[Guest]

If you look at the inside side of the exhaust header flanges, as Dev noticed, the portion where it meets the exhaust port is a bit rough and ready (metal thickness varies around the circumference, especially the sides and _may_ actually overlap the exhaust port by a fraction and impede smooth gas flow exiting the exhaust port..... sort of "trip it up".

See here a close up of an internal header flange

http://uk.pg.photos.yahoo.com/ph/ma.../detail?.dir=9597re2&.dnm=cc27re2.jpg&.src=ph


Here below is the exhaust header flanges with middle and right hand side roughly ground down a bit - notice how left hand side (the far left header flange) is thicker as I have not ground it yet.

http://uk.pg.photos.yahoo.com/ph/ma.../detail?.dir=9597re2&.dnm=d04are2.jpg&.src=ph


And here below are all three header flanges ground ready to polish up a bit. Notice the now roughly even thickness of material now.


http://uk.pg.photos.yahoo.com/ph/ma.../detail?.dir=9597re2&.dnm=df3ere2.jpg&.src=ph

If you put you finger inside the headers flange you can feel some slight weld spatter and this can be ground out too.

Lets hope this makes a difference. ;D

Devious to XS is the chap in here whom first publicised this mod so well done Dev. 8)

Mark

 

[Tight TL]

Mark,
I can't bring up any of the pictures.
Fred

 

[Guest]

I can't see them either - even when signed into Yahoo.

 

[Guest]

Dang-nabbit.

I'll try a different method later on.

Sorry - normal service will be resumed. later on.

M

 

[Guest]

Devious to XS is the chap in here whom first publicised this mod so well done Dev. 8)

Mark

Just glad to see someone making use of it.

I have a couple of questions, but the photos may answer them - I'll wait.

 

[Guest]

I did not "share" the album I've correected that so that hopefully now the photo's will show up?

Mark

 

[Guest]

Good photos. Nice work.
Interesting coloring - the fuel you use does not appear to use the same oxygenates as here in the US.

Did you remove the slight hump in the casting on the short turn radius - bottom of the header tube? This hump causes a bit of turbulence at higher rpm.

A slightly wider (0.5 mm) opening in the header sides and bottom will give a port mismatch that can aid in preventing reversion in the header. Slightly more (0.9mm) is better, but it can only be done on the sides not the bottom of the port. Decreasing reversion adds to bottom end power and throttle response at all rpm.

Keep the tapered wedges between the two sides of each exhaust port as  gentle as possible. These wedges help to smooth the exhaust flow.

Did you look into the exhaust ports? The head on my bike could use a bit of clean up work on both the intake and exhaust ports. The machining is fairly rough and crude - even for production.

 

[Guest]

"Interesting coloring - the fuel you use does not appear to use the same oxygenates as here in the US"


The fuel I use is minimum 97 octane, usually 98 octane which is readily available. Normal UK fuel is 95 octane.


"Did you remove the slight hump in the casting on the short turn radius - bottom of the header tube? This hump causes a bit of turbulence at higher rpm"

No Wayne - but I will be having a look to see if I can do something with it.


"A slightly wider (0.5 mm) opening in the header sides and bottom will give a port mismatch that can aid in preventing reversion in the header. Slightly more (0.9mm) is better, but it can only be done on the sides not the bottom of the port. Decreasing reversion adds to bottom end power and throttle response at all rpm."

Going by the third picture do you reckon I should grind a little more off anywhere - to get the reversion stopper?

"Keep the tapered wedges between the two sides of each exhaust port as gentle as possible. These wedges help to smooth the exhaust flow".

Aha! good tip!

"Did you look into the exhaust ports? The head on my bike could use a bit of clean up work on both the intake and exhaust ports. The machining is fairly rough and crude - even for production".

There is a layer of carbon hiding any slight imperfections and I could really do with a borescope to be honest before giving an opinion. And to be totally frank, I don't really know what I'd be looking for in order to offer an opinion.

