DIY Greddy downpipe for a first-timer.
 

I want to replace my stock Greddy downpipe with something custom. You all know how restrictive it is.

Stock looks like this - (photo stolen from Hornetball - no your not the last one left if you count the UK!)

Attachment 184590

And I'm looking to change it to 2.5" , to match the rest of the system, something like this infamous tony DP -

https://www.miataturbo.net/attachmen...ine=1413849999


Now I have a MIG. My dad welds well (Mig, tig, arc, braze etc,) and has given me it, to learn with. I can throw sparks and make things stick together. I'll get better.

I have a mild steel flange. I will be putting a flexi in and some way of better supporting it in place of the OEM bell housing bracket. I can get some 2.5" tube and bends easy. I guess I'll need one tight bend to come straight off the flange.

My first bit of proper fabrication. A learning exercise. Where the best way to start?

Remove original stuff. Bolt flange to turbo. Start cutting. Tack first section. Keep going till the ends meet up. Take it all off and weld up properly.

Any advice? Just go for it?

The existing setup is 2 pc - Greddy pipe, stock pipe to the cat. Doing it in one piece is going to make it a lot harder to fit, right? I guess that pictured ^ has to be snaked in from below with the turbo off.

Would it be sensible to tack it up in one piece, then if I wish to split it, just cut and add two flanges?

I'll be sure to post photos once I've started!

In for not being the only one dumb enough to do this.

I'm doing the exact same thing starting in a week or so. I can't weld very well, but I have access to a lot of welding equipment and an endless supply of SS pipe. I'll be spending the winter attempting to fab a good downpipe.

There are more of us than you may think, but we tend to hide our Greddy shame from the limelight.

I would search for pictures of the TurboTony greedy replacement downpipe and copy that.

There's also the BEGI SG Greddy DP replacement. A more complicated welding project, but gave nice gains.

Cheers guys, I think that one in the 2nd photo is a Tony pipe?

I also looked at the BEGI piece, its still listed on their site, but with import duty etc it would be a small fortune to get one to the UK.

The flange I bought would suit that type - I haven't decided yet, but I can always cut away but can't add material. Sketched it out today ready to scan in to Solidworks at work tomorrow, because... well, because i can.

http://thumbsnap.com/t/4ZGhm2jS.jpg

Simon, I am curious if you considered making a replacement manifold?

The downpipe is comparatively straight forward for the 15g with an axial mount manifold. This is a similar setup I am working on atm

Attachment 184576

When you say axial log, you mean a log specifically with the flange welded directly to the log itself?

Dann

Yes Dann that is what I meant. Axial doesnt mean too much. :)
Mid mount would be a better description?
Making a downpipe for the original Greddy top/aft mount manifold is much more difficult than for a mid mount manifold.
I never understood the Greddy turbo placement. Was it re-purposed from another application?
Attachment 184573

No idea, but it's shit. Mounted far back and high, so the downpipe always has to be a ? shape. Huge compromises are made everywhere in terms of size, location, bends, heat, etc.

My side mount downpipe looks like a straight piece of pipe compared to my old greddy.

If you look at an engine bay with a 'stock' Greddy setup it makes sense - they designed this way back when to work with the stock cross over pipe (I think?) and also requiring the cast U-bend for the AFM.

Obviously without these limitations, there's better places to put the turbo.


And - please stop putting ideas in my head :D.

I'll stick with just a down-pipe for now, in the future, who knows...

why does it curl back? to clear the shelf?

Yeah. To make one without curving back would need a L shaped downpipe. Someone here did that and it immediately glowed red due to the turbulence. Levubin or whatever it's called?

Yes it is, in fact the one I sold last month :)

here's what you do:

bolt a plate on the current outlet. Tap side of manifold. :P