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Oil pressure measurements

 
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lee16v
16 Valve


Joined: 29 Jun 2005
Posts: 1429
Location: Devon, UK

PostPosted: Fri May 02, 2008 9:28 pm    Post subject: Oil pressure measurements Reply with quote

Hi all,
having a few problems with my oil pressure light and I'm going to borrow a tester to see if it's the switch at fault or if my engine is shafted!!

Question is........what readings should I be getting from the engine at tick over and at higher revs??

Thanks, Lee
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ZeNiTh-PbArM
Alfa 33


Joined: 14 Mar 2003
Posts: 388
Location: Paris, France

PostPosted: Mon May 05, 2008 5:31 pm    Post subject: Reply with quote

hi, quicker and easier, replace the oil pressure switch with a known working one and see if the problem disappears.
checking with a gauge requires a high accuracy gauge because the cold pressure reaches 4 bar, and the hot oil pressure can drop as low as 0.2 bar at idle, Most gauges lack the required accuracy to discriminate between 0.1 and 0.3 bar!
regards,
zp
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messybloke
Alfa Arna


Joined: 29 Apr 2008
Posts: 23
Location: essex

PostPosted: Mon May 05, 2008 8:41 pm    Post subject: oil preasure Reply with quote

I do remember many years ago that my suds with oil preasure gauges showed almost nothing at idle, infact i went as far as changing the big end shells on a sprint to improve it ( made no difference). I also remember in the hand book it stated that the light could glow at idle when V hot.

If the engines still have a blank in the main oil gallery on the top of the engine, you could do as i did and fit a gauge there (again on a sud). That would be usefull at high RPM at least.

Also what oil are you useing,it might go against the grain, but synthetics are not always best on old engine with high milage 10/40 works for me.. Laughing
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lee16v
16 Valve


Joined: 29 Jun 2005
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Location: Devon, UK

PostPosted: Tue May 06, 2008 5:37 pm    Post subject: Reply with quote

Hi guys,
I tested with a gauge and it showed the drop in pressure so the switch is working correctly and I'm currently using 10/40 oil.
I'm going to drop the sump and have a look at the pump as it's relatively easy and check big/small end bearings but hopefully it isn't the latter as there's no knocking coming from the engine. Also as it doesn't burn oil I'm guessing the rings/valve guides are ok too?

thanks for your replies.
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ZeNiTh-PbArM
Alfa 33


Joined: 14 Mar 2003
Posts: 388
Location: Paris, France

PostPosted: Tue May 06, 2008 6:59 pm    Post subject: Reply with quote

once again : replace the switch! the pressure drop you measured is normal, you just have to put the threshold somewhere, and your gauge doesn't tell you where it is
try replacing the inexpensive switch before even thinking of dropping the pan and messing with a potentially sound engine.
zp
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lee16v
16 Valve


Joined: 29 Jun 2005
Posts: 1429
Location: Devon, UK

PostPosted: Tue May 06, 2008 9:06 pm    Post subject: Reply with quote

ZeNiTh-PbArM wrote:
once again : replace the switch!
zp


Ok ZP..........it's finally sunk in!! Laughing

Cheers.
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Alan
Alfasud


Joined: 15 Aug 2007
Posts: 48
Location: Slovenia - Ljubljana

PostPosted: Sat May 17, 2008 9:18 pm    Post subject: Reply with quote

I have put a 1mm washer under the spring in the oil pump pressure valve, and took 2/10mm from the cover of oil pump, so the gears have almost no axial play.

Pressure with cold oil at idle is 4.5 bar at 3000 rpm over 6 bar.
With very hot oil is 1,2 bar at idle an over 4 bar at 3000 rpm. I use selenia racing oil.

I have a mecanical oil pressure gague that is connected directli to the engine block by a pressure hose.

