I am looking to do a custom exhaust and my question is would it be better to go with 2.25 or 2.50 inch piping on an 88 hatch with an all motor B16 set-up?

 

Probably 2.5" for the B16... That will leave you room for improvement.

 

If you dont plan on going FI I would go 2.25 but since you mention all motor and I'd imagine your probably gonna mod the hell outta that b16 your better to go 2.5inch

 

2.25 is PLENTY....only problem is that you don't get many choices with 2.25. THere are more exhause choices for 2.5"

 

Honda Engine performance Book

" Some self-proclaimed motor gurus state that you should not run an exhaust pipe that is too large in diameter bc engines need a certain amount of back pressure to run correctly. Although the statement about size its correct, the assumption about engine sneedint a backpressure its not!!!!. An engine needs to have the lowest back pressure possible to produce the maximum power by keeping the pumping looses loww. an exhaust pipe that its too big causes power loss, especially low end torque, because a big pipe has less exhaust stream velocity than a smaller pipe. Velocity its essential to get the best scavenging effect =from tuned headers. To simplify things, if the exhaust gas flow its keeping high with good velocity, a vacum can develop behind the closed exhaust vavle, allowing even better scavenging when the eshaust valve openson the next exhaust cycle. Good scavenging is even more critical on the valve overlap, the part thjat the 4 stroke cycle where both the intake and exhausat valves are open.
If the exhaust diameter its too large, the flow will be slushigh with low velocity and the scavenging will not be soo good. Remember that a good exhaust has low backpressure and high velocity. The only posiblle excemptions to this rule are turbo charge4d or nitrous engines. It is almost imposible to put an exhaust that is to big for a turbo charged motor, bc the turbo depends a lot on the pressure differential across the turbine to make power. A turbo engine can have as much as 1.5 - 2 times more than an equivalent displacement N/A motor. Here are some basic guidelines:
D15,D16,B16A,ZC = 2in
B18B,B18C = 2.25in
H22,H23 = 2.5in

Add 1/2 in to the pipe to optimize for NOS use. For turbo motors, 2.5 inches its the minimum size diameter pipe that u would want to run, even for the smaller motors. For the B18 1800cc and bigger H series motors, 3 inches works well."

 

if 2.5" exhaust is too big for "high performance", why do the highly desireable "high performance" jdm headers have a 2.5" collector?....

2.5" exhaust is fine. you could lose a little velocity at very low rpm, but hondas arent known for their low rpm power anyways. build your setup for how the engine was designed to make power...screaming at high rpm. at high rpm you need a large exhasut to flow those gases out.

 

I run the Greddy MX exhaust, which is 60mm (about 2.4"). You can produce more power & torque with larger piping (up to a point, mind you), it will just be higher up in the RPM band.
For a B16, I would stay at 2.5" - especially when you say "custom" exhaust, that usually means "muffler shop crush bending", which will hurt exhaust velocity.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 91civicDXdude &raquo;</TD></TR><TR><TD CLASS="quote">if 2.5" exhaust is too big for "high performance", why do the highly desireable "high performance" jdm headers have a 2.5" collector?....
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Because boundry layers do not form at the collector- they form downstream. Optimally the exhaust pipe should start at ~1.75" and slowly taper out to overcome the boundry layer effects. Since this isn't feasible because additional losses are introduced every time the exhaust stream encounters a bend, the best way to overcome losses is to just make the whole exhaust bigger.

 

look at dyno charts. Which makes more power on a B16? 2.5" Makes more power than 2.25". I would like to see dyno charts that prove that statement wrong. SAME motor but only different exhaust piping size.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ED3-D15T &raquo;</TD></TR><TR><TD CLASS="quote">

Because boundry layers do not form at the collector- they form downstream. Optimally the exhaust pipe should start at ~1.75" and slowly taper out to overcome the boundry layer effects. Since this isn't feasible because additional losses are introduced every time the exhaust stream encounters a bend, the best way to overcome losses is to just make the whole exhaust bigger. </TD></TR></TABLE>

So what happens if you use a stright back exhaust with no bends in it?
i have that set up in my C5 powered CRX. JDM Dc header with the 2.5" collector and 2.5 straight back, no bends exhaust.
Am I hurting performance or what?
thanks
BTW, I live just north of O-town

 

Thanks for all of the responses everyone.

