Forced induction 100cc

**Sketchy_Racer** · 7th February 2013, 20:01

Originally Posted by TZ350

Congratulations ...... very impressed

PS I would like to try one, please let us know when you are ready to make one or two.

Thanks Rob

Once I get the final design done I will get a couple of interested people to test the units for me and tell me what breaks and what can be improved. Of course these test units will be free. So i'll be in touch.

Cheers,

-Sketchy

**Drew** · 7th February 2013, 20:07

Make one for my RF900 and a tidy box to go round the carbs so it doesn't push fuel out the overflows, and I'll TEST THE SHIT out of that bitch!

**ducatilover** · 7th February 2013, 20:08

Because I'm a nice bloke I'll take the burden of testing one

**pete376403** · 7th February 2013, 22:17

Originally Posted by Sketchy_Racer

Yep, it's completely normal if the throttle is shut and there is no blow off valve to relive pressure, so it surges back down the compressor. It's not bad unless it is surging under load. (and is really only an issue for turbos, not superchargers)

Um, why would it be bad on a turbo but not on your setup? from your description, they are both centrifugal, non positive displacement superchargers that vary in the method of drive - exhaust driven turbine vs mechanical drive. Surge, if it's bad enough, will knock the blades of the compressor wheel. You probably don't want that. The preferred way to avoid surge is to match the compressor and turbine to the air flow requirements of the engine.
Also I understand the primary purpose of the blow off valve is to dump pressure from the inlet plenum when the throttle is closed in order to keep the turbo revs up, so when the throttle is opened again there is less lag waiting for it to spin up again.
Still very impressed by your metalworking skills.

**Sketchy_Racer** · 7th February 2013, 23:00

Originally Posted by pete376403

Um, why would it be bad on a turbo but not on your setup? from your description, they are both centrifugal, non positive displacement superchargers that vary in the method of drive - exhaust driven turbine vs mechanical drive. Surge, if it's bad enough, will knock the blades of the compressor wheel. You probably don't want that. The preferred way to avoid surge is to match the compressor and turbine to the air flow requirements of the engine.
Also I understand the primary purpose of the blow off valve is to dump pressure from the inlet plenum when the throttle is closed in order to keep the turbo revs up, so when the throttle is opened again there is less lag waiting for it to spin up again.
Still very impressed by your metalworking skills.

Surge, unless very severe (under load surge with massive boost loads) usually only hurts the thrust bearings in a turbo, as they are only designed for small loadings.

In my case the impeller shaft is running on 6 deep groove ball bearings that will easily handle any sort of thrust the turbines tries to chuck at it.

Mine is surging when the throttle is closed at the moment because the blow off valve is not connected. Centrifugal superchargers don't suffer lag like a turbo as the turbo RPM rises with engine RPM, regardless. They do however suffer from the exponential boost curve of a centrifugal compressor.

Either way, surge is naughty and I will in the long run connect the BOV back up.

**Grumph** · 8th February 2013, 06:15

Well done and congrats on your perseverance...

Now get the bigger stepup on to the sucker and get the boost up to 20lb plus....

i note that there's a big Rotax triple used in jet skis which is centrifugally blown.
I'm told the blower is about 6 inch dia....

**Sketchy_Racer** · 8th February 2013, 15:01

Originally Posted by Grumph

Well done and congrats on your perseverance...

Now get the bigger stepup on to the sucker and get the boost up to 20lb plus....

i note that there's a big Rotax triple used in jet skis which is centrifugally blown.
I'm told the blower is about 6 inch dia....

Cheers mate,

I'm starting the re-design now the new one will have a 20:1 drive ratio which will allow me up to 300000 shaft RPM if I want it and 30PSI boost (although efficiency dropps off considerably) with a internal oil pump (probably off a scooter)

The current unit is a bit shit and needs a decent oil pump.

I need to source a supplier of precision gears? Anyone know where to get some?

**Sketchy_Racer** · 8th February 2013, 15:02

Video as promised

**ducatilover** · 8th February 2013, 15:23

Would you be using an electric oil pump, or one like a bike runs? If it's one like a bike, I've got one or three floating around

**Sketchy_Racer** · 8th February 2013, 15:24

Originally Posted by ducatilover

Would you be using an electric oil pump, or one like a bike runs? If it's one like a bike, I've got one or three floating around

One of the star wheel style ones out of pitbike and scooter motors like mine, mechanically driven

**ducatilover** · 8th February 2013, 15:31

Originally Posted by Sketchy_Racer

One of the star wheel style ones out of pitbike and scooter motors like mine, mechanically driven

Got a DR/GN250 one, would that work? Haven't split it but to my eye looks to be good.

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**speights_bud** · 8th February 2013, 17:14

Originally Posted by Sketchy_Racer

I need to source a supplier of precision gears? Anyone know where to get some?

If you want real precision, consider getting them wire cut. Not likely they will understand the fine precision tolerances you actually require at We-can, seems like Keith just decides 'he knows best' on your application these days... They also have a wire cutter but they are 2x more expensive than the Auckland machine shops were when we quoted some square holes...

**Drew** · 8th February 2013, 17:15

Originally Posted by Sketchy_Racer

One of the star wheel style ones out of pitbike and scooter motors like mine, mechanically driven

We've got a friggin enormous one for a ZX12r in the spares container.

Edit.

I also have a pit bike motor that's dropped a valve (I think), as a spare for my couple of those.

Welcome to either.

**Yow Ling** · 8th February 2013, 17:40

Printing presses use gears, we pay AU$1 per tooth on 1/8CP gearing, other machines use helical gearing , some module (?). If the gears are shit the print is shit.
Seeing as you have traction oil in the supercharger case , why not make the input gears into rollers

**Moooools** · 8th February 2013, 19:16

Originally Posted by Sketchy_Racer

Thanks Rob

Once I get the final design done I will get a couple of interested people to test the units for me and tell me what breaks and what can be improved. Of course these test units will be free. So i'll be in touch.

Cheers,

-Sketchy

I would more than happily take one off of your hands.

Even if I had to pay.

Top fucking effort getting that thing going man. Looks truly excellent. That is some top notch engineering.