V2Rocket

For those of you with twin-screw superchargers (mostly 928 guys I assume), does the unit have differently sized gears on the inside of the snout?

This seems very strange to me. I picked up the IHI twin-screw off a Mazda Millenia and after taking it apart and checking several times with reference marks, it appears that the larger screw (the more roots-type one) spins 3 times for every 5 revolutions of the smaller, sharper screw.

In addition to this there is an intermediate set (a separate set) of gears on the snoutside, where the larger gear is connected directly to the pulley. The smaller gear is attached to the large screw gear.

After some measurements, these are the numbers I've come up with.

The pulley/large intermediate gear spins once for every 2.74 revolutions of the small intermediate gear which is directly connected to the large lobe gear.

The large lobe spins 3 times for every 5 rotations of the small lobe. This is a 1.6 ratio.

This means the large lobe spins 2.74 times for every one rotation of the pulley, and the small lobe spins 4.4 times for every pulley rotation.

The pulley is spinning at 1.26 times engine speed, which at a maximum 6500RPM is 8190.

This means at maximum speed the large lobe is spinning 22440RPM and the small lobe is 35905RPM.

Does that seem like a normal lobe RPM for this type of supercharger?

jcnesq

I once knew a guy who was sleeping with the Doublemint twins ... but I guess that wouldn't help.

bd0nalds0n

I have never had mine apart, but I do believe one of the rotors has more lobes than the other.

How were you able to determine pulley revolutions relative to engine revolutions? On the Keel or DR twinscrew kits, I'd wager a lot of $$ the supercharger pulley spins at more than 1.26 engine speed, even though I don't know for sure. I would bet it spins at closer to 3x.

V2Rocket

Pulled mine into pieces, the snout comes off with some careful leverage.

I put reference marks on each of the lobe gears and my father and I counted the revolutions of each gear until the marks lined up again.

Then, with the snout off I counted the teeth on the pulley gear and the teeth on the intermediate gear, and knowing that the teeth are the same height, pitch and width I calculated the ratio of size which appears to be accurate. I can get a real diameter measurement tomorrow and I expect it to be correct.

This is not a kit; this is the stock IHI lysholm-type blower taken off a 1996 Mazda Millenia S (2.3L Miller engine). The stock supercharger pulley diameter is 106.9mm, and the (accessory) crank pulley on a 944 is 135mm. 135/106.9 ~=~ 1.26.

Vlocity

Rainman,

You are correct about the 3 lobe vs 5 lobe configuration and my SC is capable of running up 15,000 RPM.

Here is a link to the Opcon/Autorotor web site. If you click on the video, you can watch the unit in operation. I would guess that your unit is one of the 1.2 liter if it is off a Miata. There should be a model number there that you can reference.

http://www.opcon.se/index.asp?sPage=1&langID=1&cID=14

Go to "Twinscrew" then "showroom". It wouldn't let me copy the link directly.

Regards,

Ken
PS. If you want to hear one in action, click my youtube below.

V2Rocket

Thanks Ken -

But does it make sense that the lobes would be spinning at different speeds?

And when you say yours runs up to 15000RPM is that the pulley speed or the lobe speed? Like I said before, if my math turns out to be right my female lobe will be spinning over 35000RPM.

Vlocity

The 15,000 is the pully speed IIRC.

Check out the websiite above, there are operating exploded views that you can watch.

You aren't planning on putting the blower from the Miata on your vehicle are you? It would be way undersized and I don't think you would be happy with it.

Minimum sizing from our cars is about 2.0 liter.

Ken

Rick Carter

He has a 944.

V2Rocket

Yes, the Millenia supercharger is going on my 944. I'm not entirely certain of the displacement of my unit; I am trying to either find information or if all else fails do the liquid test...

I'll keep looking for information on the RPM subject and post my findings here.

Ian928

I have been spinning my Lysholm Supecharger by hand and didn't notice it, but it seems they are rotating at different speeds! See here (do not care about the comparison, these guys are obviously selling Autorotors):

http://www.not2fast.com/turbo/maps/A...RvsLYSHOLM.pdf

On the top of the last page you can see that the Lysholm has 3 and 5 rotors and that the 3-rotor lobe rotates 1,66 times the speed of the 5-rotor lobe.

You should not use water to measure volume because this compressor has a internal compression ratio and although you will not hydrolock and damge it by turning it by hand you it will probably leak back water and you will measure the compressed volume.

I tried to google it but could not find the volume of the Millenia supercharger. You could contact Opcon, send them a mail with the serialnumber and they can probably tell you all you want about the supercharger. http://www.opcon.se/index.asp?sPage=1&langID=2&cID=14

I USA the Lysholm is marketed as Whipple, I guess this is to hide that it is a swedish product and market it as american?

V2Rocket

The unit in the Millenia was manufactured by IHI.

Thanks for the link.

After some other forum searching, it seems that the IHI unit is about 1.2L. This should be a good size for my application; the Millenia engine was marketed as a 2.25L engine but was actually a 3.0L in terms of absolute bore and stroke. The displacement is considered smaller because it is a Miller-cycle engine rather than an Otto cycle, where 25% of each compression stroke per cylinder does no work.