I am reluctant to ask a question like this out of fear that all I will get is a bunch on unsubstantiated opinions. I have a B17 with street prepared head (ie. BC3+ cams, flat bottom valves, springs retainers, head work, etc). Currently running a DC B16 tri-y header. Torque on my motor is dropping off around 7500rpm (ie. http://users3.ev1.net/~turboguy/honda/b17civic.jpg). I have taken care of my "unknown" cat bottleneck, but have been entertaining another header.

My main question is with regard to collector size. People tend to actually recommend the 2.5" JDM collector size. No problem, but I don't care to sacrifice any low end just to gain some high end by making the switch to say a JDM ITR or something similar. My motor being under 1700cc is not breathing as much as say a B18c5 or LSVtec, where that 2.5" collector may prove more valuable.

So at what "point" should one realistically step up to a 2.5" collector?

 

Where are our header fabricators? I figured this would be a good question for them.

 

go with a simple jdm 4-1...if it's a torque issue than stay with a tri-y but chop the small collector and make it 2.5 all the way out...size of your motor has nothing to do with it once you pnp your head and are using higher lift cams etc etc

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by accorse07 &raquo;</TD></TR><TR><TD CLASS="quote">size of your motor has nothing to do with it once you pnp your head and are using higher lift cams etc etc</TD></TR></TABLE>

I don't agree with that, because your engine displacement in conjunction with the motor's volumetric effeciency dictate the volume and thus velocities of air through the exhaust manifold. A 2.0L will clearly be "moving" more air than a 1.6L, The question is at what point does a larger collector prove beneficial on the smaller B motors. Perhaps its great on even a stock motor, maybe not, just looking for some feedback. I appreciate your opinion though.

 

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

I don't agree with that, because your engine displacement in conjunction with the motor's volumetric effeciency dictate the volume and thus velocities of air through the exhaust manifold. A 2.0L will clearly be "moving" more air than a 1.6L, The question is at what point does a larger collector prove beneficial on the smaller B motors. Perhaps its great on even a stock motor, maybe not, just looking for some feedback. I appreciate your opinion though. </TD></TR></TABLE>

That's why you need to have your head flow tested to find how much cfm it flows at your cams' max lift. From there you can calculate what size(dia.) primaries you need and the diameter of the secondary. The length of the collector affects your powerband more than the diameter. A longer collector pipe will yield more low end and torque, while I shorter collector will help out more on topend.

From the research that I have done, this is what I dicovered.

 

2" Collector with a gradual Megaphone works well on Honda B up to and past 270whp.

This is what RMF likes.

 

I'm looking into build my own header also and from what i've found... 10%-15% of the primary size for the collector, placing the primaries in firing order in teh collector. A megaphone helps. RMF mentioned in one thread around 28" (i think thats what he said) is a good length for B motors. I'm hoping for my little header build to be able to use a slip fit collector so that i can experiment with putting smaller slip fit sections inbetween my initial primaries and collector to see if I should've made it longer or if the length i choose to use was good. RMF may help you out with what you are trying to do, he is a great guy... i plan to talk to him alittle before i make any final decisions.

EDIT: I'm talking about a 4-1 header.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by accord387 &raquo;</TD></TR><TR><TD CLASS="quote">I'm looking into build my own header also and from what i've found... 10%-15% of the primary size for the collector, placing the primaries in firing order in teh collector. A megaphone helps. RMF mentioned in one thread around 28" (i think thats what he said) is a good length for B motors. I'm hoping for my little header build to be able to use a slip fit collector so that i can experiment with putting smaller slip fit sections inbetween my initial primaries and collector to see if I should've made it longer or if the length i choose to use was good. RMF may help you out with what you are trying to do, he is a great guy... i plan to talk to him alittle before i make any final decisions.

EDIT: I'm talking about a 4-1 header. </TD></TR></TABLE>

28" collector is going to help produce that torque you want. Remember what I said a longer collector helps with low to midrange and torque, while a shorter collector will help out more on topend. Most shorter collectors are 10-18"'s.

