Defender90td5 · Oct 1, 2019

lynall said:
The boxes dont filter the smoke they only reduce the sound of the exhaust note, some are resonance chambers and others are just packed with wadding with a perforated tube through the middle, the gases dont actually pass through the wadding itself the wadding just muffles the sounds of the gases.

It is a bit fo a science and well worth a half hour on google.
Then thers back pressure/scavenging/gas flow/balancing between the cylinders (you must have seen the fancy curved manifolds on f1 cars?) and then there are two strokes which are a whole new ball park.

Newer cars/trucks with DPF are another matter and they do reduce the smoke/particulates.

Yeah I understand what you mean. I race 2 stroke motocross bikes so back pressure etc is something I understand pretty well. If I was to get a VNT turbo would a straight pipe be beneficial? My main question is weather to keep the back box or not?

300bhp/ton · Oct 1, 2019

Pappasmurf said:
But if you don't have your boxes, theres no filter for the smoke.

lol, that isn't how a silencer works

300bhp/ton · Oct 1, 2019

Defender90td5 said:
Yeah I understand what you mean. I race 2 stroke motocross bikes so back pressure etc is something I understand pretty well. If I was to get a VNT turbo would a straight pipe be beneficial? My main question is weather to keep the back box or not?

Back pressure doesn't really apply with forced induction engines to the same extent. Because the intake charge is already above atmospheric pressure. Back pressure is all about exhaust scavenging on n/a engines, which is basically using the exhaust pulse from one cylinder to create low pressure to "draw" in air into one of the other cylinders. To get the timing of the pulse matched to the right valve opening is the science and art of exhaust tuning.

The "back pressure" bit is more about stock air/fuel ratios. As in, if you improve the exhaust breathing, often cars and especially carb ones, would then run like crap. Because they would need the fuelling adjusted too. But many people wouldn't do this and just claim they need more back pressure

In reality for a 4 stroke engine you want the minimal back pressure to give high velocity exhaust gases.

With a turbo diesel it is all about flow and lowing EGTs. The bigger the pipe and less restrictive the better. On some of the big US truck diesels, when tuned they run 5" or bigger down pipes, often retaining 4" piping all the way. Simply huge. No need on a Tdi though, they are low power and low tuning.

Straight thru would be no silencing at all. But when you have a turbo it does dampen the noise a bit anyway. The Tdi isn't really all that loud from the exhaust. Location of the exit and the body config will have more impact on noise.

My brother runs a side exit just behind the passenger door in front of the rear wheel. He has a cherry bomb style silencer fitted. It sounds nice, but is very noticeable in the cabin at speed or when on the throttle. More so than a stock rear exit setup, but it is not unbearable at all.

I run completely straight thru, but mine exits in the rear cross member. Mine is also a truck cap. I can hardly hear the exist from the drivers seat, although it is slightly more audible outside. But still isn't as loud as many other vehicles.

The worst thing you may encounter is droning. If you are unlucky and the frequency matches, when cruising you may get a lot of booming inside the vehicle.

Here are some examples to give you an idea.

Defender90td5 · Oct 1, 2019

300bhp/ton said:
Back pressure doesn't really apply with forced induction engines to the same extent. Because the intake charge is already above atmospheric pressure. Back pressure is all about exhaust scavenging on n/a engines, which is basically using the exhaust pulse from one cylinder to create low pressure to "draw" in air into one of the other cylinders. To get the timing of the pulse matched to the right valve opening is the science and art of exhaust tuning.

The "back pressure" bit is more about stock air/fuel ratios. As in, if you improve the exhaust breathing, often cars and especially carb ones, would then run like crap. Because they would need the fuelling adjusted too. But many people wouldn't do this and just claim they need more back pressure

In reality for a 4 stroke engine you want the minimal back pressure to give high velocity exhaust gases.

With a turbo diesel it is all about flow and lowing EGTs. The bigger the pipe and less restrictive the better. On some of the big US truck diesels, when tuned they run 5" or bigger down pipes, often retaining 4" piping all the way. Simply huge. No need on a Tdi though, they are low power and low tuning.

Straight thru would be no silencing at all. But when you have a turbo it does dampen the noise a bit anyway. The Tdi isn't really all that loud from the exhaust. Location of the exit and the body config will have more impact on noise.

My brother runs a side exit just behind the passenger door in front of the rear wheel. He has a cherry bomb style silencer fitted. It sounds nice, but is very noticeable in the cabin at speed or when on the throttle. More so than a stock rear exit setup, but it is not unbearable at all.

