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Discussion Starter · #1 ·
I gutted my main cat for an increase and then my precats and got what feels like a decrease. I'm afraid i lost to much back pressure and need to add somemore back in any ideas. also anyone had problems fitting an offroad y-pipe to an atx?
 

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I'm new with the cougar, but not with a V6 car fitted with an ATX. With any N/A car, you need a certain amount of back pressure to get the engine to rev, then in the high end, getting rid of back pressure is wonderful. In an ATX with a Low stall speed torque converter (TC), you are pretty much losing alot of low end torque, and in an ATX you need that. In an MTX or an ATX fitted with a High stall TC, you can revv the engine in neutral, and get the RPM's up before a launch, so now th low end torque isn't as important. But still needed. The VRIS system on my engine (don't know if you guys have it) intentionally builds back pressure in the intake manny with the use of butterflies(like in the TB). At a certain RPM, they open, and allow full flow through the intake manny. That back pressure allows the engine to build some low end torque. Am i making any sense here? I try hard to type in english, but often I don't. Many people will open up the intake, headers, and exhaust by adding larger pipes, but will leave the stock cat to keep some back pressure. But remember there is a max size where the piping will be too big, and therefore you will lose air velocity of the air into and out of the engine. If yout exhaust piping is too wide, you will actually cause a vacuum tyow effect where the air towards the end of the pipe has no velicity to get out, air can actually enter the exhaust pipes and flow in the wrong way, there for losing more power. If you have a Turbo or SC, then you want to remove alot of the backpressure, still keeping a little. If you are all NA you need some back pressure, or you better be getting a Turbo, SC, or upgrading your torque converter. Good luck.

Jeremy
 

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Hey guys...check out this link How headers work..it should help to explain about back pressure...

in a nutshell, all back pressure is bad...what you need to keep low end power is exhaust gas velocity...just think of your exaust gas like it was a water flowing thru a hose.....
one way to increase velocity is to put your thumb over the end (create back pressure) to restrict most of the flow.....another (better) way to keep the velocity high is to use a hose of a smaller diameter so the water doesn't slow down in the hose...

hope this makes sense and clears things up a little
 

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backpressure is a falicy<sp>. the best back pressure is no back pressure. the reason large exhausts hurt low end power is because the exhaust gases have more room in the larger diameter piping, and since cold=heavy and hot=light, when the gases cool, they "back up" the flow, hindering exhaust port scavenging.

with a turbo, larger diameter piping is ok, because the air coming from that is so friggin' hot, it will stay hot all the way out...

the best possible exhaust setup you could have is open headers. period. that's why race cars do it.

the only thing about that is, though, that you want to have more intake flow than exhaust flow, commonly, because you need to keep the intake side pressurized.

the only part about all this i'm not completely certain of is the last part, so if anyone wants to correct me, feel free...

uRiDiAN
 
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Discussion Starter · #5 ·
off the subject, uridian? you have the tantrum rims? those are the ones i want to get? do you have a pic of your car? how much did u pay for them? did u get them online?
 

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mransr, sounds like youre contradicting yourself. You say that all back pressure is bad, but then you say that you want to increase velocity of flow by blockage. Your explanation of using a thumb is exactly what backpressure is needed for. Having the cat there is like having that thumb, giving it just enough restriction to increase velocity of exhaust gases.

Having backpressure is very important to generating torque, I know cause my launches are actually more sluggish with my y-pipe. I still have the high flow cat, but compared to stock I have to rev a little higher to get that low end grunt when taking off. Top end is great, but when it comes down to racing people at the traffic light I could sure use that low end!
 

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ok I'll try to clear it up..... a BAD way to create the effects of increased velocity is to create backpressure...it can be done but it's not good, not the right way to do things and will cause lose of performance when compared to a correctly designed exhaust system.....

uRiDiAN is correct, all back pressure is bad...
 

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ummm....... <looks around says 'ditto' and leaves>
 

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mpr: the pics

got them from discount tire direct, via the phone, for 1169 mounted, balanced, shipped, with lugs and rings

uRiDiAN
 
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