FJ40 Mark/Downey Header (16 Viewers)

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Our supplier has been working on the proof of concept tooling to create the square port shape from the 1-5/8" primary tubing. There will be tooling involved to make the ends of the tube a rectangle for the flange. You have to do this operation with the header tacked together to ensure the tube is in the correct location – so you cannot really purchase the tube pro-formed.

The test tool is 3D printed. This is development, before we go for an actual tool in hardened steel.

In the attached photos, you can see the results of forming the tube (and the damage to the 3D printed "test tool") and fitment against the existing flanges that I purchased from @65swb45. As a reminder, these are not the final flange design, and this is nothing like final tooling.

Anyway, Rev A testing is complete and needs only minor tweaking to achieve a more complete overall shape with the metal spring back.

The 3 into 1 collectors are in process as well.

Just thought a few here might be interested in the process.

1652398834319.png
1652398841616.png
1652398848839.png
1652398854803.png
 
gonzopancho said:
Our supplier has been working on the proof of concept tooling to create the square port shape from the 1-5/8" primary tubing. There will be tooling involved to make the ends of the tube a rectangle for the flange. You have to do this operation with the header tacked together to ensure the tube is in the correct location – so you cannot really purchase the tube pro-formed.

The test tool is 3D printed. This is development, before we go for an actual tool in hardened steel.

In the attached photos, you can see the results of forming the tube (and the damage to the 3D printed "test tool") and fitment against the existing flanges that I purchased from @65swb45. As a reminder, these are not the final flange design, and this is nothing like final tooling.

Anyway, Rev A testing is complete and needs only minor tweaking to achieve a more complete overall shape with the metal spring back.

The 3 into 1 collectors are in process as well.

Just thought a few here might be interested in the process.

View attachment 3007259View attachment 3007260View attachment 3007261View attachment 3007262
Click to expand...
Just out of curiosity on the process. So you'll have a "fitup" flange of sorts with round holes to locate the ends of the tubes for fitting/tacking everything up, then remove the fitup flange from the engine end of the 6 tubes, flare the round ends to square, and then install/weld the final flange? Tooling can't be cheap! Yikes. Thanks for sharing the process and taking the dive to manufacture these.
 
EWheeler said:
Just out of curiosity on the process. So you'll have a "fitup" flange of sorts with round holes to locate the ends of the tubes for fitting/tacking everything up, then remove the fitup flange from the engine end of the 6 tubes, flare the round ends to square, and then install/weld the final flange? Tooling can't be cheap! Yikes. Thanks for sharing the process and taking the dive to manufacture these.
Click to expand...
Hello All, been followin this thread... No posts in over a month...Any progress Gonzo
??
 
cruizinnube said:
Hello All, been followin this thread... No posts in over a month...Any progress Gonzo
??
Click to expand...

Funny you should ask @cruizinnube - we are working towards a final design that we can then talk about here!

Great timing, and stay tuned!
 
PabloCruise said:
Heck yeah!
Looking forward to posting some juicy details soon!
Click to expand...

We’re still working on it. CAD is done but needs reviewed before we push a button for tooling and prototype.

One of the things we wanted to try has resulted in success: We wanted the header primaries as equal length as possible. We did manage to improve this (closer to equal length than the Mark’s / Downey header) but were limited by spatial constraints.

The overall cut lengths )taking account the bend tooling and drops) ended up being, front to back, 34.5”, 34”, 33”, 33”, 33”, 34.5”.

In terms of firing order (1,5,3,6,2,4): 34.5”, 33”, 33”, 34.5”, 34”, 33”

More details soon.
 
The collector is not a good place to supply an O2 bung. That’s where I used to install mine before Holley changed its guidance to around 8” past the collector.

One thing I do know is If the flange gasket goes and the bung is right there then it takes the O2 with it. That’s one reason I know I moved all mine.
 
wngrog said:
The collector is not a good place to supply an O2 bung. That’s where I used to install mine before Holley changed its guidance to around 8” past the collector.

One thing I do know is If the flange gasket goes and the bung is right there then it takes the O2 with it. That’s one reason I know I moved all mine.
Click to expand...
That is a GREAT piece of tech Nolan. I had seriously considered having O2 bungs added to part of my next batch of headers. I would most certainly have put them where you learned from experience NOT to put them.
😎
 
The Tri Y ones I use all the time come with a bolt on flange. If this new/old header gets designed and produced a “sniper” version with a longer flange could be an option and the O2 put on that.

That said at this point you are welding in an exhaust and adding an O2 bung is the least of your problems
 
Nolan is right, you don’t want the O2 bung too close to the primaries or you can end up with the ECU a bit confused. You also don’t want it too far or the ECU won’t track the stoichiometry very well. Holley has a setting ("Closed Loop Speed") to attempt to compensate for this.

Anyway, we’re considering avoiding the 3-bolt flange and using a bit more modern clamp on at least the stainless version.

The O2 bung could be placed in the outlet side of this clamp, it would allow the customer to rotate the bung and sensor to the desired position prior to final weld.

1D51A51C-F29A-472C-A84F-71FC5D32A6E1.png
 
Last edited:
gonzopancho said:
Nolan is right, you don’t want the O2 bung too close to the primaries or you can end up with the ECU a bit confused. You also don’t want it too far or the ECU won’t track the stoichiometry very well. Holley has a setting ("Closed Loop Speed") to attempt to compensate for this.

Anyway, we’re considering avoiding the 3-bolt flange and using a bit more modern clamp on at least the stainless version.

The O2 bung could be placed in the outlet side of this clamp, it would allow the customer to rotate the bung and sensor to the desired position prior to final weld.

View attachment 3036052
Click to expand...

I like the style but I prefer the bolt on like Man a Fre provides versus those tension clamps

7655D017-3320-4829-80D9-D615DF877A6B.jpeg
 
wngrog said:
One thing I do know is If the flange gasket goes and the bung is right there then it takes the O2 with it. That’s one reason I know I moved all mine.
Click to expand...
Can you tell me more about this?
How does a leaky flange gasket kill the O2 sensor?
Thanks!
 
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