Race mods/airbox

CuckinFunt · Post by **CuckinFunt** » Wed Nov 12, 2008 3:34 pm

Hi,

New to the site and also ive just broken my KR1S virginity in the past 24hrs and now busy ripping things apart to see whats what. Already found loads of great tips

Basically going to do some racing next year, have been set on a 400 for past few months, now ive pretty much been gifted with the bike. Unfortunatley ive got absolutley no history and no contact with whoever use to race it.

Its not been started in about 18 months, so was going to set about stripping and cleaning carbs flushing all through before attempting it and getting it on the dyno, first thing i found is that its not running an airbox lid/filter and has some homemade washing machine pipe ram air to the nosecone, is running with the lid off usual mod for the track? The thing is tank was on loose, chain is off and its been emptied of oil, so I cant work out whether its been left off during/service or its meant to be like that!?!

Any thoughts would be great

Thanks

the-elf · Post by **the-elf** » Wed Nov 12, 2008 7:06 pm

Most racers run with the airbox lid and I always use a filter but I also have a full air ram setup. MJ's has a simular setup as well. If you want to have a look at my set up then feel free to pop over as I'm not that far from you.

PS Which club are you planning on racing with? Most of the 250 lads (including MJ and Me) race with Derby Phoenix.

CuckinFunt · Post by **CuckinFunt** » Thu Nov 13, 2008 10:46 am

Thanks, will find one and give it a whirl, and may well take you up on the offer of having a look at yours, need as much help getting the bike setup and running as quick as possible as im the most un-suited size rider for a 250 (will genuinly have you pissing yourself) !!

I was going to do F400 with emra but now im thinking DP is a good option, I already no a couple of the local riders running 400's so could be a good laugh, even tho Im not sure im much more capable than chasing after the backmarkers, but there's only one way to find out

the-elf · Post by **the-elf** » Thu Nov 13, 2008 2:33 pm

CuckinFunt wrote: I was going to do F400 with emra but now im thinking DP is a good option, I already no a couple of the local riders running 400's so could be a good laugh, even tho Im not sure im much more capable than chasing after the backmarkers, but there's only one way to find out

The trouble with EMRA is that they only race at Mallory Park with an odd meet at Darley Moor. which are the two worst tracks in the Midlands, if you ask me. DP race at Cadwell, Oulton, Donnington, Setterton, Croft, Anglesea and Brands Hatch so you get to do the best tracks in the country. Plus they give you a decent number of laps as well.

CuckinFunt · Post by **CuckinFunt** » Thu Nov 13, 2008 4:40 pm

I cant argue with the choice of circuits you get, but I think mallory is a crackin circuit (very much in the minority

) but ive got a couple of months yet which proberbly means i'll change my mind atleast 60 more times

rad · Post by **rad** » Fri Nov 14, 2008 11:00 pm

HI, got a race kr aswell and it has had the airbox top modded, cut away on an angle I persume, no hose on mine though. How much did you pay if you don't mine me asking. Think I've got to sell mine as I got a massive bill to pay for my drain rebuilding of all things,

Give them four strokes hell when you get out there!

mj43 · Post by **mj43** » Wed Dec 24, 2008 11:27 am

Before cutting up your airbox you need to know what you are doing.
When I started out I didn't, not saying I do now but we are getting there.

found this which is a useful guide http://www.saltmine.org.uk/randy/airboxdesign.html

Looks like an airbox needs to be two areas - one is the resonant chamber, the other the collecting area which your air scoop goes into. The mods we have been making turn the airbox into a single chamber and probably mess up any resonance in exchange for a supply of cold clean air.

I am guessing that KR box isn't perfect as the filter is inside the chamber so will act as a damper.

and another link http://motorcycleinfo.calsci.com/Airboxes.html

scooble · Post by **scooble** » Wed Dec 24, 2008 12:42 pm

Very interesting stuff and good links as usual Mark.
When I working at Ricardo, we used a CFD (computational Fluid Dynamics) software tool called WAVE that would calculate the best shape and volume for an optimised airbox and exhaust system. Produced nice animated 3D models too. Its an inducstry standard piece of software so is hideously expensive (not really for the home tuner)

With the limited confines of a motorcylcle chassis, I am not to sure if its possible to fully optimise an airbox without some compromise though.

the-elf · Post by **the-elf** » Wed Dec 24, 2008 1:13 pm

Interesting read Mark. So how is the length of the inlet tube measured with an Air Ram system where the tube goes from the front of the bike to the airbox behind the engine?

From what I read there, we need to move the air box forward and enclose the carbs to shorten the length of the inlet tube.

mj43 · Post by **mj43** » Wed Dec 24, 2008 3:08 pm

scooble wrote:Very interesting stuff and good links as usual Mark.
When I working at Ricardo, we used a CFD (computational Fluid Dynamics) software tool called WAVE that would calculate the best shape and volume for an optimised airbox and exhaust system. Produced nice animated 3D models too. Its an inducstry standard piece of software so is hideously expensive (not really for the home tuner)
With the limited confines of a motorcylcle chassis, I am not to sure if its possible to fully optimise an airbox without some compromise though.

Be nice to have a play - I drive past Ricardo most days on the way to work wonder if I knock on the door they will let me in

Kevin - I think you need to separate the airbox into two or three areas.

Area 1 is your intake - narrow mouth and a gentle taper gradually opening up - this slows the air speed down and increases pressure.
Area 2 is your clean air reservoir between area 1 and 2 is where I would put the air filter.
Area 3 is where your carbs go. Between 2 and 3 there is a seal with a tuned bellmouth in. The bellmouth tunes area 3 and allows flow from the clean air reservoir.

Volume of area 2 and 3 will be important as will be the length and dia of the interconneting bellmouth

Or at least that is my interpretation of the problem. Actual implementation is another matter and I suspect that will require dyno time and a set of different bellmouths

(It isn't actually a bellmouth but the tube between chambers)

mj43 · Post by **mj43** » Thu Jan 01, 2009 11:42 pm

There has been quite an interesting debate on airboxes over on the RGV forum

I think we have bottomed out the benefits of ram air just need to see if there is benefit in resonance

http://www.rgv250.co.uk/forums/index.ph ... opic=28639

corky · Post by **corky** » Fri Jan 02, 2009 10:12 pm

loving that discussion on the rgv site,
as well as being very educational its better than Coronation Street for entertainment