Exhaust Options - 300 Tdi

[Jock The Rock]

Gday

After fitting this new turbo I want to fit a larger exhaust. The kit came with a 2.5" dump pipe (ends just near the bellhousing) and a 2.5" extension to connect up to the join below the transfer box (normal bends)

Originally I was going to go a 2.5" with straight through muffler. That was not mandrel bent. I was quoted $375 to finish off the exhaust in 2.5"

Now I've been thinking and talking to a few others, it seems 3" is a better option.

I went back to the exhaust place and was quoted $995 for a fully mandrel bent 3" system with straight through muffler; which will join onto the 2.5" dump pipe

What are your thoughts?

I've pretty much committed to the 3" system but I just thought I'd see what you all have to say

Thanks

[Bush65]

I cut the flange from the 2-1/2" dump pipe and welded it to modified a 3" mandrel bend when I did this in my rangie.

[triso]

Yeah the price sound about right, I got quoated a grand for 3" mandrel bent, have put a mid-muf replacement on in the mean time.

[Jock The Rock]

Thanks for the replies

Seems as though I'm heading the right way

[C H T]

Just a quick note - don't be tempted to for too large an exhaust - if the diameter is too large for the engine total gas velocity will be reduced and therefore negatively affect engine performance. i have been advised that optimum for a 300Tdi is 2.5 inch mandrel bent. (if you use an exhaust with ordinary bends that crimp the pipe you might want to try 2.75 inch diameter pipe. When Beaudesert exhaust built the system on my 3.9 Isuzu turbo Defender they specified 2.75 inch, which has worked brilliantly. (Beaudesert explained that if the pipe is too big for the engine the effect is akin to passing the gas through a 44 gallon drum gas in = gas out but without any scavenge effect and at recduced velocity)

C H T

[dullbird]

I was told that you cant over exhaust a tdi.....

[spudboy]

Hi Jock - do a search here on some old posts by Tombie2 as he had definite thoughts that 2.5 was far preferable to 3" for some reason. He does a lot of stuff tuning TD5s, so maybe not applicable to a 300TDi, but worth a search.

HTH
David

[goldrover]

I have a mandrel bent 2.5 on my 300 with just a rear straight thru very small oval muffler & no centre muffler. This complements a vvt with a larger intercooler & tweaked pump. I am very happy with the low down pull which is what I was aiming for. Punts the 35's very nicely.:D I was advised not to go too big with the exhaust, something to do with gas velocity.

cheers
Philip

[saiken]

I'd recommend sticking with a 2.5" exhaust system as you don't want to go any bigger than 10% over the size of the turbo outlet.
By using a larger pipe diameter you reduce the velocity of the exhaust gases and can increase the retained heat at the turbo and detrimentally effect the turbo and manifold. This can also reduce the back pressure on the turbo enough to cause turbo overspeed which will decrease the lifespan of the turbo greatly.

**please excuse any bad english or spelling as i've been drinking to celebrate the best day of the year!!!! [australia day]**

[C H T]

Just a quick note - don't be tempted to for too large an exhaust - if the diameter is too large for the engine total gas velocity will be reduced and therefore negatively affect engine performance. i have been advised that optimum for a 300Tdi is 2.5 inch mandrel bent. (if you use an exhaust with ordinary bends that crimp the pipe you might want to try 2.75 inch diameter pipe. When Beaudesert exhaust built the system on my 3.9 Isuzu turbo Defender they specified 2.75 inch, which has worked brilliantly. (Beaudesert explained that if the pipe is too big for the engine the effect is akin to passing the gas through a 44 gallon drum gas in = gas out but without any scavenge effect and at recduced velocity)

C H T

Further to what I said above - and confirming what has been said in couple of later posts in this thread - it is important not to go too large in exhaust diameter. I recall talkig to someone some years ago (I think form Beaudesert Exhausts) that had done some serious investigation into 300Tdi exhaust diameters - they found that with a 3 inch exhaust the engine produced less torque than it did with the standard exhaust, and that, as far as I can recall, the best results were obtained with a 2.5 inch free flowing system

C H T

[Bush65]

I wouldn't hesitate to use a 3" exhaust on a 300Tdi. If I could fit a 4" (which I can't) I would use 4" from the turbo on my Isuzu, but it flows a lot more air than a 300Tdi.

I have never seen a reputable explanation for better performance from increased back pressure in the exhaust system of a turbo diesel engine. Only on internet discussions like this.

