Exhaust knowledge dump from Zero

[shnazzle]

Just got off the phone with Kevin from Zero and in 20 minutes he basically just schooled me on exhausts.
Phenomenally clever guy and he really knows how to explain things in plain stupid.

So, I'll just summarise

1) pre-cat removal degrades performance, particularly low down. Quite simply because with those empty chambers, you have essentially reduced your header length by about 50%. So anything you might have felt in the past is a lie. Anything I have written about it is BS. Removing the pre-cats means a free-flowing top end but a rubbish low and midrange as you have essentially reduced the scavenging capability by a LOT.

2) stainless steel can be easily checked for quality by using a magnet. If it's magnetic, it's not good quality stainless. The less magnetic, the better.
The better quality stainless, the more heat it retains and the stronger the metal. The more heat it retains, the hotter the exhaust, the faster the flow.

3) wrapping the manifold or applying ceramic makes the manifold hold more heat, hence speeds up flow even more. So yes, it's a genuine performance gain, although not necessary dyno-measurable on our cars. It will heat the cat up quicker if you have a 200 cell. So, good for MOT. But, if you're comparing stock to Zero, the increase in quality of steel means a wrapped stock essentially is the same as an unwrapped Zero (for heat retention only!).

4) wrapping is perfectly safe for a good stainless system. A low quality will rust because the wrap gets wet, doesn't evaporate on time, touches the hot system and causes quicker rusting. So, wrapping is good as long as what you're wrapping is good stainless. Do NOT wrap your stock mani. (see my cracked mani for evidence)

4) on charged cars, the backbox packing needs to be different or the backbox needs to be baffled. Basically to stop the turbo/supercharger from blasting packing out the back of your car. Kevin uses woven sheets in his boxes which do not come through the perforations in the box. Loose fibreglass does. So, one to consider for you boys/girls with powerful turbo/supercharger cars. If your car is much louder all of a sudden it's probably because you've blown the packing straight out the back.

5) simple one; yes the Zero is designed, by its smooth insides and design to unleash the beast with regards to flow. It enhances scavenging to no end and flows significantly better than the stock. Aside from being A-grade steel, welding and looks. Expect significant increases in low and midrange oomph. I can definitely vouch for this.


That's it...

[Gaz mr-s]

He's a nice guy to talk to, isn't he.

Because I'm hoping to get a cat pipe, & because I've bought his manifold, I emailed him re your fitting problem Patrick.  I was surprised when my phone went & he was on. 20 mins with me too.

[Joesson]

@shnazzle said

1) pre-cat removal degrades performance, particularly low down. Quite simply because with those empty chambers, you have essentially reducedyour header length by about 50%.

Is that a slip of a digit as I thought that the empty chambers would increase volume/ increasing effective length.
Not that I know anything about the science behind it but am trying to undestand.

[shnazzle]

@shnazzle said

1) pre-cat removal degrades performance, particularly low down. Quite simply because with those empty chambers, you have essentially reducedyour header length by about 50%.

Is that a slip of a digit as I thought that the empty chambers would increase volume/ increasing effective length.
Not that I know anything about the science behind it but am trying to undestand.

It certainly isn't. I explained my theory (expansion of the chamber) and Kevin, in his way of correcting me, basically said "you're such a newbie dumbass...that's not how it works at all. Let me school you, boy"

So yeah basically because the chambers are essentially areas of expansion vs the headers, as far as the flow is concerned , that's where the exhaust ends. Essentially the scavenging power ends there. Very very prematurely given the length of the pre-cat chambers.
All that flow that was rushing down the headers comes to a sudden halt in those chambers in a grand anti-climatic fashion.

So if you have a de-pre-cat mani, a 200cell cat and a nice free flowing backbox, you've essentially pee'd away all the money you've spent on that cat and backbox

[Topdownman]

Not that it affects me, but what you are saying is, dont gut your pre-cats but get a new manifold?

[shnazzle]

Not that it affects me, but what you are saying is, dont gut your pre-cats but get a new manifold?

