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Will a stock 26mm oil pump be ok on a full flow case

Engine 
6K views 34 replies 10 participants last post by  advinnie 
#1 ·
Hi all I've just full flowed my case and add an external oil filter but will the stock oil pump be up to the job or would I need to buy a 30mm geared oil pump.
Cheers
 
#3 ·
Pressure relief cover ive not seem them where is the oil sent if the pressure is to high of cause it is returned back to the sump but how if that makes sense?
I only ask about the 30mm pump because vwheritage was pushing me hard to buy one saying that once you fit an external oil filter you need the bigger pump to keep the system pressurised up and that the 30mm pump is the smallest they fit to there engines.
 
#4 ·
I think most people will be with Dave on this one, every engine I've built has had a remote filter and a 26mm pump, no issues.

I have once blown an oil hose off on a cold winter morning but to be fair that was down to busy and forgetful hands after an engine swap rather than excess oil pressure :)
 
#5 ·
I fitted a 26mm pump to my full flowed 1776 as per John Maher's recommendations. Also fitted a Berg relief cover. - http://www.geneberg.com/article.php?ArticleID=243

CSP make them as well but not out of cast iron.

They bleed excess pressure back to the non pressurised side of the pump gears. (the pickup side).

Just insurance against blown filters, hoses, oil coolers etc, especially in cold weather when the oil is thick at start up. If you do go for 30mm then I would certainly fit one.

It also means you can happily run standard off the shelf Golf oil filters and not have to pay through the nose for Fram HP1 type race filters.

Dave.
 
#8 ·
. . . Just insurance against blown filters, hoses, oil coolers etc, especially in cold weather when the oil is thick at start up . . .
I keep seeing this mentioned (I've been reading up on FF, doing my Daughter's '71 1300 soon), but I don't get it.
If the pressure Relief and Control valves are working correctly, how can the pressure rise any higher than the pressure they're set at?
 
#6 ·
Oil pump

Hi
WHS
I've got 30mm pump on my 1776 full flow,had lots of excessive pressure problems ,blowing filter etc till I fitted a CSP cover with pressure relief valve,not had any problems since even on cold Scottish morning with SAE40 oil.
If I was to do it again I would only fit 26mm pump more than enough for the job.
I still run fram HP 1 filter,but that's just my choice rather than need.
 
#10 ·
I see what you're saying, but it's a Hydraulic system, so the pressure should be fairly uniform throughout with any given set of parameters (Pump speed, Oil temp, etc).
The outlet flow from the pump will only give pressure when there's a physical restriction, in this case a reduction in cross-sectional area.
Both Filters and Coolers will have much larger areas than the oil pipes/galleries, and the relief/control valves, so the pressure won't be higher in either (Cooler or Filter), than in the oilways.

Maybe I'm misunderstanding the purpose and/or operation of the relief/control valves.
Whatever pressure(s) they're set for, surely the oil pressure can't rise above that, no matter what temp the oil is?

Or is it that the oil galleries (and/or relief valve) are too restrictive, so even when the valve(s) opens, they can't flow enough to keep the pressure down (with cold oil)?
 
#11 ·
The filter and head and cooler are the restriction, and they occur before the relief valves so oil pre the filter is un relieved.

Think about it like this.
Hot oil poured through a siv will flow through almost like water.
Stone cold oil will not flow as well,

It's that back pressure and extra resistance that causes excess pressure. And the weakest link is tested.

After the filter the oil is relieved via the spring valve and drilling to the sump.
 
#12 ·
It's been a while since I had to put any of this into practice but I hope it helps.

A pump generates flow NOT pressure; pressure is created by restricting the flow of a fluid (think about when you put your thumb over the end of a hosepipe).

I 'high pressure pump' is used to describe a pump which is capable of providing a required flow rate at a given system pressure.

As Doc highlights, pressure is affected in many ways but the three main contributors are flow rate, viscosity of the fluid and the size of the orifice(s) through which the fluid flows.

In our case the flow rate and the orafice size are fixed so viscocity is the variable and is affected by temperature. The warmer the fluid, the less viscous it tends to be.

