Sump Oil Control

Competition engines and ancillaries - general discussion
Julian
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Sump Oil Control

Post by Julian » June 26th, 2006, 9:23 am

referring to Guy's subtle hint for discussion (http://guy-croft.com/viewtopic.php?t=56)

I was always taught that oil scrapers were just one of two options for preventing creep and drag. The main purpose is to keep the oil in the bottom of the sump and as such is actual more baffle than the normally envisaged comb. Where the crank is knife-edged you shouldn't use a scrapper anyway (this is the second option - got a sneaking suspicion that this was a hot-technical-tip from a Mr Vizard writing for CCC many years ago). Using horizontal baffles is still important though (rather like the use of a swirlpot for fuelling).

Dry Sump options do make the matter somewhat moot for mid-range (cost) installations since the volume of oil in the sump is so low by comparison that the crank is well away from it all. The primary trick here is to remove excess gas pressure - either through proper venting or mechanical extraction. Unassisted venting is the cheap and nasty option and can be assisted in a minor fashion by recirculating the gas into the induction system (not necessarily a good idea with forced induction engines). Fully assisted is more complex and requires a hardy pump but offers potential performance gains in a properly assembled engine. Isolating each chamber is taking this matter to an extreme level but does offer total control (as far as an engineer can hope to achieve in such a chaotic environment).

I'm going to go away now and do some digging to see if I can find suitable documentation to back-up my arguments. Not sure what I can find on the internet on this matter...

Guy Croft
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Post by Guy Croft » June 26th, 2006, 5:50 pm

You are quite correct Julian,
everything I write is freely open to discussion.
I keep my section locked to enable me to keep continuity and to draw people to the site.
I hope that the members' section will pretty well run itself without my posting all the time! Last thing I want to see is GC as the most recent post every time I look in, kind of defeats the object.

Sincerely and thank you for your kind interest.

GC

Julian
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Post by Julian » June 26th, 2006, 7:17 pm

Thanks Guy,

There is a third compromise option that I failed to mention earlier and that is what the americans refer to as a windage tray. The idea is to capture the airbourne oil particles that are whipped up as the crank turns - especially at high RPMs. The mist that forms can result in a large quantity of air being emulsed into the oil in the sump which in turn can lead to problems in lubrication with potentially catastrophic results.

In essence the windage tray is a semi-scrapper. It doesn't sit close enough to the crank to trim the oil film but it does trap the mist below the level of the tray and assists in reducing the froth. Many modern engines come with a windage tray as standard which should help to illustrate just how useful they are.

Something else that has come out of me digging through the internet today on the subject is discussion of the best approach to shaping the crank to reduce drag and resultant spray. The old school method is symmetrical pointed edges on the lead and trailing edges but it isn't the only option with many people opting for asymetrical shaping (like a propeller blade) or bullnosing to create a smooth radius.

Thus far no-one has been able to show which is better one way or the other and from a curiosity point of view would certainly love to know which is better and more importantly why...

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Post by Guy Croft » June 26th, 2006, 7:44 pm

some photos Julian, to illustrate please!

GC

Julian
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Post by Julian » June 26th, 2006, 7:56 pm

I'll see what I can find - the only image I have at the moment is the crank from my road car

Image

This has offset knife edging while being noticibly lightened and then balanced dynamically to what most engineers would call stupid levels (happily runs on the bench at 20000rpm without any noticible oscillation).

I will see if I can find examples of traditional knife-edging and bull-nosing.

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Post by sumplug » June 27th, 2006, 9:13 am

yep RB's cranks are pretty special.
another point is where the oil pick-up should be located in the sump. how long the pipe should be with the size of the head. starvation on corners with wet sumps is an issue on both road and track cars. also some engines like high flow but not high pressure oil pumps. the theory is 10psi per thousand revs. yet time after time, i see high pressure pumps used on everything. wont this cause the oil to aerate?? build up of pressure in the crankcase/sump will lose power surely. anyone got views on this?

Julian
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Post by Julian » June 27th, 2006, 9:45 am

More thoughts on this subject with regard to the bullnose radiusing of crankshafts.

I had to give in and go to a higher authority on this matter last night, I cannot find any reference anywhere (I do not have my usual library of books to hand at the moment) on why you would want to bullnose the leading edges of the crankshaft.

