Dump pipe/Cat D40 restriction.

Chris C · Aug 31, 2011

D40 2011 dump pipe/ cat unit

http://www.use.com/6d6dd98b110420de9ad1?p=1]http://media.use.com/images

Above are some images taken of the Cat/dump pipe from my 2011 D40.

The outlet of the turbo is 2-1/16", the flange as you can see matches, but within 5 mm of entering the pipe, the pipe is down to under 45 dia, then there is the bellows section, then into an elbow, again just on 46mm OD, then into the cat, and out at the 2.25" od.

Very restrictive, even with a super high flow cat, or no cat, the elbow would be a major restriction, a 2.5" dump, with nice smooth bends would be the shot, a 3" would not hurt either.

I have seen several "cat back" exhausts , which leave the factory cat in place, these would serve no purpose other than to lighten your wallet.

There are 2.5" dump pipes on Ebay, anyone know if the bolt up to the stock system?

Bosshog · Sep 5, 2011

Chris C said:
I have seen several "cat back" exhausts , which leave the factory cat in place, these would serve no purpose other than to lighten your wallet.

While not applicable to your D40, earlier models with a DPF fitted have issues with the ECU injecting diesel on the exhaust stroke to condition the factory cat. The ECU does not get the required reading from the O2 sensor with a custom dump pipe and cat. Therefore a cat back replacement is the preferred solution.

DieselTuner2 · Sep 5, 2011

Chris C said:
D40 2011 dump pipe/ cat unit

]Navara D40 dump pipe photo, picture, image on Use.comhttp://media.use.com/images

Above are some images taken of the Cat/dump pipe from my 2011 D40.

The outlet of the turbo is 2-1/16", the flange as you can see matches, but within 5 mm of entering the pipe, the pipe is down to under 45 dia, then there is the bellows section, then into an elbow, again just on 46mm OD, then into the cat, and out at the 2.25" od.

Very restrictive, even with a super high flow cat, or no cat, the elbow would be a major restriction, a 2.5" dump, with nice smooth bends would be the shot, a 3" would not hurt either.

I have seen several "cat back" exhausts , which leave the factory cat in place, these would serve no purpose other than to lighten your wallet.

There are 2.5" dump pipes on Ebay, anyone know if the bolt up to the stock system?[/QUOTE]

I have done quite extensive testing on this and found the difference to be negligible.

Only .1psi backpressure difference at the turbine outlet with a full 3" dump over standard.
No more than 2kw gain anywhere in the rev range.

For this reason alone I normally recommend a 2.5" cat back system, but also do a turbo back system if someone really wants their wallet thinned out because their mates told them it was necessary.

As with anything related to engines, dyno testing is a must and this is exactly what most people selling exhausts dont have.

Chris C · Sep 6, 2011

Northside 4x4 said:
I have done quite extensive testing on this and found the difference to be negligible.

Only .1psi backpressure difference at the turbine outlet with a full 3" dump over standard.
No more than 2kw gain anywhere in the rev range.

For this reason alone I normally recommend a 2.5" cat back system, but also do a turbo back system if someone really wants their wallet thinned out because their mates told them it was necessary.

As with anything related to engines, dyno testing is a must and this is exactly what most people selling exhausts dont have.

Thanks for the input, I would like to ask a few questions if I can.

You said there is only 0.1psi difference between factory dump/cat to a full 3".

When you say Turbine outlet, I take it you mean as close as practical to the outlet flange on the turbo? Is this right?

Was that with a full factory system, from turbo to tail pipe? Or on a 2.5" cat back on the factory dump/cat pipe?

The "full 3" dump" used, was it a Mandrel bent system?
Did it have a Cat? If so was it a good quality high flow, or an Ebay chinese POS?

When you did the tests was it on a stock car, or a "chipped" car?

What effect did the 3" system or 2.5" cat back have on EGT?

When you take EGT reading, are they before or after the turbo?

Could you get more power/torque from a chipped car with a modified exhaust with safe EGT over a stock exhaust?

I am not doubting your findings, I appreciate you taking the time to post, I am also not trying to re-invent the wheel, I am just trying to work out where, if anywhere, there is a restriction worth removing from the factory exhaust. My car is a manual, so it has no DPF, my primary concern is keeping EGT's in check, and after looking at the factory Dump/cat pipe, it may not be too much of a restriction at stock power levels, I just cant see how it could keep up with a modified car.

Have you done any tests between full stock exhaust and 2.5" cat back? What was the difference in EGT and back pressure?
If the factory system is more restrictive than the cat/dump pipe, it must be a truly terrible set up. I would be interested to see back to back runs with full stock system and then remove the muffler, (my car only has the rear), my car sounds like a dyson when idleing, no noise at all, just a dull muffled strain.

I don’t mind spending money on my cars, in fact I like to, but I don’t like wasting it, so if a 2.5" cat back will do all I ever need, great, but if I can fit a dump pipe and drop EGT by a hypothetical 10% and keep the same power level or even higher then I would do it. Do it once, do it right is how I like to run.