One last thing to bear in mind is that the fluid will always try and find the easiest way to a low pressure area - in an engine this is managed to ensure that the fluid passes through/over/around all of the areas we need lubricating.

For a full flow system, the first restriction is the oil filter with no alternative route for the oil, therefore we need to ensure that there is a fail-safe here to prevent it from going pop. However more important than that is ensuring that we get oil to the vital areas of the engine; if viscocity is too high then it less fluid can flow trhough the restriction (fliter) generating excessive pressure in the 'upstream' pipework and within the filter itself and reducing lubrication to the vital areas. If too much upstream pressure is created, then the weakest point will burst - hence the need for a bypass to both control pressure and ensure enough lubrication.

For the rest of the system, the orafaces have been sized to both create pressure and to provide the correct flow rate to a give part of the engine. Again, when the fluid is cold, and therefore more viscous, we are at risk of building too much upstream pressure and causing the weakest point, a gasket or the oil cooler, to go pop. The pressure relief valve is again a fail-safe to protect these weak areas, but to ensure that a certain amount of pressure remains in the system and oil is directed where it needs to go.

Personally, I would NOT have a pressure relief valve on the pump cover as this could, at worst, effectively stop any flow leaving the pump and at best reduce the amount of oil entering the oil-system (and therefore starving the engine of any oil) - I would prefer everything that the pump has to offer to enter the oil system (remember flow is one of the variables) and for it to be controlled within the system - this is why it's important to match the oil pump outputs to the engine.

For a full-flow system I would be looking at a bypass in the filter (better to have thick unfiltered oil than no oil at all). Once oil is getting into the engine case, then use the correctly rated springs for the relief valves within the case to control pressure.

If, when warm, you are not getting enough pressure, then we need to look at the other two variables. Either the pump is not flowing enough oil (too small or worn) or, more likely, the orafaces have increased in size due to wear (bearings).

As mentioned, I am think back a long (very long!) time to when I was being taught about fluid dynamics within jet engines; while I reasonable sure I'm close to the mark here, I'm sure those with more recent experience will correct anything that I've missed or not remembered quite correctly.

That said, I hope it helps.

H-G
 
#13 · (Edited)
In our case the flow rate and the orafice size are fixed
H-G
The flow isn't fixed - it depends on engine rpm.

The main issue is that the engines we are dealing with originally have all the pressurised oil flowing through drillings in a metal casting - so no problems there, the design is sound.

But we are directing it out of the metal and down several feet of rubber hose.

When folk build bigger engines that benefit more from fuil flow filtering they often fit larger than stock oil pumps, or at least blueprint a stock size pump. (higher flow rates)

Those tuned engines also often have the capability to rev higher than stock. (Higher flow rates).

On a cold winter's morning the oil is like treacle and therefore if you give it a few too many revs, as many folk have found out to their cost - the contents of the sump can be blasted out of a blown hose or filter all over your driveway on a frosty morning.

I have been witness to 1 hose blowing off it's barbed fitting, one hose splitting under pressure, and one oil filter rubber gasket being forced out. (at least 2 of those engines had 30mm pumps - not sure about the other) - and I have heard of several other cases.

So it does happen in practice. Many folk will get away with it though because -
1 - Many of our cars are now sunny day only drivers and don't go out in the freezing cold as often as they used to. (especially the tuned ones)
2 - If you can afford it then using aircraft spec hose with proper swaged ends and special high pressure filter cans will help to keep the oil in.
3 - Most drivers, especially those who have had a hand in their own engine build will know not to give it too many beans until the engine has warmed up a bit.

However, your foot can sometimes slip or you may fluff a gearchange.

Most respected engine builders (not parts salesmen) will tell you that a 26mm pump is plenty big enough for most engines, but the ads in the magazines will tell you that any high power motor must have a 30mm pump.

I know who I trust.

The stock pressure valve (s) in the engine case are there to protect the stock oil cooler from being blown by the high pressure from cold oil, and they do a good job, but they don't protect what goes before - i.e. an aftermarket external oil filter (and maybe cooler and 'stat as well)

Many (but not all) oil filter cans have an internal bypass in case the filter becomes blocked.