Before the modifications i had two engine failure (bearings)

My english is not very good, i hope you will understand this post Embarassed
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ZeNiTh-PbArM
Alfa 33


Joined: 14 Mar 2003
Posts: 388
Location: Paris, France

PostPosted: Sun May 18, 2008 6:46 pm    Post subject: Reply with quote

hi, i'd strongly advise against increasing oil pressure by modifying relief valve, the whole lube circuit has not been designed to withstand it. I've already seen oil filter cartridges explode under too much pressure (well above the mentioned 6bar though)
besides, it won't enhance lubrification at all, what matters is oil flow, not pressure.
Eliminating gear play and enhancing tightness is a good idea anyway.

regards,
zp
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rsfruitbat
Alfa Sprint


Joined: 13 Jun 2007
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PostPosted: Mon May 19, 2008 1:07 pm    Post subject: Reply with quote

The 1mm spacer is a common mod used in racing / rallying. Have been using this for the past 15yrs and so far havent had any problems. Always used OE filters though.
I guess that the relief valve will stop flow if it is activated?
By raising pressure the oil will be forced through the existing oil galleries thus maintaining oil flow?

rsfruitbat
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ZeNiTh-PbArM
Alfa 33


Joined: 14 Mar 2003
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Location: Paris, France

PostPosted: Mon May 19, 2008 7:16 pm    Post subject: Reply with quote

hi, i know the spacer is a common mod but there are no benefits to this mod.
lube problems occur under heavy use, when oil is hot
oil pump behaves as a flow generator, and the flow is proportional to the engine rpm.
oil pressure is then determined by engine clearances (especially bearing clearances) and oil viscosity.
the relief valve is just a pressure limiter to avoid damage to the engine.
increasing relief pressure won't improve oil flow, won't compensate for out of spec clearances, well the benefit is nil! however the added 1 bar at high rpm will put undue strain to the pump and its drive gear, and drain extra power from the engine.
anyway, lots of guys insist on doing this mod, to my mind it's useless like adjustable fuel pressure regulators of performance air filters.
regards,
zp
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Oggie
Green Cloverleaf


Joined: 06 Mar 2008
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Location: Whitehill

PostPosted: Mon May 19, 2008 7:43 pm    Post subject: Reply with quote

Some of us guys who modify our engines need higher fuel rate to feed larger carbs or throttle bodies, therefore needing a higher rated fuel delivery pump, now most fast road or race fuel pumps flow at high rates i.e. 35 gallons an hour to which is too much for the car on start up which again would cause flooding to the engine then nothing would run!. Hence a fuel pressure regulator. Now air filters improve throttle response , increase airflow for the now more thirsty engines and the standard box does not fit the new carbs etc etc.On another note do you per chance now how to disable the alfa control unit so the rear brake lights still work when this unit is out?. Cheers
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ZeNiTh-PbArM
Alfa 33


Joined: 14 Mar 2003
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Location: Paris, France

PostPosted: Mon May 19, 2008 9:34 pm    Post subject: Reply with quote

yes yes i know all about the "we guys use to do" ; around here the vincinity is full of kiddies who think the shiny green conic filter will make the engine run better, and that increasing fuel pressure on their EFI system will gain much horsepower. The same applies for truck-like exhaust systems fitted to old diesel ford escort and the like.
Such beliefs are so widely spread that even serious modders install such gadgets on their engines. I've yet to see such naive modifications bring a single HP or increase engine life.
Serious improvements like high flow oil and fuel pumps, proper camshafts, high rate fuel injectors, and the like, cost more money and are seldom found under most hoods.
I don't mean to be rude but i'm getting tired about youngsters always trying to prove the same nonsenses all over again, and ruining some more engines and cars by doing so.
regards,
zp
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Oggie
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Joined: 06 Mar 2008
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PostPosted: Mon May 19, 2008 9:46 pm    Post subject: Reply with quote

Then you should meet some of us, I think that exhaust back box and filters are like you say a waist of time, I also know that most of Europe will deem a car illegal if modded more than the filter exhaust jobbies and therefore not street legal. But just suppose, if there wasn't anyone tinkering with there cars in the first place then F1, DTM, BTCC,GP2, GP3, WRC...etc etc would not exist, there is nothing wrong with fettling with a car , its all a matter of taste , it also gives us something to laugh at Razz .
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rsfruitbat
Alfa Sprint


