Hello all,
I'm only on here briefly whilst checking mail, so please dont ask any other questions as I probably won't be here to reply.
Increasing capacity "can" give a power increase but usually does'nt in 95% of cases. This is because it is usually the cylinder head air flow that defines the total air flow through the engine and hence it is the cylinder head that dicates power, NOT capacity.
As a good example take a 1.6cvh fitted with a stock 32/34 weber carb. Makes around 90bhp. Bolt ALL the parts onto a 1800cvh bottom end with the same compression ratio....................guess what..............90bhp!
The difference is that the 1800 will make that same power a few hundred rpm earlier but the maximum power is actually determined by the maximum air flow through the engine. In this example it is contolled by the head flow.(and manifolds of course)
To put it another way on two otherwise identical engines except one being bigger capacity than the other, provided the smaller engine can physically rev that little harder (i.e. mechanically without failure) then the power will be the same.
These rules apply to N/A and turbo.
However what can be misunderstood is that by using a larger capacity engine with a turbo, it is possible to make use of larger turbos without excessive lag that you would encounter with a smaller engine, and hence produce more power because you have a larger turbo. (Unless you are prepared to live with the reduced response from the smaller capacity engine)
And finally for all the doubting thomas's....................
A 2.4 YB fitted with a T34 will make around 380bhp running the turbo flat out. A 2.0 fitted with the same components.....................guess what................ 380bhp.
The 2.4 will simply make it lower in the rpm band, but likewise will run out of puff earlier meaning that the power band is no wider than the 2.0, simply that it occurs at lower rpms. This scenario is only usefull in cases where the engine has reached the end of its mechanical ability to rev, yet more power is required.