do you agree with this?

[BRSTYLE240SX]

im thinking about how im gonna do my custom exhaust, there's a question about it on the tech chat, but nobody seemed to answer. But here's what i think. Instead of going 2.5 inches like most people do with NA setups, i think it would be better going 2 1/4 inches, so the air can keep its velocity, and have the piping then increase to 2 3/4. Because 2 1/4 will keep it going fast, and since hot air wants to go from compressed areas to less compressed areas, it will want to go into 2 3/4 quicker in order to expand!? Creating then some low end torque, because of the velocity, yet, not too expanded air in the 2 1/4, and creating high end torque as well, because once it expands, it can move quicker!

Does this make sense? or would 2 1/2 still be the best diameter for a NA 240SX custom exhaust?

[drift into a curb]

I was pondering the same idea.  Isn't that kinda idea some full catback systems are using now?  I'm not sure if the Apex GT spec is the one.

[misnomer]

Is this for a turbo or N/A setup? Downpipe implies turbo. . .

You want to keep the diameter uniform, as the piping diameter changes, you get increased turbulence which increases backpressure. Solid 2.25-2.5" front to back would be what you're looking for in an n/a setup. Turbo is a different story.

[BRSTYLE240SX]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (misnomer @ Aug. 10 2002,1:02)</td></tr><tr><td id="QUOTE">Solid 2.25-2.5" front to back would be what you're looking for in an n/a setup.</td></tr></table><span id='postcolor'>
Which one 2.25' and 2.5' would help the most in the 1/4 time. 2.25 will prob. give you more low end torque, or at least not let you lose much. But, will you gain some prescious higher end torque between 3000 and 6000 rpm if you go 2.5'? I guess my true question is, for 1/4 mile, which is best? For an n/a setup!?

[DSC]

Cool idea, I was actually thinking about it a while back...figured it'd be a similar concept to F1's ground effects. &nbsp;But I deicded it wouldn't be worth it unless you could get a gradual slope from 2.25>2.5 or 2.25>2.75 throught the entire length of the exhaust...rather than a small pipe connecting to a bigger one...

Probably wouldn't be worth the time/effort/money anyway...for maybe 2hp or so <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/confused.gif" border="0" valign="absmiddle" alt='???'>

[BRSTYLE240SX]

how much should i be expecting to pay to have someone make my custom exhaust? for parts and labor. The only two parts you shouldnt count on the price are the high flow cat, and the muffler! how much should i expect to pay? remember that the guy will also have to remove my cat, and my stock system.

[SaintlyCharBoy]

well, depending on materials and design choices, the pipe can range 150- as much as you are willing to spend plus the muffler

i am going full welded mandrel bent stainless, it's around 400 plus my apex'i N1 about 200

[tnord]

maybe it's my massive headwound talking (via mag-lite), but iirc, 2.5'' is closer to the ideal diameter than 2.25'' is. if SCC is accurate, they say to get a 2.25'' pipe for anything up to 2.5 liter NA engines, and 2.5'' for engines 2.5L and larger, this would imply a step function, when most likely, it's just the usual linear function. this would mean that as you go up towards 2.5L, you would want a larger diameter, therefor, for our cars, something slightly under 2.5'' would seem to be ideal. not so coincidentaly, the 5Zigen is the one that seems to make the most power, and is slightly under 2.5''

so yeah, take that for what it's worth