Yes.
Granted I've always said that but I've said it for the wrong reasons haha

[Petrus]

@shnazzle said

1) pre-cat removal degrades performance, particularly low down. Quite simply because with those empty chambers, you have essentially reducedyour header length by about 50%.

Is that a slip of a digit as I thought that the empty chambers would increase volume/ increasing effective length.
Not that I know anything about the science behind it but am trying to undestand.

There twó aspects involved:
1. the scavenging ´inertia´ effect of a mass of gas moving at speed
2. pulse waves

ad. 1 By removing the insides of the cat, the gas going into the chamber has a way larger volume so slows down, slowing down the gas behind it, behind it, etc.
The ´colums´of gas in the header now has less kinetic energy, less inetertia, hence less ´scavenges´.

A continued pipe enhánced the extraction effect as the column of exhaust gas gets longer, has more mass, more inertia.
Same thing the higher speed as speed x mass = kinetic energy, so yes wrapping does work in this respect.
Now whý is more heat faster gas?
Hot gas expands, needs more space. Now the header diameter remains the same so the gas speeds up. Same quantity of gass, same maas, higher speed = more kin. energy = more inertia = more ´sucking´ effect = more scavenging.

So yes, it is wáy better to get headers without a cat than gutting the OEM one.


ad.2 A pulse wave coming at a closed end bounces back positive. Same thing a negative puls; i.e.bounces negative.
A pulse coming at an open end changes from positive to negative and vv.
The gas pulses in the header coming at the cat chamber travel back negative, whereas the cat bounced the pulse positive. Whatever the effect; it is oposite to how Toyota engineers designed it.

[Petrus]

Wrapping:
For street use wrapping has an unexpected drawback; it makes more sound.
The gas is hotter, travels faster as well as any sound pulses.
With a sports cat and sport muffler fitted it will be audible.
With OEM cat/muffler the heat gets dispersed.

[shnazzle]

@shnazzle said

1) pre-cat removal degrades performance, particularly low down. Quite simply because with those empty chambers, you have essentially reducedyour header length by about 50%.

Is that a slip of a digit as I thought that the empty chambers would increase volume/ increasing effective length.
Not that I know anything about the science behind it but am trying to undestand.

There twó aspects involved:
1. the scavenging ´inertia´ effect of a mass of gas moving at speed
2. pulse waves

ad. 1 By removing the insides of the cat, the gas going into the chamber has a way larger volume so slows down, slowing down the gas behind it, behind it, etc.
The ´colums´of gas in the header now has less kinetic energy, less inetertia, hence less ´scavenges´.

A continued pipe enhánced the extraction effect as the column of exhaust gas gets longer, has more mass, more inertia.
Same thing the higher speed as speed x mass = kinetic energy, so yes wrapping does work in this respect.
Now whý is more heat faster gas?
Hot gas expands, needs more space. Now the header diameter remains the same so the gas speeds up. Same quantity of gass, same maas, higher speed = more kin. energy = more inertia = more ´sucking´ effect = more scavenging.

So yes, it is wáy better to get headers without a cat than gutting the OEM one.


ad.2 A pulse wave coming at a closed end bounces back positive. Same thing a negative puls; i.e.bounces negative.
A pulse coming at an open end changes from positive to negative and vv.
The gas pulses in the header coming at the cat chamber travel back negative, whereas the cat bounced the pulse positive. Whatever the effect; it is oposite to how Toyota engineers designed it.

Very well-explained indeed. Thanks!

[Joesson]

Thankyou Patrick and Petrus for the reasoning, now all I have to do is try to understand it

[Carolyn]

for a bit of fun.

So you want long headers eh?  Here's some long headers for a 1ZZ.

[shnazzle]

They're insane. But necessary

[jonbill]

Are the brackets in the right place? [emoji102]

[Carolyn]

Good question. 

Next?

[Joesson]

Is the above an example of Boyle's Law?

[shnazzle]

Are the brackets in the right place? [emoji102]

Always the comedian

[jonbill]

Are the brackets in the right place? [emoji102]

Always the comedian

I try.

