CR 500 +1mm overbore

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Apr 26, 2000
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#1
I just received my CR 500 Cylinder, Head, and new piston kit, from Eric Gorr. I sent him the stock pieces about 3 weeks ago and told him I wanter more everywhere, with a focus on overrev. Eric bored the cylinder, along with re-shaping the ports and an overall cleanup. The piston that he sent me says "1mm" on the top, I assume that means that the bike is now a 1mm overbore. My question is.... What is my new displacement? I know its bore x stroke, but I have no idea what the length of the stroke is, on a stock CR 500. I figured I'd ask here, and get 25 responses from those of you who know every concievable fact about CR 500s. I'd also appreciate any feedback you might add on jetting changes, with a re-port and overbore. Should I need to change jetting? (I'm still heat cycling it, so I have no idea how it REALLY runs yet)

P.S. I had a limited amount of time between race weekends, and had to call Eric and beg him to finish it, and ship it back 2nd day air, so I could get it together for this weekend. I didn't hear anything back from him and was a little worried. Yesterday when I got home from work, there it sat on my doorstep.... THANK YOU ERIC GORR. That was above and beyond the call of duty, as bonehead here (me) forgot to note my time constraints on the original order form. Eric didn't know there was a time crunch, until Friday evening, and he was leaving for Loretta Lynn's on Monday. If I ever get the chance, I'll pay him the few beers that I owe him.
 

EricGorr

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#2
Hi Sean,
I'm back from Loretta Lynn's Amateur Nationals early because my rider re-injured his broken foot. The reason I bore CR500s to 1mm over on the first bore is to remove the decompression grooves over the exhaust. The displacement is now about 505cc.
Happy road racing!
 
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#3
Thanks Eric!

I just got back from the Thunderhill Park CCS races, with my new 505cc motor. If results are any indication, the motor mods helped :-)

I entered 10 classes, including Heavyweight Superbike and Heavyweight GP. These are classes that include GSX-R 1000s, Yamaha R-1s, etc... A CR-500 has NO business being in those races. I now have 10 new trophies, with 4th place being my worst finish for the weekend :-) The tally was.. One 4th, Two 3rds, Three 2nds, and Four 1sts. I still got smoked on the straights (no way I'm going to get a 500cc single, up to 175MPH) but the increased top speed with the new porting, allowed me to gap the big bikes through the corners and be that much more ahead going onto the straights.
 

KiwiBird

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#4
Way to go Sean!! Any idea how many rpm you are turning? Do you have any pics?
 

KLX4smoke

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#5
Sean, that's pretty cool what you're doing and congrats on the great results. You must have looked real funny on the starting grid sitting on a dirtbike next to a bunch of "real" racing machines. You've got to show us some pictures!
 
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#6
I cannot believe it, That bike must be very fast. What pipe are you running? Could you list the mods you have done?

I would love to know which bikes you beat!

Way to go!!!

Chris
 
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#7
Answers....

Mods:
17" Rims with Dunlop KR 106 & 108 Racing Slicks 120/60/17 Front - 155/60/17 Rear
Pipe - FMF Gnarly, shortened 1" in head pipe for more top-end
Moto Tissinari V-Force Delta Reed Cage
320MM Floating Front Brake Rotor, with Braided Stainless line and Galfer "Green" pads, Motul 600 Racing Brake Fluid
1mm Overbore, Porting, and Head Mods by Eric Gorr
Suspension lowered 2.5" by "Aftershocks" in Palo Alto CA.
15/39 Gearing with Regina Gold 520 (non-O Ring) chain.
Pro-Taper Bars turned upside down and backwards (like an early 80s superbike)
Scotts Steering Dampner on Applied Engineering Triple Clamps
+ Ride my ass off in the corners, and get smoked on the straights.


Faster bikes beat this weekend include CBR 600 F4, GSXR 600, YZF-R6, YZF-R1, RC-51, GSX-R750 and GSX-R1000

Pictures are on my website, at http://members.aol.com/seanalexander/supertt.html
 

EricGorr

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#8
Thats got to be pretty scarey for the road burner guys when the rear tire on the big CR5 starts to light up out of a turn and spits up every loose atom of pavement. The best thing is if you go off the track you can just play superbiker in the infield.
To Kiwibird, the cylinder is tuned for the safe maximum piston speed which equates to 8,250 rpm
Happy pavement buckling!:eek:
 
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#9
Offroad/Superbikers

LOL... I ran wide at the exit of turn one, on a warm-up lap, and when I was re-entering the track, from the gravel, I gave it a healthy goose and sent a little rooster tail off into the tulies, just for old times sake :-)

As for the old Superbikers series... I originally got the bike, to race in the SuperTT series. I've had more luck at roadracing though, the guys with more motocross expierience, seem to do better at SuperTT.