you said this in an earlier reply about getting more power for free out of the stock '99 400ex pipe:

Okay, in answer to the question about where to drill.... basically, you can unbolt the end cap on the '99 models and you'll see the restrictor there -- just remove about 1/4 to 1/2" more material and re-install it. It only increases noise by about 1 dB, and gives you about a 5-8% increase over stock hp.

I hate to sound this stupid, but can you elaborate a little more. I would like a little more detail before I consider trying. Don't want to drill or cut the wrong thing. Sounds like you are talking about making something shorter that must widen as it's length is reduced. Is this correct? Thanks in advance!!
[red]note from atvbbs: To address a specific individual you are asked to make use of the e-mail option for that person to avoid making the forum one big personal message center. Thanks for your cooperation.[/red]

 

I believe if you pull the end cap off and shine a flashlight into the exhaust, you will see a vertical plate with a 1" (or so) hole in the top, slightly to the right. I believe Pam is saying, make this hole bigger.

I have been thinking about doing this since looking into a buddies pipe back in '98, and just haven't gotten around to it...

 

there is no way she is talking about that. she said that you could replace the endpiece with another but the company that makes it said it wouldn't work. She was talking about the endcap itself and how the one on a 2000 is different. The hole that you are seeing is actually a tube that is approximately 8" long.

 

Hmmm, I was wondering about that...

Although I have had the endcaps off both the '99 and a '00, I don't remember there being any difference between the two. I didn't compare them directly though, so maybe there are some subtle differences.

I can't really see changing the endcap making much of a difference, GT Thunder has a dyno run without a endcap and it makes virtually no difference. In my testing it seemed to decrease performance.

 

Without the proper jetting, one would not see a performance gain without the jetting to go along with the additional airflow. If you adjust the jetting to correspond with the increased potential airflow through the motor, there should be a hp gain there. Before I put a pipe on my Y2k 400ex, I drilled 7 evenly spaced 3/8 inch holes (equal to 11 white brothers disks in total surface area)in the end cap, added a 165 main (with no airbox lid on), and realized a definate increase in power. Now you ask.... where exactly did you drill those holes? Take the 3 bolts out which holds the end cap in place (make sure ATV is cool). Do you see that the exhaust outlet hole is actually recessed into the end cap? Now look at the inside part of the end cap that is not seen when installed. Do you see the spark arrester and how it is made into the end cap? The placement of the holes needs to be at the largest part of the spark arrester (the area that is nearest to the end cap). When you drill the holes in a circle around largest part they will protrude into the exhaust outlet of the end cap (that is recessed in, which is why you can drill a hole through to it). It is a bit louder than stock (but nowhere near the decibel level of the free-flow exhausts out there). If you don't understand what I have explained, DO NOT think of attempting this process if you are not certain that you know what you are doing! This is a suggestion, so if you mess your end cap up, don't be complaining to me! It should be the same as the aftermarket tip offered by various companies. Tip: Drill the evenly spaced holes at 1/4" diameter or smaller first to see how loud the exhaust is at that point, 'cause if you go straight to 3/8" you can't put the material back in if it seems too loud!

 

Having not messed with the jetting on this bike myself yet.....

From what I understand, just changing the jetting alone on a bone stock 400EX will increase HP. This is due to Honda jetting the bike lean from the factory to keep the EPA happy, Honda gave us a nice little hint about this in the owners manual.

I would be interested to see how a properly jetted bike in stock form compares to a properly jetted bike with the SA mods only. I am going to guess that it would follow the lines of the posted dyno chart.

I would tend to think that a truely effective exhaust mod should show a modest perf gain with no jetting changes (with, maybe some new "flat spots" in the power curve) and a nice performance gain when jetted properly.

 

[red]**Note to atvbbs**[/red]
Although I see your point, this message sparked some interest and constructive dialog by others. Isn't this what the forum is all about?

 

Gabe,
I was looking at your reply and noticed the GTTHUNDER link. I was told that there is a link at www.geocities.com/~gtthunder/ that has the dyno specs of four different exhausts on a 400ex. I can't seem to get through on this link though. Would you happen to know the right address?

Thanks,
Greg

 

There's a couple of ways of getting there, try this one.

http://www.gthunder.com
or this one to go straight to the shootout:
http://www.geocities.com/gtthunder.geo/shootout.html
Later...