Jump to content
Sign in to follow this  

150F header polish

Recommended Posts

The other day I decided to take the header off my wifes  2005 crf150f. Inside the exhaust manifold there was a welded ring about 3/4" of an inch into it. I figured that part of the reason that it was in there was to prevent reversion, or back flow of exhaust gases into the port. So it may be a good thing. I decided that I should try and take some off it. Using a half round bastard file I removed about 75% of it leaving a bit of sharp ridge on the down wind side.

 

The bike is pretty much stock except for larger tip  with a cone on the muffler (hand made),  no airbox snorkel and some richened jetting

 

It feels pretty good. Starts first kick, ticks over slow and revs a lot quicker than before.

Share this post


Link to post
Share on other sites

Hey Lump! Appropriate name for the topic! No that weld circle protruding into the exhaust stream is not engineered, it's a byproduct of mass production. If your exhaust valve is doing it's job, no gases will be reversing into the engine ;) ! On one bike that weld will be barely noticeable and another, look looks like it's blocking 1/4 of the header. It's easy to figure a production flaw like that may have huge consequences in a place where combustion heat, expansion and velocity are the highest.

Some people say things like that or removing the 4 layer anti backfire screen under you air filter don't make a hp difference on the dyno, but I think they make a heck of a difference to your right wrist!

Share this post


Link to post
Share on other sites

Sure you are right about the exhaust valve preventing reversion into the engine when the valve is closed but the idea of "steps"

is to prevent some of the reflected pressure waves from being present while the valve is open.

 

With a mass produced exhaust I am sure that variations exist with many there is the possibility of reflecting flow. I am pretty sure that the engineers at honda are aware of this.

 

Removing the intake screen has merit. Although low speed air is relatively unimpeded as the velocity increased the small wires in the screen really restrict flow a form of "interference drag".

  • Like 1

Share this post


Link to post
Share on other sites

I removed mine.  Lost a little bottom.  Gained a little midrange.  I had to lean out the idle mixture about 1/2 turn.

 

Mine had way more weld than that of the 150 and other 230 we have.

Share this post


Link to post
Share on other sites

(Removing the intake screen has merit. Although low speed air is relatively unimpeded as the velocity increased the small wires in the screen really restrict flow a form of "interference drag".)

Very well said, I like that statement!

Guy

Share this post


Link to post
Share on other sites

I removed mine. Lost a little bottom. Gained a little midrange. I had to lean out the idle mixture about 1/2 turn.

Mine had way more weld than that of the 150 and other 230 we have.

Did you remove your backfire screen VortecCPI too? I did the exhaust weld and backfire screen at the same time so that I'd only have one jetting session, and the results were def positive not negative....I'd say I gained response all over, no loss on bottom. Makes me wonder if now maybe one of those post air filter X-Wing devices that separate the partial throttle opening from wfo may get you your low end back?

Anyone used one of those?

Share this post


Link to post
Share on other sites

The trouble with removing the backfire screen is that you can burn out the foam filter if it backfires. 

 

Do you have a pic of an xwing?

Did you remove your backfire screen VortecCPI too? I did the exhaust weld and backfire screen at the same time so that I'd only have one jetting session, and the results were def positive not negative....I'd say I gained response all over, no loss on bottom. Makes me wonder if now maybe one of those post air filter X-Wing devices that separate the partial throttle opening from wfo may get you your low end back?

Anyone used one of those?

Share this post


Link to post
Share on other sites

The trouble with removing the backfire screen is that you can burn out the foam filter if it backfires.

Do you have a pic of an xwing?

What's funny is if you Google this you'll hear about air filter fires, and each one I found HAD THE BACKFIRE SCREEN in place! What does that tell you? Guy prob oiled a clean air filter, installed it, started it before the alcohol carrier in the air filter oil evaporated! Merely speculating, cuz those details were omitted...If there's one topic that's debated to tears, it's backfire screens! I still think they exist cuz of lawyers....

X-Wing type devices are made by a number of makers, Boyesen is the Power X Wing, HCR has their Power Wing and there's another, name slips my mind, but it's quite larger and sits farther back towards the air filter in the rubber tube. Google it for pics. They're quite pricy for a little fabbed metal some might be able to make in their garage. For years magazine's like Motocross Action and Dirt Rider have given them positive reviews, low end improvement with no penalty, yet for some silly reason I've never tried one! Principle is they straighten the air flow, less turbulence = more velocity.

Can anyone else vouch for these? I still may try to make one... I'll post this as a topic.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...