what is catback exhaust

[matt11583]

what does catback mean and what is teh difference between that and a regular exhast system what makes it better??/

[Reed]

its just from the catalitic converter back. it is not better than a manifold back exhaust but it is better than jsut a muffler if you do it right. for a naturally aspirated car you should tune it by getting the right diameter pipe for the size of engine you have but for a supercharged engine you want the biggest exhaust you can get, withing reason.

[matt11583]

so its better to run the headers y pipe and exhasut pipe than a catback???

[CBFryman]

Question. why the biggest you can get? j/w, i mean i can slap a 5" pipe on my 2.4l 4cyl. with a roots blower pushing out 8psi but it would sound like ass. since a "supercharger" like a cyntrifical or roots blower has nothing to do with exaust back pressure (just creates more exaust flow, so youe bigger is better but not to the point you sound like your driving a fat mans bottom hole). not a turbo will be helped out greatly by a large exaust diameter but will still like ass if i put 5" tubeing on a 4cyl. hell 5" on a 402 would sound like crap. when it is idleing it all you would hear would be "blub........blub........blub......." and hwne he stepped on hte gass it would sound like my grandmother ripping one....

[Reed]

a turbo is a supercharger and the point is to get the exhaust out fo the engine as fast as you can to make room for a fresh fuel air mixture. the best way to do that is to open the exhaust as much as you can WITHIN REASON (again). you dont need a 5" exhaust probably jsut a 3"on a 2.4.
and who cares what your car sounds like. jsut make it as fast as you can.

[CBFryman]

yes i know a turbo is a supercharger, and even 3" pipe is quite large, but why wouldnt you want the largest pip possible for an NA engine?

[RandomTask]

Different exhaust sizes actually affect the motor differently. Larger diameter/shorter in length exhaust can give you more hp while the opposite can give you more torque, to a point though. This doesn't mean you can stick a straw on for exhaust and get incredible amounts of torque. There are a lot of other factors that play into affect as well. too. For example, if you have a turbo charged engine, you might want to choose a smaller diameter exhaust. This may be a little more restrictive but the smaller diameter makes for higher exhaust velocities, causing the turbo to spool quicker.

"Why wouldn't you want the largest pipe possible on a NA engine?" You always want a little back pressure on the motor. You wouldn't want the largest pipe, having a completely unrestrictive exhaust on a motor can cause you to burn your valves.

[CBFryman]

Thanks for the back up, yes no back pressure on the negine kills all torque on top of murdering your exaust vualve.

[sierrap615]

plus if you have really low backpressure it can screw up the O2 reading

[Kven]

the reason for a certain size exhaust pipe diameter is flow. you want it to flow as fast as possible with minimal back pressure. a pipe too small will flow fast but have alot of back pressure. a large pipe will have no back pressure but also slow flow.

[CBFryman]

No Shit?

[Kven]

Originally Posted by CBFryman

No Shit?

no shit? then why didnt you explain that before?

[Kven]

Originally Posted by RandomTask

For example, if you have a turbo charged engine, you might want to choose a smaller diameter exhaust. This may be a little more restrictive but the smaller diameter makes for higher exhaust velocities, causing the turbo to spool quicker.

youre talking about the exhaust manifold. after the turbo its better to run larger piping to reduce any pressure on the turbine exhaust side. just thought i might add that.

[bjdm151]

Kven is correct.
On a natural car, we need higher exhaust velocities to maximize the effects of exhaust scavenging. The process whereby the exhaust is moving out at such high velocity that at valve overlap (intake and exhaust open at same time) the exhaust velocity sucks out all of the exhaust andhelps pull in more of that fresh intake charge. With a properly tuned exhaust SYSTEM (sorry I don't have the formulas with me) we can actually use ther pressure pulses created by other cylinders to increase the velocity of the cylinder on the exhaust stroke.
On a forced induction vehicle, this is less important because we don't need scavenging as much. The same amount of valve overlap and scavenging on a FI vehicle as on an NA vehicle will just push fresh intake charge out of the exhasut valve and waste it when we could have closed the exhaust valve earlier and kept that in the cylinder.
There is a difference between a turbo and a supercharger, but we won't get into that here, if anybody disagrees, start a new thread.
on a turbocharged vehicle, like Kven said the most important area of the exhaust system to tune is the manifold, as correct sizing here can help decrease spool up time.

[bjdm151]

Oh, and Kven
Stop wasting your money on sea foam and octane booster