Lotus Elan

Cross drilling pressure drop ?

PostPost by: cabc26b » Fri May 28, 2010 12:06 pm

I'm looking for test data plus a quick survey -

Has anyone here on the forum tested (or know's some one who has) the oil pressure on both sides of the cross drilling to see if there is a pressure drop ?

A table that shows the pressure on "short gallery" & "main gallery" sides of the cross drilling over RPM would be helpful. oil temp would be nice as well.

Survey question -

How many have had bearing failure in a ford based motor - if so , what where the oiling systems spec - example , dry sump . wet sump / baffled pan. wet sump non baffled pan etc.

Thanks

George
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PostPost by: CBUEB1771 » Mon May 31, 2010 2:23 am

George,
I understand what your are looking for and I apologize upfront for not having a complete map of pressure v. flow for the normal oil path and the alternate where you feed the exhaust side gallery from a dry sump pump. But let us consider the obvious. If oil is flowing though the cross-block drilling of the normal block then there is a pressure drop. There is also a pressure drop between the pump outlet and the exhaust side gallery if you use the dry sump style oil delivery. The major issue with the standard cross drilling across the block is the limitation on cylinder bore. You can only go so big before the cylinder bore breaks into the cross drilling. This has been covered over and over again on this forum. Sorry to be a bore, if you pump a non-supercritical fluid through a channel there is a pressure drop. Reynolds Number and length of channel will not be denied their tally.
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PostPost by: GrUmPyBoDgEr » Mon May 31, 2010 9:03 am

CBUEB1771 wrote:George,
I understand what your are looking for and I apologize upfront for not having a complete map of pressure v. flow for the normal oil path and the alternate where you feed the exhaust side gallery from a dry sump pump. But let us consider the obvious. If oil is flowing though the cross-block drilling of the normal block then there is a pressure drop. There is also a pressure drop between the pump outlet and the exhaust side gallery if you use the dry sump style oil delivery. The major issue with the standard cross drilling across the block is the limitation on cylinder bore. You can only go so big before the cylinder bore breaks into the cross drilling. This has been covered over and over again on this forum. Sorry to be a bore, if you pump a non-supercritical fluid through a channel there is a pressure drop. Reynolds Number and length of channel will not be denied their tally.


Spot on as always Russ.
Cross drillings will cause serious pressure drops.
If my memory isn't playing tricks on me the Cosworth FVA used the same Block but was of course much more highly stressed. The solution was to provide the main Bearing Oil Feed via a tapping in from the exhaust side of the block.
This was part of it's dry Sump lubrication System & the Cosworth 5 Port Pump piped Oil to that tapping via an additional Oil Pipe.

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PostPost by: cabc26b » Mon May 31, 2010 3:29 pm

Hi Russ ,

Do you think think the tally is more than 10lbs ? I don't have a feel for a Reynolds number not having worked the formula ( or researching the numbers to plug in)

I am running a 1600 ( 159?) so I don't have the issue of the cross drilling being sacrificed to get a larger piston in there ala the FVA . The debate is over the necessity of the left side ( exhaust side) oil feed. To quote my engine builder - "its your money, I'll put one in but I don't see the necessity of it since the engines I build & have built, don't come back to me with bearing failures" - his own twin cam has 100 race week ends on it ( not an exaggeration) and has not had a bearing failure . I know his other customers and they run at the front and work the cars hard. My last twincam was set up the standard way and the "big" Junior motor was also run with out the exhaust feed ( the big junior spend its life at 9K plus) no bearing failure s there either.

If there is not a significant pressure drop I am inclined to let it run as is ( I can just fit a different spring for more pressure ) The boss fitting options are not too good or an elan and we are not a fan of epoxy on hot metal-

More of a concern and focus for us is on making the pick up work for the wet sump system I will be running ( this is more of a concern since I know that the dry sumps I used in the past would not suck air and drop the oil pressure to zero) for the first time. BTW I'm running the johnson pump....


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PostPost by: rgh0 » Tue Jun 01, 2010 5:17 am

George
I am struggling to understand what you are prposing to do - how do you intend running without the left ( exhaust) side oil feed to the main bearings ?

The redesign of the sump and pickup to work in racing for a wet sump engine I have posted details on before

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PostPost by: cabc26b » Tue Jun 01, 2010 11:46 am

Hi Rohan,

Sorry , I thought I was clear. The modification in question is to make the oil inlet from the pressure side of the pump feed the main gallery on the exhaust side of the block - this is an option b/c I am not using the ford pump for the system. Can I assume you oil in the OEM fashion ?

BTW I can send you some photos off line if you want.


