i have headers. full 2.5 mandrel bent exhaust with a resonator and no cats and zpi s-pipe. i raced my friends integre GSR with just headers and s-pipe and stock exhaust and i beat him by a car/half a car. i raced him again now with my exhaust and he BEAT ME by about half a car. i dont know if its because i need an intake or the exhaust just made my car slower.

 

maybe he got better and you got worse?

 

With the "new" exhaust, you quite possibly lost that needed back pressure to help propel the vehicle forward, faster... Almost every car made today is made to run better with that cat installed, to help build back pressure needed, to make the car run and feel FASTER...

 

with a cat u gain more torque but lose HP. i jumped a car and a half on him but when i was in third gear he started coming back fast until he had me by about half a car. he also let off early like at about 80mph so we didnt see what would happen till atleast 110mph.

 

Here are some interesting tid bits you most likely don't realize. Torque is GOD especially if you are driving a 2,900 lbs car vs. a 2,500 lbs car. The tC's redline doesn't allow for playing with Max HP for very long anyway. You want your tC fast Work with what its got and build on that. Taking away torque is the LAST thing you wanna do to a tC if you want to be into the street fighting scene. Running an S-Pipe and a 2.5" exhaust on a N/A tC is not the greatest thing to do. If you were F/I it woulda been spiffy.

 

Adding a cat fight fix some of that. Going with bigger piping and not having the cat means you lost a good amount of back pressure. And that's why you lost torque. What our cars have going for them is that they are quick from the beginning of a race. If you loose that torque then you loose our advantage.

You might want to try addinga cat to your exhaust if you're not going FI.

 

i have the CC catback that's 2.5in but has a cat. it def added hp and torque. it's gotta be the removal of the cat that screwed u up.

 

Backpressure is never good on ANY motor of ANY induction. The term you are searching for is the scavenging effect. With a larger pipe, the exhaust won't scavenge well down low, and cause turbulence, affecting power output. 2.0L KA Honda motors are showing the biggest power gains naturally aspirated on 3in full exhausts, well above 2.5in.

 

some back pressure is good. turbos do better with less but most cars need it.

 

Backpressure is never good, in any way, shape, or form. NEVER.

 

The standard for exhaust diameter is to not run too large of exhaust, for the engine needs a certain amount of backpressure. This is correct in the sense of one should not run too large of diameter exhaust tubing, but the statement of the engine needing backpressure is not. You need to have the least amount of backpressure possible to produce maximum power. Too large of diameter exhaust will cause a power loss and loss of low end torque because a larger pipe has less exhaust stream velocity than a smaller pipe. If the exhaust pipe is too large, then the exhaust flow will be slowed with less velocity. There are exceptions, forced induction or high-volume race engines require a larger diameter exhaust due to the flow characteristics of the engine. Supercharged and turbocharged vehicles can have an exhaust gas volume of 1 to 2 times more than an equivalent displacement naturally aspirated engine. In this case, one is able to use a larger diameter of exhaust for greater performance.


You are right back pressure is not good. Too big of a pipe isnt either.

 

Your exhaust is too big, plain and simple. Your motor is basically stock; the gain in hp you might get from your intake was more than offset by the power you lost by going to a 2.5" exhaust. As you increase the size of the exhaust, you also increase the available volume for the exhaust gases to expand, and as you increase that volume, the gas cools and you lose velocity, and ultimately horsepower. Now if you were running a turbo, 2.5" would be ideal up to about 400-500 hp. And put the cats back on, or get a high flowing cat. Modern cats aren't very restrictive and contribute less than 2 psi to the total system backpressure. That's more than accecptable.

 

2.5in to 500whp? WOW, you guys need to get some serious experience before you go speqing out these numbers. Most 2.0L turbos run 3in turbobacks on 300hp setups, let alone 2.4L. 2.5 in more than OK for n/a.

 

Actually Back Pressure is NEVER GOOD just like Turbo2liter said. Its all about the scavaging effects of the velocity of air leaving the head.... so thats why the header always adds the most HP in an exhaust. Also i think in this case that the 2 cars are so close that its really a drivers race and that HP is NOT THE ONLY factor in who is first. Maybe they should try racing more or maybe even trading cars to see what happens.

 

the problem was solved. he had advanced his timing and didnt tell me (which made a huge difference). this morning we retarded it back to normal and raced again. i had him by about a car but the race was more even (lost low end torque, but gained HP). before i would jump about 1 car and a half now it was just a about a half car jump. but he did not come back like he use to And i was still pulling till he let off at about 80-85 mph. Before he would creep up FAST around late 2nd early 3rd gear. i also need an intake so it can work better because its not sucking enough air for what its letting out.

 

back pressure keeps the exhaust valves clean, adn gives you a little torque. if you diont have any back pressure (which i think is impossible) and your a high rever, you can burn them up. this is especally true in BMW M motors

and horsepower is horsepower, back pressure or not. what it sounds like to me is you should go visit a chassis dyno and see that the graph says with the stock muffler and your new one.

also register your car so we all know what you drive.

 

I think the guy you raced finally learned how to drive. Tc is a nice car and all but it shouldn't be faster then a GSR

 

Bad tuning burns up valves. Back pressure is never good. If you say otherwise, then you need to read Corky's book and other's to learn about engine dynamics.

 

go dyno your car and find out if you lost HP or not


im 100% positive you didnt lose hp but gained some.

in a drag race. TAKE OFF is VERY VERY important. im guessing he was better at take off then you were the 2nd time

 

I hate idiots like you who think backpressure is the presure of the exhaust leaving and propelling the car forward like a jet engine... YOU ARE AN IDIOT, BACKPRESSURE IS THE FORCE KEEPING THE EXHAUST FROM LEAVING THE CYLENDER, YOU DONT WANT THAT!