The answer apparently is one of aerodynamics - a smoothly radiussed leading edge and knifed trailing edge is simply an effort to reduce aerodynamic drag. This is only really of any benefit with high revving engines especially where a long stroke is used (most high-revving engines use a short stroke to reduce peak piston speeds anyway). It is definitely rather old school in thinking I suspect dating back to the 50s and 60s where aero shaping was the next big thing.

The key point with this method is that it is only of any great use in a dry sump system. The removal of metal from the crank can potentially weaken the webs while the radiusing does little to reduce the impact of the crank in the oil. With a thick or cold oil the stress can be sufficient to propogate cracks if there are any flaws in the casting. If the crank was specifically developed for this purpose then it is unlikely to be a consideration but for a converted crank the results can be unexpected and more than unpleasant.

Another point to remember is that aerodynamics are not of particularly great use outside of a dry sump as the real need is for hydrodynamics since the crank will spend as much time pulling through a viscous liquid rather than a gas.

If anyone has a picture to illustrate a bullnosed crank I would like to see it!

Evodelta

Post by Evodelta » June 28th, 2006, 10:45 pm

Well here is my take on the subject, the crank does not dip into the oil so the shape on it is purely aerodynamic, as you pointed out this means that the leading edge must be blunt but rounded and the trailing edge is sharper and longer like the classic teardrop shape. The rule in aerodynamics is not only how you cut into the air but how you leave it behind that matters.
Is that a standard configuration crank you have? I notice it has eight weights, the cranks we use in integrales only have four and it is a good upgrade (for use at constant and higher Rpms) to get yourself an 8-weight crank.

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Post by Julian » June 29th, 2006, 2:20 pm

I wont comment further on the crank/oil contact situation as it really is news to me.

The crank shown is a standard production item that has been modified to suit the specific engine build. A lot of metal has been removed from the moving components of the bottom end. This isn't immediately obvious from the pictures I have.

The engine build is a little on the sly side - the block is a 16v 1242 FIRE unit, chosen because it is structurally stronger than the 8v version. It was still treated to reduce stress as a precaution though.

The internals are mostly 8v based, the only internal parts completely outside of the Fiat FIRE parts bin are the pistons which are a little on the special side. I'm expressly forbidden from stating where they were sourced from so please don't ask.

The guys at the machine shop regard the engine as a bit of a pain as the balancing tolerances are far tighter than is normally deemed necessary. The engine would rev cleanly to around 15000rpm if permitted but the valve springs were chosen to self-limit the engine to around 9000rpm.

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Post by Guy Croft » June 29th, 2006, 3:02 pm

PHOTOS!

GC

Julian
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Post by Julian » June 29th, 2006, 3:20 pm

Guy Croft wrote:PHOTOS!

GC
I thought we were talking about wet/dry sumps here?

Rods & Pistons:
Image

The Bare Block:
Image

Flywheel:
Image

Short Block Assembly:
Image

In The Car (not quite complete yet):
Image

Yes that is a *very* tight fit - the inlet manifold was incorrectly fabricated so the trumpets were in the wrong place.

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Post by cantfindausername » July 21st, 2006, 9:38 am

This is the moroso sump I'll be running on my car.

Taken from the mororso site...
- Kicked-out sumps on each side of the pan increases capacity to 6.5 quarts without restricting ground clearance and helping to lower the average oil temperature
- Solid windage tray with oil drain & dipstick cut out holes prevents oil from splashing back to the rotating assembly, robbing vital horse power
- Trap door baffling allows oil to flow …œone way‚ into the pick-up area during hard acceleration and deceleration, preventing the pick-up screen from starving for oil

I'd like to hear your opinions on this please.

Image
Image
Image

Thanks,
Ant

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Post by Guy Croft » July 21st, 2006, 10:06 am

As 'good as it gets' for a small motor.

GC

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Post by cantfindausername » July 21st, 2006, 10:10 am

cool! 8)

Its nice to get opinions from people who are more in the know :D

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Post by sumplug » July 21st, 2006, 11:16 am

Ant.
Thats one beautiful sump. Looks and does what it says on the can, or is that sump!! :lol: :lol:

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