[moto]

This post couldn't be more appropriate for me at this time. I have had my year 2000 completely standard roadster for approximately 2 years. And during my ownership I have put considerable thought to the cat problems so often talked about on this forum. This year I have decided to change my complete exhaust system. I saw on a popular auction website a roadster stainless steel header unit with apparently very good reviews with a price tag  over £250.00 pounds "not cheap" . So I made the purchase. I run a small engineering business and I am proud to have machined work for many prestigious  motorcycle and car manufacturers including formula 1 teams. I am only explaining this to add justification that I would consider myself in a very good position to judge craftsmanship and quality. On receiving the auction site purchased header unit I personally was very disappointed. The chambers so important for the efficiency of a good header unit were extremely hampered by the poor fitting of the internal tubes. From the outside the header unit looked to be of a satisfactory quality. It was at this stage I contacted Carolynne from this forum . "wish I done it before I made the purchase" . Carolynne said she thought the header units from Zero exhausts were extremely good. So I contacted Kevin at zero exhausts and what an interesting helpful guy he is. I explained I wanted a good quality header unit and before I fit it I would like to ceramic coat it for the thermal advantage. (probably not essential for the level of  performance from 1zz engine but hey that's what I want to do ) During my first phone call with Kevin I was completely reassured this guy knows his beans so a purchase was made for a zero stainless steel Mr2 header unit for £395.00. On Thursday of this week 14-2-19 I received Kevin's zero header unit. The  quality is first class and the craftsmanship is excellent. Compared with the auction site header unit the zero unit justifies its price tag in my view easily.
This  Monday I am sending the zero header unit to  zircotec to be coated . I asked Kevin what cat and exhaust he would recommend and during the conversation I asked why do you not make one. Well the conversation developed further and in May this year (obviously not surprisingly he is a busy man)  my mr2 is booked in with Kevin so he can use my car as a jig for making a Mr2 sports cat and exhaust system . On judging the quality of the header unit and seeing the work he has done on his website. It's a project I am looking forward to be involved in.

[Gaz mr-s]

Good question. 

Next?

Easy wrapping job!

[Gaz mr-s]

Well the conversation developed further and in May this year (obviously not surprisingly he is a busy man)  my mr2 is booked in with Kevin so he can use my car as a jig for making a Mr2 sports cat and exhaust system . On judging the quality of the header unit and seeing the work he has done on his website. It's a project I am looking forward to be involved in.

Kevin is acquiring a car from a local garage in order to make a jig for a cat pipe. He expects to have one made for me in approx 4 weeks.

[Petrus]

Kevin is acquiring a car from a local garage in order to make a jig for a cat pipe. He expects to have one made for me in approx 4 weeks.

Getting interesting!

I have a no cat header and plan DIY a free flow muffler next week.
In between will sit the OEM lardy one that has been there from new.
I would be interested in a new, lighter one at the right price.
The cats2u mentioned by Carolyn sets that bar rather challenging. Their shipping rate is very reasonable as well.

[Call the midlife!]

I dropped my old, standard cat pipe off at a Powerflow "centre of excellence" this morning for them to make me a 200 cell version.
The lads their looked down the flexis and all said the same thing "Christ they're tight!" and similar phrases I won't repeat here.
It's not going to be "cheap" but it's going to be well made and pretty, fingers crossed.


Sent from my iPhone using Tapatalk

[moto]

Well the conversation developed further and in May this year (obviously not surprisingly he is a busy man)  my mr2 is booked in with Kevin so he can use my car as a jig for making a Mr2 sports cat and exhaust system . On judging the quality of the header unit and seeing the work he has done on his website. It's a project I am looking forward to be involved in.

Kevin is acquiring a car from a local garage in order to make a jig for a cat pipe. He expects to have one made for me in approx 4 weeks.

Yes Kevin said he was making a jig for a sports cat for someone on this forum.

[Petrus]

Good question. 

Next?

Why not go for the cat2u on a standard 1ZZ sans pre-cat?

Why would I (assuming the motorbike muffler works out) pay a 100€ more for a custom 200 cell one?