Oil catch can for V8V
Discussion
Who has what installed ? I see there’s some relatively inexpensive ones on eBay which seem to be well enough designed, all the way up to the Redpants version, which is plug and play.
Given the wide variety of pricing and the fact that they’re a passive piece of kit, I’d be interested in whether it’s worth paying the extra or can a solution be had for well under £100.
Given the wide variety of pricing and the fact that they’re a passive piece of kit, I’d be interested in whether it’s worth paying the extra or can a solution be had for well under £100.
Just found this thread. Are there any downsides to fitting a catchcan? Nothing in the intake system is relying on slightly oily air from the crankcase?
Also, to those who have one (and I'm looking at the custom Redpants item) any guidance on how often they need to be emptied and how much oil they'll collect in that time/mileage?
As there is no active warning I imagine an over-full catchcan would be worse than no can at all, as would the engine pull neat oil?
Also, to those who have one (and I'm looking at the custom Redpants item) any guidance on how often they need to be emptied and how much oil they'll collect in that time/mileage?
As there is no active warning I imagine an over-full catchcan would be worse than no can at all, as would the engine pull neat oil?
It’s clear both the theory behind breathing gas, the pros and cons of either circulating breather gas with oil, or oil separated, into the inlet manifold, is misunderstood. For a summary statement, skip to the penultimate paragraph. For those who care for the full picture....
Any 4T engine has to evacuate from both the sump and cam covers, air / gas created from the movement of rotating and reciprocating parts, this is an entirely normal process, not an error state. If the gas stayed within the engine it would cause energy (a power loss) to overcome the resistance (pumping loss / parasitic losses).
In the 70’s emissions legislation stopped the evacuated gas being vented to atmosphere because it contained HC and oil droplets, so the gas was fed into the air induction system, pre and post throttle meaning the engine consumed its own gasses.
Because the gas in the sump is moving within an area which contains a volume of oil, the gas will inevitably pick up oil droplets, and ‘significant’ oil mixed with air going into the inlet manifold is not desirable because oil lowers the octane rating of the fuel and risks detonation / pinking / power loss. Therefore the inclusion of one way valves in the various pipework, and the cyclone valve on the V8 dry sump system, stops most of the oil getting into the inlet manifold.
So, the recirculated gas becomes a very small percentage of the make-up of combustion gas, and contains an extremely low content of oil droplets, and everything is peachy.
But...
If the piston rings wear and combustion gas seeps past the rings and into the sump (blow-by), blowby mixes with the normal gas to be recirculated and is positively forced out to the inlet manifold from both sump and cam cover breathers, now, the one way valves or gauzes might fail to properly separate the oil from the air.
In this instance there will be more oil in the recirculated gas, and that higher concentration of oil could cause the cons previously stated.
Motorsport World does not want those cons and does not have to pass emissions, so Motorsport typically vents the gas to atmosphere and catches the oil in cans (part load and full load breather).
A perfectly functioning road car engine will consume oil, some will be burnt off coming from piston and liner to the combustion chamber, and some oil will come from the valve stem seal to combustion chamber. More breathing gas than normal in this wearing state will mean more oil than normal will be pushed out into the breather system and into the inlet manifold.
Rough figures I see from servicing many cars, Across 10k miles, an average engine might consume 2L of oil, so that’s 200ml per 1k Miles. Something like 1.5L of that 2L will be (normally and not an error state) burnt off in combustion process (piston and liner to combustion chamber), the other (approx.) 500ml across 10k Miles is passed through the inlet manifold and diluted into combustion gas. That very slight concentration of oil across the very long time / distance will present no discernible problem or issues, the input of breather gas into the inlet manifold is post MAF meter, so any comments the catch can system prolongs MAF meter life is inaccurate. The Lambda sensor in the exhaust is not poisoned by that small concentration of oil in the combustion gas either.
So on a perfectly functioning road car engine, a motorsport style catch can system is solving a problem that simply does not exist.
The only benefit of a catch can system on a road car engine would be if the engine was breathing heavily (combustion gas seepage past piston rings), therefore the recirculated breather gas contained a high volume of oil which would reduce the octane rating if passed into the combustion gas supply and would cause detonation / pinking and would coke-up the combustion chamber over time. Which is why the system is used in Motorsport because race engines wear and have blowby, road car engines do not wear to the same extent / as quickly. But the answer to the wearing road car engine isn’t to install a catch can system, the answer is to fix root cause of the problem!
