Getting the most out of your stock header

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8541Hawk
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Getting the most out of your stock header

Post by 8541Hawk »

Another topic that doesn't get a lot of attention...... :wink:

So stock header or aftermarket full system? If you have raised the compression ratio, then yes some of the full systems can be beneficial but if you are still at the stock ratio then the stock unit is more than adequate IMHO.

The way I look at it is that it is a fairly well designed system, built on the cheap. It is stainless but does discolor quickly, as we all know and the welds are a bit ugly and cause some issues but we'll cover that in a sec.

There is one "controversial" bit which is normally referred to as the "restriction" if you look into the header where the right mid-pipe mounts.
I say controversial because I have heard many times that Honda just left it in there to cut costs, which I don't agree with.

The reason I say this is by looking at the header you can see that the pipe extends 25-30mm past where the weld is located. Let's call it 25mm to make it easy.
If it is just to have a bit extra tube to make assembly easier, then 5mm would have been fine and it wouldn't extend into the collector, so no blockage.

Now 20mm of stainless tubing doesn't sound like much but factor in the production run and spares made and let's say Honda made 100,000 headers.
That 20mm now turns into 2 Kilometers of wasted tubing. How is that saving $$?
Another thing is they all seem to be in the same location.
If it was just sloppy workmanship then you would think they would be at different spots in the collector but that doesn't seem to be the case.

That leaves the question, why the hell is it there? After doing a bit of research and seeing Dan Kyle's dyno charts showing the bike made 2 hp more with it in (of course that was a week after I removed mine..... :oops: )
back in '97 I finally think I figured out what is going on. I could be wrong but the big clue for me is how the left (shifter side) can gets hot at idle and low RPM while the right stays cool and then heats up as you bring the rev's up.

What I believe they have done is tricked the exhaust gasses into thinking it is a variable length system, which is the best type of system to run as you have a long system for low rpm power and a short system for high RPM power. So how did they do this with no moving parts? Well exhaust gasses are stupid..... for example the 160 degree or so turn the rear pipe makes before it joins the collector make the gasses "think" the pipe is close to the same length as the front pipe.

As the gasses exit the "restriction" it wants to go in a straight line, so most of the flow exits the left side, or as long as the system can get.
As the RPMs raise, so does the pressure in the system which causes "the path of least resistance" for some of the gas flow to now be the right pipe. As more gasses start flowing through the right side, the system "appears" to now get shorter to the gasses flowing through the system. This continues until the flow is equal through both cans at which time the system "appears" to be at its shortest to the exhaust gasses.....at least that is how I see it.

Now after all that there is a place (well two places) where I have to say Honda did blow it. Yeah after talking about Honda workmanship I have to point out a big mistake IMHO and really points out the "made on the cheap" issue and can make me question my other opinions on the the system..... I mean how could you desigh something so good then screw up so bad??

Anyways the problem is on the inside of the pipe where it bolts to the head. Take a look down the pipe and you will see the biggest, sloppiest, nasty machine weld holding the collar on.
I don't have a pic of the "before" but on mine the weld stuck out 6-8mm in one spot and a good 3-4mm the rest of the way around. This is right where the exhaust exits the head... :eek2

I started with a die grinder with a stone to rough the weld down....yes the stuff is hard....lol then switched to a Dremel with a drum sander and then a 80 grit flapper wheel and you end up with this:

Image

Not the best pic but it is hard to shoot down the pipe and get an image.

Also while on the exhaust, you should check it from time to time if you have dropped the forks, raised the rear or both as it is the first "hard part" to touch down though only in right hand turns.
What you will see if this happens will look like:
Image

Image
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MacV2
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Re: Getting the most out of your stock header

Post by MacV2 »

Good writ up fella ! :thumbup:

Was the weld the same on the rear head exit point as well Hawk ?

I can already hear the sound of furious grinding from all over the UK this weekend... :lol:

& lots of swearing when exhaust studs snap... :lol:
Making up since 2007, sometimes it's true...Honest...
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agentpineapple
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Re: Getting the most out of your stock header

Post by agentpineapple »

or you could buy a full two brothers system like i did for £150...... :lol:
good write up hawky..... :thumbup:
the headers are by far the most noticeable area where honda cut costs. a very poor grade of stainless steel.... :thumbdown:
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VTRDark
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Re: Getting the most out of your stock header

Post by VTRDark »

the headers are by far the most noticeable area where honda cut costs. a very poor grade of stainless steel.... :thumbdown:
He says as he's slowly polishing it away. :lol:

Now why did I not notice the welds when I took mine off :roll: that was stupid of me, I obviously did not investigate fully enough. :(