I stand to be corrected, but I can not recall reading such in any of the books I have and I trust the authors far more than 2nd or 3rd hand reports from the likes of someone working for and exhaust place.

It may well be that the average 300Tdi owner will not notice much difference between a 2-1/2" and 3" system on an otherwise stock engine.

But the original poster has fitted a larger turbo that flows much more than stock. IMHO he will see the benefit from a 3" system.

[marko66]

Hi All

Gale Banks says that for power a turbo motor should have a 20 degree ever increasing cone and thats from hundreds of hours of dyno testing.

Personally I believe that mufflers on diesels are exhaust brakes and havent seen an exhaust upgrade in size that wasn't beneficial to some varying degree.

The turbo is a very expensive muffler and usually all that most vehicles need :Dunless you do deep water crossings and would like to slow water from entering the turbo via the exhaust:eek:

If fitting bigger turbo and exhaust then it might be a good idea to get the injection pump tuned to the new mechanicals as it may be possible to lean the motor out.

Regards Mark

[Jock The Rock]

I ended up fitting the 3", it seems to have opened it right up

I can now hit 100 in 4th if need be :twisted: and it's not overly loud with the muffler on

Although when the turbo loads up is does get a noisy

[rovercare]

Hi All

Gale Banks says that for power a turbo motor should have a 20 degree ever increasing cone and thats from hundreds of hours of dyno testing.

Personally I believe that mufflers on diesels are exhaust brakes and havent seen an exhaust upgrade in size that wasn't beneficial to some varying degree.

The turbo is a very expensive muffler and usually all that most vehicles need :Dunless you do deep water crossings and would like to slow water from entering the turbo via the exhaust:eek:

If fitting bigger turbo and exhaust then it might be a good idea to get the injection pump tuned to the new mechanicals as it may be possible to lean the motor out.

Regards Mark

All that EXCEPT, you don;t lean out a diesel.......unless your talking about depriving it of oxygen( lean of air:p) by adding to much fuel and melting the pistons;)

[Bush65]

I'm guessing Mark has fallen into the common trap of assuming issues with petrol engines might apply to diesel engines.

Your diesel engine will love you more, the leaner you run it.

[rovercare]

I'm guessing Mark has fallen into the common trap of assuming issues with petrol engines might apply to diesel engines.

Your diesel engine will love you more, the leaner you run it.

Yep, very common misconception, with those that haven't been around desiesal engines:D

[Bush65]

Hi All

Gale Banks says that for power a turbo motor should have a 20 degree ever increasing cone and thats from hundreds of hours of dyno testing.

...
A turbo needs a diffuser immediately after the turbine exducer (where the gas exits from the impeller). A 20 degree included angle cone makes for an excellent diffuser, particularly with axial flow turbines, fans and compressor.

The turbines used with small turbos are radial inflow - a type for which has received virtually no treatment in classical or any other texts on the subject of turbines etc.

The turbine on Jock's new turbo has an exducer diameter of approximately 44mm. The diffuser in his turbine housing is not conical, but rather more complex, which makes me believe that Garrett have carried out comprehensive computer modelling using computational fluid dynamics (CFD) software to arrive at the shapes used (mad if they didn't, if they want to stay competitive).

One million hours of dyno testing will not reveal the complex behaviour that good computational fluid dynamics modelling will show.

The exit of this diffuser where the dump pipe connects is 70mm inside diameter (for everyone claiming the exhaust shouldn't be greater than 2-1/2", should know that 2-1/2" is 63.5mm).

[PAT303]

This exhaust was with the VNT fitted?.I think most people though it was with the OME model. Pat

[Jock The Rock]

Yes that is with the VNT fitted

[marko66]

Hi All

Rovercare asked me to post again so I will:D

Rovercare said you don't lean out a diesel but you can over fuel it.:eek:
Bush 65 said that your diesel engine will love more the leaner you run it:eek:

I will agree that for small simple upgrades the chances are that the original fuel parameters and boost compensator will cope - probably wont be ideal but will cope.

So if you can't lean out a diesel we get a diesel engine say a 300 tdi and compound boost it to 65psi and leave the pump standard and while money is no object and flights of fantasy are catered for we make a new dual 3 inch intake manifold:D and dual four inch exhaust and because you cant lean out a diesel all cylinder head temps and exhaust gas temps will be perfect:D:D I believe not.:o

Regards Mark

[slug_burner]

Hi All

Rovercare asked me to post again so I will:D

Rovercare said you don't lean out a diesel but you can over fuel it.:eek:
Bush 65 said that your diesel engine will love more the leaner you run it:eek:

I will agree that for small simple upgrades the chances are that the original fuel parameters and boost compensator will cope - probably wont be ideal but will cope.

