dry sump questions

[blykins]

Same principles apply, no matter whether it's a drag race engine, pulling truck, or Cup engine:  pulling vacuum on an engine requires different allowances. 

Listen, I know that you'll argue every syllable, semantic, and phrase until we're 100 pages in, so I'm just gonna hop on off this one.  I don't have time to be dragged into a 2 month argument over individual words.

[andyf]

I put a window in one of my big dry sump pans just to see what happens at various vacuum levels. I've tested really large dry sump pans and super small dry sump pans just to see what the difference is. I've run dry sump with a vacuum pump and without. Lots of various stuff to test with dry sump setups and I'm sure I haven't done 1% of the testing that the NASCAR boys have.

[andyf]

Here is a 5 stage pump with a rear mounted vacuum pump.

[blykins]

I like that rear-mounted suck pump.

[andyf]

I think one of the best things I ever did with the dry sump setup was to install a sight gage on the tank. In the dyno cell we set up a video camera to watch the sight gage. That tells us if the dry sump system is pulling oil from the engine or if the oil is getting trapped. If you don't have a way to watch the oil level in the tank during a pull then you don't really know what is going on. I have a buddy who took his dry sump engines to the salt and burned them down. The oil was filling up the valve covers and after a couple of miles he lost pressure. Had he run the system on a dyno with a video camera he could've saved himself a lot of time and money.

[scott foxwell]

Where does the wrist pin get most of it's oiling from?

I like discussions like this because they get me thinking beyond what I think I already know...
It's not personal.

[Joey120373]

Lots of semantics going on in this thread, but i love it!

I have often wondered exactly why  people claim that running too much vac... negative pressure ( just gonna call it that cause it makes way more sense to me...) would harm wrist pins.

What Brent posted makes perfect sense to me. The fog of oil that is perpetually created around the crank has to provide both lubrication and cooling to the underside of the piston as it slams into it near BDC. A multi stage oil pump that is actively pulling away this fog will have an effect on both.
So to my feeble mind, there are a lot of things at play here. I can see how two completely different engines could have the same "negative pressure" in the crank case, and one could live forever while the other would eat wrist pins, simply based on mechanical variances like oil pump inlet location, crank scraper location, piston to crank clearance, piston design.... the list is almost endless.
Like most thing in life, everything is far more complicated than it would seem.

I am very keen to run a wet sump with a vacuum pump on my engine, but i would like to get more info on the issue. Not a ton of info out there on street engines running "vacuum" pumps, how do they hold up? how much maintenance do they require etc...

[scott foxwell]

I'm quoting a friend who probably knows more about this than anyone else I know;
"When our barometer gains or losses, we still have same air. Dust stays dusty, humidity stays humid. Inside the engine we merely change the barometer level to less than the out side of the engine."

[scott foxwell]

What Brent posted makes perfect sense to me. The fog of oil that is perpetually created around the crank has to provide both lubrication and cooling to the underside of the piston as it slams into it near BDC. A multi stage oil pump that is actively pulling away this fog will have an effect on both.

I disagree that the oil pump is pulling anything away form the crank. It keeps oil out of the pan which helps control windage, but a good wet sump pan will do the same (control windage).

[turbohunter]

I cant tell you guys how many times in the last couple days Ive had a question or comment then erased it all because I was forced to think about it and figured it out myself. This is a great discussion, please don’t get exasperated or cynical.
Yes its minutia, yes it’s bench racing but its freaking interesting.
I’ve been thinking about when we see pictures of a bead of liquid in the space station just hanging there. Then when one is propelled mechanically and in the absence of atmosphere not losing any speed. Then relate that to having less atmosphere in a block, and if that liquid is a bead of oil traveling toward a wrist pin, or being scraped by a crank scraper, or, or.......
Also, I understand the concept of no suction in an area, but when is there suction? At the opening of the drain to the oil pump? In the pump?

To out there?

[gt350hr]

I'm quoting a friend who probably knows more about this than anyone else I know;
"When our barometer gains or losses, we still have same air. Dust stays dusty, humidity stays humid. Inside the engine we merely change the barometer level to less than the out side of the engine."

      Very true.

[scott foxwell]

So I reached out to a friend of mine and asked him what his thoughts were on this. This comes from one of the leading Cup engine builders in the country. Not at liberty to share who...sorry, but good read.
............
Looking back on it all, I think depression really didnt create the wrist pin issue, just exposed it with better scavenging. The depression, or lack of atmosphere, makes splash oiling slightly less effective, as it decreases it's resistance to movement. When we first started down the depression road, we pulled the wrist pins out of the piston, and blamed it on lack of oil to them. Such may have been the case slightly, as the crankcase was being better evacuated, so there was less left in the pan flying around. That, and the less resistance/effectiveness  of the splash may have caused a little of the problem. But we opened up clearance, and then pressure fed them to try and help. Nothing eliminated the problem until we went to stiffer pins. Once we got that under control, it is surprising how little they need really. We spray the bottom of the piston, but there is only. 005 clearance between the pin towers and the rod (.0025 per side) and we run no oilers to the pin via the ring groove. We are higher in depression than we have ever been, and oil them less also. Which kinda points to the story of how we got here, and that it was really just weak pins all along, and we were just covering it up with lots of oil and big clearances.

[Heo]

So that gives the pins was flexing more with "higher vaccum"
make sense in a way that there was bigger difference in pressure
over/under piston....

[gt350hr]

Where does the wrist pin get most of it's oiling from?

I like discussions like this because they get me thinking beyond what I think I already know...
It's not personal.

  Lower performance , production engines usually rely on splash oiling. Oil being "thrown around" in the crank case. For splash oiling to work , there has to be oil droplets of "fog" as you put it , present or and oil squirt hole drilled into the connecting rod ( older small block Fords for example).
  Performance and race engines usually have "forced pin oiling" that comes from oil drains located in the oil ring groove which put oil directly on top of the wrist pin. Often there are two holes per side. Sometimes broaches are added to the sides of the pin bore as an additional source. Very high end race engines ( and high turbo boosted engines) have "oil squirters" off of the mains aimed at the underside of the pistons to cool them and that "splash oiling" also oils the wrist pins.

[blykins]

Doesn't explain the issues that the Pro Stock guys were having, which arguably turn as many rpms (or more than) as the Cup engines do, while making almost twice as much horsepower. 

When you're running a very small diameter wrist pin with a piston-centered rod, there is going to be room for improvement.  Not so much with a conventional connecting rod setup and a large diameter, coated wrist pin.