jinxy

If anything it's an added nice touch that shows some time went into it. Just like your gusset adding and logos.

gon3r

yes, but is it necassary?

jinxy

no, but it can't hurt.

Captain Bondo

Actually, putting more heat into the stainless than is necessary certainly can hurt.

If the runners are actually going to crack where they meet the head flange, they will crack right at the "toe" of the fillet weld, where they are welded on the "outside" of the flange. That will be the point where stress is focused, and welding the runners on the inside as well doesn't alleviate this.

In other words it does not do anything for the overall durability of the header.

The most important thing it to make sure the outside weld to the flange is a generous fillet and is not undercut.

That's all I do, and while I've only got around 10 headers actually in service, I have not had a failure thus far.

Toysrme

That's mostly a moot statement as the welder should be welding it correctly in the first place. Enough heat to nearly anything will change the elemental make-up andthe grain structure.
Welding the insides is a big plus. The perfect weld on two pieces of schedule-40 under ASME are going to have root and face reinforcement of no more than 1/8". The weld is stronger to an 1/8". I shoot for about 1/16" on the face and 1/32-1/16" on the root on schedule 10. I one-pass but however you want to do it.
Look, the majority of people home building tubular parts are not likely going to know how & be comfortable trying to get a correct full-penitration weld on their pipes. Re-welding the inside will not only give you that penitration, but it will also give you the benifit of reinforcement. Another un-told bonus is if you're going to re-weld, you have to back-purge!

toyollAZ86

you got a lot of weight in all those pipes. you should reinforce the weight to the frame of the vehicle. all that weight is hanging on the flange right?

Captain Bondo

I agree, you are adding reinforcemnt, but the question really is- does that part of the manifold actually require reinforcement? In other words- does this reinforcement actually make the manifold as whole, stronger?

IMO, no. If a manifold were to crack at the flange, it won't be because the weld was too thin, it will crack on the pipe itself, right at the toe of the weld, not on the weld. A fillet weld there, welded from one side, is stronger than the pipe itself. Adding weld on the inside won't make the pipe stronger and therefore doesn't make the manifold stronger.

Bracing is an issue unto itself with it's own set of pros and cons..

toyollAZ86

yeah thats the word "bracing" sorry. haha.

ghettoturbo

it looks like the pipe is smaller than the flange opening by a decent amount, so welding the inside is also smoothing out the airflow i guess...

top-notch fab work, that thing is pure sex

Toysrme

Bondo that's a different subject entirely. Underbead cracking and cracking at the toe of the weld do not generally tell you anything about the weld size. It tells you:

• Inclusions & porosity in the base metal
• Incomplete fusion into the base metal
• ***The toes of a non-cover pass weld are TOO THIN
• Crater crack exapanding logitudnally

Less it starts at a section of the weld that was too thin and runs, logitudnial cracking at the toes has nothing to do with the size of the weld.
*** Also yet another reason why I recommend to anyone that has the ability to one pass their welds to do so... Its a very safe bet that many of the failed tig manifolds are a result of an early pass who's toes were too thin. Yes... That causes cracks. Yes... You need to grind that out and re-weld it just like any other mistake.



With regard to the 2F pipe to flange fillet welds. Oh contrare. The weld is most decididly stronger. AWS & ASME both will tell you in most of the general pipe coding that the fillet weld size from root to throat should equal the thickness of the thinnest joint of the base metal. Also, that if welded on both sides, the weld size does add together. (ex: two 1/4" welds = one 1/2" weld)

That being said, the majority of people making manifolds on their own undersize their 2F fillet welds (pipe to flange). .110" for schedule-10, 0.145" for schedule-40. You wont see it with any of the home tig welders. The smaller the weld the easier the control and less visibile the mistakes. Which is why most of them use small filler rods/wire. 1/16" is likely the most common size. That is a big reason why the majority of manifolds that you see have under-sized fillet welds, and the pipe welds lack penitration.
Most of these guys, by the time they do their real pass, then their backwards "traveling cosmetic" pass to even it out. They're going to have a 3/32" weld at the most once they wash it out beautifully even. That's alittle undersized for schedule-10.
In those cases, yes it is extremely beneficial to weld the insides.
Also alot of the time it really is necessary to weld the inside as it would be impossible to get away with bolt/hole interference with a full sized weld on one side.
I weld the insides of my collectors and flanges because I dont normally do stainless flanges. For me its mostly asthetic because I run full sized, full pen welds where I can. On mild flanges by god I want that stainless tied in. ---- gets to pulling apart with a bucking load on it over time.
Brinigng us to another point! Less you're running flex tube don't brace to the chassie. The chassie doesn't move when the engine moves. Brace to the engine block or a trasmission case if at all possible. Weir aint gotta worry about it. His manifolds are not sickly larger than the stock UZ manifolds Ive seen. They're all SUS too instead of CI.





To use him as a good example. With regards to Weir's v8 manifolds above. It ***looks*** like he's got what? 3/32" fillet welds on the outside and say 1/16" on the inside? .09375"+.0625"=.15625" His ideal fillet weld size would be .110". He took the perfect step to insure he had the acceptable fillet weld size for his joints.