Understanding exhaust back pressure and how to monitor it | Video

Back pressure, you don't want it NA or turbo. 

Unfortunately over the years people have confused poor exhaust scavenging through the use of exhaust pipes that are too large (which slows velocity) and think back pressure is good. 

A wise man once said, "exhaust backpressure is fine when the valve is closed."

z31maniac said:

Back pressure, you don't want it NA or turbo. 

Unfortunately over the years people have confused poor exhaust scavenging through the use of exhaust pipes that are too large (which slows velocity) and think back pressure is good. 

THANK YOU.

Now let's work on the myth of coolant moving too fast to transfer heat 

Turbos work just fine with bigger = better, at least after the turbo, because exhaust energy should all be used to spin the turbine, or at least any kinetic energy left in the exhaust after the turbine means nothing to the 20-50-80psi of pressure pre-turbine.

Paul_VR6 (Forum Supporter) said:

A wise man once said, "exhaust backpressure is fine when the valve is closed."

Not if it blows the valve open!

In reply to z31maniac :

Dont take this as an argument because Im genuinely curios. Has "exhaust too large" been proven? Ive looked for examples in the past and havent found anything, and on the platforms im familiar with, they guys with the biggest exhaust generally go faster/make more power. Internet wisdom is always you cant run the bigger headers/or 4 inch exhaust on a stock cube or close to stock motor, but when tested it always seems the larger guys end up making the HP.

Ive never seen anyone do the obvious extreme, which would be interesting.

Opti said:

In reply to z31maniac :

Dont take this as an argument because Im generally curios. Has "exhaust too large" been proven? Ive looked for examples in the past and havent found anything, and on the platforms im familiar with, they guys with the biggest exhaust generally go faster/make more power. Internet wisdom is always you cant run the bigger headers/or 4 inch exhaust on a stock cube or close to stock motor, but when tested it always seems the larger guys end up making the HP.

Ive never seen anyone do the obvious extreme, which would be interesting.

Of course not, I always want to learn as well!

I honestly don't know if anyone has done something like that. Keith, any insight?

I have never seen a bigger exhaust lose power, maybe not gain any. Totally different for header primary/secondary sizing as that is crucial. After the turbo or collector, infinity diameter is the answer  other than packaging.

In reply to Paul_VR6 (Forum Supporter) :

I've seen collector quality and primary length make a difference, but everything equal I haven't seen larger primaries lose power, but like I said I haven't seen anyone go to the extremes to test it.

So I don't know if the platforms I'm familiar with run primaries too small commonly so when people upsize, they are actually still headed in the right direction or not.

If you've got some testing or info where only primary size goes up and power goes down I'd be real interested in reading about it.

Are we talking peak power, or overall powerband?

In reply to Pete. (l33t FS) :

I'm interested in either