So if you can't lean out a diesel we get a diesel engine say a 300 tdi and compound boost it to 65psi and leave the pump standard and while money is no object and flights of fantasy are catered for we make a new dual 3 inch intake manifold:D and dual four inch exhaust and because you cant lean out a diesel all cylinder head temps and exhaust gas temps will be perfect:D:D I believe not.:o

Regards Mark

I don't belive adding fuel to it under these conditions will bring the temps down either

[rovercare]

Hi All

Rovercare asked me to post again so I will:D

Rovercare said you don't lean out a diesel but you can over fuel it.:eek:
Bush 65 said that your diesel engine will love more the leaner you run it:eek:

I will agree that for small simple upgrades the chances are that the original fuel parameters and boost compensator will cope - probably wont be ideal but will cope.

So if you can't lean out a diesel we get a diesel engine say a 300 tdi and compound boost it to 65psi and leave the pump standard and while money is no object and flights of fantasy are catered for we make a new dual 3 inch intake manifold:D and dual four inch exhaust and because you cant lean out a diesel all cylinder head temps and exhaust gas temps will be perfect:D:D I believe not.:o

Regards Mark

Via PM



Hi Rovercare:D

Didn't want to rebutt you publicly and i agree that overfueling will do all the things that you said and would also say that people not checking their injectors is one of the biggest problems.

But the way that your post could be construed is that someone could seriously boost a non turbo motor or seriously uprate the power of an already turbo motor and no tuning is required? :D

Regards Mark

But putting forward your rebuttle on there is what a public forum is all about:)

Correct, they can, all that is required is an Exhaust gas temperature gauge and some common sense, followed closely by a boost gauge helps along way:D, worlds apart from a petrol engine;)

The fact is, the temps will likely be cooler as you'll be forcing more air in, without any extra fuel to burn, how does a fire work without fuel? can;t get more heat without more fuel..............Oh, how do you propose to obtain 65psi, from the standard pump settings?, impossible

[justinc]

Ditto, no fuel, no boost.

Keeping the EGT's at an acceptable level is the most important thing, and this is infinitely variable due to the complete engine package you are working with IE some engines are more efficient than others in their initial design, these will make for good upgrades BUT they may not have the % gains of say a less efficient standard engine brought up to a decent output.

Leaning out a diesel engine will just cause it to run cooler,(Good for it) and use less fuel(Good for you) but it'll be a LOT slower on hills.

JC

[Bush65]

...

If fitting bigger turbo and exhaust then it might be a good idea to get the injection pump tuned to the new mechanicals as it may be possible to lean the motor out.

Regards Mark
Mark, your earlier post (above quote) reads to me as though you are advising Jock to have the IP tuned on the basis that by fitting a larger turbo and exhaust system that he is in danger of the air/fuel ratio becoming lean.

I responded with a post, close enough (but exactly) to what you quoted in your 2nd post (quoted below).

To explain my post:
Many people make similar remarks/warnings about lean air/fuel ratio with diesels. This comes from a misconception from trying to apply petrol engine experience to diesel engines.

A petrol engine must have air and fuel very close to the stoichiometric ratio to run, and can be damaged if too lean. the stoichiometric ratio is approximately 14.7: air to fuel (the figure after the decimal mark may be slightly out - just my memory).

With a petrol engine, the accelerator pedal operates a throttle that increases or reduces the amount of air that the engine can get (to go faster or slower). The carburation or fuel injection system then closely meter the fuel to maintain the acceptable air/fuel ratio.

A diesel engine however runs much leaner than than stoichiometric ratio. The air fuel ratio that causes black smoke (incomplete combustion) is approximately 18:1 (air to fuel), and it is best that it be not less than 20 or 22:1. This is at full load, when maximum fuel is injected.

A diesel engine does not have a throttle - except newer computer controlled diesels which can have a throttle, which is part of the emissions control/egr system. Effectively it is as though the engine always has a wide open throttle - no different at idle through to maximum speed and load.

The accelerator pedal controls, via the governor, the amount of fuel injected by the fuel injection pump (or injection system). When the pedal is depressed more fuel will be injected to make more power. The older mechanical fuel injection pump doesn't know how much air the engine is getting.

At idle, the air/fuel ratio is very high - it can exceed 120:1

The higher the air/fuel ratio, lean the motor out (to use your expression), the cooler the exhaust gas temperature will be. When the ratio gets closer to the smoke ratio (18:1) the exhaust gas temperature starts to get high, very quickly. A diesel engine can not endure exhaust gas temperature anywhere near as high as a petrol engine.

