So I am still going around on this exhaust. I would like a 5" turbo back, but for AZ emissions I have to pass an opacity test every two years which means I will most likely need the cat in there I'm sure.

I came up with another idea and that is to keep the stock exhaust system and put a 4" cutout with an electic poewr plate either after the turbo or right after the cat.

One shop told me to put it after the cat as I need some back pressure...is that true?

Thanks!

 

No....it's not true.......you do not need back pressure. The more open the exhaust the better she'll run

By the way.....WELCOME to the site

 

This is what another guy told me on a different forum...I know with gassers this is the case...wide open exhausts will cause you to loose low end.

If you yank the cat & go to a straight out or straight thru muffler, you'll loose all of you backpressure and your low end torque will go down. I speak from my own experience on my '05 and on my '00 gasser. If you go with a 5" turbo back setup, you'll loose alot of low end torque but your top end will scream. your mileage will also suffer. there was 1 memeber I know of that had a 5" setup and he said what i'm repeating here, he's now running a 4" setup.

 

Not true with a TD pressure is controlled by the turbo... let it breathe!

 

It was either this months or last months Diesel Power magazine in which they tested different types of exhaust and if I remember correctly they ended up getting more low end power and torque with a muffler installed...

 

I was always under the impression that the turbo caused all the back pressure that a diesel needs. Some military vehicles run straight piped (out the turbo, through the hood, and right next to the passenger side window). We have to wear hearing protection when we drive them. They seem to perform well, just loud as heck. I have never heard that diesels need back pressure; only gas, and that's only for the low end.

 

That test was completly BOGUS!!! They used a crappy engineered straight pipe with 3" diameter and compared it with a 4 inch mandrel bent system with a straight thru muffler. Gee I wonder which one will peform better?! It's like comparing apples to oranges. I dont think a cat will reduce the opacity of the exhaust at all, just turn the truck down, it should be fine.

 

My thought is to install this after the turbo but right before the cat.

http://gearheadgarageinc.net/store/p...35cbbff4764aca

You can open it partially or all the way open or closed.

 

OMG that is the ticket!!!!!!! I have to get that!!!!!! Forget aftermarket exhasut systems I want that installed before the cat. Total control and would scare the crap out of the ricers when you open it up under throttle... hehe
Thanks for that info qwkness!

 

I can confirm from a dyno test that a dump before the muffler on a 3.5" pipe with about 3' of 3" pipe coming from it will add 1 hp and 4 ft/lbs of torque, but it did not read for below 2000 rpm, I still feel more power at the low end with the dump closed. Even without the 3" pipe now.

 

Thanks for the info....so is the down pipe acutally 3.5 " not 4"
Do you have your cat still? where is this 3' of pipe?

I was thinking

tail pipe<<<<<Muffler<<<<<<CAT<<<<CUTOUT<<<Downpipe<<<T urbo

 

My truck is a 305hp which didn't come with a cat but did have a 3.5" pipe from the turbo to the muffler. My cutout is on a 3.5" Y pipe just before the muffler. The 3" pipe was on the cutout side of the Y pipe but I took it off because it didn't do anything but give smoke a different place to go. Go to www.buickgn.com which is where I got my cutout. The only problem is getting the Y pipe for a 4" exhaust. You may have to make one.