Making Lobster Back Piping

[scotty nm35]

I love the freedom lobster piping allows for tight bends and spiral work.

Here is a stealth boot mount GT35 in a V8 Soarer I worked on recently.

[gtr jet]

That is farking unreal Scotty. Like everyone else, I'm going to ask, what's the turbo lag like on a setup like that?

[scotty nm35]

A 4L V8 with .82 GT35? Lag is non existent. It is a little less responsive than on the manifold, although it is a GT car so the power and transient response seems to suit it.

Currently at 190kw at 4psi with an Emanage Ultimate, winding the boost up this week.

[wht510]

Very Nice Scott. Quality once again.

[gtr jet]

Oh awesome. What is the owner hoping to make with it, power wise?

[Frosty]

WOW

[scotty nm35]

Oh awesome. What is the owner hoping to make with it, power wise?

250wkw, I told him it's probably good for 400kw if he builds the engine.

The most interesting part is the dose, no bov on this setup but the noise it makes is completely different due to the pressure reversion having to go up 6M of pipe and a 100mm cooler to hit the throttle plate and back to the compressor wheel. (and the fact it comes from under the back seat. lol)

[gtr jet]

I think that deserves a video. Would love to see this thing.

[Dose Pipe Sutututu]

I think that deserves a video. Would love to see this thing.

would also give those VL boys a good "dose" haha... probably sound like a half a dozen t u r k e y s locked in the boot

(why was the word t u r k e y censored? lol)

[scotty nm35]

It doesn't sound like dose Johnny, as the boost is so low and the intake pipe so long. The noise repeats every second or so, sounds quite different to anything else I have heard.

The owner will probably end up running a venting BOV somewhere else, perhaps under the car and into a muffler of some kind was my suggestion, for the stealth.

[Mick_o]

I know this isn't lobster back piping but just thought id show what a nicely purged stainless weld looks like these are some of my welds on some pipework for a food factory goes to show you how much of a difference purging makes and how much stronger the welds are and the reason why cheap china stainless manifolds crack

[Aggroman]

well im glad ill be employing you for my new dump pipe and cooler piping around Dec/Jan.

Whats that I pay in bottles of Johnny? fan of blue or massive amounts of the swill red label?

[scotty nm35]

The reason thin walled china manifolds crack is due to expansion, they would crack just as easily if purged imo. If the manifold flange is split and the turbo/exhaust weight is carried by a well designed bracket of some sort, the manifolds would probably last for years (on road cars at least.)

I only purge exhaust pipes when the die grinder can't get to the back of the weld, this isn't food grade exhaust I am working on, and at $300 a bottle of argon I'm not going to waste it back purging unless I need to. I have never had any dump pipes or exhaust returned from weld failure either, track cars included.

One thing i can say, I definitely prefer to weld thin wall (1mm or thinner) while back purging as I am much less likely to blow holes and can crank much more current in. No doubt it is stronger, but this isn't a structural item we are talking about. Perhaps you get better pricing on Argon through your work Mick?

[Mick_o]

Thats definitely not the case Scotty ive got a toxic fab manifold on my evo which is made from shd10 stainless pipe and it is around 5 years old and was on a race car for 4 years of its life in the US now on my car and its fine because its been back purged. Have you ever seen a china manifold cracked somewhere other than at or near a weld?

Wow $300 a bottle?! Find a new supplier mate I get G size argon bottles for $120

[gumflapper]

I know this isn't lobster back piping but just thought id show what a nicely purged stainless weld looks like these are some of my welds on some pipework for a food factory goes to show you how much of a difference purging makes and how much stronger the welds are and the reason why cheap china stainless manifolds crack

welding porn...

what/which food factory was that for?

[scotty nm35]

Thats definitely not the case Scotty ive got a toxic fab manifold on my evo which is made from shd10 stainless pipe and it is around 5 years old and was on a race car for 4 years of its life in the US now on my car and its fine because its been back purged. Have you ever seen a china manifold cracked somewhere other than at or near a weld?

Wow $300 a bottle?! Find a new supplier mate I get G size argon bottles for $120

Yes, I definitely need to find a better supplier, Supergas are ripping me a new one.

The evo manifold is nearly half the length of an RB manifold, hence no real expansion. Most of the cracks I have seen have been 10-20mm from the weld, near the merge. I imagine if you could flex the runners by hand a few times, they would break in a similar spot. Stainless is a bitch for expansion rates anyway, mild steampipe is much better for mani's.

[ISL33P]

I would love to see a pic of these cracks away from a weld. This would indicate a problem with the material which would be VERY VERY strange.

Of the manifolds I have repaired/modified, the cracks have ALWAYS been on the edge of the weld or in the middle of it due to some of the gaps these chinese guys try to fill in

PS im paying $160 per G bottle from Supagas

Edited September 5, 2013 by ISL33P

[Mick_o]

Thanks Adam lol That was for a lil factory called the crafty chef that do frozen indian meals.

Look into buying your own bottle off supagas Scotty that way they can't rape you for bottle hire

My supplier is coregas.

+1 for pics of material breaks.

Agreed that stainless is a bitch for moving when heated but a back purged lighter guage stainless manifold will NOT crack regardless of runner length. Have a look at the length of the FF manifolds that toxic fab makes for evos outta stainless and he has a lifetime guarantee on his manifolds.

[wht510]

Agreed that stainless is a bitch for moving when heated but a back purged lighter guage stainless manifold will NOT crack regardless of runner length. Have a look at the length of the FF manifolds that toxic fab makes for evos outta stainless and he has a lifetime guarantee on his manifolds.

Gents,

All materials have a fatigue limit/strength. Fatigue strength basically comes down to the force on the component and the amount of times that force is applied.

This should not be confused with Yield strength, which is the maximum force the material can go to before it 'yields', or doesn't go back to where it was.

Scott suggested the length has something to do with it and he's right. Length amplifies the force at the stress concentration. Putting a turbo on the end of a manifold that is vibrating is where you have your load force and your cycles respectively. The vibration may be caused by harmonics of the system or simply the engine going through the rev range.

Typically the system will break at the highest stressed area (or where the force acts the most). Usually this is at the weld (stress concentration) or at maximum deflection of the system.

So to provide an answer: You are all right. The cracks can appear in a variety of places, but typically they will crack either close to the weld (right next to it) or due to the internal stresses of the weld itself, where the midpoint of the weld is. I have also seen failures on tubing due to a variety of reasons...

[Dan_J]

^ top post

we really need a fab picture thread, everyone chimes in on what they've done/ doing