Cost aside - dry sump or Accusump

I've been in a few spirited debates about the virtues and issues with both. From everything I read, a dry sump is the hands-down winner, yet I'm being told by some that they have problems, such as throwing a belt due to a small rock.

I had an Accusump and they're far from perfect, but are about 10X cheaper which counts for something. The catch is that the engine doesn't care if money was saved on the oil system, only whether it works or not.

I've been told I don't need one on a street car (but one that's very low, does trackdays, and is on sticky tires).

I'm told that unless I see oil pressure dropping, I don't need one. The thing is, I have no idea how close to the edge I am.

I'm told to add an extra quart. Yes, I get it, but how much can be added before it makes the problem worse by the crank whipping air into the oil?

So while I have a few knowns and a bunch of unknowns, I'm still leaning toward a dry sump due to it de-airating the oil, providing a truly uninterrupted oil source, and drawing a vacuum in the crankcase. What it does not provide is oil pressure prior to start-up like the Accusump provides. Anyhow, I still want to hear input from the Collective Mind before making any decisions.

Dry sump, no question. Is there any race series where dry sumps are allowed where you see Accusumps? You'll also get your ground clearance from a dry sump, where the accusump won't help you there.

Thanks for replying, Keith. Being a FWD setup I can't really benefit from lowering the drivetrain since the transaxle bellhousing hangs down just as low as the stock pan. Also, half shaft angularity doesn't allow much of a drop even if the bellhousing was trimmed.

Still, the list of benefits is so long it can't be dismissed even at 10X the price of the Accusump. I guess in a way my mind's made up but I posted this in case someone's got a situation I have't thought of where a dry sump isn't the best choice.

There's an interesting halfway option that's used in some LSx applications. You use a dry sump pan and a scavenge pump, but let the original oil pump take care of pressure. Gets you a lot of the benefits with considerably lower pump cost.

Problems from not having oil pressure before start up are FAR less common/severe than problems from oil starvation.

kb58 wrote: Thanks for replying, Keith. Being a FWD setup I can't really benefit from lowering the drivetrain since the transaxle bellhousing hangs down just as low as the stock pan. Also, half shaft angularity doesn't allow much of a drop even if the bellhousing was trimmed.

You're not thinking innovatively enough. Look at the Mazda V6 touring cars where the engine was so low that the right axleshaft went through the engine's V.

Just because something can be done...

Oh, I know, I know...

Unmentioned is that you need a tiny multiplate clutch and a flexplate small enough in diameter to allow you to drop the engine down until the connecting rods dig into the ground. But since that wasn't mentioned, then we don't have to worry about it, right? I suspect that getting the engine DOWN was a big part of why the C5 put the transmission in the back. Ever see how flat a C5's oil pan is compared to a normal LS1 oil pan? Then notice how deep those pans are compared to, oh, a 4L60 bellhousing...

Back to the world of reality, another point for dry stump is that there's also power to be had in not putting the engine over a bowl of oil that keeps sloshing around and hitting the crank. The oil likes it a lot more, too.

I respect KT's knoweldge/experience/expertise greatly. However, you have to give some context to your intended use, because you're comparing a $300 option to a $3,000 option (by your account)
An accusump with an electric solenoid will provide pre-start oiling and protect against "momentary" loss of oil pressure from the oil pump (hard corning) The dry sump setup doesn't provide any pre-oiling. It has a number of advantages already mentioned, but it is a lot more money. If your car is low enought to benefit from the improved ground clearance, or the extra couple of horsepower, the choice is simpler. Both options have their place. For a car that spends a lot of time going around fast corners at hi G-loads, you really need to look at the way oil drains from the valve train back into the sump. A number of common oiling problems with popular engines (BMW 6's and some LS engines) are caused by poor drainage back to the sump.

Okay, you asked for it, my twisted line of reasoning behind considering a dry sump:

1. If you check out my car at www.midlana.com, it's already done; there won't be any further lowering of the drivetrain. This was dealt with during design where due to drive shaft angularity, the FWD drivetrain can't be lowered any further. Ground clearance is roughly 4".

2. The car is around 1600 lbs and 400 whp with roughly 30/70 F/R weight distribution, on wide sticky tires. It's used for drives along the beach, spirited driving through the mountains, and most important to this thread, trackday events.

3. The engine is a turbocharged Honda K-24 and during a recent modification, a small amount of oil was found in the intake tract. Since the PCV system isn't used, the only source of oil had to be seepage through the turbo bearing due to crankcase pressure.

4. This led to examining the turbo oil drain-back path (-10 line at about a 45 degree angle). Oil is fed to the turbo through a 0.035" restrictor, so there's not a lot of flow, but it still seemed to be an issue with crankcase pressure (the turbo was checked out and found good).

5. Dry sumps are expensive but the engine's a lot more expensive. Losing the engine would make me sad and I don't want to be sad.

6. A dry sump provides a guaranteed constant source of oil, it deairates the oil which provides solid separation between the crank and main bearings, it draws a vacuum in the crank case, reducing frictional losses with the crank, it removes oil from the area of the crank, preventing the crank from whipping the oil into an air/oil emulsion. Due to the crank no longer hitting the oil, oil temperature typically drops by 10-15 degrees. Due to the reduced oil and frictional losses, engine power is increased by as much as 5%, which is a lot, though not the main reason for going with such a system. Lastly, the low crankcase pressure would help suck the oil out of the turbocharger, eliminating oil getting into the intake tract.

7. The Honda K-series has an issue where during a long left-hand turn, oil runs to the right side of the car, which happens to be toward the front of the engine where the cam chain is. Oil is quickly "conveyored" up the chain to the valve cover and depriving the pan of oil. Oil pan baffles are available and I have one but have no way of knowing how well it works.

