My understanding is that a smaller exhaust size will increase velocity, which will help with "pulling" your spent combustion fumes out of the chamber so the "new" intake charge isn't diluted by the old fumes. If you have too large of an exhaust, you don't get the scavenging effect and the exhaust, at low rpms, stays where it is, diluting the new intake charge.
That's my guess as to why you are feeling the better low end torque, you had a previously oversized exhaust. There is a chart somewhere that has a rough estimate of exhaust size vs power output. Since, generally, a 4 cylinder with 500 hp needs the same exhaust size as a 8 cylinder, it's a pretty accurate way of figuring it out. The v8 just gets to split the exhaust volume with 2 smaller pipes!
2 2.25 pipes is pretty large for a 250 cubic inch engine, unless you have some serious cam and head work. My opinion anyways!