Personally, I would NOT have a pressure relief valve on the pump cover as this could, at worst, effectively stop any flow leaving the pump and at best reduce the amount of oil entering the oil-system (and therefore starving the engine of any oil) - I would prefer everything that the pump has to offer to enter the oil system (remember flow is one of the variables) and for it to be controlled within the system - this is why it's important to match the oil pump outputs to the engine.
In any well designed engine that has vulnerable components such as oil filters or oil coolers within it - you need some sort of pressure control. This is normally a spring loaded plunger (the stock VW ones) or sprung ball valve (as in a pump pressure cover plate). If you get any bits of crap in the oil it is indeed possible that they may jam the valves open resulting in a loss of pressure.

This is why it is important to keep the filter mesh screen in place on the pickup pipe, and also to keep an eye on the oil pressure gauge so you know if an abnormal situation occurs.

The most important place for the oil pressure to be maintained is at the crank bearings. If any pressure control valves fail then, yes your main bearings will get less oil than they should. This will be the case whether it happens to the stock valves or the one on the pump cover. All the valves come prior to the oil having to do any lubricating duties. - so it's an unavoidable (if pretty minor) risk anyway.

Dave.
 
#16 ·
Thanks Dave - I knew I would overlook something! Indeed the flow will increase with revs adding more to the cold day challenge.

I think that we are pretty much in agreement regarding the need and positioning of the pressure controls, however in the last quote of mine that you refer to, I am indicating that I would prefer that the systems receives all the oil that the pump can provide and fit the fail-safe controls within the system (filter, external cooler and case) to manage these areas, ensuring that in the worst case we bypass them and don't bypass the pump, ensuring that we will alway have flow and pressure to the crank bearings.
 
#17 ·
Doc, I think that Andy198712 explains how the filter affects flow on a cold day pretty well. The cooler has a similar, but lesser, effect due to the narrow pathways through the matrix to increase surface area.

Mindful that until we start adding the full-flow element to these engines, the oil systems works well (apart from fine filtration) then I think we can discount the oil system and relief valves within the case. The problems occur when we start modifying the system; because all the flow directs all of the oil to the external filter BEFORE it goes to the case, we must provide the necessary pressure relief at this first restriction - hence the oil filter bypass. As I understand it, an external cooler should be less of a problem if fitted correctly (after the filter and with a thermostat) as no oil should flow around it until it has reached the correct working temp.
 
#18 ·
Doc, I think that Andy198712 explains how the filter affects flow on a cold day pretty well. The cooler has a similar, but lesser, effect due to the narrow pathways through the matrix to increase surface area . . .
Yes, I understand how cold oil behaves (goodness knows I've poured enough of it in my time ;))

I read somewhere a while ago, that a typical spin-on filter element has a surface area of around 300 sq/ins (or more), it would be interesting to know how much of that is the 'gaps' in the material (i.e. what the total area available for through-flow is).

The cooler oilways in the matrix must have at least 5-times the cross-sectional area of any of the galleries/pipes (as a rough guess-timate), so I can't see the cooler causing any restriction.

Maybe what we need is a nice strong, S/S, cleanable filter, that will shrug off high pressures with ease . . . but at >£200, maybe not . . .
K&N Oil Filter
 
#19 ·
Wow this post of mine has brought up some real good information. I have now got a 30 mm pump and a pressure relief pump cover set at 60 psi but reading this I don't know if I should fit this or fit a oil filter pressure relief head instead?
 
#24 ·
Hi welcome to my thread. I did go with a 30mm pump in the end But with a oil pump cover with a pressure relief valve set at 80 psi (yes I did say it was set at 60 psi in an earlier post but I was wrong). On a very cold day the oil pressure sits at 75psi at 1000rpm when first started it with in five minutes at idle the pressure would drop to 60 psi and when the oil is up to temp 95 degrees Celsius I have 12 psi at 1000rpm, 24 psi at 2000rpm, 35 at 3000rpm, 42 ish at 4000rpm and just over 50psi at 5000rpm. Hope this helps.
 
#33 ·
Mate I'm glad you finally got it up and running I did feel bad for you when you post up you had issues with your motor. Yep these 2054cc engines are bloody quick and you have larger valves than me so I would love to see how you're go
 
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