# Is it too early?

**URL:** https://forums.speedlife.net/t/is-it-too-early/242486
**Category:** Shift518 Automotive
**Created:** [March 1, 2009, 9:36am UTC](https://forums.speedlife.net/t/is-it-too-early/242486 "2009-03-01T09:36:35Z")
**Posts on this page:** 1
**Showing post:** 20

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### Author: ![JaceSTi](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/jacesti/32/6481_2.png) [@JaceSTi](https://forums.speedlife.net/u/JaceSTi)
#### Post date: [March 1, 2009, 3:02pm UTC](https://forums.speedlife.net/t/is-it-too-early/242486/20 "2009-03-01T15:02:35Z")

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> [@what to do today...](https://forums.speedlife.net/t/what-to-do-today/14897/13):
>
> trust me when i say wait til you have a catback to go on with the downpipe. the downpipe helps with spool but feeding it into a stock catback is a true bottleneck…

Thermo-dynamics says other wise:

3" dia, hot gas, PV = nRT, as T drops the other side of the equation needs balance, easier to reduce volume by dropping pipe diameter, keeps pressure and gas velocity constant, helps reduce bacpressure, helps get exhaust away.

Alot of people arque both sides, at one point we made a MatLab flow model that shows the 3" -\> 2.25" step to work better, I gotta find that.

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