CR480 Carb Upgrades

[Lozza]

The motor completely overwhelms the brakes and suspension, which I assume was in a reasonable balance beforehand. Owner was/is mad as a cut snake and too much was never enough, it has a "lot more" than the standard 480, power was smooth and predictable, got many holeshots but would all go pear shaped at the hairpin turn on the second lap(front brake was only good for 1 application). Last I heard from the owner he had sourced a disc for the front, but I think that moved him into another class.
I haven't seen the pipe you mentioned but that pipe is about the correct tuned length for the rpm ceiling   

[Tahitian_Red]

How's that upgrade worked out?

I was not running the stock PE before the switch.  The bike had a 38mm Mikuni round slide with a UFO slide kit. 

The carb conversion worked great!  The starting and idle to off idle performance is improved (but I did the carb and the V-force at the same time). I started the bike 8 days in a row, using my same routine and it fired on the first full kick each of those times.  I am dealing with a PVL issue now and that is why I have not posted recently.

This carb would not be legal for most racing associations where I live, but for the one event I will race it at it should work fine.

[sa63]

Here is a pic of the standard and PFR pipe.. pretty different.. I have just blown the dents out and acid cleaned the standard pipe, still to be painted then tried.
the  bike is a tractor with the PFR pipe, but not a ball tearer .. but hard to see how the PFR would improve performance, it is 110 dia in the belly as opposed to 100 mm for the standard pipe.

sorry bit of a hijack as you were quiet:

So I have the PE carb. it seems ok. Its easy to start with the decomp, but wasn't nice before I did that.

[Tahitian_Red]

The decompression valve and squish band head mods are the single best thing I did for the bike. 

The PFR pipe mellowed the hit and the PVL helped to lengthen the powerband.  I changed to the PWK carb to improve starting and idle circuit even more.  With an Ohlins shock, Simons Link and Cartridge Emulators already installed all I have left is to do is fine tune the front brake.
 

[sa63]

can you detail the squish band mod?

the bike I bought has the ohlins. I would like to look at combining the later CRs uppers into the lower legs.
Would like to source the Simons link ( where , how?), but the forks are more of an issue than the back in choppy stuff. All works well on smoother tracks.
The front brake is terrific on mine and the rear brake is pretty dam good too.

[Tahitian_Red]

http://forum.ozvmx.com/index.php?topic=35638.0

[Lozza]

I wouldn't be doing that to the squish,that runs against everything a squish band is meant to do.

[Tahitian_Red]

Lozza,

Are there other methods to modify the squish on 2 stroke big bores?  I have only seen the Eric Gorr method and this RK Tech method:



What would be the downside(s) to making these modifications?  My bike seems to run fine, but I was planning to pull the head soon and check things out.

[sa63]

Yes, interesting. What does the Eric gorr method look like?

[Lozza]

Kelsey's(RK tek) head is a different way of doing the same thing. That is create turbulence. When you have a very short time to get an effective burn turbulence is what allows that. Faster the burn time less deto more power. If you want to know what happens at the highest levels of 2 stroke tuning. Works on any engine. full stop.
http://www.pit-lane.biz/t117-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked

You will have to join to see the pics, up to pg 16 it's in French (pics are in English though)

Eric Gorr method is a dual taper squish.

[sa63]

got me curious enough over the morning coffee to pull out bells 2 stroke book and read his take on 2 stroke heads..

a basic summary with out all the formulas though a 0.9 -1.2mm squish for a 500, and a wider squish band better for torque, narrower for revs, but compensating and checking compression ratios. too many pages for me to sift through now to find pics on that link you have suggested lozza, will look at  it later .
I will be checking out my squish dimensions though..

[John Orchard]

That RK Tek head just looks like what I did to my 500RE head  :-)

Loz, even though the pics are English, they will have a strong accent I feel  ;-)

[Lozza]

got me curious enough over the morning coffee to pull out bells 2 stroke book and read his take on 2 stroke heads..

a basic summary with out all the formulas though a 0.9 -1.2mm squish for a 500, and a wider squish band better for torque, narrower for revs, but compensating and checking compression ratios. too many pages for me to sift through now to find pics on that link you have suggested lozza, will look at  it later .
I will be checking out my squish dimensions though..

I suggest you put Bell's book under the leg of that wonky table and put the time into reading the link. You will find Frits' Formula to be ideal squish gap is 1% of stroke. The most powerful engines have a "shadow" of the squish band on the piston.That is from the piston almost touching the head in over rev and over run when cylinder pressures are not so high.

Spot the mistake here, granted a 500 isn't about extracting the maximum

[Tahitian_Red]

Lozza,

I am not trying for max power, just trying to eliminate most detonation. 

Are there any detrimental effects you know of using the Eric Gorr cut, besides less than max power?

[Lozza]

I know that Jay and Gorr modification will do nothing to lessen the chance of detonation, any effects it does have is from slightly less compression.

Take the time to read the link I posted it will explain it all