 

Remember that a free flowing will not benefit the low end. Look at the torque differences between a 2.25" and a 2.5" exhaust. SUre it will make more HP but HP isn't what you feel in the "seat of your pants" and that increase in HP is usually 6K RPM and higher....who drives there car to 6K when crusing? OK a few of you do but most of the time you'll keep it around 3-4K shifting normally where the 2.25" exhaust will benefit you most. Torque is what loweres you E.T. and makes the 60's better. It also pulls you out of turns. I am not saying that 2.25 is better than 2.5, I am just stating some facts.

 

Ive been wondering this same thing. I want to go with a turbo in a year o rso after the swap, but I couldnt decide if 2.50 would be the way to go, cause Id lose so much low end for now.

 

I am more or less talking about a NA engine. 2.5 is a good starting point for a turbo. A more restricted exhaust on a turbo makes it spool quicker. You can change that by trying different mufflers.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bontke &raquo;</TD></TR><TR><TD CLASS="quote">Remember that a free flowing will not benefit the low end. Look at the torque differences between a 2.25" and a 2.5" exhaust. SUre it will make more HP but HP isn't what you feel in the "seat of your pants" and that increase in HP is usually 6K RPM and higher....who drives there car to 6K when crusing? OK a few of you do but most of the time you'll keep it around 3-4K shifting normally where the 2.25" exhaust will benefit you most. Torque is what loweres you E.T. and makes the 60's better. It also pulls you out of turns. I am not saying that 2.25 is better than 2.5, I am just stating some facts.</TD></TR></TABLE>

You're pretty on point. However, you are kind of stating some common misconceptions about exhausts. HP and TQ are both higher when adding a 2.5" exhaust. Look at the dyno charts. Not to be rude, but you have to look at dynos. 2.5" Simply makes more power(tq) all the way through. Many people are under teh impression that a slightly smaller exhaust is beneficial down low and in the midrange...while there's something to that, you will notice the same gains down low with a 2.5" plus a little more in the upper-mids aswell as much more up top.

If you don't believe me, look at the dyno charts of a SMSP exhaust compared to a Mugen(2.5" bottle necked down to 2-3/8".) The bottle neck of the mugen definitely gives a little more grunt in the midrange, but the SMS full 2.5 makes more throughout.

 

That all depends on the muffler flow as well. Are these dyno charts on a stock engine or an engine that is modified. My statement above is refering to a mostly stock car. If you are refering to a mighly modified and precisionly tuned engine then yes it will benefit. If the inflow of air is surpassed by the outflow then you aren't doing much, like a big exhaust on a stock engine with an intake. BUT if you change the engine to flow more air (turbo, cams, supercharger, Nitrous) then the engine can benefit from a larger exhaust. Just how large takes in many other factors.

 

I'm speaking on a fairly stock engine. The tq difference below VTEC will be 1-2lb/ft...To me, even on a stock engine, if you can keep very similar #s down low, while still make more up top, then that's the better route.

I think you and I are essentially on the same boat here.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bontke &raquo;</TD></TR><TR><TD CLASS="quote"> SUre it will make more HP but HP isn't what you feel in the "seat of your pants" and that increase in HP is usually 6K RPM and higher....who drives there car to 6K when crusing? </TD></TR></TABLE>

Who modifies their car just so it gets around town better? If you're racing someone with a B16 your revs should never be below 6K.

I've got 2.5" on my B16 because when I'm racing its at 8K, for driving around I could really care less if there is a 3hp loss at 3000rpm, if I take off from there a Geo Metro would kick my *** anyway...

 

Well I am a bit different than most who want to see 10,000 RPM in VTEC. I could care less if I see 8K. What I want is 150 ft torque at 3000 RPM. Now that won't happen easily on all motor, but a nicely tuned turbo will do it. VTEC is cool, but it just isn't for me. If I want 10K I'll get a renesis rotary engine....and some how fit is in a civic . If I was only a billionaire

 

i have a jdm dc , 2.5 carsound cat and, 2.5in exhaust and didnt loose torque.. i gain some doesnt feel like i lost any power...