I run completely straight thru, but mine exits in the rear cross member. Mine is also a truck cap. I can hardly hear the exist from the drivers seat, although it is slightly more audible outside. But still isn't as loud as many other vehicles.

The worst thing you may encounter is droning. If you are unlucky and the frequency matches, when cruising you may get a lot of booming inside the vehicle.

Here are some examples to give you an idea.

Thankyou that’s the answer I was looking for. I’ll have a look at those videos when I’m home from work. Thankyou much appreciated

lynall · Oct 1, 2019

Defender90td5 said:
Yeah I understand what you mean. I race 2 stroke motocross bikes so back pressure etc is something I understand pretty well. If I was to get a VNT turbo would a straight pipe be beneficial? My main question is weather to keep the back box or not?

I reckon a vnt would be the nuts on a 2/300 tdi, but theres not much info out there so assume not many people have done it, cost being the main barrier I would say.
There are some articles on diy vnt tdi conversions but they seem a bit hit and miss, the guys know what they want the car to do but cant quite get it right.

I dont think the diameter of the ex pipe will really change how it drives to any extent especially is a such a low revving diesel, the silencers will be the only potential restrictive bit in the entire system.
Easy way to tell if the current system is restrictive is to unbolt the pipe halfway down the car and drive it to see if it revs more freely or pulls better, but dont let the noise make you think its better, stealth is way better.

I think like anything old you can improve it, but it will never be as good as a more modern version, bit like people who spend a fortune tuning up some old ford, when a modern diesel mondoe will run rings around it in more compfort and getting twice as many mpg!

300bhp/ton · Oct 1, 2019

I don't think there was a dramatic performance increase with the straight pipe, but if you plan other mods it will help most likely, mostly with EGT's if nothing else.

I would say mine runs substantially better than a stock Tdi however.

Some stats from a dyno day.

We had a couple of 'stock' Tdi's run. This was the best stock run.

Please Note, the estimated engine power should not be compared to that claimed by LR, that isn't how dyno's work. Take this as a baseline for what a stock Tdi would make on this dyno.

This is mine which has a few mods on it, but stock internal engine and stock turbo. Note, due to not having a tacho or working speedo at the time of going on the rollers, the dyno operator had to guess some inputs. But the speed quoted on the run doesn't match the gearing, thus the figures are probably slightly higher than recorded.

And here is one running a VNT turbo and other mods. The engine estimate power is higher, but note the wheel power is not much changed.

The biggest thing a VNT should do, is allow a slightly broader powerband. And if you look at the graphs, you can see the VNT help on longer at higher rpm. If the rpm recorded is correct that is.

I would say a VNT does offer gains, however the cost of doing so is probably a poor £/hp trade off. We did have another vehicle runnin a VNT also, along with all the bolt on mods, but it made less power than mine.

Defender90td5 · Oct 1, 2019

300bhp/ton said:
I don't think there was a dramatic performance increase with the straight pipe, but if you plan other mods it will help most likely, mostly with EGT's if nothing else.

I would say mine runs substantially better than a stock Tdi however.

Some stats from a dyno day.

We had a couple of 'stock' Tdi's run. This was the best stock run.

Please Note, the estimated engine power should not be compared to that claimed by LR, that isn't how dyno's work. Take this as a baseline for what a stock Tdi would make on this dyno.

View attachment 190856

This is mine which has a few mods on it, but stock internal engine and stock turbo. Note, due to not having a tacho or working speedo at the time of going on the rollers, the dyno operator had to guess some inputs. But the speed quoted on the run doesn't match the gearing, thus the figures are probably slightly higher than recorded.
View attachment 190857

And here is one running a VNT turbo and other mods. The engine estimate power is higher, but note the wheel power is not much changed.

View attachment 190858

The biggest thing a VNT should do, is allow a slightly broader powerband. And if you look at the graphs, you can see the VNT help on longer at higher rpm. If the rpm recorded is correct that is.

I would say a VNT does offer gains, however the cost of doing so is probably a poor £/hp trade off. We did have another vehicle runnin a VNT also, along with all the bolt on mods, but it made less power than mine.

I understand your point, do the VNT turbos come made for the 200tdi or do modifications have to be made? I watched a video of a 200tdi with a VNT turbo and it sounded amazing and seemed to pull like a train, maybe no speed increase on the whole but acceleration seemed to be improved which would be helpful for me as I plan on towing fairly heavy trailers.

Defender90td5

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300bhp/ton

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lynall

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300bhp/ton

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Defender90td5

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