Topic: CB500/4 racer resurrection - airbox finished, didnt quite work....

[turboguzzi]

Indeed, I dont have good access to a reliable shop nearby that will do seats or uses Serdi at a reasonable price for me... There are shops in Italy's "motor belt" (around Ferrari/Ducati area in bologna) that do this type of work as you can imagine, but a quote i got was up in the sky. As all my projects, I have a strict price cap, so in fewer words, im too poor to afford that much work outsourced! Just bought my house, so pennies were put aside for that during last years.
Maybe one day....

[MRieck]

Indeed, I dont have good access to a reliable shop nearby that will do seats or uses Serdi at a reasonable price for me... There are shops in Italy's "motor belt" (around Ferrari/Ducati area in bologna) that do this type of work as you can imagine, but a quote i got was up in the sky. As all my projects, I have a strict price cap, so in fewer words, im too poor to afford that much work outsourced! Just bought my house, so pennies were put aside for that during last years.
Maybe one day....

I understand. Well....at least you have one more step in engine development to pursue.   We've hit the wall with Brent's 550 head.

[turboguzzi]

Engine buttoned up after some swearing, with valve cover in place, two threads gave up.... considering the 4 season ive run it, constant opening/closing, acceptable at the end. Here's one of the bastards...

Two little personal tips for HiPo-potams:

If you run a degreed performance cam, it's a real bummer to degree it again each time you open the motor while scribe marks on the cam wheel can get confusing. by putting the motor on exact TDC, i took advantage of the little slot at the cam end and measured with feeler gauge the gap. from now on this is all i need to check inorder to put the cam back after disassembly with the right degreeing.

The other is to use the top starter bolt hole to have a proper marker for the degreeing wheel, beats shaky bent coat hanger wire any day

[MRieck]

 A fine example of an aluminum "helicoil"

[turboguzzi]

have two "little" projects i want to do for the reborn 500/4

One is an oil surge plate to add on top of the sump cover. Will post on this as i proceed

The other one i kicked off today is an airbox to supply carbs with still cool air and maybe get some gains through tuning it. So this is the first mock-up, got up to 3 liters volume, i.e. 6 times the engine displacement. from all i read, seems like the magic number is 8-10 times the displacement, so will be adding some volume on the rear of it where you see the black marker lines, no more room behind the carbs.... 

[Tintop]

An air box was one of the things I looked at with my 550 filter kit, interested to see were you go TG.  One thing to check now is leg clearance, might find some knee/leg interference being a race bike.  Maybe angle the outer edges (same as frame?), and extend it as high as you can.  my .02

[scottly]

Is the goal to provide "still" air, or to also add filtration?

[turboguzzi]

TT, you are right, that's why i mockuping first with stock tank airbox is not an issue, but with the narrow GF i plan to use, yes, edges touch slightly my inner calves. might need to add some knee pads to tank to avoid contact.

Scottly, it's a race bike, so no filter

only still air + not drawing hot air behind the engine + hopefully find some power gain due to hemholtz resonator effect

https://motorcycleinfo.calsci.com/Airboxes.html

the sides of the box are a solid wall, air entrance to the airbox will be from a snorkel on the rear. thats the main resonance element to play with.

[Ramrod_Racing]

only still air + not drawing hot air behind the engine + hopefully find some power gain due to hemholtz resonator effect

https://motorcycleinfo.calsci.com/Airboxes.html

the sides of the box are a solid wall, air entrance to the airbox will be from a snorkel on the rear. thats the main resonance element to play with.

Very interesting link. I'll be diving into this more deeply and waiting to see where your experimentation takes you since I was already planning on playing around in this department myself after Barber.

[simon#42]

have been using air boxes on my 250s since the 90s with good effect , are you going to pressurise the air box yossef?

[bwaller]

Those damned frame rails..... One issue is the distance inside the back wall of the box and the bellmouth of the stack. I've started more than once but always balked because of this.

I commend you for tackling this again TG, we just will never know until it is actually tried to see if there is any power gain. There certainly is difficulty managing anything other than square corners. No room for gentle curves and rounded edges.

The other important issues is dyno proof, with and without the box. I hope you can find a good co-operator to help with dyno time.

[turboguzzi]

not seeking ram air effect if that what you mean simon. bike's too slow for that
How far from the outer wall where the stacks in those 250s ? (see picture)

Brent, agree that outer stacks are close to the back wall, but after seeing sections of the aprilia RSV4, not sure it's an issue., I might as well run shorter outer stack anyway. central ones are going to have a deep box extension in front of them so might be longer. Different length stack pairs is pretty common practice for better spread of torque.

I think that now that you can print stacks in decent nylon materials and CNC the front and back walls, the whole enterprise is easier. 

[simon#42]

on an aprilia the distance is only about 30mm  , the outer side of the box is the fairing lower . on a honda it is much better as both carbs sit opposite each other in the v .
the early yamaha ( pre 2000 ) is a complete dogs breakfast .    i disagree that your bike is not fast enough though , it would give you a bit more but i doubt it would be worth the extra hassle .
jetting can be tricky and you need a way of loosing the pressure quickly when you brake . the last aprilia 250s made 118hp so it works !

