I mainly do subaru stuff so runners are very long and with quite a few welds on them. I spend a lot of time on fitment and making sure everything is square with no gaps, do you run of the mill prep, bevel, clean. Now when it comes to welding I notice after its all welded up its ends up being like .25" shorter than it was some times more.

Sometimes I tack up the joints in several places real good and weld it up, other times i leave it on the jig and weld it up which makes it more difficult. Even when its on the jig it shrinks and pulls inwards once its unbolted.

I currently bevel the joints to a thin landing.....should i make the landing thicker? I hate having to go back after welding it together after i spend so much time getting the fitment correct and have to go back in cut the manifold apart and add material. Is there something so obvious that im missing?

TIA

 

I don't bevel the pipes too much, just enough to make it easier to penetrate. I mean, technically with more bevel, the less heat you need to get 100% penetration, and the pipe should shrink less because not as much heat is being used.
It may take more time, but maybe try doing two passes, one at a lower amperage and move faster so the pipe doesn't heat up so much in one area? Or maybe try welding small sections of each pipe and letting each cool?
Then again, I have never dealt with anything like subie headers, which, like you said, are very long and have a lot more to weld than your average ramhorn.

 

i currently do make 2 passes already and i move fairly fast but slow to make sure i dont induce too much heat. Im not sure, im going to try and not bevel as much and turn down the heat

 

We fought this for awhile as well with Subaru turbo headers. Our first solution was to put slip fit connections before the collector for a couple production runs and that worked ok. You just weld the slip fits up last and let the header fully cool before you do it. The permanent solution was shifting one of the cylinder bank head flanges a certain distance outward linearly. So basically the head flange locations in the jig were wider then the final part. I can't remember the exact amount we moved it, but it took a couple header builds to get it right (and an engine close by to test fit). After we changed the jig, the customer never had fitment issues again (well over 200+ headers built in that jig since).

 

Im not sure who it is I've been talking with, but ive been talking with someone over at your place about doing a run of some stuff for me. Most likely get the 1.25" sch10 primaries bent out in 4 solid pieces since thats where im having the biggest issue.

 

That will help for sure, but it wont eliminate the problem. When we build them, they were almost completely CNC bent (although thin wall which tends to warp more).

 

I would like to say that subies are a son of a bitch when making them with sch40 els. It is THE HARDEST manifold ever to make consistently. The tolerance stacking on subie stuff is borderline retarded and my hats off to you for even working on those cars, lol.

As far as shrink goes, everything shrinks. When dealing with super long runners like subies just make sure there isnt any gap between elbows. Good fitment with no light gaps will shrink very consistently and then its just a matter of practice makes perfect.

I personally prototyped and perfected the subie kit that Full-Race sells, took over two years to work out all the bugs and consistently churn out a top of the line manifold and up-pipe package. We started making them with sch40 1 1/2 and evolved into CNC mandrel bend 1 1/4 sch40.

 

Ur right it is retarded. Its def hard I guess I just need to work off of my cut lengths from mock up and then add some length and find that sweet spot. But I'm leaning towards getting atleast the primaries cnc bent since the secondaries and uppipe are easier. Thanks for the words of encouragment, and tips. Guess I'll just need to keep plugging away at it.

I def picked the most pain in the *** vehicle to work on, but I like that its a niche market and isnt overly populated with parts.

 

I primarily work on subarus, being in a prime location for it (New England). Though I haven't made a manifold for one, I have seen a lot of the aftermarket tubular manifolds out there, and I've seen pretty much all of them crack or fail. The ones that don't break, tubular or modified OEM, all use a flex piece on the crosspipe (pipes). A slip fit thing will leak, I've welded up a few of those for customers, but the flex I think gives it enough play to take up the slop.

I wouldn't say subarus are the most PITA vehicle to work on, I like them almost as much as Hondas for ease to work on, design, and modularily of parts. My first time pulling a subaru engine was out of an 08 STi and it took under two hours from pulling the car in to finishing up cleaning up and having the longblock on the stand, definitely not bad at all. The market isn't that small either, it's just not as big as the Honda market, which is arguably one of the largest (if not THE largest import market anyway), the brands are different but it's all the same ideas.

 

My post is not about cracking or failing manifolds. Its about spending all the time to get a quality spot on no gap fit and then when welding it up the material will shrink which means adding material and all the work and fitment is thrown off.

Theres only about 3 produced headers for subarus that come from the U.S. full-race, perrin and amr. The reason you see so many cracked is for example aps who for some reason basically just fusion welds their manifolds with barely any filler at all and i question the material used. And the widespread use of china made manifolds which are rebranded by basically everyone. The chinese stainless is a lower quality material and is "soft" compared to the like of rath gibson u.s sourced stainless. My hole saws/bits go through the gtspec/maddad/gruppe-s/etc.... parts like butter, I can basically zip right through that stuff with a hole saw. Where as when making stuff from U.S sourced material (rath gibson) I have to work slow with the hole saw so that I dont introduce heat to where the material hardens and i can get it through it with the hole saw due to the material hardening and wearing out the hole saw in pretty much 1 maybe 2 cuts.

I dont think slip joints/flex joints are as needed as everyone makes them out to be. Ive welded perrin units and their still going to this day. And subarus arent a "pia" to work on, its just their preturbo exhaust stream is redicously long. Yes motor installs are cake as well are some other things. But I would love the convenience of being able to swap, cams, etc.... with the motor sitting right there being an I4. Dont get me wrong I love subarus and love my 06 sti for the most part, but some stuff is just a pain...like fabrication.

 

IMO flex pipes make the lowers much easier to produce because they can stretch and bend to make up for warping due to final welding. The bad is that they are pretty weak and will fail over time, why pair up a weak flex to bullet proof sch40? Full Race's first gen subie lower came with flexes and to add reliability I developed an sleeving process for them but there were still failures. I just don't think there is a flex on the market designed to take that much pressure and heat for a lifetime.

Mandrel bends for the subie is where its @. Using the cnc bent material I was able to reduce the amount of welds drastically which in turn produced a more consistent and higher quality product that was less prone to failure compared to anything else on the market.

 

ya thats where im headed and once i get all my measurements and drawings done, hopefully crmb can make my life a little easier. Thanks again for your input.

 

The 2 to 1 t-3 divided must be a serious fit-up PITA with sch40.

 

Actually its not too bad, just takes a bit of hammer forming before you fit it on the flange. And really t3 divideds aren't even worth the effort for big power because there isn't a big enough hotside on the market. Go big or go home if you are spending the cash for a lower/up-pipe combo.