No cat all the way! Whoever said you need backpressure

[eboy0]

I'm amazed to say how big a difference removing a cat converter makes. I read through the threads about back pressure and such, but decided to do it anyways. The car feels/sounds amazing, even with some exhaust(after turbo)/boost leaks. Now I don't have any dyno numbers to prove anything, but just by driving around on a 3" cat and swapping it in with a 3" straight pipe, makes a BIG difference.
If anyone else has anything to add, by all means please.

 

[xXaTaXx]

No.

You just could not resist. Could you?... Red Devil

 

[gdmbat85]

No.

You still seem hooked on the idea that backpressure is needed. The link I provided, and xXaTaXx's excellent post clearly describe how backpressure is merely an unwanted side effect of the smaller, usually stock, exhaust systems that cars can use. These exhaust systems are usually tuned very well for a balance in low end and high end power. As previously mentioned, the smaller the exhaust the higher the velocity and greater the scavenging effect, but you can only go so small before backpressure is too great and you've reached the point of diminishing returns.

So, when IS back pressure good? It's not, its just a side effect of a relatively small exhaust.

Also, as mentioned and should now be implicit, for an N/A engine we don't want backpressure and for a turbo engine we don't want back pressure.
Your post touched on how turbos don't need back pressure because the turbo itself "baffles" the air.

When in actuality, turbos don't "need" backpressure the same as N/A's don' t "need" it. Backpressure prevents the smooth unrestricted exhaust flow that turbo cars love.
The reason turbo cars like a large 3" 3.5" and even 4" exhaust is because our scavenging effect is almost conmpletely obstructed by the turbine in the exhaust housing of the turbo to begin with.
So by means of scavenging, a turbo car's low end has already been killed. No loss in going to a large diamter pipe - only a gain in the top end.

And as already stated once more, the only reason N/A's typically like smaller exhausts is because they can benefit more from scavenging than their turbo cousins. But go to small and backpressure is too high and performance is lost and go too big and the increased diameter piping will inhibit the scavenging effect, thus losing performance.

Now that everything has been said 10 times over hopefully you will see the light.


Just be extra extra clear, no one is saying go put a massive exhaust on your honda, v8 or 420a. We're saying don't go too big else you'll loose your scavenging effect.

i donno man, ive seen some 1.6L hondas with an exhaust big enough to use as a watermelon launcher

 

[xXaTaXx]

i donno man, ive seen some 1.6L hondas with an exhaust big enough to use as a watermelon launcher

True, but then again, the auto community frowns upon 98% of all the honda 'G-thug racer bigger-is-better unit' breed. Most of those type guys from around here goto kelley's auto performance (complete sellout and ripoff company IMHO) and ask for a new exhaust, they get the same pipes-- but with a huge potato cannon can. You could probably smoke him in the 1/4 w/ a base model Citroen. ;D

Kelley's wanted about $500 + incidental parts/labor just to bend piping from the end of the headers, to the cat, then to the muffler. They do mandrel, but use only aluminized exhaust pipe. I told the rep that for $500, I better atleast get an air freshener and some candy too.

5:30AM on the way to work. Probably delerious.

Morning Gent's
Chris