Custom Exhaust Elbow Design

[never monday]

looks like a great design with little chance of reversion.

[DeepFrz]

Nice job on the mock up.

[barnakiel]

Two issues here:
- the water injection point looks a bit high, if this is a single tube design, note it is lower on the original part,
- mind the part will get very hot so you will want to wrap it and make sure the rubber hose that injects the water is heat-proof,

b.

[never monday]

Originally Posted by barnakiel

make sure the rubber hose that injects the water is heat-proof,

b.

will it be pumping 900*F water?

[akio.kanemoto]

Howdy,

Just a quick question on the PVC mockup... I'm about (very flexible word that...) .. to redo an elbow myself as well and was wondering:

* Your elbow looks like it has no support apart from where it bolts on to the exhaust manifold - considering that it will be vibrating all its life - are you not concerned about cracking etc considerning that it's quite a bit of leverage/overhang? (I am thinking of making something similar and this worries me...)

* Are you injecting water directly into the exhaust stream - i.e. there is no jacket? Or is it jacketed?

* General question to the forum - clearly, I would prefer to keep my work simple (or costs down if I job it out after finding out that I can't weld it myself!) - and thus would prefer to inject the water directly into the exhaust stream without a jacket. Is there any reason not to do this?

Very nice mockup by the way!

[barnakiel]

Originally Posted by never monday

will it be pumping 900*F water?

Like funny or something?

In a single tube design the hose attachment point temp will be dictated also if not predominantly by the temp of the exhaust gases, not by the temperature of the gases. This i.a. is why someone invented the double wall design. If the wall is hotter than 100 degs cent then the water will be vapourized causing a number of problems and the rubber will deteriorate.

In many single wall design the injection point is removed to the further part of the tube where temps are less because they get dissipated over the area of the tube and into the surrounding media -air (water/vapour in double wall designs).

Some basic engineering issues.

b.

[never monday]

Originally Posted by barnakiel

Like funny or something?

In a single tube design the hose attachment point temp will be dictated also if not predominantly by the temp of the exhaust gases, not by the temperature of the gases. This i.a. is why someone invented the double wall design. If the wall is hotter than 100 degs cent then the water will be vapourized causing a number of problems and the rubber will deteriorate.

In many single wall design the injection point is removed to the further part of the tube where temps are less because they get dissipated over the area of the tube and into the surrounding media -air (water/vapour in double wall designs).

Some basic engineering issues.

b.

experience has shown your assumptions to be incorrect.

[barnakiel]

Originally Posted by never monday

experience has shown your assumptions to be incorrect.

Experience will be gained by using this specific design too. We might yet hear from the designer/owner.

My experience taught me that if engine designers designed something in a specific way, we have only very slight chances of improving on their design.

Slight, not nill.

Now if the design could be single wall with injection point close up and high, WHY IS IT NOT on Volvos, Yanmars and the rest of the crowd?

b.

[never monday]

Originally Posted by barnakiel

Now if the design could be single wall with injection point close up and high, WHY IS IT NOT on Volvos, Yanmars and the rest of the crowd?

b.

you should examine more exhaust systems before making a statement like that.

[barnakiel]

Originally Posted by never monday

you should examine more exhaust systems before making a statement like that.

Well, I share my limited experience and opinions with others. If I am wrong, I am willing to listen, learn, correct and go on.

If you want to present the advantages of single wall high injection system over the double wall, low injection one, this can in fact add to our understanding and help me correct my allegedly incorrect opinions.

But telling me 'you do not know' and not presenting the alternative and better solutions (and, why not, explaining why they are the better ones) does not move the discussion forward, does it?

barnie

[James S]

Before I built my exhaust system I did all the research I could on the Internet and looked at every example in the marina where my boat is, that would let me on their boats.
What I found is that the dbl wall with the water injected between the two was by far the most common,
One reason for this seems to be (IMO) that it allows you to use a flexible hose that is not high temp.

[never monday]

Originally Posted by barnakiel

Well, I share my limited experience and opinions with others. If I am wrong, I am willing to listen, learn, correct and go on.

If you want to present the advantages of single wall high injection system over the double wall, low injection one, this can in fact add to our understanding and help me correct my allegedly incorrect opinions.

But telling me 'you do not know' and not presenting the alternative and better solutions (and, why not, explaining why they are the better ones) does not move the discussion forward, does it?

barnie

I won't compare your parameters.

I can tell you a single wall exhaust with an injection port downstream from the highest point. Meets or exceeds A.B.Y.C and most engine builders specs.
Therefor, the design is applicable.

[barnakiel]

Originally Posted by never monday

I won't compare your parameters.

No, you will not.

Cheers,
barnie

[never monday]

Originally Posted by James S

Before I built my exhaust system I did all the research I could on the Internet and looked at every example in the marina where my boat is, that would let me on their boats.
What I found is that the dbl wall with the water injected between the two was by far the most common,
One reason for this seems to be (IMO) that it allows you to use a flexible hose that is not high temp.

water injected double starting at the engine exhaust outlet. Is done to control heat in the engine room. Without the water cooling the pipe engine room temps could climb above the spec 120*F. Bare exposed single wall tube also creates a burn hazzard.

This is why single wall systems are wrapped in fiberglass or some other heat insulating blanket.

Look at a new Catalina.....most all of their systems are single wall.

[akio.kanemoto]

Originally Posted by never monday

water injected double starting at the engine exhaust outlet. Is done to control heat in the engine room. Without the water cooling the pipe engine room temps could climb above the spec 120*F. Bare exposed single wall tube also creates a burn hazzard.

This is why single wall systems are wrapped in fiberglass or some other heat insulating blanket.

Look at a new Catalina.....most all of their systems are single wall.

Is there a rule of thumb to follow for how far away the rubber exhaust should be attached from the injection pointto allow sufficient cooling? (i.e. so the exhaust hose doesn't burn)