[gschuld]

https://www.cycleforums.com/forums/77-performance-speeeeeeeeed/14861-ram-air.html#/topics/14861?page=2

See post 17.

Food for thought.

George

[turboguzzi]

not doubting it can help.... above 110-120 mph... thing is that most of our tracks are a bit Micky Mouse, highest top speed i ever GPS recorded for the 500/4 was a tad under 120, cant remember if it was the straight of Vallelunga or Maggione which are almost one kilometer. Daytona or IOM would be something else.

power wise, we're talking 65+ rwhp for the 500/4, apples and oranges compared to a 110+ aprilia in terms of top speed

The ducting project to bring ramair to a rear mounted airbox would be a BIG challenge too.

Last, very likely our tech will not approve!

so it's off the table, at least for me

[turboguzzi]

Some other little improvements... I ran my seasons with the 500/4 using a nylon block chain slider, mainly to avoid a stiffening gusset welded under the chain, but also helps maintain constant chain tension across the travel.

On my following bikes i switched to a tnesioner wheel which is less maintenance/greasing needy.

That little idler roller swingarm is held to a bracket bolted to that gusset, still need to add a small tie rod to regualte it's height

[gschuld]

Yossef,

The potential benefits of ram air is certainly reduced further when racing on slower tracks.  Creating a proper system is rather complicated anyway.  Plus of course rules acceptance...

I like your chain idler wheel.  I assume increasing both the sprocket sizes to gain clearance was not worth considering or just wouldn’t offer you enough?

I assume you have a pretty good high speed bearing in that little wheel?

George

[turboguzzi]

george, if anything i would need to reduce sprockets to avoid that bracket , but cant go there either as top run is already close to swingarm top.

The whole issue begins with the need to raise the rear for quicker turning with longer shocks, swingarm becomes quite angled compared to stock and at this point the change in chain tension when susp is fully compressed becomes rather big, i.e. means chains has to be adjusted quite slack so it doesnt stretch at full suspension compression. the idler wheel really solves that geometry issue.

Idler sure has bearings, been running similar setup on my Gpz 810, Gpz550 and XTZ 700 supermono, no relaibility issue so far,
Admitedly,  none of these ever see much more than 120 mph. 150 mph would be a different story i guess

[gschuld]

Right...

I was thinking about clearance to the top of the swing arm...

At what point is it worth considering altering the factory frame to lower the swing arm pivot position to realign the chain for the new swingarm angle?  I realize that would require an awkward(holding the frame properly) milling operation, installing new custom made machined pivot lugs, and lining them up very accurately.

Not a simple undertaking.😏

[turboguzzi]

At what point is it worth considering altering the factory frame to lower the swing arm pivot position to realign the chain for the new swingarm angle?

At the point where you have the money, time, spare frames and fully equipped workshop to do it

Dont think i have even one of the requisites!

[gschuld]

Oh I understand.

I’ve worked through the mental process previously and it is certainly an undertaking.

It does however seem to be the only ideal solution to all the problems associated with a fairly severe swing arm angle.

George

[bwaller]

After a crash that required a new steering head section, my plan was to also address the swingarm angle by changing pivot position and using a larger hollow axle. This crash bend the rear wheel axle in three directions and broke the front axle. The swingarm pivot was unscathed and it surprised both Denis Curtis and myself. After seeing this we decided to leave well enough alone.

It is a big job setting up to do this pivot replacement properly. Continuing to deal with chain rubbing with an improper arm angle on a road based frame is the easy option.

I originally tried a wheel TG......hope yours lasts longer than mine did!

[turboguzzi]

I originally tried a wheel TG......hope yours lasts longer than mine did!

See Brent, this is what happens when you dont use original TG idler wheels....

Seriously now, the idler wheel on the 90 rwhp Gpz750/810 lasted 5 seasons and still looks ok.... it was original for off-road bikes, maybe Acerbis or UFO brand, but there was nothing special about it.

[bwaller]

See Brent, this is what happens when you dont use original TG idler wheels....


Guess so. Actually I one from an off road model, then made one with better material and larger bearings. You were the guy that suggested a rubbing block!    The one I use now is curved and lasts threes seasons, then I replace it. As long as we're all happy, that's what matters! LOL

[turboguzzi]

Trying to free some extra depth in the future airbox project and managed to shorten manifolds by 5mm.
Brent, as you can see, from the internal caliper pic. this leaves 45mm between stack and frame tube, so even subtracting 10mm for the airbox cover, you still have 35mm distance stack to wall.
When you consider that carbs are 29mm, having 35 ALL AROUND the stack edge means that “curtain area” is something like 5-6 times that of the carb bore area.
Alas, two steps fwd, one step back…. In the more fwd position of the carbs the throttle cables get too close to the venting nipple in the top cover…
dismantle again, shut off the stock exit with a custom plug, then weld a new nipple where it doesn’t disturb.