My 4Runner has about 220k on the exhaust now and the cat is clogged up. So it's about that time to replace the whole system. I've done some research on what setup I should run and this is was I've come up with: Thorley headers, some heat shielding and a starter blanket, a Magna flow (ca legal) oem cat., and a Borla turbo muffler. I'll also have a shop fab. me up a 2 1/4 test pipe for when I'm offroading.

The stock exhaust system measures right at 2 1/8" diameter, which creates a torque output of 180@3400rpms. For every 1/8" of an inch added to the diameter, your torque output peaks 500rpms higher in theory. My plan is to run 2 1/4 from the headers to the cat., then 2 1/2" the rest of the way. From looking under the truck, the back end of the cat looks like it’s the halfway point in the length of the exhaust. So if I'm not mistaken, a 2 1/4" into 2 1/2" setup should bump my peak torque output up to roughly 4150rpms. Here's the question, will the 3VZE be able to take advantage of the 2 1/2 catback, or is that diameter to large for it? Like using a straw to blow air through a Tuba...

By the way, I'm new to posting here but not new to the site. This place rocks. It's seems like a pretty cool crowd and all the questions I've searched for have been already been answered, for the most part

 

Hey I'm interested in this question as well. If anyone can also speak knowledgeably about REDUCING the exhaust size moving the torque curve DOWN any, that would be interesting.

I'm more concerned with highway performance and as we all know, the 3V is pretty anemic at speed and in cruise.

 

Id like to know as well. Would be good info for when I do my exhaust later down the road

 

Exhaust tuning works on 2 cycle engines, but I've never seen any empirical data to show it does much on a 4 cycle engine...

 

Reducing the diameter to anything less than stock spec wouldn't be a good idea. If anything, you want to go up in size for highway driving.


Its definitely not the same type of tuning, but your playing with backpressure. It should work, I just want to make sure 2 1/2 isn't too large for the 3.0.

 

so whats the stock exhaust size? 2 and 1/8

 

2 1/4" is plenty big for the 3.0 Your best bang will be the headers.

 

The exhaust was installed two weeks ago. Sorry about the delay, but for some reason this facebook login doesn't always work for me. I took the truck to Warner Mufflers in socal for the install. They flanged all the pipes, moved some of the lines out of the way and heat wrapped everything properly. I'm very meticulous so it was nice to see a shop that treats their customer’s vehicles in that fashion.

Anyways, I ended up going with 2 1/4 to 2 1/2 catback and I'm pretty impressed actually. I don't know how much of a difference this made rather than going with 2 1/4 all the way through, but I now reach peak torque right around 3900rpms. When I'm driving around the city the exhaust doesn't feel too big and pulls significantly harder from 2k - 4k. There are some big hills that I can glide right up in 4th gear at 2500rpms when I use to rev over 5000rpms in 3rd just to make it up. The truck feels great on the freeway too since most of the time I'm driving right in the best part of the power band. It will easily push up to 100mph+ unlike before.

Overall, there are no more bogs in between shifts, I get much better gas mileage, and I don't have to floor it just to keep up with traffic. I'm really happy with the setup. It was well worth the money and I would still go with the same layout if I did it over again. The 2 1/4 to 2 1/2 piping seems like it gives the truck a good balance for city/freeway driving but I can’t be certain since I don't know how a truck with 2 1/4 feels on the freeway. My next project is to finish off the motor with fab'ing up an intake, the corolla maf, possibly a DOA throttle body, and installing and electric fan. Then on to the steering & suspension.