Is This Exhaust Connection Acceptable?

[rebuilder86]

Anyone with experience in exhaust flow know if this seemingly ridiculous 80 degree but weld of the exhaust pipe just beneath the manifold would be causing me a power or economy issue?

Its not a joke, it really is welded like that, due to the steering arm and housing being in the way.

This is the Philippines where quality workmanship is few and far between and I will probably have to spend a week driving around to find someone with the welding ability and ability to move the steering mechanism to make it all line up.

As this is such a mission for me to endeavour to fix, I want to know not opinions, but actual fact, if this would be causing an excessive back-pressure at the exhaust valves.

My gut tells me it would be nothing at idle, but at high RPM when lots of air is flowing through, my uninformed opinion would be that this is a major restriction.

 

See attachments for photos of this crazy piece of work.

 

Cheers

[altezzaclub]

A 90deg bend adds the same flow loss as a metre of pipe.... If I were you I wouldn't worry about it until you're doing something else like fitting extractors or some exhaust rusts through. The local exhasut shop should be able to replace it with a slightly curved piece, but it is in such an awkard place it will have to be pulled out of the car.

 

I'm sure you will find the mechanics you need sooner or later, there has to be some good ones who are expert in keeping old cars running, its like Africa. Just think of how cheap it is to have anything done compared to Aussie!

[rebuilder86]

That's quite comforting advice, however I'm not entirely sure that I bring myself to believe that a 90 degree snap bend like this could so simply be compared to an extra metre of pipe....

Is this some rule of thumb that is commonly known??

If so, how would someone come up with such a rule of thumb, is it common for car manufacturers to inadvertently introduce sudden 90 degree changes of direction in an exhaust and therefore a science has been developed to calculate how much effect it has?? hahahahaha

I'm not writing off your knowledge, just trying to work out where you got that really perfect description of my exact situation.

Also, this isn't a bend, its more like a t junction with one of the Ts blocked up.

[LittleRedSpirit]

I don't know where the idea that a 90 degree bend equals a metre of pipe comes from. I've heard pretty much the opposite, that 90 degree bends are desirable in some circumstances. Particularly with inlets and that they help to accelerate the charge, I can't see why an exhaust would be different.

 

I want to see your working Altezza club, that line has the ring of an old wives tail, the kind of thing you hear, assume true and repeat forever without ever knowing the truth potentially.

[rebuilder86]

oh no no please don't tell me its desirable, that's the last thing I want to hear, I want to be able to make this thing more powerful haha.

I can understnad how the 90 degree bend in an inlet helps, air flowing around the outer portion of the BEND will have to move faster than that flowing around the inside, causing a good vaporisation of the fuel in that charge.

But remember, an exhaust has nothing to do with fuel delivery and this is not a bend, its a sudden change in direction, where the design of the join itself causes the passage to be narrower than the diameter of the pipe.

 

This is how i imagine the flow is being disturbed during high power high RPM periods.

I would like to know if there is any truth behind my theory.

see the waves bouncing off the pipe wall pushing the exhaust gases through a narrower passage to escape.

[rebuilder86]

DELETEED POST

Edited February 14, 2016 by rebuilder86

[rebuilder86]

mind you i may have jsut foudn the first bit of evidence in favour of Altezzas theory

No idea how reputable the source.

My pipe would be about 1.6 inch so lets assume a 2 inch pipe with a mitred 90 degree elbow, thats the same as 10 feet of pipe. thats 3 metres.

Now mine is more lliek 1.6, and the angle is more like 70-80 degrees, so I'm going to guess that smaller pipe means more restriction per degree of mitre.

Base on the data below, I created a polynomial average trendline on a graph in excel and found that a 1.5 inch pipe with 80 degree mitre would equate to 7.5 feet of pipe, so about 2.3 m.

also, the losses become exponentially greater as the velocity increases. Double the air speed, quadruple the loss. So when at idle, this is barely noticable. so i was correct in assuming this would have more an effect higher up the revs.

 

Losses in equivalent feet of straight pipe:

 

SMOOTH BEND ELBOWS

Pipe Size 90-degree standard 90-degree long radius 45-degree standard 180-degree standard

2 inch 5.0 3.3 2.6 8.2

2½ 6.0 4.1 3.2 10

3 7.5 5.0 4.0 12

3½ 9.0 5.9 4.7 15

4 10 6.7 5.2 17

5 13 8.2 6.5 21

‘Standard’ = radius/diameter ratio of 1. ‘Long Radius’ = radius/diameter ratio of 1.5.

 

MITRED ELBOWS

Pipe Size 90-degree 60-degree 45-degree 30-degree

2 inch 10 4.5 2.3 1.3

2½ 12 5.2 2.8 1.7

3 15 6.4 3.2 2.0

3½ 18 7.3 4.0 2.4

4 21 8.5 4.5 2.7

5 25 11 6.0 3dfsd

Edited February 14, 2016 by rebuilder86

[corollaart]

Well there would be a small restriction i guess but unless its a full on performance racer i wouldnt be to concerned .

 

You could spend money fixing it for 0 gain.

 

I wouldnt over think it ,lots of guys spend to much time and money trying to reinvent the wheel.

 

I say drive it !

 

Rob

[ke70dave]

Every time you bend a pipe, you add additional pressure drop and you ruin any sort of laminar flow inside the pipe.

 

On the first point of "additional pressure", a normal straight pipe has pressure drop across it, and when looking at bends often books talk about an "Equivalent length" of pipe of a bend. Ie, how much extra pipe is that bend worth in pressure drop.

 

The amount of pipe is related to the diameter of the pipe though, so the "1 meter" is probably correct for a certain diameter of pipe, but its not a general rule.

 

http://www.katmarsoftware.com/articles/pipe-fitting-pressure-drop.htm

 

if you look at that, in section 3.1 it gives the calculation for a 90deg bend as 13 = Le/D

 

where Le is the equivlent length, and D is diameter.

 

if we assume an internal diamter of 1.5" (guess)

 

that gives the equivelent length of 13*1.5 =19"

 

so essentially its like adding 19" of pipe.

 

As for the ruining flow, that is probably more of an issue with the bend, as you are then starting to talk about the "extracting" properties of an exhaust, not sure how you calculate the effect of a 90deg bend though.

 

How much difference is this going to make in the real world on a tiny K motor? i would say close to zero.....

 

If you were making an exhaust, sure don't put a 90deg bend. But if that bend is not leaking i wouldn't worry about changing it until you get some nice extractors etc.

 

This was an interesting video from the roadkill boys on dented headers, gives an idea on how much difference it makes.

 

[rebuilder86]

sweet, not worrying!

convincing post!

[altezzaclub]

I want to see your working Altezza club

 

err... I think it was a couple of years ago when I was planning on an extraction vent in the grille on the oven at home... I had to chase up a lot of education on flow mechanics, then never got around to doing it!

 

Mind you, I think they were talking about a nice 90deg curve!

 

Anyway.. buried in remote thermostat 4AGE problems currently, something I'm sure you've had to solve on the ZZ.. The 4AGE wagon with no t'sat has terrible, violent surge when cold...