Is there a smaller turbo for a Td5 ?

[Anderzander]

BAS remapped my Td5 a few years back when I asked if he could smooth out the torque curve coming off idle.

If you drive one with mechanical sympathy you'll appreciate why... Anyhow he said he was limited in what he could achieve with the std turbo. He did improve it though.

So a few years later I still think it'd be nice if it was smoother from idle but can't anywhere near afford / justify the VNT - and there is more than enough power higher up that I never use (must be a slow driver ?)

So just curious if anyone knows of a smaller turbo that might fit ?

[ToyRoverlander]

Sure there is. But it will choke on higher rpm as it is...well... too small. It will be less efficient at higher rpm (less power/torque) and if the turbo is way too small it will turn too many revs and the turbo will not live long.. Unless you keep engine rpm down..

Thats the downside of a little capacity diesel engine with a turbo. Off-boost there's just hardly any torque, untill the turbo kicks in..

[Aragorn]

You'd have to have it remapped again so it didnt try to run the smaller turbo at the current turbos larger power figures.

Might be worth looking at something like a VNT from another car. The Audi/VW 2.5tdi for instance uses a VNT version of a turbo very similar to the TD5 unit.

You'll have to put some effort into making it fit and getting the VNT actuator working, but that wouldnt be massively different to getting any other turbo working on the TD5.

[MECCANO]

What about a different a/r ratio compressor housing on the same turbo core (keeping the original wheels) a smaller a/r will make it spool quicker but obviously impact top end, but overall make a smoother power band.

If you can get one its just a case or swaping the housing over by undoing the big cirlcip or bolted clamp. Possibly re-drilling and tapping the waste gate bolts.

[Anderzander]

Thanks for the replies everyone.

I understand it would choke the top end as the bottom end improved - but my thinking was moving in that direction would bring the balance closer to my needs. I sort of bimble around one the roads and drive smooth and gently off it.

I hadn't thought about a different compressor housing - but Ive started doing a big of reading and cross referencing to understand if there is anything available in the GT20 series.

VNT wise - the Audi one is the GT2052V I think isn't it ? Just having different manifold shapes. Perhaps that is the route to look at - a little adaptor plate to mate it up and see how the plumbing looks ...?

Food for thought. Thank you.

[Aragorn]

yeh the adaptor plate is typically fairly straight forwards. The bigger issue is the VNT actuator.

Most modern cars use a vacuum actuated VNT system controlled by the ECU, rather than the traditional boost pressure capsule on the TD5. Converting them to boost control isnt trivial. I've seen a small "ecu" that can take some basic inputs (boost pressure, throttle position and RPM) and use these to drive the vacuum VNT system which seems like the best way, albeit a little more fiddly to setup.

Another option would be the Garrett GTB1756V used on the 2.7TDI Q7 and similar engines. GTB series have 3rd generation VNT assemblies which both spool much better and flow a lot more. The GTB1756 will likely spool significantly better than your existing turbo AND offer more top end! Or you could consider the GTB1749V, for less top end, and even better still spool.

GTB series are almost all electronic actuated though, so they'd need even more fiddling to convert.

[Anderzander]

Thanks for that - lead me to more reading

How does the BAS/IRB actuate the turbo ? Is that an additional function of the boost box ?

What stops simply swapping the boost actuator from the existing turbo onto it ?

[Aragorn]

No, BAS/IRB's VNT unit has been modifed to take a traditional boost capsule.

This is the mini-ECU thing i found to control the VNT if you'd like to do some further reading:

http://dmn.kuulalaakeri.org/vnt-lda/