Another benefit of a catch can system would be on DB9 / V12 where it’s commonplace for the separation valves to fail. Instead of replacing with a new part which is destined to fail because the quality issue with the valve hasn’t been addressed, it might be better to rip the factory pipework off and fit catch cans to separate oil and vent the breathing gas to atmosphere. However, I personally think catch cans on a road cars is lacking refinement and grace, and I’d go instead for installing separation valves which work!
If it gives owners a warm cozy feeling that the insignificant amount of oil carry over is being separated from combustion gas into catch cans, crack on, fit the kit. But, it’s solving a problem which does not exist because the normal amount of oil carry over is something the engine (combustion process) can handle without any adverse effects or the driver perceiving any, in fact, the catch cans do present an annoyance, the owner has to keep on checking the catch cans are not full because if they were to overfill, that would present problems of its own. The mistake being made is thinking that the volume of oil in the can across a normal interval, causes any detriment whatsoever.
On one car which had a catch can system fitted which I saw in the workshop, when operated on full load, the new pipework collapsed (inadequately specified material) and ironically, the collapsed pipe caused oil pullover into the engine where otherwise there’d have been none! The plumbing I’ve seen of some systems is also, questionable, not following orthodox engineering practice.
Written by someone who measured blowby and impact on combustion during AMV8 prototype development!
Any 4T engine has to evacuate from both the sump and cam covers, air / gas created from the movement of rotating and reciprocating parts, this is an entirely normal process, not an error state. If the gas stayed within the engine it would cause energy (a power loss) to overcome the resistance (pumping loss / parasitic losses).
In the 70’s emissions legislation stopped the evacuated gas being vented to atmosphere because it contained HC and oil droplets, so the gas was fed into the air induction system, pre and post throttle meaning the engine consumed its own gasses.
Because the gas in the sump is moving within an area which contains a volume of oil, the gas will inevitably pick up oil droplets, and ‘significant’ oil mixed with air going into the inlet manifold is not desirable because oil lowers the octane rating of the fuel and risks detonation / pinking / power loss. Therefore the inclusion of one way valves in the various pipework, and the cyclone valve on the V8 dry sump system, stops most of the oil getting into the inlet manifold.
So, the recirculated gas becomes a very small percentage of the make-up of combustion gas, and contains an extremely low content of oil droplets, and everything is peachy.
But...
If the piston rings wear and combustion gas seeps past the rings and into the sump (blow-by), blowby mixes with the normal gas to be recirculated and is positively forced out to the inlet manifold from both sump and cam cover breathers, now, the one way valves or gauzes might fail to properly separate the oil from the air.
In this instance there will be more oil in the recirculated gas, and that higher concentration of oil could cause the cons previously stated.
Motorsport World does not want those cons and does not have to pass emissions, so Motorsport typically vents the gas to atmosphere and catches the oil in cans (part load and full load breather).
A perfectly functioning road car engine will consume oil, some will be burnt off coming from piston and liner to the combustion chamber, and some oil will come from the valve stem seal to combustion chamber. More breathing gas than normal in this wearing state will mean more oil than normal will be pushed out into the breather system and into the inlet manifold.
Rough figures I see from servicing many cars, Across 10k miles, an average engine might consume 2L of oil, so that’s 200ml per 1k Miles. Something like 1.5L of that 2L will be (normally and not an error state) burnt off in combustion process (piston and liner to combustion chamber), the other (approx.) 500ml across 10k Miles is passed through the inlet manifold and diluted into combustion gas. That very slight concentration of oil across the very long time / distance will present no discernible problem or issues, the input of breather gas into the inlet manifold is post MAF meter, so any comments the catch can system prolongs MAF meter life is inaccurate. The Lambda sensor in the exhaust is not poisoned by that small concentration of oil in the combustion gas either.
So on a perfectly functioning road car engine, a motorsport style catch can system is solving a problem that simply does not exist.
The only benefit of a catch can system on a road car engine would be if the engine was breathing heavily (combustion gas seepage past piston rings), therefore the recirculated breather gas contained a high volume of oil which would reduce the octane rating if passed into the combustion gas supply and would cause detonation / pinking and would coke-up the combustion chamber over time. Which is why the system is used in Motorsport because race engines wear and have blowby, road car engines do not wear to the same extent / as quickly. But the answer to the wearing road car engine isn’t to install a catch can system, the answer is to fix root cause of the problem!
