would removing the exhaust expect for the headers and cats hurt?

[crazycrz]

would removing the exhaust expect for the headers and cats hurt anything and will it add or remove horsepower? I do not car about sound. i will be running my car Wednesday and this came into my head

[InsightRacer]

I can't see how it would hurt. It should improve power a little due to better exhaust flow. If you replace the downpipe and 2nd cat with a test pipe, it would do even more. You probably also should consider a SRI/CAI to improve the intake flow as well. But doing too much more than that would probably upset the ECU because its critical O2 sensors would be missing.

And you can't remove the header - it's integrated with the head!

[crazycrz]

wow thanks for telling me about the headers i had no idea about that. as of right now i removed the muffler and i had no problems i wanna remove the pipe betweeen the cats and where the muffler use to be sorry for not nowing the name

[roddy]

it will be very loud once you remove a cat and leave it open, but if you don't care, then it's no issue.

small engines usually require some amounts of backpressure from exhausts. that being said i can't go into much detail about it. haha. try it out and see what you butt dyno says.

[crazycrz]

this Wednesday im running 3 times at the track i will keep the exhuast on and then remove everything but the cats and then open headers i will give you times. thank you so much guys

[RedefinedCRZ]

Generally removing exhaust completely on a small engine, even everything up to the cats, will not increase hp at all. Actually it may hurt it. Torque on a small motor is normally partially determined by back pressure. Your best bet would be just to remove the axle back section if you can't afford to replace the entire thing with freer flowing exhaust. The 2 main restrictions in the system are the 2nd cat and the rear muffler, just removing the second cat and changing the muffler to something free flowing seems to give about the most net HP on this car.

However with out any actual dyno numbers I can not confirm this. But normally only open exhaust works on turbo cars.

[MachVEvan]

I actually met a customer with a classic CRX trying to save as much weight as possible while still retaining a muffler and ended up using (and getting good results from) a supertrapp universal muffler.

http://www.supertrapp.com/product_se...t.asp?CatID=32

Like others have said you will need the backpressure for a small engine, and this type of muffler will allow for your exhaust to be maybe 3 feet long while keeping that backpressure. Plus you can dial in your system by adding or deleting plates from the end of the muffler tip.

[91CRXTC]

With this car having an ima system, could that be looked at as a means of getting the "back pressure" that is "needed" for this motor?

[RedefinedCRZ]

Originally Posted by 91CRXTC

With this car having an ima system, could that be looked at as a means of getting the "back pressure" that is "needed" for this motor?

No, the IMA system has nothing to do with the gasoline motor in terms of exhaust or what not. Back pressure is just the resistance of air flow out of the motor. Basically try blowing into a straw as hard as you can. Than blow into a stirring straw, and than into a cut off piece of 1/2 in pipe. You will notice that as you blow harder into the stirring straw or even the regular straw that there become some pressure built up in your mouth, you just can't blow any harder. Now with the 1/2 in pipe, cut the exact same length it just blows right through, almost like there is no pressure build up at all. Now make all of those pipes longer, lots longer. It gets harder and harder to blow through the straws at a high pressure, and you will start to notice it is getting harder to blow through the 1/2in pipe, so if you increase the size again to say 3/4 but leave the length the same it becomes easier again.

This is an example of back pressure. And like we are saying your engine needs it. The supertrap is a good way of making the system lighter but being able to adjust pressure by changing tips. However with the exhaust being so short you run the risk of exhaust gas coming into the cabin of the car.

So why we built my exhaust the way we did. Well the car only has about 1in & 7/8 exhaust on it from the factory. (About 1.875in) We upgraded the entire system to 2in pipe, removed the resonator, the secondary cat, and replaced the muffler with a higher flowing one while also making the pipe runs a bit more in line, less bends (which also increase restriction and backpressure). So by doing this we removed weight by getting rid of the heavy components in the exhaust, retained sound by not increasing the pipe size very much, and reduced backpressure (restriction) in the worst areas, but retained the overall factory design for the most part. This brings the exhaust flow about right in line for the type of mods I currently have and should be good to taking the car up to around 160hp or so. More than I most likely will achieve with this car. However if we turboed the car it would be a different story and we would need to increase piping size to about 2.5in possibly 2.75in

So on a turbo car why run larger piping yet. Well take my old Subaru cars for example. They have about 2.5in piping on them from the factory, 2 cats, a resonator and a muffler. When people modify them to go fast they generally remove 1 or all of the cats, the resonator, and put on a open muffler while increasing the piping size to 3in. Why? Because the Turbo creates the backpressure for the motor, spinning the turbine creates a restriction in the exhaust, enough for the motor to run properly. By opening up the system behind the turbo you can increase the rate at which the turbine can turn, allowing you to increase boost pressure with out getting the exhaust temperature too high (another thing you need to think about on a turbo car). Increasing flow to the turbo also becomes important because it increases spool rate. However, if your wastegate is not large enough on your turbo, allowing the excess flow to pass, and you do not have enough restriction behind the turbo, say a cat and a muffler, you may over boost or see boost creep issues. This means there is not sufficient backpressure, or the wastgate can not handle the load. In an instance like this you would either upgrade your wastegate to an external design, or you would install a downpipe with a cat. Which is what most Subaru owners do to prevent this and it keeps them legal.

[91CRXTC]

I understand back pressure, what I don't understand is why engines need it, I see BP as a neg. When drag racing cuz you want nothing to hold your motor back from producing power. When track racing you need BP to slow your motor down when you let off the gas peddle, but if the ima offers Resistance to the crank as to exhaust BP offers resistance to the crank via the pistons and rods.

I'm not trying to be a d!(k I just want to understand what and why the difference is so important.