The excess air from higher air/fuel ratios, also removes a considerable amount of heat from the engine.

If a diesel is working hard and blowing black smoke for much time, it can be close to the limits of the materials used in the pistons and turbine. Changing to a lower gear will quickly bring the exhaust gas temperatures down, because the engine will get more air, due to higher rpm, but at the same time the injection system will reduce the amount of fuel injected, because the governor will sense the reduction in load - in other words, lean the motor out (your expression).


Hi All

Rovercare asked me to post again so I will:D

Rovercare said you don't lean out a diesel but you can over fuel it.:eek:
Bush 65 said that your diesel engine will love more the leaner you run it:eek:

I will agree that for small simple upgrades the chances are that the original fuel parameters and boost compensator will cope - probably wont be ideal but will cope.

So if you can't lean out a diesel we get a diesel engine say a 300 tdi and compound boost it to 65psi and leave the pump standard and while money is no object and flights of fantasy are catered for we make a new dual 3 inch intake manifold:D and dual four inch exhaust and because you cant lean out a diesel all cylinder head temps and exhaust gas temps will be perfect:D:D I believe not.:o

Regards Mark
There is no doubt whatsoever that the original fuel parameters and boost compensator will cope.

A diesel engine does not require a boost compensator on the fuel injection pump. The boost compensator is there for emission reasons.

The function of the boost compensator is to reduce the amount of fuel that is injected if the boost pressure is low. If the boost pressure is low, the engine will not be getting as much air flow and the boost compensator will then reduce the amount of fuel (to lean the motor out) reducing emission of particulate matter (black smoke).

The higher the boost pressure providing the compressor (or compressors) are operating at a reasonable efficiency value, the more air that is provided to the engine and the lower the exhaust gas temperature.

Unnecessarily high boost pressure is a waste of energy. The engine pumping losses increase, and the engine will be operating away from peak efficiency. The engine efficiency increases with temperature and similarly for the turbo with exhaust gas temperature. These temps need to be high, but not exceed safe limits for the component materials.

The necessity to meet reduced emissions requires improvements in efficiencies. The latest crop of diesel engines are using staged (compound) turbos for increased boost pressure. Turbo manufactures are using better materials and investing in research to allow the turbo to operate with higher exhaust gas temperatures.

[isuzurover]

Just a quick note - don't be tempted to for too large an exhaust - if the diameter is too large for the engine total gas velocity will be reduced and therefore negatively affect engine performance. i have been advised that optimum for a 300Tdi is 2.5 inch mandrel bent. (if you use an exhaust with ordinary bends that crimp the pipe you might want to try 2.75 inch diameter pipe. When Beaudesert exhaust built the system on my 3.9 Isuzu turbo Defender they specified 2.75 inch, which has worked brilliantly. (Beaudesert explained that if the pipe is too big for the engine the effect is akin to passing the gas through a 44 gallon drum gas in = gas out but without any scavenge effect and at recduced velocity)

C H T

There is no such thing as a "scavenge" effect on a turbo diesel. I think too many exhaust manufacturers and tuners come from a petrol background and think the same principles apply. (however - as an aside - have a look at the exhaust size on a 2.0L turbo WRC car...)

I agree with John's(Bush65) posts above that bigger is better wrt turbo diesel exhausts. Ignoring legalities, just the dump pipe alone and no exhaust would be optimal in terms of maximising engine output. Like this:
http://images.dieselpowermag.com/events/0709dp_09_z+bentz_racing_team_7_second_diesel_drag ster+p_pump.jpg
https://www.aulro.com/afvb/images/imported/2010/02/1597.jpg

[PAT303]

At the same time outright power isn't what we need on a road vehicle,if you had that drag car engine in a road car it would be undriveable,imagine trying to park.There isn't a right and wrong with road cars as they must be useable under all conditions so the exhaust that gives the best off-idle and midrange is the best pick.On a few of the brit sites they go with the 2 1/2'' mandrel on a stock Tdi but Jocks has a VNT with bigger outlet so needs a bigger pipe to suit. Pat

[isuzurover]

At the same time outright power isn't what we need on a road vehicle,if you had that drag car engine in a road car it would be undriveable,imagine trying to park.There isn't a right and wrong with road cars as they must be useable under all conditions so the exhaust that gives the best off-idle and midrange is the best pick.On a few of the brit sites they go with the 2 1/2'' mandrel on a stock Tdi but Jocks has a VNT with bigger outlet so needs a bigger pipe to suit. Pat

Where is the evidence that exhaust size has any affect on low speed driveability??? I think you are also confusing petrol engines with diesels.

