bike cam overlap question

[S2 PTH]

Hi guys,

I am trying to source aftermarket cam wheels to close down some of the valve overlap of a Honda CBR600RR.

The engine isn't in a bike, but a 250kg single seater, which breathes through a 20mm diameter orifice (upstream of the TB). Hence we need to get all the air we can into the little 4cylinder!


Any help would be much appreciated,

Phil

[Ducky]

That's a small entry, any reason for that..assume you're not using the original airbox on it?

[Flat on my back]

.

Could try Race Techniques, Cheltenham...they do alot of bike tuning and the work is top notch...

01242 245640

Ask for Andy or Mike.

[Rusty]

Formula Student

Could always make your own vernier style pulleys, not too difficult a design.

[GazzaG60]

whats the issue? too much overlap?

is drilling the 20mm pipe an optionm to increase flow.

[S2 PTH]

Yes its for formula student.

Unfortunately we cannot drill the inlet pipe... and our engine is limited to 610cc or something like that.


I believe the team would like to see the difference between changing the Valve overlap +/- 5 & 10 deg with a series of holes drilled into the cam wheel.

Our engine is limited to 12k rpm, and with that stupid restrictor, we're not sure what's best for the engine.

We have older engines, so it is probably easy enough to modify an older cam wheel. But I was just wondering whether an aftermarket supply has already tried something like this?


Thanks
Phil

[GazzaG60]

nice project. its a bit of a black art cam timing. id be worried about getting a hole the correct distance for accuracy. also laybe offset woodruff keys if they work that way.

id expect a fair bit of overlap on cammy cams is the usual for bikes to be able to scavenge air properly. that 50p of an inlet will cause issues id expect. less cam overlap map mean rpm is limited.

[S2 PTH]

50P? We tried to force a 20p piece in there a few weeks ago - didn't fit!

Its mental really, but then, thats our challenge! I don't actually have to implement this change, merely design something for the aid of a University report. I do want it to work though, so won't make it theortically possible, but practically impossible!


Our engine is tuned for max power around 10k with torque coming in strong at 7.5k. Our exhaust has to resonate at 9k for testing (it was 112dB when measured the other day).

So, do you think it would be sensible creating some kind of cam-wheel slot/woodruff key device allowing the team to alter the CAM positioning during testing?


Phil



PS - I parked my E55 estate next to it the other day, two VERY different cars, one weighing almost 10 times the other!

[GazzaG60]

maybe worth measuring how many degrees a tooth is. maybe just set a tooth out?

maybe a cam swap if possible. 750 or 900 cams. or maybe import 400 cams.

im no expert here though.

[goodall]

There wouldn't be that much to design and machine if you where make yourself, or as said how about a tooth of adjustment? if theres 40 teeth lets say that makes each one 9 degrees which would a nice amount to adjust each time see if any gains were to be had. Also are you certain the pulleys aren't on tapers as standard?

Are you allowed to radius the entry of the restrictor or have a tapering velocity stack arrangement ontop of it? And if where tune length it as well you could make it resonant so produces positive pressure at inlet side the restrictor perhaps. For if you can reach as close to 1bar manifold pressure as possible you wouldn't need much adjustment to the engine. Anyway I am sure you have all already thought of this

[S2 PTH]

Thanks for all of the help again guys.

I think we are going to go ahead with the series of slots. It will be like a smily face cut out of an old cam wheel with an identical male-smily face insert slotted back in, with accurately drilled holes for +/- 5 &10 degrees.

Re: the restrictor, I meant in my original post that it sits just downstream of the TB (underneath), and yes the walls inletting into the it do have a radius.

The intake is tuned to reduce impulse waves rebounding to the restrictor and effectively choking it. However, our CFD model has yet to be coupled to our ricardo WAVE simulation model, and so far any 'tuning' has only been done using best automotive principles and 1-D (crap) simulation.


How I'd love to just fit a I5 turbo to it and see how well it flies! BTW - sold my old type 85 to our Uni motorclub for £600 + two engines (says something about the state it was in!) Hope to hear that worble soon...

[robert_n]

Glad to see formula student featuring on this forum! Sadly i'm going to be no help whatsoever as I was a suspension/tyres kind of guy.

Garrett provide free turbos anyway i think but after seeing the amount of work a friend of mine put in to figuring out how to get the best of it, i reckon the gains are not big for FS.

Which uni are you from?

[S2 PTH]

Loughborough. I'm not actually part of the team, but just a 'design engineer' - Masters Automotive engineering degree module. Load of ****** as an accademic module, but kind of cool from the perspective of doing something thats not just a means to an end! Plus the lecturers who supervise the module are actually switched on and enjoy being away from their PC screens for once!

I must say I'm quite impressed of how the forum's responded, better than the two bike forums/clio forum and merc forum who all said nowt! I guess if you're not putting big wheels on a clio or doing a supercharger conversion on a merc they don't care - but the bike forums... ashamed!


Phil