I thought the EGT could easily reach the melting point of aluminium. I'd be looking at steel for that.

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'God told me' is no excuse for stupidity -- Steve Quarrella

thick alloy is fine. don't forget the manifold is alloy ;)
its just corrosion that you have to watch.

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D22 ZD30 egr+butterfly mod, 2" lift extra leaf springs, enk-tek dump pipe, 2.5" exhaust.
single cab workhorse, to muddy to clean

I have been reading through this thread and to be honest I am pretty curious about it.

Normally I would not accuse the swirl control valve of having much to do with the EGR system directly, particularly given the write up from the manual by Shonky.

Does anyone have what the manual lists for the EGR operation of the shutdown valve? Does it partially close this valve when EGR is active? If that is the case then I would be inclined to think that is the important one when EGR is going on as it would induce a partial vacuum in the inlet to help draw exhaust gas through into the inlet manifold. Especially as the swirl control valve is listed as closed only below 1250rpm and EGR is active in light load cruise conditions such as freeway running at 100/110 kmh. It would not be required for a petrol engine as they would be in vacuum under those conditions anyway.

Swirl control/dual inlet tract systems are normally used to increase low down torque, at the rpm they are normally active they do not really present a flow restriction on the engine as such, rather that shut one inlet off to increase gas speed in the other one and aid cylinder filling to boost low speed torque. No idea if it is any more effective on the Navara but Toyota were about the first I can recall using it, Nissan used it for a while on petrol engines and then largely abandoned it. My grey import HR31 Skyline had a dual tract inlet setup which I removed when I took it off the road to make it a track only car. It made no noticeable difference to low rpm performance and significantly improved performance at high rpm. The next version of the engine (RB20DET) did not have it and to my knowledge it was never reintroduced before they stopped building RB engines over a decade later.


If it did not foul the inlet manifold and by the sounds of things, create a restriction in the inlet to make it work I would say that there would be little argument for disabling it. EGR is used to reduce emission of oxides of nitrogen by reducing combustion temperatures. Presumably that is also why most modern deisel engines run a lot lower compression ratio then older ones, higher compression means higher combustion temps and more Nox emissions.

you make some good points.

compression, nothing to do with emissions. direct injection doesn't need high compression like older direct injection motors. you simply need enough compression to ignite the fuel. indirect injection has high heat loss so they need higher compression to get the air hot enough to ignite the fuel.

these are not really dual manifolds like petrol motors. diesels don't have the rev range so manifold design is not so critical. later petrol motors use variable valves to achieve the same effect.

EGR butterfly is purly there to increase EGR flow (even says so in the manual, remind me to go find it again) which is common in many different makes since the early 90's. at idle and in neural the butterfly is fully open and EGR is off. butterfly also opens at 3000rpm when presumably the exhaust backpressure is high enough to maintain required egr flow. (engine is typically at full boost at 3000rpm).

swirl valve.
couple things to remember, common rail ZD30 doesn't have it.
swirl valve was typically used with these radial pumps which was a stop gap before common rail came in. quite a few motors use this setup eg BMW. these where all the first of the high egr motors and most didn't have cooled egr.
in operation the swirl valve only operates when egr is on. notably swirl valve is off at idle
it not hard to see that when you block off 50% of the airflow your going to increase EGR in a big way. the swirl effect is a good thing, helps mix the egr to ensure an even burn as these don't have the injection pressure like the later common rails. even tho later common rail motors use even more egr the higher injection pressure means they don't require swirl valves to get a good burn.

EGR reduces combustion temp which also has the side effect of reducing the power you can get out of that stroke. but that is partially offset by increase in heat rejection ie combustion chamber stays hot so little heat is transferred through block/head and is used to make power. however the incomplete combustion caused by the EGR is what really kills the power and economy. thats also why they need cats/dpf to clean it up.
once they get Nox filters sorted you will find EGR systems a thing of the past.

one thing i havn't tried, is just doing the butterfly mod. ie disable the egr butterfly only. this would reduce the amount of EGR rather than stop it all together and reduce power loss due to intake restriction.

