Exhaust improvement.

[BuGS]

I am trying to make sence of this. Can anyone help me out?
Original Post

I was cross referencing OEM P/N# the other day for the factory flex pipe. It
seems that the pipe for the (8V)1.6 SOHC is the same as the pipe for the
(16V)1.6L SOHC but I also found that the same part number is used on all
the 1.8L SOHC and the 1.8L DOHC to the end of the '93 model year.
Considering that it is a pretty restrictive design of the 1.6L I can't image
how much it is holding back the 1.8L DOHC that is a heavy breather on the
top end. I dissected an old OE Mazda, a Walker and a Bosal front pipe. On
the outside all 3 pipes look to be a good size diameter but what you are
seeing is actually the outer steel shell over the thermal insulation. All
the pipes start out at 2" OD but the pipe is crunch bent which reduces the
cross section down by 1/3. Then all three pipes have a flex joint with an
accordion pleated interior that is only about 1 5/8" ID and creating a lot
of turbulence. Then there is a further reduction in diameter just after the
flex joint just before the flange to the cat, although if you understanding
of hot gas flow dynamics this last reduction in diameter can be a good
thing and actually improve the volume of exhaust gases flowing through the
pipe before this point. I recently picked up text books on fluid dynamics
and hot gas flow phenomenon's plus I now have access to a piece of software
called Flowmaster which can computer model liquid and gaseous flow dynamics.

If any of you read the MX-3 list I was talking about this a couple week ago.
I needed to replace the flex pipe on my 323 anyway so I went out in the shop
and scrounged up leftover material from other projects. First was to find a
flex joint with a smooth interior. My first choice was a ball and socket
joint like on the '95+ Protégé, VW, Audi, etc. but in the end I found a
Canadian made flexible joint with a 2" ID smooth flat spiral wound core that
would not disrupt the flow to much. Next was to machine out the two flanges
and weld starter tubes on to them so they could be bolted to the manifold
and cat to start mockup. The new flex joint is much shorter than the OE and
OE replacement length so it allow me to play around a little more than if it
were just making a replacement piece. According to my calculation and
computer modeling a 2" OD mandrel bent pipe still as frictional losses in
air flow on the short side of the bent. I found that if I were to cut two
different mandrel bends with different radii at the centerline of the bend
and weld them together I could make a pipe with the flow of a straight
piece of pipe. All the sections of pipe were welded together and installed
on my 323. On the first test drive what a difference it made. This is
probably made more of a difference that all other modifications put
together. Changing the front pipe is something that no one ever considers
because there is not a bolt on aftermarket replacement other than stock
replacement part. With these modifications I am running door to door with a
2.0L Protégé. I've had people think I swapped a 125hp B5-ZE or a 128hp BP-DE
in the car by the change in the way it pulls over a weekend. I took the
pipe off and slipped in a machined taper ring into the pipe for the cat
flange. This insert made the interior of the pipe have the profile of a coke
bottle or the body of a Wasp. Most people would think that this would reduce
performance but the opposite is actually true. It actually improves low end
power and torque and on the top end increase volume of exhaust flow over a
straight piece of pipe. This is caused by the venturi effect which squeezes
the exhaust gases increasing velocity. As the gases expand after the
venturi. It releases heat and creates a low pressure zone which in turn
sucks even more exhaust gases through the pipe greatly increasing the
scavenging effect. Since making this last modification I've noticed the
following. First is I to learn not to tip in the throttle as much off the
line. I also seem to surprise other drivers merging into traffic as I am
accelerating much faster that they expect for a 323. Another benefit is that
gas mileage has increased by as much as 8%. One down side as I've been
finding is I'm burning plugs if I keep the revs to high for to long of time.
This lean out condition was to be expected. In NASCAR and IMSA racing when
they started to use the venturi in the exhaust, the increase in the
scavenging effect would be so great that additional fuel had to be supplied
and more aggressive cam time was necessary to counter the lean out
condition. An adjustable rising rate FMU and retarding the cam pulley
another degree or two, seems to have solved this issue. I've done a couple
extra mods to the pipe the couldn't be reproduced in mass production or by
the average exhaust shop but is a mandrel bent 2" pipe and a good quality
flex join can make significant gains on a 8V 1.6 SOHC just think how much
the 1.8L are being held back by the soma OE pipe.