Again, I appreciate you taking time to respond, I have ZERO experience with the D40, but a reasonable amount of time modifying other high power turbo cars and from my time playing most turbo powered engines they all respond to the same thing, get more COOL air in, get it out as fast as you can, it never hurts.

Old.Tony · Sep 6, 2011

I'm looking at page 178/290 of EM.PDF (from the D40 manual) and can't help but think that the primary restriction in the entire exhaust is the join between the exhaust manifold and turbocharger. That opening, and the turbine just downstream of it, is where most of the heat will be created. Without changing the exhaust manifold and turbo, that's the puppy that will slow down the gases the most.

Remembering back to my fluid dynamics lessons (now the early 80s were quite some time ago, and things might have changed), the pressure - and therefore the heat - at that point will increase dramatically, and as the gases pass through the turbine and expend energy on the turbine, the temperature will drop because of the expended energy AND because once the gas is past the turbine, the temperature will drop because of the allowed expansion of the gas.

Things should heat up again in the DPF and in the CAT as both of these are restrictive, of course, but the effect of these on the engine's output and thermal activity should be nearly zero (not zero, because of the increase in pressure upstream due to the downstream restriction) given the direction of flow and distance.

This "nearly zero" would be the 1-2% that Northside keeps talking about as the only improvement gained by a larger exhaust.

A bigger improvement would be obtained by removing the restriction at the exhaust manifold/turbocharger junction by, say, using headers and twin (stock) turbos, halving the restriction across the 4 exhaust ports. You could go up in exhaust manifold outlet and turbocharger size - although you'd do that at the cost of increasing turbo lag, so in order to reduce that, you'd have to build in a waste gate, blow-off valves and by the time you're finished, you'd have a Subaru Impreza. With lower EGTs and much, much more boost. Could the intercooler handle that? Who wants to find out?

Bluenavara · Sep 6, 2011

Thought I could support Tony's post by putting in some pics of the stock manifold. Run of the mill logstyle, minimum volume manifold. They give decent response but aren't ideal for the flow in the upper half of the rpm band (though some might say that isn't required on a diesel truck).

My new one looks like this:

And the turbo that goes with that looks like this:

Bluenavara · Sep 6, 2011

Chris C · Sep 6, 2011

Blue Navara,

Nice work on the manifold, looks very neat, they realy do wake the engines up, the BA-BF-FG 4lt falcons really respond well to a nice matched lenght pipe manifold.

I doubt I would ever go that far on my work truck, but nice to see others doing it just the same.

I am going to have a play over the next few weeks, I will build a 2.5" dump to match to the stock system, and a little drop pipe to come off it, so I can back to back them. then put the stock cat back on and check it.

Also keen to see how the stock inlet piping runs, it looks a bit yucky, I think a neat stainless or alloy replacement would be worth the effort too.

I have a dyno I can get on to use, so I will keep details of all runs etc.

DieselTuner2 · Sep 6, 2011

Chris C said:
Thanks for the input, I would like to ask a few questions if I can.

You said there is only 0.1psi difference between factory dump/cat to a full 3".

When you say Turbine outlet, I take it you mean as close as practical to the outlet flange on the turbo? Is this right?

Was that with a full factory system, from turbo to tail pipe? Or on a 2.5" cat back on the factory dump/cat pipe?

The "full 3" dump" used, was it a Mandrel bent system?
Did it have a Cat? If so was it a good quality high flow, or an Ebay chinese POS?

When you did the tests was it on a stock car, or a "chipped" car?

What effect did the 3" system or 2.5" cat back have on EGT?

When you take EGT reading, are they before or after the turbo?

Could you get more power/torque from a chipped car with a modified exhaust with safe EGT over a stock exhaust?

I am not doubting your findings, I appreciate you taking the time to post, I am also not trying to re-invent the wheel, I am just trying to work out where, if anywhere, there is a restriction worth removing from the factory exhaust. My car is a manual, so it has no DPF, my primary concern is keeping EGT's in check, and after looking at the factory Dump/cat pipe, it may not be too much of a restriction at stock power levels, I just cant see how it could keep up with a modified car.

Have you done any tests between full stock exhaust and 2.5" cat back? What was the difference in EGT and back pressure?
If the factory system is more restrictive than the cat/dump pipe, it must be a truly terrible set up. I would be interested to see back to back runs with full stock system and then remove the muffler, (my car only has the rear), my car sounds like a dyson when idleing, no noise at all, just a dull muffled strain.

I don’t mind spending money on my cars, in fact I like to, but I don’t like wasting it, so if a 2.5" cat back will do all I ever need, great, but if I can fit a dump pipe and drop EGT by a hypothetical 10% and keep the same power level or even higher then I would do it. Do it once, do it right is how I like to run.

Again, I appreciate you taking time to respond, I have ZERO experience with the D40, but a reasonable amount of time modifying other high power turbo cars and from my time playing most turbo powered engines they all respond to the same thing, get more COOL air in, get it out as fast as you can, it never hurts.

