Thread: TD5 Exhaust - How Big?

The standard system is 2.75", so 3" is the go

Hi That_kid,

I am getting mine done tomorrow, done a lot of reading and ringing around and have opted for a 2.5 system in mild steel and budget had a lot to do with my choice... cat gone, muffler replaced with a high flow item. I will let you know the outcome tomorrow! This is something I read off the Alive tuning site that do a lot of Td5 tuning ..

"Why dont we make 'Big Bore' systems? A 3 inch bore system would not be appropriate for modern land rover diesels, since the turbo outlets are only 2 1/4 inches in diameter. Age old (Proven) tuning theory states that the optimal turbo down pipe should be 10% larger in diameter than the turbo outlet casting. This is precisely why land rover chose 2 1/2", as it's a perfect match to the turbo. Using 2 1/2" pipe maintains a rapid flow of exhaust gasses to get them out quickly! Using 3" pipe would reduce the velocity of exhaust gasses, their fore retaining excess heat at the turbo, and exhaust manifold. Another factor is the reduction of back pressure you'd get from a 3" exhaust, as the wide open space of the exhaust takes more gas to fill it, and hence push out the tailpipe. The result could potentially cause turbo over speed, which can seriously decrease the life span of your turbo!"

Take care,

Aaron.

Originally Posted by Redback

The standard system is 2.75", so 3" is the go

Originally Posted by Aaron40

"Why dont we make 'Big Bore' systems? A 3 inch bore system would not be appropriate for modern land rover diesels, since the turbo outlets are only 2 1/4 inches in diameter. Age old (Proven) tuning theory states that the optimal turbo down pipe should be 10% larger in diameter than the turbo outlet casting. This is precisely why land rover chose 2 1/2", as it's a perfect match to the turbo. Using 2 1/2" pipe maintains a rapid flow of exhaust gasses to get them out quickly! Using 3" pipe would reduce the velocity of exhaust gasses, their fore retaining excess heat at the turbo, and exhaust manifold. Another factor is the reduction of back pressure you'd get from a 3" exhaust, as the wide open space of the exhaust takes more gas to fill it, and hence push out the tailpipe. The result could potentially cause turbo over speed, which can seriously decrease the life span of your turbo!"

.

interesting, but still conflicting.

will be interested to see how u go aaron

There have been a few threads about this. e.g.

Exhaust Options - 300 Tdi

Thanks Isuzu rover.... was very informative thread and got a bit complicated...was interesting however was directed at the larger turbo... don't think I would do the bigger turbo considering the cost except if I killed the standard, then the 2.5" system would need to be replaced with a 3"

Originally Posted by Aaron40

Thanks Isuzu rover.... was very informative thread and got a bit complicated...was interesting however was directed at the larger turbo... don't think I would do the bigger turbo considering the cost except if I killed the standard, then the 2.5" system would need to be replaced with a 3"

Regardless of the size of your turbo, the laws of physics remain the same.

Plenty of turbo/exhaust experts have experience with petrols but not diesels.

I had a lot of trouble with that subject at school so I will have to take others advise! Thanks again for the info..

Careful!!!

Well known Landrover modification specialists B.A.S and TD5 Alive both advise that the MAXIMUM for a TD5 is 2.75" (Factory is 2.5").

TD5 Alive also advises that if you fit a 3" exhaust with their upgraded turbo they WILL NOT honour warranty.

3" allows the turbo to overspeed on spool up damaging the turbo and causing overboost under hard throttle.

An issue I was unable to resolve in Lara with the original 3" dump pipe.

So either stay 2.5" and fit a straight through muffler / no muffler or go no larger than 2.75" (mandrel bent)

My current recommendation is stay factory size and just improve mufflers/flow. Vortex mufflers do a great job, but any improvement to the system (straight pipe, de-cat etc) will give benefits.

The factory pipe is Stainless, so worth keeping...