Topic: racing cb500 F

[turboguzzi]

Hello All

I am based in Italy and planning to enter classic racing here. Up to 75' CB500F's are accepted into the classic 500cc class.

Starting to evaluate tuning possibilities and would appreciate advice from people with hands-on experience in racing tuning.

Regulations say that I can only use a +0.5mm overbore so all those big-bore kits are irrelevant..... Have to stay 500cc!

Items I am seeking information about:

Racing 4-1 system maker

Reasonable carburetor solution without going into expensive CR's/smoothbores

Camshaft supplier / grind.

Valve springs / retainers

High compression pistons (500 cc only)

Cam chain drive tensioner improvements (is the nice tensioner made by M3 applicable?)

fork mods ( I am going with original forks with damper tubes)

Frame mods/ regulations/ride height/gearing

Racing brake pads? staying with two original honda calipers.

thanks you all

going to post a link to racing CB500's in italy soon. very nice stuff

Thanks
Yossef

 

[MRieck]

Megacycle for the cam (they offer 2 grings for NA, stock displacement engines). Kibblewhite for springs...I don't think they offer Ti retainers. I'm very sure the M3 tensioner is for the 500 twin, not the 4. Pistons....good luck. The only way I see to get compression up is to deck the cylinders and mill the head. Then you have to modify the domes for enough piston the valve clearence especially with any sort of performance cam. Nothing available for performance exhaust in the USA (I mean real performance, not a MAC pipe). I'm sure you you could find pistons and a good pipe in Japan. As for the front end, Race Tech did list a cartridge emulator valve for that bike. Those and some springs and you'll being great.Port that head too!

[turboguzzi]

Thanks MR

Already got the feeling that there exists little in terms of pistons. What about XL125's ? they are 56.5 and still within my 0.5mm overbore limit. any 1:11's out there?

Looks like I am going to mill only the block in order to maintain the little squish cone existing in the head. going to take off between 1-1.5 mm, still undecided.

First race is in 6 weeks so going to start putting back together soon.

Cheers
Y

[MRieck]

Yes I'd deck the cylinders first too. Those pistons are probably .040 to .060 down the hole. Remember, when you mill the head you make the chamber smaller which improves your squish/quench zone(especially with a larger bore). I personally don't know about the XL125 pistons. Stuff like pin height etc. Hey....you can get Carrillo's for that engine again (from another post).

[turboguzzi]

Wow! I know am a newbie here.... but what an amazing response....
 
Lets try this way:
 
Does anybody know where to find info/ a link / pics about this guy racing a CB500 in Formula 500? Think his name is Gary Smith.
 
Thanks again for your help, appreciate

Y

[bryanj]

CG125 pistons are the same bore and domed BUT may be too domed!

[turboguzzi]

Hi Bryanj

Thanks for the info. Funny enough, spec sheets say that CG has also about 9:1 comp ratio, like the cb500-4 so never really thought about checking those slugs. Maybe I should.

In case you have such a psiton at hand, think I could ask you for some measurments/pics?

Cheers
TG

[MRieck]

Hi Bryanj

Thanks for the info. Funny enough, spec sheets say that CG has also about 9:1 comp ratio, like the cb500-4 so never really thought about checking those slugs. Maybe I should.

In case you have such a psiton at hand, think I could ask you for some measurments/pics?

Cheers
TG

If you get the chamber cc's for both heads you'll pretty much get your CR answered...I'd think they'd be very close. That Mr. Jones is a plethora of information! 

[ttr400]

Hi,
I am more into racing and performance upgrades for the CB400F but I will have a go at answering some of your questions.

For the exhaust you might be able to get a Yoshimura 4-1 from yoshimura Japan. or you can get a 4-4 from swarbrick racing in the UK.
In the 70's the racers used the CB750 28mm carbs on the 500, slight dinging of the tank was required for the cable linkage to clear the tank.
The CB400F racers sometimes use the CG125 pistons with Carrillo rods and some work to the domes. so they should work in the CB500. Yoshimura made a 56mm 2 ring slipper piston(I have some in my 400 racer) but these are no longer available.
I have used the Ferodo race compound pads and have found them to be very good once they are hot, don't know where you would get them now, or you can get good pads from AP racing in the UK.
Kevin.

[bryanj]

I do have a set of 0.25 overs sat in my lockup BUT the chances of getting to them are a bit remote as the lockup is VERY full and i aint sure what box they are in. I do know the rings are a different width from the 500 and i also know that Mr silver did have 0.25 piston kits for £10 per piston or £40 per engine(a steal in my humble opinion) but as i aint got this years catalogue i dont know if he still has any. The "dome" is quite prominent and i had 2-3mm "shaved" off the top (which was about the MAX possible to leave any strength) and i havent yet tried to put them in an engine as i keep moving my own goalposts--now its a 605 kit instead!!! To repeat the pistons are CG125 and CB125J. Next time up the garage i will try and look but that is at least 2 weeks away from now as the boss only gets every other weekend off and next week is it!!!!

[turboguzzi]

Hi there
checked out last night and pistons are flat with the top of block. did some math and looks like shaving off 1.5 mm / 1/16" + turning a cone area with a late in the piston ( like in the gentlemans express article) could give me 11:1 and let me have a nice squish ring.
While there.... this is asuming a stock top gasket. I could mill less if I found a thinner one.
Going to contact Silver spares anyway and see if they can confirm cg125 in cb500 fit. 10 pounds a pop is quite economic indeed.
Keeping it low budget at the moment so dont know if I'll go with Carillos right away. am I taking to big  a risk here?
Cheers