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D22 ZD30 egr+butterfly mod, 2" lift extra leaf springs, enk-tek dump pipe, 2.5" exhaust.
single cab workhorse, to muddy to clean

The tip off for me though, assuming Shonky's quote to have come direct from a factory manual is that Nissan describe the swirl valve in terms of the low RPM performance benefit that dual tract systems are supposed to produce rather than an aid to EGR. They do not block off 50% of incoming air as such, they simply raise the gas velocity of what flows through the other tract for each cylinder. When gas velocity is becoming high enough to mean it is a restriction (With an essentially open inlet I would assume that would be at lower revs than an equivalent petrol engine) they open them up. A lot of the time the inlet lengths are different as well as long runners produce more torque at lower revs and shorter ones at higher revs. The manifold design does look to have different runner lengths for the two parts although it is not a major difference, but then the operating range for these engines is not exactly large. I would be perfectly prepared to accept on faith than Nissan have also used the swirl valve as an aid for EGR but I reckon the primary use would be as described by the book. My guess without seeing a drawing would be that the EGR is injected into the port that remains open in the EGR range so your recirculation is put into a higer velocity gas flow to promote better mixing of the recirculated exhaust gas with the normal combustion charge.


I am wondering how they manage EGR on the common rail engines actually. After a lot of browsing on Patrol forums (Considering one to replace my R51) the Patrol ZD30 and presumably the YD25 with the VNT hairdryer seem to be pushed up onto almost full boost in cruise conditions. I would think that would reduce the effectiveness of EGR as you have 15+ psi of boost to contend with. Unless of course the vane position to achieve that boost under cruise load produces high enough pressures in the exhaust manifold to promote EGR flow against the boost pressure.

Edited to add. Shonky posted that the swirl valve is closed until approx 1250rpm and you are talking about 3000rpm or so. I wonder if different parts of the book are listing different rpm as they are talking about different operating conditions and different functions (increasing low RPM torque versus increasing EGR operation) Going by what Shonky wrote I am a bit intrigued as about 1300 rpm is where mine lights up and starts to go properly. I am tempted to disable the swirl control valve to see if it pulls better from down low.


I stand by what I posted about compression ratios, NOX emissions are the biggest reason petrol engine CR dropped significantly for a lot of the time since emission controls were introduced. It is a quick and easy way to reduce NOX emissions, the higher the CR, the higher the combustion temp and the more NOX is produced. Diesels I would assume to be worse due to the open inlet as effective compression is a lot higher at cruise load with an open inlet than with a throttled off petrol engine. Ratios are on the rise again now, it just took the boffins 30 years or so to figure out how to produce low NOX emissions and retain high ratios. The assumption I am making is the diesel engines suffer from it as well. It is a pity the CR of the ZD30 is so much lower than the traditional old oilers, my biggest gripe against the Nav is lack of grunt from idle when off boost and trying to get my trailer moving. Uphill I wonder if the thing is going to move off or the clutch is gong to smoke first.


I suspect just doing the butterfly mod would have exactly the effect you are thinking. The loss of the partial vacuum under light load and moderate rpm should reduce EGR flow considerably.

Edited to add. Shonky posted that the swirl valve is closed until appros 1250rpm and you are talking about 3000rpm or so. I wonder if different parts of the book are listing different rpm as they are talking about different operating conditions and different functions (increasing low RPM torque versus increasing EGR operation) Going by what Shonky wrote I am a bit intrigued as about 1300 rpm is where mine lights up and starts to go properly. I am tempted to disable the swirl control valve to see if it pulls better from down low.

if the swirl was for "low RPM performance benefit" then older motors and common rail motors would all have it.

the manifold is two parts. 1st part has egr inlet on it. 2nd part has swirl valve on it to block it off. so at mid revs swirl valve is open so you (very crudly) have air+egr from 1st manifold and air from 2nd manifold. at low rpm (under 1300 rpm) the swirl valve closes so you have air+egr from 1st manifold, nothing from 2nd manifold. ie less air going in so overall its an increase in EGR.
the swirling effect of keeping the velocity high is a good side effect.
there is a mention i think in the BMW manual that swirl valve failure results in rough running but better volumetric efficiency.
i notice a slight gain in low rpm performance with swirl valve disabled.

don't forget the navara ZD30 is fairly under fueled in the low rpm. the patrol has much more low down power and guys that have chipped the navara have mentioned that it now performs like a real diesel ie decent low rpm grunt.

motors with VNT turbo's use the turbo to push more egr in. for eg they may be running 10psi boost but will have 15psi backpressure. its a better way of doing it than using butterflys in the intake to throttle the intake airflow.

