2001 426 performance gains


6 replies to this topic
  • sky-bot

Posted November 10, 2006 - 07:09 AM

#1

I was thinking about removing the screen in the air box and was wondering if anyone has had any issues from a backfire causing a fire?
also if anyone knows of any other inexpesive performance gains that can be done please post them.

Thanks

  • YZ426F Rider

Posted November 10, 2006 - 09:44 AM

#2

IMO the single best mod you can do to that bike is repacing the stock exhaust cam with the Hotcams auto decomp. cam. It gives you performance gains in the low to mid RPMs, in effect it smooths the power while increasing it. It also allows you to get rid of the manual compression release lever and makes starting much simpler and easier. It is not expensive or hard to do if you have reasonable wrenching skills...you can find the cam on Ebay for around $130.

Also, I would raise your forks 5mm and then make sure that you have the sag set correctly...that's free stuff there.

I don't know how much you ride or what your skill level is but one easy performance gain to get that is really overlooked by casual riders is tires...especially the front. It's winter time...put a Michelin S-12 on the front and for the rear mount up an S-12 or a Dunlop D773. My personal preference is the Dunlop D773...that tire hooks up so well in soft stuff that it is freaky. Seriously, if anybody reading this has not run a D773 you gotta try one. Warning: they wear out pretty quickly and if you are riding in rocky stuff it will chunk up...but damn do they bite!

  • Florida_426

Posted November 10, 2006 - 10:22 AM

#3

Try out Motoman393 site, hosted here, for some mods to improve the scoot, most are no or low cost:

http://motoman393.thumpertalk.com

Jet the bike carefully, keep the carburetor clean enjoy the ride. I'd agree with YZ426F Rider on his recommendations. I used the Dunlop 773 front and rear for 2 years, went to 756 since I am MX tracks only and the new tracks here are now a harder surface than before, the 773 is a great tire.

Bill

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted November 10, 2006 - 12:41 PM

#4

A lot of money has been spent on kits to remove the flame screen, and a lot of people using their "butt dynos" will swear otherwise, but no one I know has conclusively demonstrated that there is any benefit to it. I've done a number of air flow tests that showed no advantage to it. When Doug Henry was riding the Super Moto YZ450 he was on before he went to Timex, his crew spent a lot of time on a dyno fooling with air box configurations, and concluded that removing the screen did nothing measurable. Their conclusion was the same as mine; the filter element is more restrictive than the screen is on a YZF, so it isn't the "bottleneck" everyone thinks it is.

You can remove it if you want, but I wouldn't. If you do, use a flame resistant filter.

  • sky-bot

Posted November 10, 2006 - 01:16 PM

#5

I mostly ride the woods any more, but ocasionaly I like to get out on the track and flick it if I haven't forgot how to fly, and my beer gut doesn't get in the way hahaha!

Thanks for the tips and the link , I just put a maxxis IT tires on it because I've got the yz set up street legal and wanted to see if I can get a little more life out of the rear tire( riding alot of the mccct trails). But I used to run Dunlop 773 on my CR 500 on the track and I can say they do hook up.

  • Fastest1

Posted November 11, 2006 - 10:37 AM

#6

A lot of money has been spent on kits to remove the flame screen, and a lot of people using their "butt dynos" will swear otherwise, but no one I know has conclusively demonstrated that there is any benefit to it. I've done a number of air flow tests that showed no advantage to it. When Doug Henry was riding the Super Moto YZ450 he was on before he went to Timex, his crew spent a lot of time on a dyno fooling with air box configurations, and concluded that removing the screen did nothing measurable. Their conclusion was the same as mine; the filter element is more restrictive than the screen is on a YZF, so it isn't the "bottleneck" everyone thinks it is.

You can remove it if you want, but I wouldn't. If you do, use a flame resistant filter.


I normally agree with almost everything Gray states (he gives very good advice and seems to speak from a lot of experience) however on this issue I differ. I have not tested any airbox configurations or air filter cages but my experience building protective cages for fans has shocked me. ANY screen placed in the main airflow will have a large effect on flow. I am not saying it would be measurable though I think it would be significant. Simple test, bathe the stock screen, when it is clean place it to your lips and pull a breath thru it, does it feel restrictive? Noticeably more effort to inhale thru? If the answer is yes to either one of those questions I would think it makes a difference in power. Screens are generally measured in % of blockage/flow though the screen is so much larger than the carb venturi it might be a moot point. Dynos, though a great tool for tuning dont always tell all. What ever you decide, I do think the flame resistant filter would be wise. But to test your idea, why dont you clean the airbox very good, take out the screen and filter, then run down a street and see if there is a difference. If not put it back together (stock) and save some cash on the filter. Let us all know what your opinion was.

  • grayracer513

Posted November 12, 2006 - 07:36 PM

#7

Of course, I did not say that a YZ450 with no air filter or screen would not flow more air than with one. What I said was that it would flow no more air with a filter and no screen than with a filter and a screen. Connecting a 40 CFM fan to an air box with an oiled filter alone produced a vacuum of 5.5 inches of water (about 0.4 in/hg. Adding the screen into the assembly did not change the depression at the air boot measurably. The screen alone with no filter produced a depression of less than 4 inches of water. My conclusion was that the filter restricts airflow significantly more than the screen, and that there is no difference between having a screen and not in terms of the air that the complete assemby will flow.





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