Tapering headpipes by cutting out a wedge of the pipe

[Dvsrd]

Maybe a silly question, but it is related to my Higgspeed pipes with what I believe is oversized headpipes, 41 mm ID.

I have been planning to machine two tapered pipe sections to replace the straight section of the headers, then cutting a wedge out of the bend, squeeze it back together, and tig weld it shut. Ideally without cutting the headpipe to diffuser cone weld, but if required, I'll cut and reweld that too.

So my question is this: If I cut out a wedge on the INSIDE of the bend, what will happen to the bend when closing the gap? Will it tighten or will it open up? And what if I cut&shut on the outside of the bend?

[jradnich]

Someone mentioned this on the old site. They suggested using hose clamps to pull the edges together. I tried it. Made cuts on the inside of the bend. It worked great. Just get some extra hose clamps, you will strip a few out.

[m in sc]

yup.

use t-clamps. ;)

[Dvsrd]

yup.

use t-clamps. ;)

Yes, got that  ;D  I have split straight pipe and re-welded lots of times before, but not a bend.

So I am mostly curious what effect it will have on the bend radius. We are not talking about a massive taper, only 2.4 mm diameter reduction over 205 mm along outside or 120 mm along inside of bend. Or put differently, a wedge shaped gap starting at 7.5 mm over that length.

1.6 mm of the total 4 mm diameter reduction will be in the straight 110mm section of the header, which I plan to machine from a piece of 42x3.0 mm SS hydraulic tubing.

[rodneya]

In theory it will make the bend radius smaller.

[Dvsrd]

In theory it will make the bend radius smaller.

Do you mean when splitting on inside or outside?

(If I can get away with splitting on the inside, it will look a little bit neater)

[rodneya]

Doesn't matter witch side is cut. You are removing material so the radius will get smaller.

[EE]

I've made tapered headpipes using uncoated automotive exhaust tubing u-bends, bit of a pain but hey. Unfortunately you can't find it in 20 gage in the size i needed only 18 gage (thicker) so lots of hose clamps, hammering and clamping but it's doable. i like to do my welds on the inside of the radius. Ed

[Dvsrd]

I've made tapered headpipes using uncoated automotive exhaust tubing u-bends, bit of a pain but hey. Unfortunately you can't find it in 20 gage in the size i needed only 18 gage (thicker) so lots of hose clamps, hammering and clamping but it's doable. i like to do my welds on the inside of the radius. Ed

Thanks Ed! Any thoughts around what happens with the bend radius when doing this?