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D22 ZD30 egr+butterfly mod, 2" lift extra leaf springs, enk-tek dump pipe, 2.5" exhaust.
single cab workhorse, to muddy to clean

I was actually surprised to see it on the ZD30. It first showed up in the mid 80's (about the first to use it were the original Toyota Corolla twin cams) and Nissan adopted it on the Japanese built RB engine series in about 86, but as I posted before, it disappeared again in about 89 never to be seen again. Most of the modern ones use something like the Falcon setup where instead of blocking off one valve there is a complete double inlet tract setup and valves to divert air through the longer one at low RPM to improve torque. Modern engines get much more benefit out of variable valve timing, and on twin cam engines they can even fiddle the exhaust valve timing to effectively produce EGR without all the plumbing problems.

Again, I am relying on what was posted up as coming from a ZD30 manual for what I am basing this on. Also again, having removed it completely from my Skyline I would have to say that as a performance enhancing thing at low RPM it was always a pretty minor benefit. If you need a dyno to detect the difference and it is almost impossible to feel it by the seat of the pants, what is the point?

If Nissan have also found that the setup can be used to improve EGR operation then at least someone has found something that valves blocking off one port at low RPM are actually useful for. At least it is simpler than what was on the Skyline, it had a set of shafts the full length of the head and six butterfly valves that individually shut off the secondary port, needlessly complicated.

1st off, nice to see some good quality discussion :)

As a diesel, I'd say that the egr actually decreases performance period. No throttle, no vacuum, all the engine really wants is as much fresh air as possible. Exhaust gas is only acting as an inert gas, replacing the fresh air, slowing the burning of diesel, subsequnetly reducing the temperature in the cylinder and intern reducing the velocity of the exhaust gas.

In a Turbo diesels case, its also decreasing the velocity of the exhaust gas running the turbo.

The Inert gas and reducing the turbos driving gases might have something to do with the boost threshold of the zd30's being quite high.

The theory suggests that closing the swirl vavle (ie incresing the velocity of the fresh air) will reduce the pressure at the opening of the egr intake port, essentially suck more egr through to the intake manifold.

Looking at the EGR in detail, all I can come up with its an Emissions control response from nissan to comply with the stricter emissions. I think, 'the additional performance' quote is BS. There is no way anything but more fresh air can help performance. Doesn't matter how that is come about, but all the exhaust gases do is fisplace the oxygen rich fresh air.

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2005 Blue/Silver STR Navara ZD30 w/
ARB Canopy, EGR plated, Boost + EGT Guages on A Pillar, AGM Dual Battery, Engel fridge on slide, Pioneer Head, Amp, 6.5" Splits and 6" rear speakers behind the factory Trim, 2" Efs lift, 2" Body Lift, 3" exhaust and 145L tank, Dtronic Chip & 285 Khumo KL71's

hi guys id like to do the mod but im concerned about the engine life! dose it shorten it? also after you do the mod do you have to do anything else to monitor the engine/mod? eg any gauges or anything else. is there any thing else i have to do or be concerned about?

Tommy, I am not talking about the swirl control valve from the EGR perspective at all, only from the perceived low rpm torqu improvement.

From that point of view they were a pretty minor benfit. More air as such is fine, but it is like the age old performance argument about large porting versus smaller. Big free flowing porting can produce high horsepower numbers but is invariably compromises low rpm torque and drivability as the gas velocity falls over. In theory at low RPM if you cut off one inlet valve from each cylinder where you have a foru valve per cylinder design you get higer gas flow rates at low rpm and better cylinder filling. Smaller ports and valves (Whcih is the effect of the swirl valve as a performance aid) actually DOES equate to more fresh air.

It may even be a benefit but with moedr deisel tuning to meet emissions meaning that they can not fuel it up to max power through the rev range it is probably a wasted effort.


All of that said, it is about time I got a ZD30 manual for myself, I do all my own servicing and my ute has enough kays on it that straight oil and filter, coolant and air cleaner element changes are not going to cut it for much longer.