Thread: 4BD1T Turbo Sizing and Performance Prediction.

Originally Posted by Bush65

Thanks for the thread Dougal.

Now you only have the exhaust pipe restrictions and intercooler to do, plus videos for Mat (rovercare)

I'll see what it'll do with the T25 back on it. The T2560 has nowhere near the bite off the line. In the mean-time can someone go give Mat a hug?

Because I'll be swapping to a 93 body at some stage, all the body cutting to fit the intercooler in will be wasted in a year or two. The stop-gap strategy is first fit the T25 wastegated to 20psi.
Then go back to fitting the GT2256V I have lying around.

I have another pneumatic VNT control idea which is two-stage.
First stage, dawes valve or just vacuum vs boost to set the maximum boost level.
Second stage (takes output from the first stage) is a 3 port valve connected to the throttle linkage, the first stage output and atmospheric. So this will vary the vanes between max boost and full open depending on pedal position.

It looks like without extending the rpm range or fuel pump mods a 56mm compressor is about as good as garrett gets.

Originally Posted by Ancient Mariner

Yeah I think there on the wrong forum Quantum physics Rocket science and
Brain surgery two floors up

Rocket science you say: [ame="http://www.youtube.com/watch?v=rNnzi4NcKKY"]Brain Surgery vs Rocket Science - YouTube[/ame]

Originally Posted by Dougal

...

I have another pneumatic VNT control idea which is two-stage.
First stage, dawes valve or just vacuum vs boost to set the maximum boost level.
Second stage (takes output from the first stage) is a 3 port valve connected to the throttle linkage, the first stage output and atmospheric. So this will vary the vanes between max boost and full open depending on pedal position.

It looks like without extending the rpm range or fuel pump mods a 56mm compressor is about as good as garrett gets.

It will be interesting to see how your 2 stage VNT control works out.

I'm not convinced people should limit themselves to a 56mm Garrett compressor wheel. The major problem illustrated by those 60mm compressor maps, mass flow too far to right, was due to the high trim, i.e. larger inducer.

The 60mm, 60 trim wheel has a 60.1mm exducer and 46.5mm inducer. 60mm, 55 trim has a 60.1mm exducer and 44.6mm inducer.

For others who may not know, it is the cross section area of the inducer (proportional to diameter squared) that has the major influence on air flow. The exducer diameter influences boost pressure, proportional to tip velocity squared. Trim = (Inducer2/Exducer2) x 100 and indicates what the efficiency will be like.

The 59.4, 52 trim (59.4mm exducer, 42.8mm inducer) map was a good match, IMHO better than the 56mm wheel which was close to choking at about 2000 rpm (with an intercooler).

Originally Posted by Bush65

It will be interesting to see how your 2 stage VNT control works out.

I'm not convinced people should limit themselves to 56mm Garrett compressor wheel. The major problem illustrated by those 60mm compressor maps, mass flow too far to right, was due to the high trim, i.e. larger inducer.

The 60mm, 60 trim wheel has a 60.1mm exducer and 44.5mm inducer. 60mm, 55 trim has a 60.1mm exducer and 44.6mm inducer.

For others who may not know, it is the cross section area of the inducer (proportional to diameter squared) that has the major influence on air flow. The exducer diameter influences boost pressure, proportional to tip velocity squared. Trim = (Inducer2/Exducer2) x 100 and indicates what the efficiency will be like.

The 59.4, 52 trim (59.4mm exducer, 42.8mm inducer) map was a good match, IMHO better than the 56mm wheel which was close to choking choking at about 2000 rpm (with an intercooler).

That's exactly the problem John, the problem is tip-speed and the answer is a bigger wheel. But Garrett are playing the petrol turbo game and don't do many wheels that suit high pressure 4 litre diesels.
The T28R that Ben is using has an even bigger inducer than the 60mm 60 trim I was using. But he's got a 0.86 A/R turbine housing to go with it.

I have two VNT's here with the 56mm, 50 trim wheels. One is the GT2256V from a 2.7L merc which I will fit to the 4BD1T one day. The other was a GT1849V which has had the same wheel fitted (GT1856V) for my 2.2tdi work car.
Maps aren't available for these, but the 56mm, 55 trim wheels we do have maps for can do a PR of 3 and 30lb/min, which could deliver a very conservative 200kw on our engines. Pro-rata on inducer diameter would suggest 27lb/min at PR of 3 is possible. Which is still possibly enough for 190kw at 2600rpm and 800rpm at 2200rpm.
As you can imagine, these start getting peaky and the peak torque and peak power start to converge.
My figures here are all using 60% intercooling. Which is quite conservative. But fuelling requirements nudge higher than a stock pump could deliver.

If I limit power by fuelling (140cc/1000 shots) I get a wide torque curve (740Nm) from 1900 to 2300, peak power of 192kw at 2,600rpm and peak airflow of 27lb/min at the same rpm (I drop boost after that to stay within 27lb/min, but BSFC starts pulling the power down from peak anyway).
If I crank intercooling to 80% then boost requirements drop to below 25 psi for the same power and slighter flatter torque curve.
The other very conservative part, I haven't dropped BSFC as it would with intercooling.


The rover GT2256V turbo will take more work to fit (all new piping and connections) but will be easier to control as the rover has a throttle cable.
The work car GT1856V turbo will only need a new dump-pipe to fit, the rest is bolt on from the existing turbo, but it will be harder to control (electronic throttle, no cable).

T25 (0.49 A/R turbine) fitted with a 22psi wastegate actuator.

It appears the wastegate is blowing open and it's dropping boost. Max is about 19psi and past 2600rpm it starts dropping. It gets down to around 12psi just before the rev limit.
Adjusting this is a slow process, I have to wait for the manifolds and turbo to cool right down. Takes about an hour.

4mm more preload on the wastegate later....

Looks like it's good. Hits about 21psi peak, drops to 18-19psi later in the rev range. A smaller wastegate hole would fix this.
I can pull 80km/h in 3rd (~3200rpm) before it drops off and 4th is good past 100km/h.
EGT's are similar (750C up hills at 2000rpm) to the 24psi peak I was running before, which suggests I'm hitting the predicted higher efficiency and getting similar total airflow with 3psi less boost.

The turbo whistle turns to a shriek at high load and high rpm. But that's not surprising, there's about 30kW going through the turbo shaft at that point.

This is where I think I'm at:


The noisey turbo I have (at high boost) is likely the result of a badly balanced compressor wheel. I'm making enquiries to order a complete and balanced chinese T25 core. It'll be cheaper than getting mine balanced.

Originally Posted by Dougal

I also went through just now and put in cruise conditions. 8psi boost, 716F EGT (380C), 2000rpm.
The EFR couldn't do it. But I got a match by pulling boost down to 6psi and EGT up to 900F. This puts drive pressure only 1psi above boost.
BorgWarner MatchBot

Yeah needs intercooling..