 

^ you mean primary length correct? and 10-18" would be way the heck to short for a primary, that would probably peak around 20krpm. Collectors are only a few inches long. 28" primary im thinking is probably around 9k? i've read a 26" is about 10krpm

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by accord387 &raquo;</TD></TR><TR><TD CLASS="quote">^ you mean primary length correct? and 10-18" would be way the heck to short for a primary, that would probably peak around 20krpm. Collectors are only a few inches long. 28" primary im thinking is probably around 9k? i've read a 26" is about 10krpm</TD></TR></TABLE>

No I am speaking of collector piping length.

Read this.
http://www.popularhotrodding.c...m_exh/

 

you are takling about the collector extension pipe... not the actual length of the collector (I interpreted what you said wrong). Yes a longer pipe inbetween the collector and a megaphone or open header will move the torque lower in the powerband, and a shorter one will move it higher. I see what your talking about now. Dont forget they are talking about V8 motors in that article, so i'd see if you can find some stuff that apply to 180 inline 4 motors. (they even mention in that article primary length makes more of a difference on inline 4 motors, so i'd imagine the extension pipe length would make a bigger difference also) I plan to try out a 4 inch extension pipe into the megaphone, and also adjust the lengths of that to figure out what suits my motor best. I like the graph they have on there about choosing a piping diamter based on head flow... good find man.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Rocket &raquo;</TD></TR><TR><TD CLASS="quote">2" Collector with a gradual Megaphone works well on Honda B up to and past 270whp.

This is what RMF likes.</TD></TR></TABLE>

megaphone

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hybrid_vtec &raquo;</TD></TR><TR><TD CLASS="quote">
Read this.
http://www.popularhotrodding.c...m_exh/</TD></TR></TABLE>
I don't think I would go by what that article says .First they are talking about A totally different style of header.That 502 that is in that picture.I built those headers that are on that motor when I was working at Hooker in 1991.So I would say that it is A pretty old picture.And they are not straight 2 1/2.They are stepped 2 3/8 to 2 1/2 with a slip on 4 1/2 collector.That none of the fast guys are using today.

 

2005/6 minus 1991 = 14/15 years....................old *** ...muwhahahahahaha

 

Your asking for it you little ****.LOL

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by accord387 &raquo;</TD></TR><TR><TD CLASS="quote">you are takling about the collector extension pipe... not the actual length of the collector (I interpreted what you said wrong). Yes a longer pipe inbetween the collector and a megaphone or open header will move the torque lower in the powerband, and a shorter one will move it higher. I see what your talking about now. Dont forget they are talking about V8 motors in that article, so i'd see if you can find some stuff that apply to 180 inline 4 motors. (they even mention in that article primary length makes more of a difference on inline 4 motors, so i'd imagine the extension pipe length would make a bigger difference also) I plan to try out a 4 inch extension pipe into the megaphone, and also adjust the lengths of that to figure out what suits my motor best. I like the graph they have on there about choosing a piping diamter based on head flow... good find man. </TD></TR></TABLE>
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RMF &raquo;</TD></TR><TR><TD CLASS="quote">
I don't think I would go by what that article says .First they are talking about A totally different style of header.That 502 that is in that picture.I built those headers that are on that motor when I was working at Hooker in 1991.So I would say that it is A pretty old picture.And they are not straight 2 1/2.They are stepped 2 3/8 to 2 1/2 with a slip on 4 1/2 collector.That none of the fast guys are using today.</TD></TR></TABLE>

Yes the article is mostly mentioning V8's however doesnt most of the information apply to exhaust design in general? That article is also very old as it has been used in several magazines over the years.

 

RMF said its really outdated so im going to say no. And an inline four and a v8 are very different in terms of firing order/firing degrees. inlines are 180, i think v8s are every 90?