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PostPost by: CBUEB1771 » Tue Jun 01, 2010 3:40 pm

George,
If you run a large diameter line from the pump discharge to the exhaust side gallery and route it nicely I am sure you will have less pressure drop than with the standard cross-drilling arrangement. Are you planning to autocross your Elan or engage in some other form of competition? For normal road use I would stick with the standard arrangement. There are several approaches to feeding oil to the exhaust side gallery. John McCoy at Omnitech makes a fitting that bolts to the block which requires that you drill into the oil gallery. I have seen some blocks in which one of the engine mount holes was drilled through into the gallery. I can't remember which one it is that is close to the gallery. Gary Anderson posted photos of this modification a year ago or so. Of course now you can only attach the engine mount with three bolts. If you are up for spending serious money most of the alloy blocks for BD series motors are cast with a feed into the exhaust side gallery.
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PostPost by: cabc26b » Wed Jun 02, 2010 2:37 am

Hi Russ,

I scoped out the options a while back - When the block was being prepped I assumed that pump would be feed to the left side (exh) . My guy enlarged the Oil pressure fitting to take the oil into the block - We discussed this and he pointed out the dozen or so race engines including 2 of mine that have not have mod done and lived happily with drysump systems and the cross drilling.

Le left me with a "he would be more than happy to modify my block ( something to the effect or its your money) " , but, out of curiosity would I mind seeing if there were any data to support the theory -

So I asked - and so far it looks like my best option on the data it gather with my own engine.

However, I grow impatient with this never ending motor build. if its 5 to 10 pounds I will adjust at the pump

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PostPost by: rgh0 » Wed Jun 02, 2010 12:01 pm

AH - I know think i understand

The standard oil gallery arrangment is fine for any engine application I am aware of in terms of oil supply and pressure, provided you use a high volume / high pressure pump for a 8000 rpm plus race engine. This high vol / high pressure pump need is more about oil circulation rate and bearing and oil cooling needed than specific bearing oil film stability requirements for bearing oil pressure and flow rate issues also.

The use of a direct feed to the left hand gallery from the oil pump is only needed if you are building a big 85mm plus bore block that makes the standard cross feed gallery between 2 and 3 cylinders not practical due to lack of space between the bores it is not driven by pressure drop in the standard oil galleries

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PostPost by: GrUmPyBoDgEr » Wed Jun 02, 2010 12:38 pm

Measuring pressure drop within an Engines lubrication System usually means a lot of work getting all of the locations connected up to Manometers or pressure Transducers.
I once gave myself the task of finding out why Oil pressure relief Valves on a well known V12 Engine were showing marked signs of movement & corresponding wear after durability runs.
The lubrication system was a fairly complicated one with an external Oil Filter connected via Hoses & a mass of cross-drilling's within the Engine.
The Pump itself had a regulating valve set to 4 bar & an overpressure Valve set to 8 bar.
The Relief Valve got its pressure signal from the Main Bearing Gallery.
I found that at high revs & with hot Oil there were Oil pressures in the engine of up to 11 bar, which were causing the overpressure Valve to function as a pressure relief valve (The Pressure relief Valve was only seeing up to 4 bar) so hence the high amount of wear that I had discovered.
The lubrication System is a bit too complicated to describe here but suffice it to say that pressure drops can be considerable.
That's something to be born in mind if you're considering piping in external Filters or Oil Coolers.
As has been written here before, use the biggest Hoses & use 90? etc., Bend Adapters with the biggest possible Radius, never Right-angle Blocks.

Cheers
John
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PostPost by: SJ Lambert » Tue Jul 31, 2012 1:28 am

Slightly off topic, but I figure this question has a connection!!

If plumbing in a dry sump oil feed hose to the short gallery, the re are two obvious options to mill and tap for the bigger fitting.

Firstly at the front where the oil pressure gauge sender normally resides.

Secondly, at the mid point in the region of the top of the engine mount where theres is often a secondary drilling or two that is typically blanked off in standard guise.

If given the choice is there any perceived advantage from locating the feed at the front or at mid point?

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PostPost by: SJ Lambert » Tue Feb 17, 2015 10:44 am

I've been advised to go across to the main gallery (near the front of the motor) for a circuit racing engine, as this gives the crank highest priority without the restriction from coming across the block.

Have very high revving engines with cross drilled cranks suffered at the rear (#5 main & #4 big end) from slightly depleted oil supply - would tapping into the rear section of the main gallery further prioritise the rear crankshaft oil feed drilling, or are we talking unmeasureables here?
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PostPost by: rgh0 » Tue Feb 17, 2015 9:38 pm

I have never seen any problems with crank oil supply in high revving twin cam engines even when using standard volume oil pumps.

I have seen issues where people have not set up correct tolerances on the bearings ( especially the cam bearings) so that excess oil goes to one location and potentially starving others.

I would also be reluctant to put in any more cross drillings into a block unless I knew exactly where to do it so it did not weaken the structure.

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PostPost by: SJ Lambert » Wed Feb 18, 2015 10:44 am

P1100442.JPG and


Am currently set to go in here.
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PostPost by: SJ Lambert » Wed Feb 18, 2015 10:47 am

image.jpeg and


But the Bengal Tiger tells me to go in here!

- as adding a boss to the exhaust side of the block, directly into the primary oil galley, (7/16) avoids the restriction of the oil going around the corner twice and then across the block which is only 5/16 ......
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