Vaughn Nishimura
Laguna Blue '93 2.5L V-6 MX-3GS
and Laguna Blue '92 1.6L(8V)SOHC 323SE
http://members.allstream.net/~dragon64

[perhapsadingo8yerbaby]

Here's a stab but this is an oversimplified and technically incomplete explanation. The essence of what ya need to understand is in the excerpt below of Vaughn's post about the coke bottle shape.

Vaughn's statement:
"This insert made the interior of the pipe have the profile of a coke bottle or the body of a Wasp. Most people would think that this would reduce performance but the opposite is actually true. It actually improves low end power and torque and on the top end increase volume of exhaust flow over a straight piece of pipe. This is caused by the venturi effect which squeezes the exhaust gases increasing velocity. As the gases expand after the venturi. It releases heat and creates a low pressure zone which in turn sucks even more exhaust gases through the pipe greatly increasing the scavenging effect... One down side as I've been finding is I'm burning plugs if I keep the revs to high for to long of time. This lean out condition was to be expected. "

So now picture the exhaust gases exiting your motor and flowing into the exhaust pipe toward that "coke bottle" narrowed "venturi effect" section. When that flowing stream of hot gas is squeezed thru the narrower "coke bottle", the squeezing of exhaust gases increases its escape velocity (and temp/heat as it's compressed through the narrow spot) - and that increased velocity is what improves low end torque. It's the same principle as when you blow thru a narrow diameter straw/tube vs. a larger diameter one. You're able to achieve greater velocity using the narrower tube.

Next, the high velocity "squeezed gases" flow into the larger volume of larger diameter straight pipe once past the narrower "coke bottle/venturi" restriction. So now the exhaust gas is suddenly under less pressure... = creating a low pressure zone. Creating a low pressure zone right next to/after a higher pressure zone (the coke bottle) means the higher pressure "zone" will literally be sucked in (further down the exhaust pipe in this case) by the low pressure zone. In other words, even more exhaust gases will flow at higher velocity and volume. The more exhaust gas you can remove from your engine at the highest velocity = the performance gains Vaughn gets from this mod.

The low pressure zone concept is just like when you breath/inhale. You are able to take in a breath because your collapsed (evacuated) lungs create a low pressure zone when you attempt to expand them by inhaling. The air you are about to breath in is then under a higher atmospheric pressure than your lungs so it is sucked into your lungs to fill the low pressure area.

The "scavenging" Vaughn talks about has to do with how much more effectively all (or most) of the exhaust gases are "sucked" or evacuated out of the engine/exhaust system. The resulting "lean out condition" is a side effect of this improved exhaust gas scavenging because now a greater volume of fuel/air mixture is needed on the intake side to keep up with how fast and completely the exhaust gas is evacuated.

Hope that all makes some sense cuz it kinda hurt to attempt writing it for clarity...

<small>[ October 31, 2004, 02:20 PM: Message edited by: perhapsadingo8yerbaby ]</small>

[Yoda]

That is actually very good explaination of how a merge pipe works. It's good to see that there are "new school" people out there that understand the complex principles of fluid dynamics. In NASCAR some teams are running a merge from 3.5" down to 1.75" then back up to 3.5-4" at the collector of the header which by itself is good for a 30-35hp gain on a engine already making 600+hp which makes no sense to an old school thinker who assume this to be some sort of restrictor rather that a power adding tuning device.