The O2 sensor in the exhaust was sooty so I've washed it down, dunno if this will help anything.

When I get the exhaust welded up again (precat gone) I'll look into the cost of ceramic up to the collector.

I'm not sure about the look - I did a quick mock up as seen below. (Ignore the British Air Force Bomber Roundal roundal - it's a photoshop mock up).

Stock colour zorst

http://uk.pg.photos.yahoo.com/ph/ma...detail?.dir=/d231re2&.dnm=e047re2.jpg&.src=ph


Mock up ceramic up to collector

http://uk.pg.photos.yahoo.com/ph/ma...detail?.dir=/d231re2&.dnm=e7a6re2.jpg&.src=ph


Mock up to TORS

http://uk.pg.photos.yahoo.com/ph/ma...detail?.dir=/d231re2&.dnm=363bre2.jpg&.src=ph


Last image look hideous to me?

Mark

 

[premier]

It would look better in real life. The lighting in your mock ups is off.

 

[milq]

Been following this one....are you guys using the gaskets as a guide for the amount of material removed? Or are you simply trying to get an equal amount of material on all sides?

I guess I'm asking.....how are you differentiating between a .5 mm undercut and .9 mm?

Have not had mine off so the gasket question may be stupid as I have no idea what they look like.

 

[Guest]

I suspect DVS is the one to answer this with knowlwedge, I'm just an rank amateur hanging onto his shir-tail for the ride lol.

Basically I removed the exhaust to get rid of the pre-cat.

Whilst the 'zorst is off it would be rude not to clean up what is a rough casting (header flange).

The gaskets are not a good judge because they sits within a recess butting up against the 'zorst ports...... But the zorst ports are "taller" (wider) than the gaskets....... but the zorst port may not be as tall as the header flange as the header flange is uneven.

Hence clean up is worth doing.

I bought a set of digital calipers from ebay (£5.65) which measure to 1/1000 inch (or micro-meters) if you need to differentiate to a fine degree but your eyes can tell you a lot.

Over to DVS. ;D

Good luck.

Mark

 

[Guest]

On my header, I took a lot of measurements with a digital caliper and then scribed marks to cut. On the second header, I did it by eyeball from what I learned on the first one - not calibrated, but close.

The limit on the bottom of the header is the exhaust flange. Normally I like to cut 0.035 inch (0.9mm) minimum for a mismatch. But it is not possible here due to the flange design - the sides have the room to do what is needed.

The port mismatch does not make the reversion stop, but it does make the airflow act like the port is much smaller - thus reducing reversion.

This is not going to add a lot of power, but the small things add up. Getting rid of the precatalyst is a big increase in flow in the already too small collector. What I noticed was more power and torque at all engine speeds - the low rpm gain was not expected, but noticeable.

You will find that the engine wants more fuel now. ;D
More fuel = more power.

 

[milq]

Cool, starting to sound like I have a shopping list and a winter project ;D

Depending on finances. maybe I can score Tuneboy and some Chain reaction exhaust by Christmas break....that would be nice.

I told myself I'd wait until the warranty was gone, but this all sounds too good. ;D

 

[Guest]

Ok e it has finally all been welded up and the exhaust re-fitted.

The noise is slighly louder and slighly deeper.

The low end seems stronger but it's hard to tell as the weather is very cold, dry and that makes the engine feel better anyway.

I've not had a chance to open her right up past 7,000 rpm but from seat of pants for a few hours today so far I'd say it feels better all the way through.

I'll be doing a dyno benchmark in a week or two.

Mark

 

[MONKEYHANGER]

I've been following this thread too. My baby is parked up waiting for some nice weather so I would like to have a bash at taking the precats out.
From the pictures I have seen of the removed cat they/it looks hollow not like a car type honeycombe cat brick.
Does anybody have any close ups of the holes left after the spots have been drilled out?
MH

 

[Guest]

Take it, it's no good