I am sure that the difference between a 2" and a 3" exhaust would make no noticeable in low speed driveability.

When I drove my 110 to the exhaust shop with no dump pipe or exhaust connected to the turbo it was perfectly driveable across the whole rev range.

[PAT303]

Yeh the exhaust is just for decoration,it doesn't do anything usefull like having a bearing on engine performance. Pat

[Fusion]

I have a straight through system on my 300tdi . No mufflers at all ! bit noisy but spools up quicker :twisted:

[weeds]

can they do normal bends on 3" pipe? thats what i would go with

i have a normal bend 2.5" no mufflers on the defender, normal bends are way cheaper than mandrel.......under $200 fitted, with flex pipe and they bolted up my pto shaft

didn't notice and power increase but the turbo does spool up quicker, apparently it has a nice note

[rick130]

Yeh the exhaust is just for decoration,it doesn't do anything usefull like having a bearing on engine performance. Pat

I wasn't going to comment on this thread, most everything that needed saying had been said, oh well.......

Hi Pat, all that Ben, John etc. are saying is that you can't oversize a turbo diesel exhaust.

A 3" system has no negative impact on the torque curve of a Tdi engine but it does allow the turbo to spool more quickly.
Building my 3" system enhanced the bottom end, off idle pull away was much improved.

The major downside IMO is the noise factor. You do need a good muffler and resonator, anyone that says a Tdi doesn't need a muffler on a 3" pipe has never heard one uncorked or is stone motherless deaf :p
I doubt a smaller system would have this issue, if my experience dyno testing naturally aspirated merge collector/dumps is anything to go by.

Would a 2.75" system work as well on a Tdi ?
Sure, but the tubing is much more expensive and harder to find.

How about a 2.5" ?
Probably little difference, except maybe in a longer 130 system and at high revs.
The 3" pipe allowed about 15km/h higher speeds in third and fourth gear over the OE (2,3/8", 60mm ) system, so you can conclude that the OE 130 system, even with an OE straight through muffler was restricted.

Someone earlier on in this thread alluded to a bigger pipe potentially overheating the exhaust manifold and turbine housing.
For the record, my EGT dropped well over 20*C, probably closer to a consistent 25*C at the same ambient, same pump and timing settings (all stock) on my 2.5km long, 200m gain test hill.

IIRC I used a 15* wall/30* included angle diffuser from the dump to the 3" exhaust, and throated the dump to suit the ID of the 2.5" pipe I swaged up to 3".
The 15* angle is an arbitrary one I use as one of my reference books from years ago mentioned that anything over about 15* taper induces flow separation in a duct and therefore turbulence.

[PAT303]

Trouble is Rick that I think half the posters thought Jock was fitting an exhaust to the OME garrett,thats where the 2.5'' size has come from but the VNT has a 3'' outlet so we weren't all on the same page. Pat

[isuzurover]

The 15* angle is an arbitrary one I use as one of my reference books from years ago mentioned that anything over about 15* taper induces flow separation in a duct and therefore turbulence.

Exhaust flow (and intake flow) is almost always completely turbulent. A very rough calculation gives an Re of ~90000 for a Tdi at 2000 rpm with a 3" exhaust and 500oC egts. That is above the limit for laminar flow even with the smoothest possible transitions and a laminarisation screen at the inlet (which a turbo is not).


Yeh the exhaust is just for decoration,it doesn't do anything usefull like having a bearing on engine performance. Pat

Not at all. On a Turbo diesel engine, an exhaust serves the purpose of controlling noise and directing the exhaust gases behind the vehicle. The manufacturer sizes the exhaust so it will give acceptable flow restriction within cost (and mass) constraints.

[rick130]

Exhaust flow (and intake flow) is almost always completely turbulent. A very rough calculation gives an Re of ~90000 for a Tdi at 2000 rpm with a 3" exhaust and 500oC egts. That is above the limit for laminar flow even with the smoothest possible transitions and a laminarisation screen at the inlet (which a turbo is not).



<snip>

So I haven't gained, but haven't lost anything ;)
It looks nice though, and the blokes in the workshop I used were intrigued when I was turning up the flaring mandrel and flared the 2.5" tube. :D

[isuzurover]

So I haven't gained, but haven't lost anything ;)


Smooth transitions are always good.