I have looked and looked on the site for answers cause I know that it has been brought up a hundred times but I need help , I just spent 5 Hrs yesterday putting a custom exhaust on my truck . I ran a 3 in pipe from the down pipe to the front of the bed and split it into two super 40 delta flow mufflers and continued the 3in out to two tips with no cats . An I drove the truck home and it feels like I'm pulling my 4wheeler now ,it seems to have lost quiet a bit of power ? My q is do u all think the computer will adjust to the change or am I going to have to step down in size ? BTW its sounds great an almost too loud !

 

Sounds like you don't have enough back pressure.
I have a 2.5" single exhaust with a high flow muffler that works great.

I plan on replacing with a stainless system when it rusts out.

 

Well I've always heard of the whole back pressure-scavenging thing but ,never thought that it would make this big of an impact .cause I have run 3 in custom cat backs on every yoter I have had and seen nothing but gains . I guess where I changed it from the front cat ( the bend from the down pipe) that it lost what little scav it had but I also didn't think a 2 3/4 to b exact would make that big of a diff ? If it was yours would u replace it now or wait till rust has come upon us lol

 

Also is yours 2.5 jus from CAT back or all the way ?

 

My exhaust is 2.5 from headers back, no cat.

I would try a section of 2.5" before the mufflers.
Got nothing to lose at this point.
Listen to mine on the link in my sig.

 

Its sounds really good too you can really tell the diff those headers make ! I can post any links on my phone but I have bid of my truck an exhaust if u would want to look ?

 

i put the headers on when i did the swap so i never used the stock manifolds.
i also fabbed a custom crossover under the motor instead of behind it.
post vids or pics.
am having trouble with yt website, can't get to homepage on my phone at all right now and it's a pita to get away from forum page on my desktop too.idk.

 

I'd love to do away with that crappy crossover deal !why Toyota done that I'll never know ??? But I'm gonna go to a single pipe all the way 2.5 and turn it out like factory cause it runs Like crap I have drove it all day and it hasent got any better lol

 

Tacomabr is my YouTube channel name and it is the 3rd video down with no name on my channel if u wanna hear mine

 

I think you went too big if your engine is stock. It would be different if you had performance cams and head work to take advantage of the larger exhaust.

I have done the same thing in the past. The larger exhaust on a stock engine killed my bottom end torque.

When I went with performance cam, intake and head work it all came together. Too big of an exhaust is really no different than the guy that puts the huge cam in a stock engine and can't figure out why he lost power.

 

It is most likely that you went too big but it is NOT due to lack of backpressure. Backpressure is bad no matter what the engine or power goals. This is a common internet myth from before it was understood.

The true reason for loss of low end power with too large of an exhaust on an NA car (does not apply to turbos, the bigger the better with them, some factory cars come with 5" downpipes of 250hp engines) is the lack of velocity/scavenging.

By going bigger you reduce velocity, this means the air does not leave the engine as fast and can actually "backup" to create a not loss of power by reduced scavenging.

Honestly the stock exhaust is fine for a stock engine, change the muffler if you want it louder for no reason to change anything else until you move to some kind of boost. Even then on my supercharged truck it was not holding me back much.

 

How do you keep the MIL from being on all the time.

No cat so does that mean your also not running your sensors as well??

Are you running a stand alone fuel management system in that case??

 

Talking to me? When I gutted the cat I made a simple O2 signal skewer from radio shack for $15. Works great and not a problem in 4 years.

 

Well I fixed the low end prob I put a piece of 2 1/4 pipe from where the from cat was to the axle ( nothing in the pipe) then 1super 40 delta flow muff -2 3/4 out kinda where the factory exit it to a 3 in tip and it runs better than ever! I never thought that scavenging made that big of a deal ! Wow

 

Thanks for the info ,learn something everyday lol