If you have done all of the supporting mod's i.e., enlarged the cyls., enlarged the valves, port matched, intake upgrades, and advanced the MAF, then I can see why feel you had less performance w/the smaller exhaust then before, however w/an engine in its stock/near stock form a 2.5" tube and open muffler is simply too large.
Wrong again
I didn't FEEL like I lost low end, I did. It wasn't merely my opinion, it was an actual occurance that happened on my truck, not a story told to me by some dudes who worked at a muffler shop. I totally respect the guys who run the exhaust shop I deal with, but they feel all you need for toyotas is 2" and still sell me 2.5" without batting an eye. They're learned over the last 14 years that I test my theories and ideas before buying the more expensive parts.
I started out with a 20r in my 80, went to a stock 22r and found a nice gain, then swapped out the head with a stock 20r unit and again noticed another gain, and only after settling on my engine setup did I start experimenting with different size tubing.
If you had to leave the line at 3,000 rpm after installing 2.5" exhaust, something else is probably wrong with your truck. Again, nothing special with my engine, simple hybrid setup, crap-tastic weber, nwor tri-y header (which I'm only running because it's supposed to be torquier than the downey), 2.5" tubing with no cat before a 2.5" magnaflow, and with stock gears and 33s I can take off at idle. The lack of gearing obviously hinders my take-offs on inclines and in snow or mud, but I have plenty of grunt to take off at a very low rpm and gain easily in normal driving conditions.
Everybody's obviously entitled to their opinions, and what works on my truck may or may not work on the next guy's truck, or he may not execute it the way I have and may end up with different results. I guess what I'm trying to stress is there is no blanket *perfect tubing size* like so many people like to pretend.
Ok, that's the end of my thread hijack, there's probably nothing good that would come from any more discussion on this.