Sorry I should have posted a bit clearer on the testing we done, but I was in a bit of a rush last night.

We have tried stock >CB2.5" | stock > CB3"| CB2.5" > CB3" >
CB2.5" > Full 2.5" No cat & with cat.
CB2.5" > Full 3" No cat and with cat.
I have posted some of the dyno results up on the forum in the past but I have no idea where they are now.

The cats used were high quality 200cel diesel cats, tried also 400cel cats for reduced emissions but they do offer considerably more restriction.

The main difference we found was going from stock to 2.5" cat back.
All other results from there on were greatly diminished/marginal.

As for the EGT drops, they were measured at the turbine outlet. Although the full system did drop the egt further than a cat back, it was actually by a very small amount (5-10deg at the highest point)

The funny thing was though, the egt actually increased at a faster rate with the 3" system over a 2.5", but did level off and run a touch cooler once it got close to its maximum temp.

Chris C · Sep 7, 2011

Thanks again Northside, its info like this that stop us from pissing away $$$ when not required.

I hould love to have a play with an aftermarket manifold and upgraded turbo, just for fun, but given that this is my "work Truck" and will do 1000km per week, I dont have the time to take it off the road for long enough to do.

I will however look inot intercoolers and plumbing, if its anythin like the Falcon, there will be built in restrictions to slow it all down a little, the BA BF series falcon has a pretty decent set up for the cooler piping, right until a little cast alloy section on the return run to the plenum from the cooler, it is 2.5" id in and out, looks good, but under the battery, where you cant see, the pipe is closed up in size to under 25mm wide by 40mm high inside dims, yes, they make it go from 2.5"od round to smaller than a box of matches, and hide it under the battery, this pipe alone (on a car with a "chip") can be worth over 20rwkw and allows for instant boost.

If Nissan are like all the other manufacturers there will be similar "restrictions" hiding in the Navara.

Unsure what to do with exhaust, need to drill and tap manifold for EGT probe first, then go from there.

Thanks again for the info, I will keep you posted.

Bluenavara · Sep 7, 2011

A cheap and easy $15 mod to free up IC flow is to remove the plastic hotside IC pipe baffle, in which flow diameter necks down to about 1.75":

After that, i'd go with replacing the rubber piping "balloons" with some hard piping, and step 3 would be a bigger intercooler.

Old.Tony · Sep 7, 2011

I'm not sure that removing that baffle will have the desired effect, but it will do something - perhaps just not what is immediately obvious.

Because the air behind the restriction is under pressure, the restriction serves merely to accelerate the velocity of the air at that point. The change requires some energy input, which will equate to extra strain on the turbocharger. Removing the baffle SHOULD (if the fluid dynamics lecturers are right) result in the temperature at the turbocharger's turbine changing a few degrees. It should also reduce turbo lag a little but this should be next-to-indistinguishable. You would probably measure the EGT difference at a couple of degrees and put it down to environmental factors.

As for what that piece is, functionally - the manual doesn't even describe it. The components list on page 162 of EM.PDF clearly shows it, but doesn't give it a number or a description. If there are no sensors internally (eg flow) then removal won't cause problems with the engine management and the only thing you'd need to do is find an alternative method of supporting the hose up there.

Bluenavara · Sep 7, 2011

I agree the performance gain is not quite mind boggling, but neither is the effort to remove it. It has no sensors. Best to remove it while switching to hard piping. There's another intake sound baffle in the Spanish built airbox suction tube, that's easy enough to remove:

Removing both sound reducing intake baffles may well produce a nice little increase in response.

Chris C · Sep 7, 2011

Bluenavara said:
A cheap and easy $15 mod to free up IC flow is to remove the plastic hotside IC pipe baffle, in which flow diameter necks down to about 1.75":

After that, i'd go with replacing the rubber piping "balloons" with some hard piping, and step 3 would be a bigger intercooler.

I had a look at the Blue pipe on the hot side, very soft and flexable, I would like to see it with 20psi up its guts, may even do that just for kicks.

An alloy replacment would be easy, mock it up then have it tigged.

Do you know how big the cooler can be to fit in there without chopping into body work too much?

Bluenavara · Sep 7, 2011

Chris C said:
Do you know how big the cooler can be to fit in there without chopping into body work too much?

Have a look at the thread in my sig (so as not to drift too far off in this thread).
Zero bodywork mods.
EDITED TO ADD: And the shortest, straightest IC piping possible.

streaker · Sep 9, 2011

Northside.
got a simple question
wich would be the best exhaust upgrde for the d40 diesel? If there is one?

We appreciate your work knowlage and infomation on this site, keep the good work up buddy

DieselTuner2 · Sep 9, 2011

A simple 2.5" cat back systems will be the best for about 80% off cars out there.

a full 2.5" or even 3" system if your shooting for over the top power like Bluenav.

But up to around 130rwkw is easily achieveable out of a 2.5" cat back system.

Dump pipe/Cat D40 restriction.

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