# Question about backpressure **URL:** \ **Category:** SON240sx Automotive\ **Created:** [April 7, 2005, 11:25am UTC](https://forums.speedlife.net/t/question-about-backpressure/84825 "2005-04-07T11:25:56Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![S14\_Silvia](https://avatars.discourse-cdn.com/v4/letter/s/ed655f/32.png) [@S14\_Silvia](https://forums.speedlife.net/u/S14_Silvia)\ **Post date:** [April 7, 2005, 11:25am UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/1 "2005-04-07T11:25:56Z")
I did some searching but never really got the information i was looking for. Im planning on going KA-T in the next year or so, and my current exhaust pipe and cat need replacing. Instead of going stock I would like to throw in an exhaust that will still work nicely when turboed, currently my ka is near bone stock, only an injen intake. Now, my question: Would the stock cat provide for enough backpressure with a 3" exhaust system (Apex’i N1 Single)? If not, how much hp/tq would be lost in the swap? Thanks ---
**Author:** ![Belluz](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@Belluz](https://forums.speedlife.net/u/Belluz)\ **Post date:** [April 7, 2005, 11:45am UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/2 "2005-04-07T11:45:04Z")
> [@S14 Silvia](#): > > I did some searching but never really got the information i was looking for. > > Im planning on going KA-T in the next year or so, and my current exhaust pipe and cat need replacing. Instead of going stock I would like to throw in an exhaust that will still work nicely when turboed, currently my ka is near bone stock, only an injen intake. > Now, my question: Would the stock cat provide for enough backpressure with a 3" exhaust system (Apex’i N1 Single)? If not, how much hp/tq would be lost in the swap? > > Thanks the stock cat is pretty restrictive, even still, when i was planning to put the SR in i had to replace my exhaust. i ran 2.5" with a high flow cat and straight though muffler on the stock motor with an intake. i didnt have any problems. however that motor was knocking and i didnt care about it. it still made a 3000km road trip like that, plus the KMs i put on in town mike ---
**Author:** ![Axlerod](https://avatars.discourse-cdn.com/v4/letter/a/8edcca/32.png) [@Axlerod](https://forums.speedlife.net/u/Axlerod)\ **Post date:** [April 7, 2005, 12:07pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/3 "2005-04-07T12:07:34Z")
[http://forums.neo240sx.ca/viewtopic.php?t=1811](http://forums.neo240sx.ca/viewtopic.php?t=1811) > [@ken.lagarec](#): > > If the pipe diameter is too small, at high rpm, when the amount of gas flowing out of the engine is high, the exhaust system won’t be able to scavenge properly because of turbulence. Without good scavenging, more exhaust gas will remain in the cylinder, reducing the volumetric efficiency of the engine. So small piping might be good in the low end, but it will kill in the top end. > > **Notice I am NOT saying backpressure is good. Backpressure is ALWAYS bad**. People say it’s needed because an exhaust system that is optimized for the low end with small piping will cause back-pressure in the top end. Because American engines produce a lot of torque in the low end, people assume back-pressure is needed for torque. Not true (in fact, there is very little or no back-pressure at the rpm where the torque is made!). ---
**Author:** ![s14\_2Nv](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/s14_2nv/32/5476_2.png) [@s14\_2Nv](https://forums.speedlife.net/u/s14_2Nv)\ **Post date:** [April 7, 2005, 12:41pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/4 "2005-04-07T12:41:53Z")
Just go straight 3" with a high flow cat. You should gain some top end power and lose a bit bottom end. There shouldn’t be any real disadvantages, I know there are a bunch of stock ka guys on here with 3" exaust… ---
**Author:** ![S14\_Silvia](https://avatars.discourse-cdn.com/v4/letter/s/ed655f/32.png) [@S14\_Silvia](https://forums.speedlife.net/u/S14_Silvia)\ **Post date:** [April 7, 2005, 1:35pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/5 "2005-04-07T13:35:16Z")
Alright thanks guys, I just needed some clarification on the subject. In my searches i found many contradictory comments, its hard to find a credible source for some things on the net. Now for an NA engine you would still recommend a high flow cat? So am i just trying to minimize backpressure? ---