Another benefit of a catch can system would be on DB9 / V12 where it’s commonplace for the separation valves to fail. Instead of replacing with a new part which is destined to fail because the quality issue with the valve hasn’t been addressed, it might be better to rip the factory pipework off and fit catch cans to separate oil and vent the breathing gas to atmosphere. However, I personally think catch cans on a road cars is lacking refinement and grace, and I’d go instead for installing separation valves which work!
If it gives owners a warm cozy feeling that the insignificant amount of oil carry over is being separated from combustion gas into catch cans, crack on, fit the kit. But, it’s solving a problem which does not exist because the normal amount of oil carry over is something the engine (combustion process) can handle without any adverse effects or the driver perceiving any, in fact, the catch cans do present an annoyance, the owner has to keep on checking the catch cans are not full because if they were to overfill, that would present problems of its own. The mistake being made is thinking that the volume of oil in the can across a normal interval, causes any detriment whatsoever.
On one car which had a catch can system fitted which I saw in the workshop, when operated on full load, the new pipework collapsed (inadequately specified material) and ironically, the collapsed pipe caused oil pullover into the engine where otherwise there’d have been none! The plumbing I’ve seen of some systems is also, questionable, not following orthodox engineering practice.
Written by someone who measured blowby and impact on combustion during AMV8 prototype development!
Mike
As always a great detailed response. Can I ask a question?
I had a catch can on my V8V for about 40,000km and emptied every 10,000 approx - normally about 150ml. I then had a fault with the throttle body which ultimately needed replacement (car at about 75,000km) due to being significantly oiled up. I couldn't understand the connection but the AM tech said he thought it was due to the catch can. Could that have been the cause?
Graeme
As always a great detailed response. Can I ask a question?
I had a catch can on my V8V for about 40,000km and emptied every 10,000 approx - normally about 150ml. I then had a fault with the throttle body which ultimately needed replacement (car at about 75,000km) due to being significantly oiled up. I couldn't understand the connection but the AM tech said he thought it was due to the catch can. Could that have been the cause?
Graeme
Graze01 said:
Mike
As always a great detailed response. Can I ask a question?
I had a catch can on my V8V for about 40,000km and emptied every 10,000 approx - normally about 150ml. I then had a fault with the throttle body which ultimately needed replacement (car at about 75,000km) due to being significantly oiled up. I couldn't understand the connection but the AM tech said he thought it was due to the catch can. Could that have been the cause?
Graeme
Hi.As always a great detailed response. Can I ask a question?
I had a catch can on my V8V for about 40,000km and emptied every 10,000 approx - normally about 150ml. I then had a fault with the throttle body which ultimately needed replacement (car at about 75,000km) due to being significantly oiled up. I couldn't understand the connection but the AM tech said he thought it was due to the catch can. Could that have been the cause?
Graeme
Thanks!
The throttle blade oiling up happens, at service simply pull off the plastic inlet tube and clean the blade / bore, a 30 second job.
When present, oil clings to the blade and at shallow blade angle (idle or return to idle), reduces the opening / surface area and can promote stalling due to reduced airflow. There isn’t a link between the oiling of the blade and the normally seen electronic issues which cause the throttle body to fail. So in my mind your throttle did not fail because of any mechanical influence / the oiling was coincidental and not significant.
It could be argued that the catch can system prevents throttle oiling up issue. True. But the blade seldom needs cleaning more regularly than annual service, and blade clean (should) be a service action. So again, the catch can system solves a problem which doesn’t really exist.
The obvious question is that why with a catch can fitted, did any oil at all make it through to the inlet manifold? Of course, save for unorthodox plumbing.
BamfordMike said:
It’s clear both the theory behind breathing gas, the pros and cons of either circulating breather gas with oil, or oil separated, into the inlet manifold, is misunderstood. For a summary statement, skip to the penultimate paragraph. For those who care for the full picture....
Written by someone who measured blowby and impact on combustion during AMV8 prototype development!
Thanks Mike. That £250 you just saved me can go towards next year's insurance Written by someone who measured blowby and impact on combustion during AMV8 prototype development!
Edited by LTP on Sunday 24th November 19:45
Edited by LTP on Monday 25th November 19:49
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