Deception

iTrader: (1)

hey guys well soon enough im gonna be boosting but right now for NA is it okay to run 3 inch exhaust piping's? i have heard that some people had said that its okay if its on a 6cylinder. i have the world sport2 exhaust but i want something deeper after hearing my friends exhaust. but am i going to notice sunificant loss of power on NA as a temporary until turbo is bolted on.

sleeper408

iTrader: (6)

How long before you begin boosting? I wouldn't run 3" piping N/A for long unless the engine was fully-built. Or you could have some custom flanges. That way you can switch between 2.5" and 3" piping (if you ever go back to N/A). You will probably feel loss of torque on the low end with 3" right now.

GSteg

iTrader: (15)

You'll be okay with 3" exhaust for now. It's not like the engine will sputter and die out. LOL. 3" isn't too bad. It's actually more exaggerated because you hear how bad it is from guys who have small 2.0l 4cyl NA engines.

Deception

iTrader: (1)

i might not be boosting till next year. still missing some parts, such as fuel management, and wideband. im a full time student and trying to do this as a hobby. lol
but gsteg your right as if you run 3 inch on a 4cylinder it would sound funny and lost of power. but i was thinking 6 cylinder should be okay under 3 inch piping.

macd7919

iTrader: (10)

3" will be fine. All of the catbacks use a 3" midpipe then split to dual 2.5" or so which is bigger than one 3" anyways. You will be fine but honestly there is no reason to go bigger than what a catback such as a Tanabe comes with, you won't make anymore power, even boosted with larger piping, just more noise.

Deception

iTrader: (1)

oh that what my other question when i add a dual exhaust if should i do 3 inch and then when it split to the rear to 2.5".

so if i can do the 3 inch no problem then i would start selling my apexi ws2

macd7919

iTrader: (10)

You can run 3" for the mid-pipe and split it to dual 2.5", thats fine and will flow plenty. Your Apex should already be that diameter isn't it? Trust me, unless you are making BIG power 3" is fine.

sleeper408

iTrader: (6)

You should take Macd's advice. He's boosted right now so he should be able to tell you a bit about piping diameter. I thought you were going to run 3" all the way.

JeffTsai

iTrader: (1)

The rear section 3" is fine. If you ever make real power you can still keep that rear section. Just change the downpipe and B-pipe to a 4" and put a electric cutout on it. When you really need to unleash hell, then open the cutout and a ton of backpressure will be released. That's what I'm doing on my new setup. This way you can still keep the 3" rear section by running a 4 to 3 inch converter flange. That's what I plan to do on my setup very soon

macd7919

iTrader: (10)

Unless you are looking to push 700whp or above a 4" isn't needed. It's been tested on multiple cars and the gains made don't warrant the increased sound and cost. *IF* you are worried about the flow just running a cutout on a 3" downpipe will provide more flow than a 4" pipe alone. A 4" pipe with a cutout, while may be cool to say, is strictly overkill and won't do anything except make more noise.

If you do a little reasearch on it you will find people who did back to back dyno's with 3" to 3.5" to 4" at the 700-750 wheel horsepower level. The MOST they have gained was 15whp at 4" with large turbo's (74mm etc). In Jeff's case he is planning on running an Hks T51R so he *may* pick up a little extra power when running high boost.

Continuing on, for all the guys that were under 700whp there was absolutely NO increase in power or spool, with most of them selling their 4" to go back to 3" due to the noise.

For those who aren't a member of Supraforums where pre-manufactured 4" exhaust are readily available, here are some quotes from people who made the switch:

"I went from a 3" with WG plumbed back into the DP, to a 3.5" with atmospheric WG and as strange as it sounds, I didn't pick up ANY power. No improvement in spool either. This was at the 750-770 whp range.......The lack of spool improvement doesn't surprise me as I never really have seen any physical reason that larger DP (when you're already at 3") would make a meaningful difference at those relatively low flow requirements. But, I was expecting to see SOME improvement in power output."

"The 4" will definitely help but if I wouldn't be in a hurry to get one. I have all 3" and you can see my 709 RWHP with 67/.68. Maybe the 4" would add 15 RWHP or so, but it would also add a considerable amount of "boominess" to the low rpm operation noisewise."

"I had a 4 inch dp/mp and exhaust combo and switched to 3 inch due to the loudness of the 4 inch stuff. I now have a Super Dragger and PHR 3 inch dp/mp. I lost no power and no spool by doing so. This is at the 500whp on pump and 650whp on race gas"

"I have seen the "15-30" rwhp in dynos by switching exhaust setups, but mostly those turbos were T74 and bigger"

Etc....

Deception

iTrader: (1)

so i guess 60mm or 2.5inch will work for a turbo unless its more than 400hp...

macd7919

iTrader: (10)

You mean on the rear section where it splits? Ok, from the top just to be clear. This is what you want:

3" downpipe
3"midpipe
2.5" from the split back.

That will give you the best performance for the money, anything over that is overkill until your making At Least 600whp.

Deception

iTrader: (1)

Ok i am clear with this. Thank you macd7919. I do apologize to everyone and macd7919 for being frustrating. I do thank you for the info.

i was confused if i could run 3" all the way to the back. but it could work but pointless. i understad it clearer now, thanks.

macd7919

iTrader: (10)

Don't worry it's not frustrating, sometimes it's just hard to convey "custom" work in words you know? As far as the exhaust it's not necessarily pointless if your making big power but at this point you would need to have a custom exhaust fabbed up etc....when you could use that money for other stuff. Are you planning on going turbo soon? Already have a kit?

Deception

iTrader: (1)

yeah i have the kit already, along with intercooler and pipings. just missing right now is my electronics. im awaiting to get a aem fic and a uego wideband. i dont think i will start the project till next spring.

yeah i can understand engine work but with the exhaust i didnt know if it would be fine with 3 inch all the way or 3 to 2.5 at first.