So, I have searched and couldn't really find a good answer to this question.

I have been told both ways, that I would need to have some back pressure in newer vehicles and some that say I need little to none in a boosted application.

Which is it? I have a 408 with a whipple at hopefully about 10psi and am trying to figure out if I need to have cats or no cats.

Suggestions?

 

No cats needed, go for it. And while you're at it get some 1-7/8 headers.

 

Awesome, now just need to find a place in TX that will do exhaust with no cats. Need a custom dual setup.

Also, I already have 1-7/8 primaries from Pacesetter.

My project thread has all the other goodies too.

HERE

 

You want very little back pressure in NA/spray/supercharger setups. However a little bit will help with lowend torque in some cases. On turbo setups you basically want zero.

 

Thanks man, I think with the whipple and 4.10 gears, it should be able to make up any little bit of lowend torque loss.

 

You want none in all applications. Why would you want pressure the exhaust you have to overcome on the exhaust stroke?

This is one of those lies based on ignorance that has been told enough everyone believes it.

You want exhaust velocity, not pressure. The higher the velocity the lower the pressure. It helps draw air out of the combustion chamber, slightly helping low end response. With a 408 and a blower you are forcing air in the front with a bulldozer so dont bother worrying about pulling it out of the back with a string. You will loose more power on the top end trying to "keep backpressure" than you would with a good sized exhaust.

 

Make sure you have both sides of the engine going to a catch can or a breather.
You don't want the pressure to build in the motor.

 

This.

100% spot on. Go dual 3" after those headers and either maintain it or Y to a single 4".

 

Spot on!

I am still amazed at how there is still so much "you need back pressure talk" and I love it even more when I hear without back pressure you will kill you engine.

 

Man, I really appreciate all the feedback guys, I called a local shop and they are going to do 3" dual pipes into 2 magnaflows. Just headers straight back to mufflers and out. Can't get any less restrictive without just straight headers!

It makes sense that you would not want to have any restrictions, that's what I have always thought, just wanted to make sure cause the person that had the back pressure talk was another shop I had been to a while back and they weren't very knowledgeable in performance.