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PostPosted: Tue May 20, 2008 7:38 am    Post subject: Reply with quote

Hi Zenith.
I am hoping you can clarify a few things for me as you have raised some good points. My understanding is this:
Pressure relief valve limits maximum oil pressure.
It is not mechanically linked to the oil pressure gears but operates independently via a spring.
At low rpm the additional pressure will be having no effect.
If the pressure is related to rpm then the relief valve is only likely to operate at higher rpm.
The relief valve works by allowing the oil to drain back and not be forced through the oil system once a certain pressure is achieved.
If the oil system is not capable of flowing more oil then increasing pressure will have no effect.
One of my questions is where is the limiting factor / the bottleneck in the oil flow in the Boxer engine and when is it reached?
As competition engines run at higher rpm than std, oil will consequently be that much less viscous as it will be hotter. Wont this compensate for increased relief pressure as lower viscosity will flow more readily?
As oil is thinner when hotter, as you have said wouldnt you want to maximise pressure and flow rather than allowing a bleed out of the system.
If pressure didnt affect flow as well as pressure how do turbo chargers work?
If you consider me a boy racer then thats fine..

rsfruitbat
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Admin
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Joined: 19 Feb 2003
Posts: 1223
Location: Stafford, UK

PostPosted: Tue May 20, 2008 3:23 pm    Post subject: Reply with quote

Hi

With any well developed car there are minimal gains from bolt on pieces.

Modern efi car with a lambda probe then bolting on a rising rate fuel presssure regulator will just make it run rich at high revs until the lambda probe feedback remaps the fuel maps. At the same time the higher fuel pressure will just wear the injectors out quicker.

More fuel does not equal more power.

Personally I would doubt a K&N type filter gives more than a couple of hp at best, such a small amount that it would be within the margin of error for dyno runs over a few days. Dumping the airbox just means you get a load of hot air to the filter and are likely to loose power.

Main place to get power in an exhaust is from a careful manifold design (lengths, diameters and joins of the different pipes are all important). Unfortunatly most aftermarket stuff just consists of a large diameter exhaust.

All the best

Keith
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ZeNiTh-PbArM
Alfa 33


Joined: 14 Mar 2003
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Location: Paris, France

PostPosted: Tue May 20, 2008 11:46 pm    Post subject: Reply with quote

hi,

Thanks Keith you've expressed what i meant better than i could have!
Besides i won't despise any mis-informed 33ist, some boy racers learn and evolve, too.
So i'm going to try an explanation of the lube principles.

When an engine gets designed, considering all the clearances for crank and rod bearings, tappets and bores, camshafts bearing, even turbocharger bearings get summed up and the equivalent cross-section for oil flow is obtained. How much oil flow the pump shall provide is a requirement that comes from engine design.
Then the pump is designed to provide sufficient flow to ensure proper lubrification in worst conditions, that is engine & oil hot and low revs.

When engine is cold, oil is too viscous and can't get through bearings at a sufficient rate. The pressure would increase in excess of 20 bar and destroy filters and seals. That's the reason why there is a relief valve in the pump, which opens around 4 bar. When oil is cold, the valve opens and limits pressure. Oil flow to the bearings in this condition is minimal and stressing/revving a cold engine will not do much good to the bearings.
When engine is hot, oil is hot, the relief valve closes. Oil pressure increases then whith rpm, from 0.5 bar at idle to 4 bar at around 4000 rpm. Above 4000rpm, maximum oil flow is reached and there is no need to increase pressure further. The relief valve opens above 4000 rpm to keep the pressure at 4bar.

Increasing relief pressure by shimming the spring will have two effects : engine cold, pressure will be at 5 bar instead of 4 ; engine hot, pressure will reach 5 bar at 5000rpm.
But oil flow and pressure will be exactly the same between idle and 4000rpm when hot.
Above 4000rpm the pressure increase will have little or no effect on the oil flow.

What do serious modders do? Race engine have increased bearing clearances (precision job!) to reduce friction hence losses and improve efficiency. As a result they require more oil flow. Remember GTA/GTAm oil pumps? gears were ~ 1cm higher than standard ones to improve chamber volume and increase flow, even at low rpm. Race engine oil pressure, when hot, need not even be in excess of 4 bar.


