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Old May 12th, 2006, 12:57 PM
artm
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going to 3" or 4" exhaust

So, now that my stock exhaust on the Tdi is cracked right after the middle muffler it's time to change out the whole thing (with the cat).

Is 3" the way to go or more? I do plan on turning up the fuel.

Do I start the 3" at the manifold or after the downpipe?

I assume you keep the flex pipe?

Plan is to include a muffler in the middle and see if this is quiet enough. The truck is a people mover so not looking for grunt or "performance" sound.
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Old May 12th, 2006, 02:56 PM
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May not gain you much at all, and it may even cause a drop in power if you go too big. If your exhaust is too big, it won't scavange very well and the flow will be uneven. The engine just doesn't have enough displacement to justify more than a 3" exhaust. Most diesels you see with the 4" tubes are usually 7 liters or more with turbos, which push a LOT more air than the TDI will ever see.

-Hans
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Old May 12th, 2006, 03:08 PM
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Hans - do you feel that the scavenging effect applies also to a turbo diesel? I've been told that the objective with a diesel is obtain zero backpressure (which is why some people don't run a muffler). So theoretically you couldn't go too large. Having said that, I have a 3" exhaust with my 6.5 diesel, and the measured backpressure was quite low (" of H20). So yeah, I would expect the 3" would be more than adequate on a 300 Tdi. 4" would most likely be a waste of money, and probably very difficult to fit (it wasn't easy running the 3").
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Old May 12th, 2006, 04:25 PM
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Scavenging: I thought this is more an issue in high-performance engines or at higher rpm? I doubt LR designed this motor to benefit from scavenging effects.

Zero back pressure is ideal but not practical - unless you can run a 3" system with low noise. I'll be pleased to get the cat out of there and hopefully the rear muffler.

So, what about the other two questions?

Follow-up Post:

Found this really informative site on exhaust design:

http://superchevy.com/technical/engi...t/0505phr_exh/


Determining pipe size and muffler FLOW rate is the key to an efficient system. Assuming a tuned-up rating of 130HP, a flow rate of 2.2x130 = 286 cfm is needed from the muffler to allow for a 1% power loss through back-pressure.

As to pipe size, it appears we need to know the pressure of the exhaust air. This article uses 10.5 in-mercury to yield 115 cfm per square inch of pipe resulting in 560 cfm from a 2.5-inch diameter pipe.

So, it seems taht for a well-designed system even 3-inches is overkill.

Need to look into this some more...
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Old May 12th, 2006, 04:36 PM
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Scavenging is something that is always something of concern, and present in all exhaust systems. It has to do more with the air flowing through the pipes than what is coming out of the engine itself. Diesels may have some differences in variables, but fluid dynamics don't change in concept despite the change in engine design.

Here is a really good article I found a while back that describes a lot of the different factors in exhaust design.
http://www.bigcitythunder.com/pages/...ng_exhaust.pdf

-Hans
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Old May 12th, 2006, 09:59 PM
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In a diesel, there is no such thing as too little backpressure. It is totally different than a gas engine. To answer your questions artm, you need to replace the downpipe and go to 3in right after the headers. No flex pipe, no cats. The neck at the bottom of the header manifold is still going to be the limiting factor for you. I believe that 3in is fine. I have no data to back it up, other than personal experience. I run a 3in exaust with one 90 degree turn and no muffler. I noticed the performance difference right away. It really made the engine come alive. That said, I was dissapointed in the EGT numbers. It dropped, but just a tiny bit. The engine did seem to recover faster though, like when I was at 1150, it would drop very quickly when I let off the fuel. Faster than before. As to noise, its not really loud. It is louder than a muffer, but not nearly as loud as what a car would sound like. At $180 or so, this was the best thing that I have done to the truck for the money. Good luck.
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Old May 13th, 2006, 07:25 AM
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A performance Diesel guy by me recommended this muffler to me when I do my system.. http://www.tunedproducts.com/DNA/truck.html

by the way, what size are the stock pipes? I never measured
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Old May 13th, 2006, 09:12 AM
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David,

It is unfortunate that EGT's don't drop more with a larger pipe. Perhaps the lack of a tuned header is the cause.


Randy,

I've always gone with 65mm for the stock pipe on a Tdi. That's 2.6-in. I'm going to 3 since it should be more readily available (cheaper) than 2.6.

That DNA muffler sounds weird - cracking at higher revs (10 secs left in the audio file). I need quiet with good flow. I am surprised that flow rates aren't readily available.
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Old May 13th, 2006, 09:28 AM
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I want to get my system done over as well with a 3" pipe and just one muffler. IT just is not top priority right now.

I have never heard the muffler in person. It was just reccomended by a Diesel performance guy that owns a machine shop by me
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Old May 13th, 2006, 01:23 PM
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Quote:
Originally Posted by artm
David,

It is unfortunate that EGT's don't drop more with a larger pipe. Perhaps the lack of a tuned header is the cause.


Randy,

I've always gone with 65mm for the stock pipe on a Tdi. That's 2.6-in. I'm going to 3 since it should be more readily available (cheaper) than 2.6.

That DNA muffler sounds weird - cracking at higher revs (10 secs left in the audio file). I need quiet with good flow. I am surprised that flow rates aren't readily available.
It could be me too, the engine is turned up as much as I can and it still be safe. It would be cool to see what a set of custom headers would do for the truck. It would probably be expensive, but if someone could make a nice pair that uses a full 3in outlet and got rid of some of the wierd stuff, it could really help. Also, don't forget to take the kink out of the tube from the turbo to the intercooler.
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Old May 13th, 2006, 08:00 PM
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Quote:
Originally Posted by artm
David,

It is unfortunate that EGT's don't drop more with a larger pipe. Perhaps the lack of a tuned header is the cause.
.
The amount of air allowed in, and if on a turbo an intercooler, will have more of an effect on a diesel EGTs.