**Author:** ![s14\_2Nv](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/s14_2nv/32/5476_2.png) [@s14\_2Nv](https://forums.speedlife.net/u/s14_2Nv)\ **Post date:** [April 7, 2005, 1:55pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/6 "2005-04-07T13:55:56Z")
Pretty much. I think Jantos had/has 3", so do I, but I’m not stock ka, I think Mr.Skinny has 3" too, try checking with one of them. ---
**Author:** ![Axlerod](https://avatars.discourse-cdn.com/v4/letter/a/8edcca/32.png) [@Axlerod](https://forums.speedlife.net/u/Axlerod)\ **Post date:** [April 7, 2005, 5:51pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/7 "2005-04-07T17:51:13Z")
If you go too large a diameter on an NA motor, the low end of the powerband won’t push enough air to get a good flow; the flow will be really slow and there will be turbulence. The bigger the exhaust, the more low end power will suffer… but high end power will increase. And vice versa. ---
**Author:** ![Heatw](https://avatars.discourse-cdn.com/v4/letter/h/cdc98d/32.png) [@Heatw](https://forums.speedlife.net/u/Heatw)\ **Post date:** [April 7, 2005, 6:20pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/8 "2005-04-07T18:20:54Z")
yup, i have a 3" JDM Bee\*R catback on my basically stock ka at the moment, i don’t even have a cat but that’s going to change… other than noise there are no serious ill effects, if you plan to turbo go with it forshure… actually it’s rather hilarious the tone of this system is so low it jsut nuts, it’s loud but good loud, and when turbo ought to be quite nice ---
**Author:** ![Jesse](https://avatars.discourse-cdn.com/v4/letter/j/c77e96/32.png) [@Jesse](https://forums.speedlife.net/u/Jesse)\ **Post date:** [April 7, 2005, 6:55pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/9 "2005-04-07T18:55:46Z")
mmm 3in test pipe to 3in straight through exhuast… ---
**Author:** ![SHIFT\_KA24DET](https://avatars.discourse-cdn.com/v4/letter/s/b9bd4f/32.png) [@SHIFT\_KA24DET](https://forums.speedlife.net/u/SHIFT_KA24DET)\ **Post date:** [April 7, 2005, 7:11pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/10 "2005-04-07T19:11:10Z")
mmmm… 4" downpipe, 4" cat and oooeeee here it comes… 4" Exhaust 😉 ---
**Author:** ![Heatw](https://avatars.discourse-cdn.com/v4/letter/h/cdc98d/32.png) [@Heatw](https://forums.speedlife.net/u/Heatw)\ **Post date:** [April 7, 2005, 7:17pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/11 "2005-04-07T19:17:25Z")
hehe yeah you got a deal on that man, that was some good luck i wish my 3" exhaust turned out to be 4" when it got here ---
**Author:** ![S14\_Silvia](https://avatars.discourse-cdn.com/v4/letter/s/ed655f/32.png) [@S14\_Silvia](https://forums.speedlife.net/u/S14_Silvia)\ **Post date:** [April 7, 2005, 8:22pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/12 "2005-04-07T20:22:09Z")
Ok, now does anyone know a good reliable place to get a custom exhaust made? Im considering this option to compare prices, so any approx prices on what is out there would be a big help. ---
**Author:** ![SHIFT\_KA24DET](https://avatars.discourse-cdn.com/v4/letter/s/b9bd4f/32.png) [@SHIFT\_KA24DET](https://forums.speedlife.net/u/SHIFT_KA24DET)\ **Post date:** [April 7, 2005, 8:30pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/13 "2005-04-07T20:30:19Z")
Metalex Motorworks in Mississagua Contact Radim at 416-894-4457 Tell him Adam from Neetronics Highly Recomended you… ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex034/uploads/speedlife/original/2X/b/b7170c8eddc0b95ece6b88172b2f416a08489a45.png) [@system](https://forums.speedlife.net/u/system)\ **Post date:** [April 7, 2005, 9:01pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/14 "2005-04-07T21:01:24Z")
> [@SHIFT\_SR20DET](#): > > Metalex Motorworks in Mississagua > > Contact Radim at 416-894-4457 > > Tell him Adam from Neetronics Highly Recomended you… Yah, Adam recommended me there for some welds I needed done… Just from talking to the guy and his workers, and looking around at their cars/projects, i was very impressed… Give him a call. ---
**Author:** ![S14\_Silvia](https://avatars.discourse-cdn.com/v4/letter/s/ed655f/32.png) [@S14\_Silvia](https://forums.speedlife.net/u/S14_Silvia)\ **Post date:** [April 7, 2005, 10:08pm UTC](https://forums.speedlife.net/t/question-about-backpressure/84825/15 "2005-04-07T22:08:12Z")
I will do so, thank ya sir.