ChrizXx

I have a Honda civic EX and the exhaust is a but small/closed if it was more open would it perform better?

kaiba

It depends. Yes and no.

BoM

Yes, usually always gain topend power, but most of the time you lose low end and mid range torque. You need it to be tuned and set up for it to be effective. Something with a e-cutout of something along the lines of that.

On turbo setups you gain a lot of mid range and topend power. Turbos don't like back pressure. N/A setups usually need some backpressure. Unless it is an all out drag car...

OMGWTFBBQ!

Nothing needs backpressure ever. The less back pressure there is on the exhaust side of the turbo the more easily gasses from the manifold side can spin the turbine, decreasing spool times and increasing horsepower by increasing boost on the low end and decreasing the choking effect the turbo has on the high end.

Forced induction vehicles really don't need to worry too much about their exhaust set ups, since they have positive manifold pressure they don't need any scavenging to clear out exhaust during the overlap period. Almost all turbo/SC cams have almost no overlap anyway to minimize the amount of boost flowing out of the head at BDC and the first part of the compression stroke. You can basically just run the best manifold you can afford, and the biggest/easiest/most cost effective turbo-back exhaust. I would recommend you stay under 3" in size unless you're shooting for 700+hp, as you can still affect your horsepower/torque curves with the layout of your turbo-back (just not nearly as much as us NA guys).

Now for NA vehicles, the header is the most important piece of the exhaust. The best header design you can ever have is a 6" straight pipe coming from each cylinder and exhausting to the atmosphere. This was discovered in WWII when they put exhaust systems on the aircraft to hide the blue fire leaving the cylinder heads, which would give the position of the aircraft away to enemy AA during the nighttime bombing runs. All the pilots immediately noticed an increase in performance, and thus exhaust design was born.

For proper header selection on a street driven vehicle, you need to determine the RPM at which you wan't your peak torque. From there you use several equations to determine the proper length of the header before the collector. These equations, which I don't remember off the top of my head, depend on RPM, cross sectional tube area, exhaust valve duration and the volume of gas flowing from each piston. The collector length, and nominal angle of convergence is determined in a similar manner, along with final diameter of the collector, and from that, the exhaust. There are additional equations that will take mufflers, cats, resonators and the like into account, and all will effect the exhaust sizing. Length of the exhaust is also affected, but is not as important as all the major pulse wave action takes place at the collector and the exhaust length just weakens the gas pulse wave. Thats where we get to the point of an exhaust on an NA vehicle, as the exhaust gas pulse exits the exhaust, newton's third law states there must be an equal and opposite reaction. Thus a rarefaction wave, basically a vacuum pulse, will travel back up the exhaust and to the head of the engine, stopping at the valves. If your exhaust is properly tuned, this wave will reach the valves during the overlap period, sucking out all remaining exhaust in the cylinder, which is what we call scavenging.

b16binside

+1
it depends on your build mostly because on mildly built to stock motors backpressure isnt the best thing in the world.

93egSLEEPER

OMGWTFBBQ your post is partially correct yes. but it HAS been dyno proven that running an exhaust with a bit of back pressure on a small displacement honda motor shows more benefits over an open header. If the motor is a completely built motor from the crank up then yes open header will give best performance. On a stock honda motor though you will have better track times with an exhaust on your car. open header is all for top end. you need mid range to get the hondas into the top end more efficiently.