Running vacuum in a wet sump circle track engine

[RedRacer]

We have built late model dry sump engines that we run 14-16 " HG vacuum, but never a wet sump (pump in pan <traditional SBC location>) motor, with an external vacuum pump. Anyone care to share some of the tips they have learned such as oil pump modifications? For starters, I would assume that the oil pressure will go down when pulling a vacuum in the cranckcase... so attention would have to be put into the pressure relief spring in the oil pump to counter the vacuum in the crankcase? Any particular vacuum pump that is better than others? Considering the Moroso 4vane new style pump, but open to all options,

thanks, RR

[SW]

We have ran the Peterson "wet/vac" external wet sump pump in a late model before. This is the one that has a vaccum stage in it. After a few different tries, we settled on putting the pickup in the center of the intake manifold valley.It seemed to be the "dryest" place to stick it. On the dyno, it worked well in the valve cover, but on the track we couldn't keep the oil out of it.When you plumb it into the valley, make sure you build a good baffle system around it, to keep the oil splash up into it to a minimum.It was a pain in the ass to get it, but well worth the effort, especially in a highly restricted class. Also keep in mind that you do have to have a little oil going into the pump, or you could burn it up.
Shawn

[RedRacer]

Thanks for the input Shawn... what kind of gains were you seeing, and how much vac were you pulling? thanks!
RR

[SW]

We would see gains of about 10hp, depending on the combo. You have to make sure that the motor is completely sealed up, or you won't get the full potential.This will also vary the amount of vaccum you get.We would run the system without any bypass at all.You should get 7-10 without alot of trouble,depending on what pump you get and how hard you drive it.We have seen as much as 12-14.

Shawn

[Guest]

That is a good tip about getting the motor sealed up. We have used the special two lip style crank seals, and that has worked great... but what was really surprising is that once we put a seal in the distributor housing, it gained about 2 "hg on the dry sump stuff we have been doing.

[SW]

you'll probably laugh at this one, but on good dry sump motors we would put the rear main seal in backwords. I haven't had the guts to try it on anything else, though. Those distributor seals are really trick, too.
Shawn

[RedRacer]

That was me posting on the dist seal, but it says "guest"... not sure why. Anyways, yeah on the dyno mule motor we did not have any of those two lip seals around and we put the stock type seal in backwards... worked alright as far as I can remember! You're right, I'd be scared to put it in anything without a good amount of vacuum being pulled!

[Guest]

We have built late model dry sump engines that we run 14-16 " HG vacuum, but never a wet sump (pump in pan <traditional SBC location>) motor, with an external vacuum pump. Anyone care to share some of the tips they have learned such as oil pump modifications? For starters, I would assume that the oil pressure will go down when pulling a vacuum in the cranckcase... so attention would have to be put into the pressure relief spring in the oil pump to counter the vacuum in the crankcase? Any particular vacuum pump that is better than others? Considering the Moroso 4vane new style pump, but open to all options,

thanks, RR

Why would the oil pressure go down? I can see that the gauge reading would be lower due to the atmospheric reference, but wouldnt the pressure drop from the oil galley to the crankcase be the same?

[Rick360]

Why would the oil pressure go down? I can see that the gauge reading would be lower due to the atmospheric reference, but wouldnt the pressure drop from the oil galley to the crankcase be the same?

The pressure would go down because the oil pump's relief valve is also referenced to crankcase pressure (or vacuum). You are correct that the pressure the bearing "sees" from oil galley to crankcase would not change.

An external pump system would not drop oil pressure (refereneced to atmosphere or gauge) as crankcase vacuum increases since it has a pressure relief outside the crankcase. In this case the oil pressure the bearing "sees" would increase.

Rick

[Racer7088]

If you drop pan pressure too low there may not be enough pressure in the pan to force enough oil flow up the pickup and to the pump at the rate it is already pumping it out or at least matching that and when you start starving the pump it will cavitate and start detroying itself slowly. You WILL see pressure drop if you pull enough vacuum since the most the pump can lower it's inlet to is 0 psi and the differential is solely based on what is left in the pan as far as pressure vs that 0 psi (or higher) at the pump inlet.

At 15" HG vacuum you now only have half an atmosphere or 7.5psi pressure feed up to the pump through the stock pickup. If 7.5 psi and whatever cross section pickup you have is not flowing as much as the pump is kicking out since it is a mechanical positive displacement it will pump a void or vacuum which will collapse back on itself on the high pressure side (cavitation).

You can run larger cross section pickups to help keep the suction side fed under high vacuum or run lower vacuum to keep from smoking the rod bearings. A lot of engines still have more than enough pickup side oil flow even at low pan pressure anyway so it may not be a problem if you don't see low pressure developing. Also never run more oil through the engine than you need anyway and you will already have the ability to run more vacuum since the oil flow out of the pump won't be as high anyway. Some of the aftermarket wet sup pumps made for Vacuum have huge or even dual pickups so they flow a lot even with very low pan pressure (high pan vacuum).

The feed on a drysump is both gravity fed AND at atmosheric pressure (~15psi feed pressure) so no amount of pan vacuum will afect the dry sump's delivered oil pressure.

[onovakind67]

I'm a little confused about the difference between the presentation of oil to the suction side of the wet sump pump vs the dry sump pump.
I understand that you can't generate more than 30" of vacuum at the suction side of the pump, and that lowering the pressure at the inlet to the pickup tube will reduce the flow through the tube. At some point you don't have enough pressure drop across the tube, oil flow is restricted and problems ensue.
If the pump is moved from inside the crankcase to an external position, how does this change the ability of the pump to attract oil? If I have 30" of vacuum in my pan and 30" of vacuum at the pump head, how do I get any oil to the pump?

[Racer7088]

I'm a little confused about the difference between the presentation of oil to the suction side of the wet sump pump vs the dry sump pump.
I understand that you can't generate more than 30" of vacuum at the suction side of the pump, and that lowering the pressure at the inlet to the pickup tube will reduce the flow through the tube. At some point you don't have enough pressure drop across the tube, oil flow is restricted and problems ensue.
If the pump is moved from inside the crankcase to an external position, how does this change the ability of the pump to attract oil? If I have 30" of vacuum in my pan and 30" of vacuum at the pump head, how do I get any oil to the pump?

Depending on space and the actuall car and application you can run the external pump lower than it is in the stock location or even lower than the oil level and then you have some gravity feed too to help with whatever pressure feed you do have left. Also you can shorten the pickup and/or make it a bigger pickup that can flow more oil at the lower preesure drop it may now see with the lower pan pressure. With these mods you woul have more oil flow to the pump and/or could run even more vacuum before losing the oil pump feed again or just have it as more safety margin.