Depending on the difference between the high and low pressure zones with in the exhaust system it is in theory possible to acheive a naturally supercharged effect. If the increase in the scavenging effect create a strong enough vacuum pulse and timing is right, it will as you say suck more of the exhaust out of the cylinder on the exhaust stroke but also depending on the cam timing the scavenging effect can also extend to affect the air intake as well. First the exhaust gases rushing out of the cylinder creates a stronger vacuum pulse as the exhaust valve closes and the intake valve opens there for sucking air into the cylinder filling it more completely. Normally the pressure in the intake manifold is a vacuum but depending on intake restrictions it is possible for the intake manifold to see positive pressure for a split second as the intake valve closes.

Also it is important to keep the exhaust moving all the way through to the tailpipe. Straight through glasspack mufflers sound cool but add backpressure once that adsorb the heat from the exhaust unless they are so big in diameter that they do little to dampen the sound levels. A well designed and properly sized reverse flow or chamber muffler will do more for performance and reducing sound levels by creating another pressure drop before the exhaust exits the tailpipe.

Originally posted by perhapsadingo8yerbaby:
Here's a stab. The essence of what ya need to understand is in the excerpt below of Vaughn's post about the coke bottle shape.

Vaughn's statement:
"This insert made the interior of the pipe have the profile of a coke bottle or the body of a Wasp. Most people would think that this would reduce performance but the opposite is actually true. It actually improves low end power and torque and on the top end increase volume of exhaust flow over a straight piece of pipe. This is caused by the venturi effect which squeezes the exhaust gases increasing velocity. As the gases expand after the venturi. It releases heat and creates a low pressure zone which in turn sucks even more exhaust gases through the pipe greatly increasing the scavenging effect... One down side as I've been finding is I'm burning plugs if I keep the revs to high for to long of time. This lean out condition was to be expected. "

So now picture the exhaust gases exiting your motor and flowing into the exhaust pipe toward that "coke bottle" narrowed "venturi effect" section. When that flowing stream of hot gas is squeezed thru the narrower "coke bottle", the squeezing of exhaust gases increases its escape velocity (and temp/heat as it's compressed through the narrow spot) - and that increased velocity is what improves low end torque. It's the same principle as when you blow thru a narrow diameter straw/tube vs. a larger diameter one. You're able to achieve greater velocity using the narrower tube.

Next, the high velocity "squeezed gases" then flow into the larger volume of larger diameter straight pipe once past the narrower "coke bottle/venturi" restriction. So now the exhaust gas is suddenly under less pressure... = creating a low pressure zone. Creating a low pressure zone right next to/after a higher pressure zone (the coke bottle) means the higher pressure "zone" will literally be sucked in (further down the exhaust pipe in this case) by the low pressure zone. In other words, even more exhaust gases will flow at higher velocity and volume. The more exhaust gas you can remove from your engine at the highest velocity = the performance gains Vaughn gets from this mod.

The low pressure zone concept is just like when you breath/inhale. You are able to take in a breath because your collapsed (evacuated) lungs create a low pressure zone when you attempt to expand them by inhaling. The air you are about to breath in is then under a higher atmospheric pressure than your lungs so it is sucked into your lungs to fill the low pressure area.

The "scavenging" Vaughn talks about has to do with how much more effectively all (or most) of the exhaust gases are "sucked" or evacuated out of the engine/exhaust system. The resulting "lean out condition" is a side effect of this improved exhaust gas scavenging because now a greater volume of fuel/air mixture is needed on the intake side to keep up with how fast and completely the exhaust gas is evacuated.

Hope that all makes some sense cuz it kinda hurt to attempt writing it for clarity...

[BuGS]

Ok thats what i was thinking. Does anyone know how you could make one of these for our car?? It sounds like get a bigger then normal flex section then make a bottle neck area that releases into a bigger section. I am looking into redueing my exhaust and this would help me out i would assume.

