Forced induction 100cc

[husaberg]

Ah, the good old diesel wade with alloy shafts. gave my last one away. Better to use a big blower run slowly, even if it seems like it's blowing mixture up in big chunks. never seems to make a significant difference to carburation or the way the thing responds.

I found a couple of Wades the other day.

[Flettner]

Ah, the good old diesel wade with alloy shafts. gave my last one away. Better to use a big blower run slowly, even if it seems like it's blowing mixture up in big chunks. never seems to make a significant difference to carburation or the way the thing responds.

There must be some minimim speed where the supercharger bocomes inefficient?

[Sketchy_Racer]

There must be some minimim speed where the supercharger bocomes inefficient?

Yeah there is, you can see it in the boost curve fairly easy if you log MAP. A roots blower should be linear in it's boost development but the slip at low blower RPM causes quite a lot of lost boost under 3000 engine RPM, but thats not really a problem.

I'm recovering a heap of this by running the blower wet. Makes a big difference to the pumping efficiency it seems.

The blower is certainly more than happy running at the speeds I'm planning. After all the lads in Australia are running the same blower on a 100cc and are making 27.5hp so there's potential.

They've been kind enough to send me their cam profiles so I spent the arvo profiling the stock cam. Needless to say I need to do some work! I have significantly less duration, lift and overlap than them. I've come up with a idea to make a el-cheapo cam grinder using a follower so I'll CNC out a profile and regrind the stock one. I can take quite a bit off the base circle.

So also I've got the head off at the moment and so far everything is looking pretty good inside the motor. No detonation (even at 25+ psi and 100* + IAT!!) and the valves also look sweet after about 2 dozen dyno runs. The poor little motor is also pulling to 12k RPM and seems happy about it too! Better than I was expecting from the pit bike motor!!

[Ocean1]

There must be some minimim speed where the supercharger bocomes inefficient?

I've been looking for a graph, but I think it died with my last laptop...

Looks like this:

But it really depends on the specific blower, some of the later designs are getting far better adiabatic efficiency than the old roots blowers we stuck on small block Chevs.

[Grumph]

The problem with most traditional roots blowers - like the Wade - is that just when they overcome the slippage at low rpm and start getting serious they start losing efficiency from churning losses and turbulence at the intakes and exhaust ports. The guy who did the development of the refined martin blower in ChCh used high speed video and smoke in bench tests, Even the biggest martin was only about 1800cc displacement so it was intended for high rpm use. He developed flow separator bars on both inlet and ex. Worked a treat, ours held same boost to 13000 plus blower rpm. Reached max boost about 3000 rpm and held rock steady as far as we ever went.

Cams - I don't know what the setup is in the motor you're using. If it's flat followers, no probs cutting into the base circle. If it's sohc or similar with curved followers, cutting in can give you fits trying to grind to a desired lobe separation when in the motor. All the cam guys in NZ now use the Eutectic rod as an overlay and it works very well indeed. machines well and very good wear characteristics. Not too expensive either.

Could you post the cam figures the aussies are using or maybe PM me if they're sensitive....

[husaberg]

The problem with most traditional roots blowers - like the Wade - is that just when they overcome the slippage at low rpm and start getting serious they start losing efficiency from churning losses and turbulence at the intakes and exhaust ports. The guy who did the development of the refined martin blower in ChCh used high speed video and smoke in bench tests, Even the biggest martin was only about 1800cc displacement so it was intended for high rpm use. He developed flow separator bars on both inlet and ex. Worked a treat, ours held same boost to 13000 plus blower rpm. Reached max boost about 3000 rpm and held rock steady as far as we ever went.

Cams - I don't know what the setup is in the motor you're using. If it's flat followers, no probs cutting into the base circle. If it's sohc or similar with curved followers, cutting in can give you fits trying to grind to a desired lobe separation when in the motor. All the cam guys in NZ now use the Eutectic rod as an overlay and it works very well indeed. machines well and very good wear characteristics. Not too expensive either.

Could you post the cam figures the aussies are using or maybe PM me if they're sensitive....

Honda "pitbike" like grinds.
http://www.x386.net/TTR/tech/cam2.html

[Sketchy_Racer]

They're really happy to share information so no problem posting.

In the attached file (xcell spreadsheed) You can see two different profiles. One is a stock CRF100 and the other is what they are running on the 27.5hp motor. They got to 21hp with the stock cams retarded 3deg.

I haven't got the file on me at the moment for my cams but to give an idea, measuring at 1mm lift my intake valve is opening at 0 deg TDC and closing 21deg ABDC. 0-21 intake and I can't remember what the exhaust is, but it is equally shit.

The motor is a SOHC with curved followers. I was curious about trying to get the lobe separation. Although I have seen a cool mod using two cams machined and modified to allow adjustment of intake and exhaust separately. Might be worth looking into.

[husaberg]

Manx Norton/ international ......11 holes shaft 12 holes cams. Well that's how I thought it worked but maybe not...........
http://www.racingvincent.co.uk/14%20...Norton-10.html
Had an idea the AJS 7R had veneir adj cams as well

[Grumph]

[QUOTE=Sketchy_Racer;

The motor is a SOHC with curved followers. I was curious about trying to get the lobe separation. Although I have seen a cool mod using two cams machined and modified to allow adjustment of intake and exhaust separately. Might be worth looking into.[/QUOTE]

As i suspected, sohc. The main problem with cutting into the base circle here is that you finish up with the follower attacking the cam at a different angle...which changes the lobe separation. For the sake of your hair and maintaining some semblance of correct follower/valve tip geometry, I'd do a build up on the cam lobes. If you can keep the same base circle, that's one variable removed.

If you can do a vernier cam, it's worth trying. Lobes can also be on a taper - adjustment becomes difficult but it is possible.

[speedpro]

He'll only need one lobe to be adjustable plus a slotted sprocket. That will allow any adjustments required, apart from lift and duration.

[Sketchy_Racer]

This is what I am thinking of doing.

[mr bucketracer]

my mate with his nc30 just cut the cam in 2 , he run a snug bolt down the middle of the cams with a good ground finsh on the ends , worked fine , i would make a 1 piece cam when sorted as its small and piss easy to make

[Ocean1]

This is what I am thinking of doing.

Some friction hub designs are getting quite compact now: http://mdmetric.com/prod/rfn/PDF_W-300-2.pdf

Not sure if they'd be quite low profile enough to mount each cam lobe individually onto a parallel shaft, but maybe.

[Grumph]

This is what I am thinking of doing.

Yeah, that or as MrB suggests, just cut it...ask him if they've got a suitable profile. way easier than doing it yourself.

[Sketchy_Racer]

my mate with his nc30 just cut the cam in 2 , he run a snug bolt down the middle of the cams with a good ground finsh on the ends , worked fine , i would make a 1 piece cam when sorted as its small and piss easy to make

Did he just use the friction between the two clamped halves of the cams to stop them slipping? Sounds nice and simple, I like simple!