Exhaust restriction

[Chris H]

Picture that maybe of interest to all you hardcore B4 fans who are after that bit extra power showing the restrictive exit at the collector.


Must be worth a couple of BHP.
Outside pipe is the 2" pipe you can phisically see, the middle one is the sleeve that you can see when you cut the tail pipe off to fit a race can and the 1.5" inner pipe is at the end of the collector. The picture shows the 1.5" pipe after the 2" was cut about 1.5 inches along the 2" pipe.

[tomacGTi]

Whatever you do, DO NOT cut the horizontal part that you see in that picture.

That "divider" acts like the final part of the 4-2-1 of the exhaust. You can if you want but you will open up a whole can of worms rejetting and also working around the flatspots when you do. You'll turn it into a 4-1 pipe.

It isn't the same effect as a full exhaust but your slip-on will be noticeably louder after cutting out the reducer. You will also need a good, sharp cold chisel and plenty of Dremel discs because the perforated reducer is very hard as well as welded clamshell-style as part of the final collector. Also make sure to have a grinding stone to smooth out the interior, it's very difficult to get it all out but you can grind out what you can't cut/chisel to make it unnoticeable to the exiting gas.

After this, you'll have to jet accordingly as well, almost to the point of a full system.

My.02$...

I have no dyno proof or even hard empirical evidence to support it but I did it awhile back when I had the exhaust off for shits and giggles. There is a chance you'll lose velocity in the exhaust doing this mod just eyeballing the reducer but you may gain elsewhere. I can guarantee you that you will pick up more bark out of your pipe though.

-Randy

[Chris H]

Hi Randy,
Your comments could be of use to anyone cutting their pipe. I remember your eairlier post altho ive just put the picture on as an insight for others. I already use a 4/1 as my pipe is a Ti BeetRacing system, it gave no running probs but ive a VV model with a 444 kit on so the midrange is very strong to start with. I think you would deffo be best keeping the 4/2/1 on the standard motor.
Chris.

[Banditmax]

Chris will this pipe be there when i come to fitting my link pipe? Would you recommend removing it?

[Chris H]

Yes mike, it will be there and you want to cut it out so as only the 2" outer is left. Ive had a good look inside and i dont think the peice inside is big enough to make the pipe a true 4/2/1 its more to guide the gasses. I spoke to a guy from Akrapovic at a show about a collector they had openned up to show a similar plate and that was his answer so i'll go with the experts.

[tomacGTi]

I guess cut it and see! It's REALLY in there though so you'd have to do some real surgery to get it out.

I just remember reading somewhere that the divider exists in that location as a less expensive/easier to mass produce 4/2/1 split. If you take a close look, the pipes "feed" into it the same way a 4/2 does ie. the pairs of opposing cylinders for scavenging. It also has enough length to mimic it but like I said, I have no solid evidence that backs the theory up.

If the Akro tech said so, I'd tend to believe it as well. Their cans are worth more than the bike I'm riding.

-Randy

[Chris H]

Ye Randy i agree its got to do somthing or why put it in. Theres no way id try and cut it out, just grind the 2" out.

[Thief400]

Took it out on mine years ago when I put one a slipon, Made a big difference. 

[tomacGTi]

http://www.supermotojunkie.com/showthread.php?t=73936

I just did this to my factory headers since I had the time. There is ALOT of weld material that shrinks down the header diameter. I used a Dremel and brought it down to the diameter of the pipe and blended it to the header flange. Using an air die grinder would of course work faster but there's no way I can run one with my little pancake compressor.

Still not a not the same flow as an aftermarket header but considering how hard they are to come by, it's worth a shot trying to make the stocker a bit better.

-Randy

Edit: Another one I found that basically is what I did:

http://www.motorcycleanchor.com/katana/header.html

[gixxer]

It seemes like there are alot of opinions on this exhaust-mod.  Is there anyone who has taken their bike to the dyno to verify it? 

[tomacGTi]

No dyno (as much as I would like to).

That sort of stuff costs money which is the main reason why I waste my time with mods like this.

Time to play with jetting again... It has changed the way the bike responds to throttle.