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sirch345
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Re: Getting the most out of your stock header

Post by sirch345 »

Some very good points there. Good write-up Hawk :thumbup:
I'm in the team that thinks the 25mm bit that you refer to is meant to be there, I like your reasoning why :)

Chris.
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lloydie
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Getting the most out of your stock header

Post by lloydie »

Here is the weld before (its as bad front and rear )
Image
And after
Image
I did these on the 2-1 and need to do it on the current system.
And yet another good write up hawk :Thumbup:
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lloydie
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Re: Getting the most out of your stock header

Post by lloydie »

cybercarl wrote:
Now why did I not notice the welds when I took mine off :roll: that was stupid of me, I obviously did not investigate fully enough. :(

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8541Hawk
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Re: Getting the most out of your stock header

Post by 8541Hawk »

Yes they are the same front and rear. I started with the rear one to figure out the best way to remove the excess weld material due to the fact it is easier to hold on to and work with.

As for not seeing it,well it is something easy to miss.

I guess it stuck out to me as I have set up a few bikes for what used to be the local club racers while I was living in the SF Bay area which had a "stock" class where you were only allowed to set up the suspension (springs and minor "cleaning up" of the stock valving) and brake pads.

So you did spend a bit of time trying to get the most out of the stock bits.

Though most were nowhere near as bad as the VTR header. In fact the only one I can think of that comes close is the old XR400 header.

I guess I might have also started a run on those copper gaskets to seal the exhaust to the head..... :lol:
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tony.mon
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Re: Getting the most out of your stock header

Post by tony.mon »

Good points.
Now take a look into the exhaust port in the head and tell me how many valves you can see...... :wink:
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8541Hawk
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Re: Getting the most out of your stock header

Post by 8541Hawk »

tony.mon wrote:Good points.
Now take a look into the exhaust port in the head and tell me how many valves you can see...... :wink:
None 'cause it was dark in there I was skeerd...... :lol:

We can start a exhaust port shape thread but as this is more of a header thread and it would just get lost here.......

Though for a quick reply.....sure it looks like you could make improvements fairly easily but I'm going to stick with Moriwaki, Dan Kyle and I believe Roger D. also, With the Don't mess with the exhaust port advice....not worth the time.

A STG 1 engine does just fine with the ports just cleaned up and maybe the floor flatted a little bit and that is it.
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sirch345
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Re: Getting the most out of your stock header

Post by sirch345 »

Hard to believe you wrote this so long ago Mike, it doesn't feel like it 8O

What can you use if you don't have access to a die grinder I wonder :?:
I can imagine something similar to a Dremel wouldn't really be man enough with the welding bead being so hard,

Chris.
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8541Hawk
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Re: Getting the most out of your stock header

Post by 8541Hawk »

sirch345 wrote: Wed Oct 28, 2020 8:31 pm Hard to believe you wrote this so long ago Mike, it doesn't feel like it 8O

What can you use if you don't have access to a die grinder I wonder :?:
I can imagine something similar to a Dremel wouldn't really be man enough with the welding bead being so hard,

Chris.
Actually I have done the job with a dremel tool without much issue. They do have carbide cutters if it is one of the headers with really bad welds but a drum sander followed by a flapper wheel will do a good job :thumbup:
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sirch345
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Re: Getting the most out of your stock header

Post by sirch345 »

8541Hawk wrote: Wed Oct 28, 2020 8:51 pm
sirch345 wrote: Wed Oct 28, 2020 8:31 pm Hard to believe you wrote this so long ago Mike, it doesn't feel like it 8O

What can you use if you don't have access to a die grinder I wonder :?:
I can imagine something similar to a Dremel wouldn't really be man enough with the welding bead being so hard,

Chris.
Actually I have done the job with a dremel tool without much issue. They do have carbide cutters if it is one of the headers with really bad welds but a drum sander followed by a flapper wheel will do a good job :thumbup:
Thanks for that information Mike :thumbup:

Cheers,

Chris.
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fabiostar
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Re: Getting the most out of your stock header

Post by fabiostar »

As you said honda made a good system, they just done it on the cheap but the design is good and that extra bit im sure honda didnt overlook it..

i was actually able to try 3 different downpipe designs last year when i had a few storms here,, starting from cold.

honda system vents steam through the left hand can.

Akra vented more through the right can

mori vented equal through both cans.

so different makers have different ideas how to make it work.
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Flatline
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Re: Getting the most out of your stock header

Post by Flatline »

And here I am, refurbing some downpipes

Time to start looking inside methinks :plainsmile
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