Thread: Turbo Over Speed From 3inch exhuast. on td5

theres the potential for it to happen, but I havent seen first hand evidence of it and the fueling regiem of the td5 should prevent it anyway unless you have something thats making the brain see a dissociated reality OR you have the worlds worst ECU porogrammer.

I had a 3inch on my 300tdi with one vortex muffler. The turbo was stock. The fuel was turned up. The engine did about 150,000km with it untill it did a bottom end. My new 2.8tgv was fitted to the same vehicle and exhaust. It is stock and has done 70,000km.

Seems Im more to worry about than the exhaust....

I think Rick130 has some thoughts on your subject.

I've run a 3" pipe on a Tdi for I don't know how many years without issue so far and the fuel is turned right up.

I'm sure it's possible in theory to overspeed a turbo when using an oversized exhaust, but IMO I think it's much more likely from overfueling and using high boost levels outside of the design range of the turbo.

A quick peruse of the map for the turbo should show what boost levels fall outside the efficient range and where it's safe.

In other words, from what I've read (and I'm no expert) keep the fuel and boost levels sane (ie. in the efficient range) and it shouldn't happen unless a wastegate sticks closed or the actuator is sluggish for some reason.

A mate of mine has a 3'' on his wagon and it drones badly. Pat

Tombie claimed he had observed it in one of his many rants on the subject. (I recall he (temporarily) took his bat and ball and left on that occasion too. ) However he could offer no evidence, and had run a 3" on his tomb raider defender without turbo failure (It may still have a 3" fitted?).

There is a big difference in restriction between an XX" exhaust on a 90 and an XX" (same size) exhaust on a 130.

The 90 would be the most prone if it is going to occur (shortest exhaust so lowest pressure drop). However I very much doubt it is a serious issue. The only talk of it seems to be from td5 alive and their business associates.

I thought that getting drop across the turbine equals lower egts and increased power ? I can say from experience that a over speed failure is due to what has already been said and mine was due to increased fueling and pushing the thing past its limits im also asuming that once the compressor goes way beyond its efficiency range the speed increases but the output does not increase which im guessing vibrations occur and then lead to failure...outcome was turbine wheel out the exhaust pipe
In the performance side of things a large exhaust on a turbo diesel is recommended along with a 7° taper from the outlet out into the exhaust is most efficient.. dont know why but im asuming it has something to do with dragging it out causing higher velocity ?

Now I'm no auto engineer, but.....

Surely the velocity of the gasses from the CYLINDER HEAD PORTS determines the speed of the turbo?

A turbo would experience increased resistance from the inlet air that it is trying to compress, therefore it's not a free-wheeling system?

Simply saying that increasing the diameter of the exhaust is risky means that all those Isuzu NPR trucks with stock 3-inch+ exhausts are at risk, surely?

Originally Posted by jakeslouw

Surely the velocity of the gasses from the CYLINDER HEAD PORTS determines the speed of the turbo?

No.

In fact velocity is largely irrelevant, it is the mass/energy flux and pressure drop across the turbine that is important.