8. Some people say just add an extra quart of oil. I get that, cheap and easy is good, but the effects are a mixed bag. To "some point" it'll help, but the larger oil mass is also getting beat up even worse by the crank, inducing more air into the oil, and heating the oil more.

9. Some say that a street car doesn't need a dry sump. They don't know my car...

10. Some say that if it's not sucking air now, it's not a problem. This line of reasoning bothers me because it ignores the fact that I'm probably near the edge already. All it's going to take is a warm sticky track, really sticky tires, and a looong turn such as Turn 2 at Willow Springs to find that edge... or not. That's the concern, the not knowing.

11. Some say just get an Accusump, that it'll work practically as good for 10X less. I had one and my main issue was that while it provided cold-cranking protection of the bearings, it can't help with deairating the oil. I have a theory that air bubbles sucked up by the pump get compressed along with the oil. The result is an air/oil emulsion that's at full pressure, but is masquerading as 100% oil, and isn't, but neither the oil pressure gauge nor the Accusump can deal with something they can't sense.

So that's pretty much my thinking on the subject, but came here, hat in hand, to ask how my thinking might bare improving.

I've been looking at this quite a bit recently, given that I have a track car with an LS3. Accusumps don't save them, FYI.

I think the ability to pre-pressurize the oiling system is overblown. You can run a street motor for a quarter of a million miles without pressurizing the oil before a start. Engine starts are a low stress, low speed event. If you're really concerned, put in a separate switch so you can crank without firing the ignition and build up pressure.

That's why I've been zeroing in on the scavenge-only solution. You get all the benefits of decreased crankcase pressure, de-aeration, constant oil supply - but with easier plumbing, tighter packaging and a lower cost.

Interesting logging of oil pressure fluctuations in an LS7.
http://www.corvetteforum.com/forums/c6-z06-discussion/2323798-oil-starvation-on-track-hard-data.html?styleid=139#post1570018874

kb58 wrote: with roughly 30/70 F/R weight distribution

FTFY. Granted, I don't have any first hand experience with either. But for what you've put into that engine, I would definitely lean towards at least a basic dry sump system as described by Kieth.

My brother went down the same path, recently putting an LS3 into his Stalker. He read up on it and said that the OEM pump in the LS3 had cavitation issues, so chose to go with a full-blown dry sumps system from ARE. He hasn't tracked the car yet but I expect him to have no problems.

And I agree with you about the cold-cranking issue being a bit overblown. Looks like I can see what's on the horizon for my car...

Driven5 wrote:

kb58 wrote: with roughly 70/30 F/R weight distribution

FTFY. Granted, I don't have any first hand experience with either. But for what you've put into that engine, I would definitely lean towards at least a basic dry sump system as described by Kieth.

Oops, fixed that, it's mid-engine so it's 30/70 F/R. Forgot to say that the engine's built to last, but it won't help if the oil goes away.

I'm not sure how big an issue this would be, but would the extra oil capacity of a dry sump affect getting the oil up to temp in a daily driven car?

Do not discount too much the effects of aerated oil. That eats bearings and causes problems internally when the entrained air expands once the pressure starts dropping.

One statistic that shocked me was in a Mazda rotary, at some certain RPM, 100psi oil pressure in the engine block meant only 7psi oil pressure in the crank. Centrifugal force was keeping the oil from entering the crank almost as hard as the oil was trying to be pumped in. The RPM was in the realm of K24 use (either 7000 or 8000rpm) and bear in mind that rotary main bearings are smaller in diameter than most piston engines'.

Centrifugal force at the rod throws works equally well (harder, really) to pull the oil through, but what happens if the oil is 25% air? It expands in the crank... sorry rod bearings, you get the short end of the stick.

As pointed out, overfilling the oil makes this aeration worse, not better. You're trading off not momentarily uncovering the pickup for constantly sucking oil foam.

If money is no object then +1 for dry sump, easily.

Knurled wrote: Do not discount too much the effects of aerated oil. ...

Your reasons are much of why I started leaning in the dry sump direction. A mechanical engineer buddy recently went down his list much like yours, but left out the bit about how when the pressure drops, the entrained air bubbles expand. Very good point.

Soooo why not both? You can pre-oil and if you lose your drysump drive belt you have a little insurance still.

Dry sump. IIRC there was a thread on here a while ago about cheap scav pump solutions, use the factory pump for pressure.

There was a guy somewhere in net.land (corner-carvers?) putting together a turbo V6 Camaro for track duty, and he posted links to some VERY inexpensive dry sump stuff. I think it was like three stage pumps for $299-399 or somesuch. You still need acres of plumbing and a tank but you could probably piece together a complete dry sump setup for a thousand or so.

Hmmm, I'll search for that, but in the world of bargains, it always reminds of the joke, "Would you like to buy our regular parachute, or our best parachute?" I'm all for bargains, but there's always a magical line where my fear of its failure rises above the perceived bargain. This one's firmly over that line and I haven't even found it yet...

Also look into NASCAR surplus, "dry sump pump nascar" on ebay, turns up plenty around $500. You probably only need half that much pump for a 4 cylinder, but most of those are modular IIRC, so you can remove excess scav pumps and the pressure pump. I'd run the stock internal pressure pump on anything street driven, that way if you lose the pump belt, you wont lose pressure until the reservoir empties, an idiot light to indicate the scav pump has stopped (perhaps a GM oil level sensor mounted on the tank) would be a good idea.

I can count on one hand the number of lost belts I've seen. If its really a concern once you mount the pump you can make a cover for it like some dirt track cars do. Pre oiling is not impossible either. On the stock car we took the belt off the crank, slipped it over the chuck of a 1/2" drill and spun the pump until we had pressure.

Go for the dry sump. You won't be happy until you do.