Cracks In Exaust Manifold

[Humbla]

Hey guys,I've been running a kakimoto spli dump and front pipe,plumbed in no screamer. :-)

[KiwiRS4T]

Put a flexi in the system.

[Humbla]

Put a flexi in the system.

Did that years ago,thinking this front an dump pipe might be my prob. :-)

[scotty nm35]

If it has a flex then it's likely running a little lean. Without an exhaust temp gauge in the manifold or wideband running you will have no idea what is going on.

My exhaust temps usually run around 600c, but yours must be much hotter to cause cracking.

[jiffo]

Any idea of injector condition?

Useless theorising about A/F ratios as it mixes in the exhaust, so a crook injector or two will be masked by the others.

220rwkw is getting up there for a stock turbo so I guess it's not stock?

[tridentt150v]

How much movement is in the motor when you start it or rev it? Can you almost balance coins on it or is it shaking? A suspect engine mount or even a gearbox mount moving the motor around when you are driving could also be a cause.........not the first option, but one worth checking.

[Trex]

How much movement is in the motor when you start it or rev it? Can you almost balance coins on it or is it shaking? A suspect engine mount or even a gearbox mount moving the motor around when you are driving could also be a cause.........not the first option, but one worth checking.

inb4 pass side engine mount broken and whole engine is leaning.

This is a joke btw. But did manage to fool a mate once.

[Roy]

Your exhaust has bends in it everywhere which effectively make perfect expansion joints.

Just nake sure its rigid and supported at the turbo and its got a flexiblevsupport off the gearbox that ensures no weight on the dump-turbo but lets the pipe grow.

[Humbla]

The funny thing is there's no loss of power,hits boost hard as it has for years.

[PN-Mad]

When you get another manifold, why don't you get the surface machined flat, and make sure your mechanic is following both the torque and the sequence of doing up the nuts.

The only other thing I can think of is check your base timing to make sure it's not overly retarded and producing excess exhaust temp.

[XGTRX]

I thought exhaust gases are hot when u r running lean

[GTSBoy]

I thought exhaust gases are hot when u r running lean

That depends on what you mean by "running lean". People use that term without reference to whether they mean "leaner than stoich" or if they mean "leaner than is needed to stop the engine burning up".

The simple answer is that the highest combustion gas temperature occurs at stoich. If you run leaner than stoich or richer than stoich the temperatures fall, due to dilution either from the extra air or the extra fuel.

If you need to run at 11.5:1 in order to keep the engine happy (no pinging, no self destruction), then going leaner from there will definitely raise the gas temperature. But until you get to 14.7:1 you are still on the rich side, so describing it as "lean" is only relative to the mixture it should have.

[scotty nm35]

We are talking about what's happening in the manifold really, just after combustion. As Alex said, if your timing is out you may get similar symptoms.

[zebra]

High temps alone wont really crack it, Ive had mine glowing on the dyno and it never cracked.

But Shock loading it will.

Driven through any big puddles or anything Genelle?

[scotty nm35]

Glowing red is only 500c, white hot is up nearer 1000.

[Trex]

I still stand by that being on boost for hours everyday in a tuned car can have this affect.

Doing this everyday is a lot different than getting a manifold red hot on a dyno once or twice or on a track a few times a month.

Didn't everyone agree that heat wrapping etc will cause cracks over a long period of time because of the heat, in the heat wrapping thread. Same principal applies.

The manifolds are worn and old now, shrink and expand with every drive. It's bound to happen

[GTSBoy]

I don't think you could splash enough water up into the engine bay while thrashing it red hot to cause quenchy type cracking.

But I'm dead sure that an inadequately supports exhaust could exert enough force to damage the manifold, especially while it is hot. The hotter it is running the worse it could be. So you probably have to have more than one causative factor at the same time. Scenarios follow.

1) Thrashing it on the dyno. EGTs up around 900°C, so the manifold getting really hot. But there's little mechanical load because the car isn't being driven on the road so there's no up/down jiggle over bumps and no lateral loading either. Result.....probably no damage.

2) Driving it normally on the road. EGTs running around 500-600°C most of the time, occasional spikes to 700-800°C for short durations. Exhaust manifold doesn't run real hot, mechanical loading is applied from bumps etc. Chances of damage, probably small.

3) Thrashing it hard on a hills drive or sick dorifto styleez. Plenty of high temp exhaust gas to get the manifold really hot. Plenty of mechanical load from bumps or sick sidewayz action. Result, much higher chance of twisting the manifold past its happy point.

Edited April 30, 2015 by GTSBoy

[XGTRX]

If you need to run at 11.5:1 in order to keep the engine happy (no pinging, no self destruction), then going leaner from there will definitely raise the gas temperature.

Yes that's what I mean.

Also a consideration is the turbo not being supported correctly.

[XKLABA]

What is the manifold made out of ?

Waits for some smart cock to say steel

Tubing or steam pipe, stainless or mild steel etc

Got a pic of it ?

[Ben C34]

What is the manifold made out of ?

Waits for some smart cock to say steel

Tubing or steam pipe, stainless or mild steel etc

Got a pic of it ?

Stock