exhaust port inserts/porting

markee · Full Member Joined: May 23, 2008 Posts: 57

650 Central sells insert to go into exhaust port when using non standard headers to replace the bit that goes into port on end of standard headers. My question is re the usefullness/need of these as i just looked at a spare set of both sort of pipes on a spare head & the original pipe spigot bit isn't long enough to go hard against the lip inside the port anyway. So there would've been a gap between the inner lip & the spigot end on pipe anyway So what was the point of this originally anyway. ?If this is the case why not smooth down the smaller inside lip when using non standard pipes?? I noticed Jacks guide to porting usies a similar ring.

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

On the exhaust port, the exhaust flow is forced along the roof not the floor and if you'll notice how the stock roof is radius upward from the pocket to where the step is,that the exhaust flow must make an abrupt turn and in doing so,this turn will cause some turbulence of resistance during this transition and the fix would to fill is the gap for a smoother path,plus it extends the port for a stronger pull and reduces port volume some. Even with a small gap after installing the step reducers that you speak of when using the stock headers,you've still gained a flow advantage of transition from port to header,regardless of the %gain.Hope this helps you.

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

deleted

nj1639 · Posted: July 18, 2009, 12:44 pm Post subject: Re: exhaust port inserts/porting

markee wrote:

650 Central sells insert to go into exhaust port when using non standard headers to replace the bit that goes into port on end of standard headers. My question is re the usefullness/need of these as i just looked at a spare set of both sort of pipes on a spare head & the original pipe spigot bit isn't long enough to go hard against the lip inside the port anyway. So there would've been a gap between the inner lip & the spigot end on pipe anyway So what was the point of this originally anyway. ?If this is the case why not smooth down the smaller inside lip when using non standard pipes?? I noticed Jacks guide to porting usies a similar ring.

Did that space include the exhaust gasket?
Sorry for the obvious but you never know!

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

5twins wrote:

I think the original intent was to center the pipe perfectly and provide a nice area for the seal ring to fit onto and work. Yes, the step was machined deeper than it had to be, don't know why. Even with no seal ring, there's still some gap there. Apparently, making the ports bigger is not the best thing for increasing flow so I wouldn't grind that lip down.

If you're going to run some aftermarket headpipes, you can make your own head insert from the ends of some old stock headpipes. Add a pipe ring to fill the rest of the gap and you're all set. These did a fine job of solidly mounting and sealing my ill-fitting MAC headpipes. They leaked like crazy before I made the inserts.

About two years ago I had a machinist make a couple aluminum inserts to fill in the bigger step in the exhaust port with a threaded outlet to utilize the BMW header pipe lock ring with screw on exhaust flange nut to centralize the header and prevent exhaust leakage,will be tig welded in place, more vintage looking than the cheesy Xs set up

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