Thread: 4BD1T Turbo Sizing and Performance Prediction.

Well think I will have to read this thread 20 times now, my Turbo is shagged, time for a new one.
(Garret 2260 vnt)

Suggestions?

Originally Posted by taylorslandy

Hi Dougal, please explain what the limitations are for the GT2260vnt on the 4BD1, what do you mean it will "reach the limit of its map quickly"?

I haven't found a garrett map yet with a shape suitable for the whole operating range of the 4BD1T. The GT2259 starts well on the surge line but doesn't have the pressure capacity or flow capacity to use what the stock fuel pump can deliver.

Originally Posted by taylorslandy

I have rovercares old beast with the said GT2260vnt turbo and while I can't compare it to the other turbo's you reccomend, I can say it spools up pretty much off idle and produces seemless grunt from very low revs, but must admit up top it is pointless reving it (no tacho yet so don't know what RPM), but you don't need to rev it that high anyway. Compared to my old gu patrol with factory turbo TD42, it has a massive amount more torque and will cruise up hills way more easily. Just thinking the other two turbo's you reccomend must be pretty bloody good to be heaps better than the gt2260?

I have no idea what rovercare is up to. He's been on my ignore list for a long time now.

The GT2260V has a turbine that is both less efficient and has less flow capacity than the wastegated turbos I'm recommending.
The lower efficiency is caused by the VNT mechanism, put simply extra vanes are a flow restriction and trying to turn the flow to create more boost causes more flow restriction. This lower efficiency means higher exhaust pressure to deliver the same boost. The higher drive pressure reduces engine power. Particularly as rpm builds.

The lower flow capacity is a huge problem with VNT turbos. They have no ability to bypass extra exhaust flow around the turbine which means on a larger engine (like 3.9 litres) they reach flow limits quickly and start to spike exhaust pressures. Limiting boost and engine response.

If you have an engine around the 2.5-3 litre mark there are plenty of VNT turbos that will work nicely. But our 3.9 litre engines have nothing suitable. The VNT turbos are also an intermediate step in turbocharging which doesn't offer the performance or fuel economy possible.

I have a 300tdi now. I won't be putting a VNT turbo on it. I'll be doing something else which is far better.