lowlight

going to upgrading the exhaust on my em1 soon, right now all i have is an cai, ive seen a lot of people jumping on the jdm headers. if i go with this on my b16 will i lose back pressure, or will bolting a high flow cat and running 2.5 all the way give me gains. i need to know if i should just go with the usdm dc 2.25 or the jdm 2.5. i plan on upgrading the cat and getting an es oval muffler, and eventually cams, but nothing too much more aggresive. but i wanna know for sure 2.25 or 2.5 and why. ive done a search and gotten mixed reviews, someone enlighten me please, thanks.

lowlight

really? sweeeet.

lowlight

ttt

gezer

what are ur plans for the future any turbo or just all N/A for exhaust i think 2.5 would be a good size 2.25 is a bit small imo. and for headers the only dc i see worth buying are the 4-1 jdm they get u more high end power if thats not what ur looking for then go with a different kind.

EARLdaSQUIRREL

well there isnt much of a bottom end to begin with on the b16.. but the top end shines.. and i have seen jus as good gains in the midrange with the 4-1 2.5 as i have with a 2.25 4-2-1.... so its all up to you... but forexhaust i would only go with a 2.25 with b16

TrboInteg

The 2.25 is to small! If you plan to keep building your motor, go with the 2.5. You may lose a little tq, but you'll make up for it with hp. And by your choice of header, your looking for hp. Because if you wanted the tq, you would probably choose a 4-2-1 style header.

Also, Back pressure is bad. You do not want any. What you want is velocity and that can be achieved perfectly with a mandrel bent 2.5 exhaust and high flowing muffler.

uncle

Yes you do want back pressure.

TrboInteg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by uncle &raquo;</TD></TR><TR><TD CLASS="quote">Yes you do want back pressure.</TD></TR></TABLE>
Why?

If you have back pressure, your exhaust can not flow to the best of it's ability.

thinkbrianthink bu

^^^ dont listen to this guy. do more searches.

TrboInteg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thinkbrianthink v2 &raquo;</TD></TR><TR><TD CLASS="quote">^^^ dont listen to this guy. do more searches.</TD></TR></TABLE>
Yes, do a search. As i just did for "back pressure". Back pressure is good for a little tq. That is it. But it will hurt hp and the tread starter stated that he was thinking of going to go with the jdm header which is 4-1. That header is better suited to top end hp. If you wanted back pressure, you'd just keep the damn exhaust that came on the car. That way you'll have plenty of backpressure.

transmission11

oh snap boyeee..haha well done

uncle

Well why doesn't everybody run without an exhaust mainfold if we don't need back pressure? THINK about it. Back pressure = Good Too much back pressure = Bad

jaxle

No backpressure is the best, the only time backpressure is good is to keep the unburnt fuel going out of the combustion chamber before the valve closes... and to accomplish this you need a highly tuned exhaust manifold and ignition timing, just not worth it for the avg person.

Lysawy

went from 2.25 to 2.5 with dc 4-2-1 header and anything below 4k is gone but top end shines little more now.. overall the car is more responsive when you punch it...from 4k+

thinkbrianthink bu

watch out... choo choo choo000. here comes the internet fueled train of knowledge.

Hash Browns

Backpressure is bad. The optimal exhaust system you can get will have zero backpressure and maximum exhaust velocities throughout your expected operating range. With a given size of piping, you may have a non-restrictive system for high-flow conditions (ie: your 'top-end'), but you will have lost too much exhaust velocity in low-flow conditions (ie: your 'bottom-end'). From what I understand, a moving fluid gas creates a pulling effect behind it. If the exhaust velocity becomes too low, the effects of this diminish.

So this is what you do. You pick what operating range you want to optimize your exhaust flow for, and then you get the corresponding size piping.


It is funny how someone can mention 'losing torque' and 'gaining horsepower' in the same sentance when horsepower is a function of torque and rpm.

TrboInteg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by uncle &raquo;</TD></TR><TR><TD CLASS="quote">Well why doesn't everybody run without an exhaust manifold if we don't need back pressure? THINK about it. Back pressure = Good Too much back pressure = Bad</TD></TR></TABLE>
If I could get away with running an open header on the street, I would. We drive Honda's and Honda motors liked to be revved high because that is where they make the majority of their power. Back pressure will cause you to lose precious horsepower in a high revving motor. So, please THINK about this... If your motor is spinning at 8500rpm and your exhaust is fighting through your beloved back pressure, how is that not causing you to lose horsepower?

FlatBrokeHatch

Go ahead and run with an open header buddy...as long as you want to burn up your exhaust valves in the process...
Have you ever seen a top fuel drag car blazin' down the track without some sort of exhaust???...NOPE...and they run 11,000rpm+
Back pressure IS needed.

uncle

I didn't say run with an open header I said try running without an exhaust manifold then you will realize that back pressure IS needed. Why not just run with 3" exhaust instead of 2.5 on an NA motor?? Or bigger for that matter??

Blazin Si

like Hash Browns said above... Backpressure is bad. it's exhaust velocity that affects how much horse power/torque you gain or lose. too little exhaust velocity is bad... too much is also bad.

Hash Browns

Running a well tuned, equal-length header with well-designed gas scavenging properties will outperform an engine running without an exhaust manifold.

Why?

It's not because of that 'backpressure', it's because of the employment of the gas scavenging concept that allows a gas exiting to have a pulling effect on the gasses following it. That is why nobody uses a 'no-exhaust-manifold' setup. There are no benefits from the pulling effect when you are lacking an exhaust manifold, all you get is the lack of backpressure. The well designed headers let you get both, and ultimately more performance.

uncle

So let me get this straight, pressure has nothing to do with velocity? Doesn't pressure help create velocity?

lowlight

ok, so if i run a 2.5 in collector into a 2.5 inch cat. and connect that to a 2.5 inch b pipe on a 1.6 liter motor, will i lose low end power, or will the increase in power in the top end make the bottem end feel sluggish. yes i have searched, i would just like someone who has this setup on an em1 to tell me how it runs

uncle

Alright I searched and will now admit I was wrong. Back pressure is a restriction thus it cannot be good at all. Velocity is probably what I was thinking of.

Sketch_hs

[QUOTE=will i lose low end power, or will the increase in power in the top end make the bottem end feel sluggish?[/QUOTE]

both my friend.

I went 2.25 rs*r and gained top AND low end according to my butt-dyno.
sounds good too!