I currently have a stock manifold and cat with a custom 2" SS exhaust through a cherry bomb style muffler and out behind the rear wheel on a 22re.

This is for those with 2.25" and 2.5" exhuasts: When you upgraded from stock did you notice a bigg improvement in larger pipe size? Or do you think 2" is fine and a header is really where the improvement comes from?

 

Exhaust size is gonna depend on where you want your torque gain to be.

2" will geared towards lower RPMs where 2.25" will gain torque in a higher RPM range and 2.5" will be in even higher RPM ranges.

I have a 2.25" from a header back, no cat through a thrush turbo. And like it for the most part. Since the truck came with the header, I cannot speak as to factory manifold versus header.

But I do know the factory manifold is a 4 - 2 - 1 style, where most other headers are 4 - 1 style, except the TRD/Thorley, and I believe NWOR ???? has a 4 - 2 - 1 header as well.

With a 4 - 2 - 1 header the torque gain is gonna be in the lower RPMs compared to a 4 - 1 header.

Although gains throughout the entire RPM will be seen, just will be more noticeable in certain RPM ranges based on what size exhaust pipe and type of exhaust manifld/header is used.

This also all depends on air intake as well. Which will further the improvement of an exhaust size change.

IMO, changing exhaust size shouldn't be done until you get at least a better air flow though the motor. Whether it be a deckplate mod, CAI, or just a K&N drop in filter.

Too large of an exhaust size for the setup can also cause a loss in some cases. Ie, you don't want to run a 3" exhaust on a normally aspirated 4cyl or even a factory boost 22rte.

 

I feel like I've made imprvements on the intake side, I'm not running a bigger afm, yet, but I have a k&n and deckplate. And there was a noticeable improvement in throttl response and launch with those.

I know my 2" is bigger than stock (1.75"?) an wasn't sure if it would be worth while to go 2.25 or 2.5" or just leave it.?

 

Probably not. Like said, the 2" will give better low end as opposed to the others.
2.25 does sound good, though.