2.5 or 3 inch Exhaust for TD5.

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Originally Posted by Blknight.aus

IVe done some cross sectional measurements for a couple of the ricers on base to help solve the which is better.

on a 90 degree bend a mandrel bent 2.5 inch exhaust has the same cross section as a normally bent 3 inch.

So have I. Mandrel is only option for me

the 3 inch normal is cheaper than a full 2.5 inch mandrel bent exhaust.

my thoughts for the td5 based on the flow rates from the rice boys turbo petrols and a maintenance POV are thusly

I like the higher velocity of gas out of the 2.5inch mandrel better than that of the 3 inch normally bent in theory its got less back pressure on the turbo than the normally bent 3 inch.



the 3 inch exhaust gets a mite close to some componants for my liking and does make changing the oil filter a bit of a pita.

Lara and Big Red both run about the same times and HP, big red does it through pure brute force Tombie Insane chipping where as lara achieves it through a very mild chip, bigger intercooler and an excelent 3 inch exhaust system

I think you left out the 2.8 bit :D

Since Im home today and tomorrow if you like you can come for a run in big red to see how the big chip runs on a normal exhaust and intercooler (Money ran out for the upgrades due to some bad luck with the house and some illnesses in the family)

According to tombie mines 200kw or 268hp. How does std IC cope?

IC was the first thing I did

While I still have her your welcom to come and benchmark your vehicle off of big red when you do mods as you need to.

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I would be keen to drive both back to back to see the difference the 3" mandrel and tombie IC makes

ben...

Taipan exhaust is on the gold coast, in burleigh heads, i asked for a quote for my defender 300tdi and it was approx $1800, it is a good system they suggested i replace the intercooler and get a dyno before fitting as that will effect the performance after. Dyno to compare before and after. all stainless steel so not prone to rust.

Getting my 02 Disco done tomorrow at Fat Pipes Kallangur,

my td5 130 is chipped and has 3 inch mandrel exhaust.had no muffler when i bought it but put straight thru in middle.still sounds mean but not as loud.running 18 psi boost,heaps of go,26 would be unreal.dont know for how long though.

Boost don't kill them egt's will :D

Exhaust tracts are carefully designed (within all the given constraints) to give the best compromise in terms of backpressure, volume, heat dissipation, etc.

Whatever modifications are made the equivalent size x length should remain approximately constant.

Smaller pipe means higher exhaust gas velocity (less heat absortion) but greater back pressure (increased turbo lag).

Larger pipe will cause increased turbo and exhaust manifold heat retention (in other words higher EGTs) and can potentially cause turbo over speed in detriment of its life span.

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Originally Posted by mturri

Exhaust tracts are carefully designed (within all the given constraints) to give the best compromise in terms of backpressure, volume, heat dissipation, etc.

Whatever modifications are made the equivalent size x length should remain approximately constant.

Smaller pipe means higher exhaust gas velocity (less heat absortion) but greater back pressure (increased turbo lag).

Larger pipe will cause increased turbo and exhaust manifold heat retention (in other words higher EGTs) and can potentially cause turbo over speed in detriment of its life span.

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I was going to post some thing along those lines but mturri beat me to it, I agree totally.

Quote:

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Originally Posted by mturri

Exhaust tracts are carefully designed (within all the given constraints) to give the best compromise in terms of backpressure, volume, heat dissipation, etc.

Whatever modifications are made the equivalent size x length should remain approximately constant.

Smaller pipe means higher exhaust gas velocity (less heat absortion) but greater back pressure (increased turbo lag).

Larger pipe will cause increased turbo and exhaust manifold heat retention (in other words higher EGTs) and can potentially cause turbo over speed in detriment of its life span.

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I don't understand why you would end up with greater heat retention with the use of a bigger pipe.

Is it a case of greater surface area to transfer heat to? I don't see how a reduced gas speed necessarily equates to a hotter pipe or turbo. The rate at which you are able to dump heat out to the atmosphere via the gas leaving the end of the pipe I would think is determined by the pressure differential from the source out to the atmosphere and the resistance to flow by the pipe. Are we going to get more gas leaving the system by restricting the flow and therefore increasing the pressure differential??

I need a bit of help with understanding this. I can understand electrons but gas/fluid flow is not one of my strong points.

Both the larger surface contact area and the increased residence time account for greater heat exchange (loss) across the pipe. The rate at which you are able to dump heat out depends on how fast you can get it out. Its like being thrown a hot potato in your hands, the sooner you get rid of it the lesser you burn. A more proper example to cite would be an engine intercooler, as you pump more air it decreases its ability to cool because of the shortened residence time.

The amount of gas leaving the system is always the same (for a given engine running condition that is), but a smaller pipe will cause the gas to flow at a higher velocity resulting in a higher pressure differential because of the increased friction losses. Atmospheric pressure is constant, what goes up is pressure downstream of the turbine which affects turbo response (smaller pressure difference across the turbine). On the other hand if the turbo sees a higher differential across the turbine it will have less of a "hold" and tend to over spin.

Hope to have made it clearer now....

Quote:

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Originally Posted by mturri

Both the larger surface contact area and the increased residence time account for greater heat exchange (loss) across the pipe. The rate at which you are able to dump heat out depends on how fast you can get it out. Its like being thrown a hot potato in your hands, the sooner you get rid of it the lesser you burn. A more proper example to cite would be an engine intercooler, as you pump more air it decreases its ability to cool because of the shortened residence time.

The amount of gas leaving the system is always the same (for a given engine running condition that is), but a smaller pipe will cause the gas to flow at a higher velocity resulting in a higher pressure differential because of the increased friction losses. Atmospheric pressure is constant, what goes up is pressure downstream of the turbine which affects turbo response (smaller pressure difference across the turbine). On the other hand if the turbo sees a higher differential across the turbine it will have less of a "hold" and tend to over spin.

Hope to have made it clearer now....

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un poco,

if amount of gas leaving the system is tha same all the time then the rate at which it leaves the system must be the same. For a given cross sectional area if you get x molecules across an infinetely thin slice then if you half the cross sectional area you will need to double the speed of transfer to get the same number of molecules across. So I don't see how the gas spends less/more time in the pipe to transfer less/more heat.