dry sump scavenge(vacuum) pressures

[powered by wattard]

Were running a dry sump setup to prevent the friction welding of our billet crank and conrods which occured 5 days before the Australian FSAE event in 2003.

We have made our own scav pump which is driven internally inside the casing which is a bloody tight fit. It is 1.5 times bigger in capacity than our oil pump and our oil system runs an external oil relief valve. All works successfully however we have some issues with blowby as we only run a single ring.

Some insight into the following questions would be helpfull

1)What size scav pumps to other teams run compared to the oil pump

2)What vacuum do other teams pull inside their casings

3)does this vacuum occur at all speeds and loads, or ar there speeds where the scav pump can't suck out all the blowby, thus pressurising the casing

4)Do other teams run a sealed casing and try to pull a vacuum to reduce windage or just vent the casing to atmosphere

5)if all the blowby can't be evacuted by the scav pump, do other teams vent the casing to atmosphere via a one way valve allowing the scav pump to still pull a vacuum at some speeds


Thanks

WIlliam Attard
MUR Motorsports 04
Melbourne University FSAE. Australia

[Mark100]

Here's a shot at your questions:

1. We ran a total (geometric) scavenge ratio of 4.04 in our 2001 car and up (4stage). Our 99 car had a 1.5 scavenge ratio (2 stage). Our 2000 car had a scavenge ratio of around 3.4 or so (4stage). (Your scavenge ratio appears to be 1.5). The amount of scavenge ratio you need depends on a lot of things, what you want to do, and how you have set up your entire system (ie - pumps, res, baffles, everything). Asking what other people run is not neccesarily going to tell you what you need.

2. We never saw more than 7 psi vacuum. 4.9-5.0 psi vacuum was more typical of the max.

3. The amount of vacuum you get is dependant on scavenge ratio, rpm, load, ring condition, how well the engine is sealed, engine temperature, and what your oil relief valve (or lack thereof) is doing. On the dyno, you will see crankcase vacuum vary signifigantly with load and rpm.

4&5. Seal your crankcase and try to pull a vacuum, especially if you are running one ring. Even if your not, I would seal your case. Obviously, when you seal the case, you have all the blowby going through the return lines, and has to be vented out of the reservoir.

Are you running ONE ring only? Or are you running the top ring with the oil control ring pack? If you still want to run one ring, think about the clocking of the gap relative to the pin axis.

Also, you can flip your shaft seals around backwards, and you might gain some vacuum. Just make sure everything else is sealed up nicely.

Oh, may I ask why the billet crank?

Hope that helps.

[Frank]

1 a randomly chosen 750cc dual rotor one from a wrecker

2 5 psi

3 all speeds, as our rings are standard, and the motor is not tired.. yet

4 seal the casing (didn't touch the oil seals.. interesting idea mark) and vent the swirl pot to atmosphere

man your gonna learn heaps doing this.. but it seems a painful life, and IMO an expensive and unreliable life for your team

[powered by wattard]

Thanks for the insight, the reason for the billet crank and rods as we made our own prototype inline twin engine last year.