For those wanting to do the math, the pump is a flow generator (volumetric pump) whose flow is proportionnal to the rpm. The circuit can be modelled as a restrictor whose pressure vs flow characteristic will determine the operating condition of the engine.

Now when using thinner oil like 0W30, when hot the oil flows more freely through the bearings, hence pressure is lower and flow increases. The trouble is that more flow is required because the oil won't stay much in the bearings. Breaking the oil film will cause wear and thrown rods. Higher viscosity is a preferrable solution, like 15W50 or 20W60.

For boxer engines, i'd say bottlenecks in lube system are
- filter : most aftermarket cartridges do not have the bypass valve, which opens when engine is cold and allows for the oil flow to reach bearings, unfiltered. Standard filters deprived of this feature restrict cold oil flow and most of the time, cylinder number 2, the farthest from the oil pump, is worn more than other. Guess what? Cold oil starvation. Won't happen with oem filters
- oil : engines fitted with hydraulic lifters require proper oil grade, preventing the use of heavy viscosity and racing oils. frequent (5,000 kms) oil changes won't hurt the engine, mine is in excess of 700,000kms now thanks to such care. However, most of the time the previous owner was a cowboy, not replacing oil in five years...
- sump : baffling is not sufficient for heavy cornering and numerous rods have paid the price of a bad compromise between good handling and poor sump design.
- bottom end : block design lacks of rigidity, when it comes to very heavy use, and the block has a propension to twist itself, distorting bearing clearances and causing the oil flow to escape. I've seen a block explode (literally) due to this problem.

In my opinion, there are very few mods liable to provide significant improvements in terms of reliability or performance without much money or much work. If shimming of the pump was liable to increase engine reliability, the factory would have done it for sure, at no extra cost. Some improvements can be made to an engine by carefully adjusting and matching the parts, to ensure optimal clearances, minimal losses, and good balancing. But they all require care and efforts to obtain minimal gain. Further optimization requires expensive performance parts and further hassle to assemble everything right. Just have a look at Adie Hawkin's engines to convince yourself of the work quality level required to achieve significant performance.

regards,
zp
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rsfruitbat
Alfa Sprint


Joined: 13 Jun 2007
Posts: 241
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PostPosted: Wed May 21, 2008 10:33 am    Post subject: Reply with quote

Appreciate your explanation comments and thoughts ZP.

Always use OE filters for oil

The 1400 16V that I have just been involved with building has been put together professionally after I did all the donkey work of making sure the bits would go together etc.
The outcome of that at the moment is 134BHP at the flywheel and 98lb/ft torque at about 6800 rpm.
This engine does have the shim in the oil pump as have all my other competeition engines.
I will bear in mind yor thoughts when this has to be rebuilt and discuss what you have said with the guy who put it together.

Regards rsfruitbat
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Brit01
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PostPosted: Fri Mar 09, 2012 7:13 pm    Post subject: Reply with quote

zp:

bringing up an old and tired thread probably sorry.
Just curious about your comment here about thicker oils/racing and hydraulic lifters as this is my case.

Quote:
- oil : engines fitted with hydraulic lifters require proper oil grade, preventing the use of heavy viscosity and racing oils. frequent (5,000 kms) oil changes won't hurt the engine,



After a recent re-build, crank journals were within specs but close to their limits. Just measured/polished/cleaned and new shells fitted.
Factory recommended oil is 15w/50 for my model. (but this is for a new tight engine from factory)

I have been running my engine recently with Motul 300v 20w/60.
My engine appears much happier with this.

Cooler, revs easy, no loss of power, actually had to reduce the idle rpm compared with the break in 20w/50 mineral so an increase in power was evident.
lifters quieter.
And pressure just great when hot. 50 psi at 3000 rpm when hot and pushed hard.

BUT I do want to fit a oil temp gauge to make sure the temp is around 85 optimal.
Maybe in the next week or 2.

Cheers

Chris
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