ok i swear hes wrong but i had to make sure, guy at my work is telling me that if i get 3'' all the way back im going to loose hp because of loss of back pressure, in my mind im thinking bigger pipe = more flow = more hp, but if im wrong point me out, and btw im getting a turbo kit within 6 months any wayz so im going to need it regardless

You will feel a loss in low end torque because of the loss of backpressure, but if you can live with the loss until you get your turbo you should do it, because bigger is better when your turboed.

3" is overkill on a n/a



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You would only want 3" on NA if your car is pushing about 200whp NA!
Other wise stick with 2-1/4 or 2-1/2.
People bnever seem to understand how important Back Pressure is.

the problem isnt back pressure. back pressure is never a good thing.


the problem is exhaust velocity. When you go too big of an exhuast on a NA car, exhuast gases have time to cool and that slows down exhuast velocity. the perfect exhuast has zero back-pressure and maintains maximum exhuast velocity throughout the entire system

I'm going to go with "your wrong".
Talk to any shop, they will inform you that Back Pressure is a necessary evil on a 4 banger.
Try running your engine with just the header and see how well it runs.....it will run like crap. You HAVE TO HAVE a certain amount of back pressure in the lower RPM's.
Back Pressure = Torq, Free FLow = HP.
HP is no good if you have no Torq to push it with.

A prefect motor would not need Back pressure, this is true. The problem is, no one has made a perfect motor.

You want to get the best combo of Back pressure to HP out of your exhaust system. Once your engine has enough power to operate on its own power, then you can start to find ways to get rid of the Back pressure.
IOW: Stick with 2-1/4 "or" 2 1/2 piping until you get over 200whp or a FI setup.

No. People mistake exhaust gas velocity with back pressure as an explanation. Velocity is important, NOT back pressure. It's a myth that backpressure is a good thing. Or someone using the term wrong.

I don't even know that 200 whp would require 3", 2.5" should be sufficient, I think.

http://forums.2gnt.com/dcboard.php?az=show_mesg&forum=5&topic_id=12816&mesg_id=12816&listing_type=search
Take a read.



15.9 @ 86.7mph

Smooth idle? We don't need no stinking smooth idle.

Mods List:
http://highlander.dsmpower.com/sig.htm

If the shops your speaking too talk about the postives of back-pressure, than your talking to the wrong shops.

Exhaust velocity and pulse timing is how to make power in regards to exhuast.

Your advice is dead-on: the reasoning behind it is off though. 2.25" exhuast works best on a NA 420a becuase the smaller piping keeps exhuast velocity high. It flows enough to not bottle-neck the system (ie doesnt create an access of backpressure ;)) but keeps exhuast velocity high. Once you go to large, exhuast gasses begin to cool and slow down.

The reason a stock 420a runs like crap w/ just a header has nothing to do with backpressure. it all goes back to pulse timing and exhuast velocity.

to use ur extreme-reverse method of debate, see what happens when you throw a .5" exhuast on a 420a. you will have plenty of back-pressure, but your car will go no-where fast.

You will never find an established and trust-worthy enigne builder or exhuast designer "tuning" for more back-pressure.

And to be honest, we have run a NA 420a with just a header...and it goes 12.80's in the 103-106mph range (of course, its a 2000lb neon w/ quad-t/b 2.4L on slicks ;) )

The only truely beneficial use of back-pressure is the air-brake system used by many diesel trucks ;)

>I'm going to go with "your wrong".
>Talk to any shop, they will inform you that Back Pressure is a
>necessary evil on a 4 banger.


No.. You are mistaken.

http://www.teammatrix.com.my/CarMods/exhaust_1.html

Here is just one of many explainations of the way exhaust systems, velocity, and scavenging work. Try google, people fight over this topic all over the internet. I'm not going to argue with you, i'm just working to dispell the myth that any amount of backpressure is needed for any internal combustion engine.

haha newbs.."back pressure is important.. tune for it" lol
ohh and a 2.5" exhaust will do you goo to about 300hp. no need for a 3" unless you are looking for some serius HP.