine at idle.. the way to get around it is to step the idle up or, which is an industry standard, split the crank pin 15 degrees... is a fantastic solution to the issue... none the less frequency issue exist as well.
The new series of V-6 diesels by duramax and cummins suffer from the same effects however due to reasonable piston speeds .. or limited RPM, it's not such an issue as in a gas engine spinning over 6K.
For the money, the inline is the best deal... not only is the Inline Cummins the most tried and proven of the offerings it's inherently balanced... add to it, maintenance is a breeze.
One way to think of it is any imbalance or frequency is a waste of energy as some of the fuel burned is consumed in excessive friction, imbalance, etc... I admit they've come a long way since GM was taking short cuts with their insanely huge 4.1 thrashing about under the hood........