Backpressure is needed for most all NA motors to run properly. Cats and mufflers are what provide that needed backpressure for the motor. Running a 2.5 inch exhaust or bigger on a NA eclipse motor is not a good idea. 2 to 2 1/4 would be the ideal "performance" exhaust size for it. Cats aren't bad, youd be suprised how much they can actually flow.

 

An engine doesn't need backpressure to run. That's a very old misconception. Backpressure is just a restriction on getting the exhaust out of the cylinder efficiently. What an engine needs is a properly sized primary exhaust tube off the port to keep flow up and help scavenge the cylinder without restricting flow at higher rpm.

Also, lots of guys running NA run open header without any problems other than loud noise. Black Venom ran his LT1 Firebird open header for a few hours just to try it out and the cutout we welded into the exhaust was right after the Y.

 

As Jordan Y. has stated is true there is absolutely no problems running a N/A car without restriction.

There is one thing that is overlooked here, for the most gains possible the power will come from a slightly restrictive exhaust for N/A.

I would have to say not many people or companies can tell you what the proper restriction is for every car or every part of the U.S.
Elevations, Fuel Grade, Engine Effiencies these all play a role. Yes a small role in the search for the very best setup. But then again were searching for the best amount of restriction in the prime location in the exhaust system, for the most power achievable on a N/A car. Then were going to do another mod and screw every single calculation up......


Yes there are Engineers that can do the calculations and use the equipment, to build you the very best system. Give them your car for a month and lots of money, so they can build it. Then again were not all in the search for the greatness of 3-5hp so make sure you have no leaks and atleast 3 feet of pipe past the collector.




Oh and some aftermarket companies rely solely on making all of the scavenging in the header.

 

Apparently you didnt listen to well to what I said. Oh well.

 

I think you were talking specifically about a NA eclipse motor is what benefits from a little back pressure...

 

I think what is not understood here is that a well designed header can provide the needed restriction for that particular motor.


How many different restrictions does this engine need, and what form of restriction provides the best scavenging for this motor?
And don't just throw a Catalytic Converter in there for the "power making restriction"

 

This car 2 yrs ago ran the same setup I'm putting back into it with no problems... Pacesetter header system, 2 1/2" Test Pipe, and 2 1/2" piping all the way out the exhaust. Had no problems... the problems I found were that I had 2 exhaust leaks (BIG ones) so I went ahead and ordered a testpipe from SBR and called Pacesetter for the other parts needed to solve my problem. The car hasn't run a catalytic converter in 2 yrs. The whole catalytic converter... back pressure changed my mind after reading this... why would I want to restrict when it ran this same setup 2 yrs ago with no problems? Black Venom and Jordan made me realize the mechanic guy who told me the whole back pressure thing and needing a cat was full of crap. It was his welding skills that messed everything up causing the system to have 2 exhaust leaks. Which is why I believe its running like crap. As soon as I get the parts I will be posting how everything went. BTW, before Saturday it was running stock NT headers, 2 1/2" Test Pipe, with 2 1/2" Piping all the way to the exhaust with no problems... the reason the original pacesetter header system was taken off was because the downpipe split in half. But when the system was on the car it ran perfectly fine.

 

Where were the exhaust leaks? Were they at the exhaust port/header flange connection, or somewhere in the header before the collector? That kind of leak would be the sort to cause you real trouble. If it was somewhere after that, I'd be less inclined to think it was the cause of the problem, but fixing it would make a good first step in troubleshooting since it's something that needs to be fixed anyway.

Really. What great insight did I miss in your post? Please go into greater detail explaining why reducing the size of his catback and putting a cat on the car is going to fix his lean condition and drivability issues. What theory or personal experience are you going off of to back up your statement?

 

One leak is where the exhaust manifold connects to the downpipe... another one is at the end of the downpipe where an extra piece of pipe was welded. I had an exhuast leak once on the car but it was by the exhuast and didn't have a problem plus it was a pin hole leak. The 2 leaks that are there now are at the beginning of the system and are more then a pin hole leak so I'm thinking thats the problem.

 

I have no idea what Mike is saying Jordan "missed".

Having a really large exhaust on a N/A engine (with no other mods) is going to result in a decrease in low-end power and, in the case of this motor, minimal top-end gains. I don't know whether a 2.5" exhaust (with an aftermarket header) is going to be overkill or not, though - it sounds big. If I were interested in modding my 2.0 N/A, I'd go with a 2.25" exhaust. But, then, what's the point in that?

With that said, as I mentioned on the Tampa DSM board, you should swap another o2 sensor just to rule that out as the culprit.