7 replies to this topic

[DeadSquare]

This is obviously a "How long is a piece of string" question", but getting the oil pressure up before starting a rebuilt engine last summer, provoked the question  "How much of the oil gets dumped straight back into the sump" ?

 

I was turning the 948 Midget engine over at about 250 RPM with the starting handle in a big 5/8" chuck Black & Decker and had asked the owner to tell me when the needle flickered on the oil gauge.

 

Almost at once he said "It's not flickering", adding a moment later "It's almost 50 PSI".

 

Delighted, I quickly replaced the plugs, heated the inlet manifold with a gas torch and the engine sprang into life with a healthy 80 PSI, and ever since then, I have been wondering how much of the oil that is being sucked out of the sump, actually gets to the bearings etc: to lubricate the engine ?

 

When Racing Mini Se7en in the 60s, every scrounged 1/10th of a BHP counted, so the dynamo had no windings, the water pump was gutted and the water circulated through the front mounted radiator with a washing machine pump and Aston Martin heater motor.

 

Can anybody tell me, if I had also gutted the oil pump, how big an electric oil pump would I have needed ?

 

 

 

PS  The length of a piece of string is always...................................twice its doubled length.

 

 

 

[nicklouse]

Mmmm to answer your question I don’t know.

 

but then there are differing designs (forgetting the Metro Turbo pump) there were the 4 and 5 lobed pumps. And the 5 were the preferred pumps back in the early 90s but they are just not out there now.

[Avtovaz]

oil pressure dosnt exist so they say, its the restriction to flow. So in any hydrolic system you have the relief valve, that "makes up" for the wear in your engine and also set the restriction to flow. The pump will be over specked for the application so it can "never" under flow. Main reason you r engine never wants to idle low is at low speed the oil pump wont provide enough flow for the engine, its out of its range for application. Also note that the relief valve is after any point of the flow that could "dead head" usually to create this "pressure"

 

 

What im getting at is, with the elekky water pump will use Pulse Width Modulation to control the engine temp, so the pump is on and off very quickly, there will be points where it maybe not doing anything at all hardly and thats why its so efficient. Also, if its 2-3 seconds late sensing and pumping, it dosnt really matter. you cant do that with an oil pump. you go around a corner and oil surge, the pump has to either be over pumping to start with and reliefing like a standard pump, or be able to instantly pump oil at a very fast rate which cant happen. So the standard mechanical pump is very reliable, very efficient and very old design.

 

HTH

Edited by Avtovaz, 09 November 2022 - 10:43 PM.

[weef]

By design there is about 30 to 40% of the pumped oil dumped directly back to the gearbox via the pressure relief valve so there is always plenty in the "sump".

There are figures for pump rates, not sure at what RPM though, but they are in the region of 1.2 gallons/minute for the standard pump and 1.3 gallons/minute for the turbo unit. The pumps are better at lower RPM but on average they are estimated to be 75% efficient, I suppose it depends on oil viscosity, temperature and the mechanical condition of the pump/engine.

[stuart bowes]

PS  The length of a piece of string is always...................................twice its doubled length.

 

unless you tie the two ends together, in which case, infinite

 

I keep seeing this post title and thinking, how much wood could a wood chuck chuck, if a wood chuck could chuck wood

 

sorry nothing of value to add obviously

[DeadSquare]

By design there is about 30 to 40% of the pumped oil dumped directly back to the gearbox via the pressure relief valve so there is always plenty in " HAND ".

 

There are figures for pump rates, not sure at what RPM though, but they are in the region of 1.2 gallons/minute for the standard pump and 1.3 gallons/minute for the turbo unit. The pumps are better at lower RPM but on average they are estimated to be 75% efficient, I suppose it depends on oil viscosity, temperature and the mechanical condition of the pump/engine.

 

 

I wonder where I should start looking to find  "figures for pump rates" ?  not that knowing, would help me to find out how much gets dumped and how much goes round the filter.

 

Perhaps, next time I rebuild an engine, I could re-plumb the inlet and dump, and running it over a dustbin in stead of a sump, take measurements at various RPM, but where to do it ?

 

It would need to be somewhere like a farmer's gateway.

 

 

 

 

 

[mini13]

couple of good videos on oil pumps here,

 

 

 

Also i seem to remember that  in one of his books vizard mentioned skimming down the pump for race motors to cut wasted power
 

Edited by mini13, 11 November 2022 - 11:17 AM.

[DeadSquare]

couple of good videos on oil pumps here,

 

 

 

Also i seem to remember that  in one of his books vizard mentioned skimming down the pump for race motors to cut wasted power
 

Thanks for those two videos.

 

I must ask AC if his improved scavenge would suck oil through an oil filter, and thus extend the life of the oil pump.

 

The second bloke's camera positioning was good, but .........................................................