[Yoda]

No there is that old shool thinking again bigger is not better. At no point should the ID of the pipe ever get bigger. What you want is a uniform diameter for beginning to end and keep the pipe diameter to smallas possible for the displacement of the engine and Rpm range it will be operation in. For a 1.6L engine a 1.75" is more than big enough. As far as the merge is concerned you really need to know how to make the calculations. The angle of approch and the angle of departure from the narrowest diameter and position are very important otherwise the gas flow will compress to rapidly and become a restriction or the velocity of the gas flow will go sub-sonic and become a restriction.

[Spotted]

So, what needs to be done to get a proper merge done?
Where does it need to go and what calculations need to be made?

Can it be used with a turbo setup?

[wytbishop]

Like I have said before in another thread, I am not an expert on this specific branch of physics, but as far as calculations go, you can't just bust out the ole calculator and figure out the optimal diameter and gradient of decreasing radii and yada yada yada. You would have to be able to measure exhaust gas velocity and make qualitative comparison from one trial to the next and determine the best set up for a given engine experimentally. Ultimately, horse power is what we are after, so you would design a pipe you think makes sense and try it on a dyno. Then using a whole bunch of data measurments at different points in the system, determine where losses are happening, try to correct them and do another run. This is why the aftermarket parts that work are so expensive. Someone has spent a butt load of time using this process to figure out what works.

And to answer your question Spotted, a turbo is very different in terms of exhaust than a NA engine. The gases have to be kept as hot as possible up to the turbo and then have the freest flow possible after the turbo. The key to the efficiency of the turbine is the pressure differential between pre and post turbine gases. So you want really hot, high pressure up to the turbo and then low pressure in the turbine and on the way out to atmosphere. This gives the exhaust gases the greatest room to expand, which is what is really what moves the turbine to a much greater extent than the velocity of the gas.

I wish I had been having this discussion when I was taking Fluid Mechanics and Thermodynamics in school. I would have paid more attention.I will have more consice thoughts to share soon. I might even try to design something. Add some fuel to the fire.

Wyt

[wytbishop]

What I forgot to say and i really wnated to get accross to you all, is that what Vaughn is doing is a time honored tradition is hotrodding. If you have an idea try it. If it doen't work then no harm, but if it does great, you made a step forward. This is the process only not in a lab, we do it collectivly, over time. Nobody is going to spend thousands of hours on R&D for these cars, there's no profit in it. If we are going to get a really great exhaust or set of motor mounts or whatever it will be because someone tried it and it worked. So keep tryin stuff and asking questions.

[BuGS]

Originally posted by Spotted:
So, what needs to be done to get a proper merge done?
Where does it need to go and what calculations need to be made?

Can it be used with a turbo setup?

in other words NO. You want like a 2.5" all the way back up to 250-300 HP then so to 3" from 300-450. Then from there its all expeiramental... Those calculations come froma garret turbo technition by the way.

[Yoda]

I like your way of thinking. Many mods I make are developed from ideas that didn't necessarily have an automotive original. Much of what I do is thinking outside the box. The problem with the whole Compact scene is that almost no one is doing it for themselves. Almost everybody is looking for bolt-ons, brandnames and flash. The other problem is that people are afraid to inform themselves, take responsibility for there actions and they put down other peoples ideas if it does fit the half truths they read on the internet. A lot of great inventions were developed in someones garage or basement by DIY'er but those seem to be fewer and farther between. Speaking profits a lot of the best car modifications are dificult to mass product at a price people are willing to pay so the only way to get these mods is to DIY and evaluate the results and improve on it.

Originally posted by wytbishop:
What I forgot to say and i really wnated to get accross to you all, is that what Vaughn is doing is a time honored tradition is hotrodding. If you have an idea try it. If it doen't work then no harm, but if it does great, you made a step forward. This is the process only not in a lab, we do it collectivly, over time. Nobody is going to spend thousands of hours on R&D for these cars, there's no profit in it. If we are going to get a really great exhaust or set of motor mounts or whatever it will be because someone tried it and it worked. So keep tryin stuff and asking questions.