Thread: Intake systems

Originally Posted by steveG

Care to explain the second statement in a bit more detail?
I can't see why with the same engine load/RPM it wouldn't be consuming the same amount of air regardless of what happens to be under its feet and what speed its travelling at.

Steve

You are correct - at the same load/boost/egt/fuelling then intake flow will be the same.

I believe he is trying to say that 2000 rpm while puttering around offroad will be less load then the same RPM while travelling at 100 km/h.

For cyclonic precleaners, the capture efficiency is proportional to Kinetic Energy - so Mass*Velocity^2. You need to make sure you buy the correct size precleaner or it will be less effective.

I believe Donaldson states that its precleaners are for "off-highway" use. On a sealed road they would be doing bugger all (unless you are driving through a dust storm). You would be best advised to use a ram head on bitumen and swap to a precleaner when anywhere else.

Originally Posted by Rick Fischer

Note for young "players". Donaldson is a "particle separator" needs air velocity sufficient for the swirl to centrifuge the particles out. 3" flow velocity on LR turbo 2.5s is "just good enough".

Note that with a turbo, 2000 RPM "suck" off road is flowing now where near as much air as 2000 RPM and 90-100 kph down the bitumen.

Hope this assists.

Cheers

RF

What is this 2.5 you speak of?

Cheif, ram-air makes no difference at legal speeds. If you can do 300km/h it's worth doing.

Originally Posted by Dougal

What is this 2.5 you speak of?

Cheif, ram-air makes no difference at legal speeds. If you can do 300km/h it's worth doing.

Have you got some proof behind the ram-air statement? Or is that just gut instinct?

Originally Posted by slug_burner

Have you got some proof behind the ram-air statement? Or is that just gut instinct?

Pressure from velocity.
P= 1/2 density x velocity squared.

Air density is around 1.2 kg per cubic metre.
100km/h is 27.8 metres per second.

P = 1/2 x 1.2 x 27.8^2
P = 463 Pascalls of pressure maximum.
This is 0.5% of atmospheric pressure or 0.07 psi.

An amount known throughout the English speaking world as SFA.

To get this maximum 0.07psi, you have to have an intake soo big than the air speed through it to your engine is close to zero. Which isn't practical. So when driving down the road at 100km/h even a ram-air head is going to be sucking.

Originally Posted by isuzurover

Not compared to a diesel the same capacity at the same rpm (even NA, let alone turbocharged).

That statement has me puzzled; does a diesel for some reason have significantly higher volumetric efficiency than a petrol engine?

Originally Posted by POD

That statement has me puzzled; does a diesel for some reason have significantly higher volumetric efficiency than a petrol engine?

Diesels have a higher VE than petrols, plus (usually) run an excess air level (up to 200 %). If you were running a petrol engine that high above stoichiometric it would be running so lean the pistons would melt.

Originally Posted by POD

That statement has me puzzled; does a diesel for some reason have significantly higher volumetric efficiency than a petrol engine?

Not so much the VE. But higher airflow.
Two reasons:
1. No throttling.
2. Turbochargers.

Originally Posted by isuzurover

I believe Donaldson states that its precleaners are for "off-highway" use. On a sealed road they would be doing bugger all (unless you are driving through a dust storm). You would be best advised to use a ram head on bitumen and swap to a precleaner when anywhere else.

Donaldson used to call these gadgets "swirl bowl pre-cleaners". They now call them "full view pre-cleaners". The catalogues have always listed them as for off-road use and their purpose is to extend the filter life of agriculture and construction equipment.

We were always told that they are a waste of money on anything other than stationary or slow moving equipment as they do virtually nothing when used in a stream of fast moving air as on a motor vehicle.

They have to be correctly selected for size to match the engine and air cleaner. Donaldson air cleaners have a centrifugal section and oversizing the air cleaner negates this effect. Heavier particles are spun out and trapped then engine intake pulses expel the particles through the vacuator valve.