Pete
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Old May 13th, 2006, 10:34 PM
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Quote:
Originally Posted by Buckon37s
...don't forget to take the kink out of the tube from the turbo to the intercooler.
Plan is to either make a 2" full frontal IC or replace with water/air type using space for existing IC for the its radiator (and pull fan). Problem is I have AC so need to see if 2" full frontal will fit. In either case the silly kinked tube is out. Stupid design!

As for a custom header job if it can be done for $300 or so then it's worth a shot. .But how much quality can you expect for $300? And by quality I mean a good design.

I'm not looking to squeeze out every last drop of performance from this thing. I'm sure turning up the fuel with a new IC and exhaust will be plenty good enough.

In the end I need an auto tranny in this thing so I'll probably be yanking out the 300Tdi for something suitable...but that's another story.
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Old May 14th, 2006, 12:57 PM
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Quote:
Originally Posted by artm
Plan is to either make a 2" full frontal IC or replace with water/air type using space for existing IC for the its radiator (and pull fan). Problem is I have AC so need to see if 2" full frontal will fit. In either case the silly kinked tube is out. Stupid design!

As for a custom header job if it can be done for $300 or so then it's worth a shot. .But how much quality can you expect for $300? And by quality I mean a good design.

I'm not looking to squeeze out every last drop of performance from this thing. I'm sure turning up the fuel with a new IC and exhaust will be plenty good enough.

In the end I need an auto tranny in this thing so I'll probably be yanking out the 300Tdi for something suitable...but that's another story.
Your going to be more than fine. The EGT's are really not that bad for me, unless I floor it up a hill. Then I can get the motor up to 1250 pretty quick. I just have the fuel really turned up. I turned it up even more when I started trailering the rig. The longest I have to have it floored now is going up sand dunes. I have an aftermarket intercooler from Twistedperformance, but I think it's a piece of crap. On the intercooler, keep in mind that surface area is more important than thickness. I would check out bell intercoolers. I was going to go that direction but had to finally give up due to my winch being mounted right up next to the radiator. If I ever run out of projects, I really want to move the radiator back 2.5in and push the winch fully behind the front grill. But thats a ways away now.

You will be extremely happy with just mild tweaks if you are okay with the performance the way it is now. The engine really comes alive. I don't have any idea what someone would charge for custom headers. Last time I got a quote on it was 1998 and not for a 300!
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Old May 14th, 2006, 04:42 PM
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Yes, I have heard that Twisted is crap. No reason really to go outside the US for an IC, except for better price (i.e. China).

Yes, I know thin and full coverage is better. Can't get much thinner than 2-in. Looked into Allard and was going to copy their design with a Bell custom job. They (Allard) say about 2-in should fit in an AC setup - not their standard 3-in.

Then I got sidetracked with water/air types - easier to fit and about the same price. Plus you get cooled air at low speeds. No need for a custom IC, as everything's stock: IC, radiator, fan and pump.

As for the headers, again, a luxury at this point. I'm sure the tweaks will be fine - until the need for the auto gets extreme and then it's out with the Tdi!
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Old May 15th, 2006, 04:03 PM
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Tdi exhaust

Don't worry about the noise from a 3" pipe, even with basically no muffler it will do fine. I had a 3" system with a muffler "for looks" only (basically just the little resonator from an NRP system stuffed in) and it had plenty of flow, a good sound, and it kept the EGTs low. The mistake we see on some converted Defenders is that people go with too much of a muffler and this makes higher EGTs in some cases, especially if you have turned up the boost.
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Old May 15th, 2006, 05:11 PM
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Well, with all the muffler options out there, I decided to stick a straight pipe and see how it goes. If it's too loud I'll deal with the muffler later.

What do you consider low EGT's, Mike?
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Old May 15th, 2006, 05:22 PM
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Mike do you recommend any good straight through style mufflers for the TDI?
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Old May 15th, 2006, 06:27 PM
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Tdi mufflers

If it were my own rig I'd skip the muffler all together. If you do need one just find a nice stainless one (I live in Maine, everything has to be stainless or it is gone in one season) and make sure you can look right through it (aka no internal baffles that prevent direct pass through).
For customers we just use a small silencer.
I ran mine with a staright pipe for some time and never thought it was loud or had any issues.
We were fighting high EGTs on mine with the larger turbo and such. In the end it turned out to be a back pressure issue(too much muffler) mixed with too much boost.
Once I set boost back to about 15 psi and went with basically no muffler all was well in every condition including loaded over the Rockies on the way to Moab.
My truck does have a cat on it though.
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Old May 15th, 2006, 06:30 PM
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Quote:
Originally Posted by ECR
If it were my own rig I'd skip the muffler all together. If you do need one just find a nice stainless one (I live in Maine, everything has to be stainless or it is gone in one season) and make sure you can look right through it (aka no internal baffles that prevent direct pass through).
For customers we just use a small silencer.
I ran mine with a staright pipe for some time and never thought it was loud or had any issues.
We were fighting high EGTs on mine with the larger turbo and such. In the end it turned out to be a back pressure issue(too much muffler) mixed with too much boost.
Once I set boost back to about 15 psi and went with basically no muffler all was well in every condition including loaded over the Rockies on the way to Moab.
My truck does have a cat on it though.
Hi Mike,

Thanks for posting! Do you have a max EGT that you are willing to accept on a TDi?
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Old May 15th, 2006, 06:31 PM
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Wait a minute...what about the cat? Surely that's more restrictive than a typical muffler? Why do you still have it on?
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