Topic: racing cb500f

[turboguzzi]

howdy

Back at building my CB500F racer again, first race in the 2007 italian classic championship is in mid march, so I am working at fulll steam.
Got hold of a nice set of ex kawasaki 650 27mm carbs, should be an easy fit. Just need to weld together new inlet runners.... already installed an ex-GSXR ignition, came out very neat. pictures soon.

Two questions though to the big masters:
 From all what I am reading, if I am aiming for good inlet tuned length for a torque peak,  say at 9000, total inlet length from bellmouth entry to valve should be something like 10"-12" and yet, in all the tuned bikes I've seen (including 70's AMA superbikes, etc, see here http://oldskoolsuzuki.info/patrick/projects/knarf_gs1000/clink/ ), total inlet length seems too short. more like 7"-9"
Is there something that I am missing? According to my math, a good tuned length should see the velocity stacks start rearwards of the two downtubes at the seat/gas tank junction.

Second, still doubting about what megacycle cam grind to use with the stock 500c.c. motor. Or does somebody preffer webcam?

 Will be nice ot hear people's ideas or experiences on both issues.

Grazie Mille
T-G
 

[my78k]

I'd comment here but you lost me at "Howdy"     

[turboguzzi]

What can I say? spending a summer in Texas selling ice cream from a truck back in 87' must have had a strong impact on me.

Hope to find you back 

 

[MadDogMcq]

Shucks, be friends y'all. 

Bike looks gorgeous!!!!!!!! (And mean!) Wow!

[Tim2005]

I believe your math is right, some time back I worked out how long a set of velocity stacks for my 460/4 should be and it came out at something like 6 inches.

Someone must know more...

[turboguzzi]

Tim
6" is actually what you get form a normal setup i.e. stock manifolds and carbs. inside the head there are about 2" from valve to end of port + carb length is 4" = 6", at least on a CB500
the formulas I've seen where for Velocity stack entry to the face of the inlet valve distance.
I want to go longer, to something like 9"-10"

see pic and graph
T-G

[MRieck]

I'd worry about lower RPM signal loss with that length intake manifold and large carbs especially if you are using a cam with a good amount of duration.

[turboguzzi]

Hi Mriek

I'm going road racing so dont really care much for under4000- 5000 rpm performance.

On the other hand, not going for huge carbs either, installing 27mm (ex KZ650) at the moment and staying 500c.c. displacemnt in order not to jump to 750 class.

currently looking at the 126-60 megacycle cam, it's got 54 degs closure atdc, 260 total duration.
Do you think it's too wild from your experience? Shooting for torque peak at 8000-8500.

Guess I'm going to stay for the time being with short manifolds and play only with velocity stacks when I get to the dyno.
cheers
TG

[MRieck]

You really don't have much in the way of choice in regard to a cam with that engine. You won't make any real good power without some lift so that would be the cam to use IMO (126-20). You will definitely make your torque further up the RPM range (around 7,500 range I'd guess) with some compression in it. Don't be afraid to stagger stack lengths either i.e. 2 longs on 1&4, 2 shorts 2&3

[turboguzzi]

Nice.....
sounds like a grand idea
Thanks