Thread: 25 PSI boost on 300Tdi

Bush,

Is that what they call a cartridge in your photos?

Thanks for the comments on the baby.

How much does the VNT/VGT make up for the bigger turbine eg, going from a GT20XX to a GT25XX? or perhaps the question should be how would a GT2556V compare to GT2056 in terms of driveability?

The way I understand it is that the bigger the turbine the greater the engine rmp required before you start to creat boost. So will the variable geometry drop the engine RPM required before you get boost. Don't want much! just low down boost and good highway speed towing from a little 2.5 ltr 300Tdi.

Originally Posted by slug_burner

Bush,

Is that what they call a cartridge in your photos?

Thanks for the comments on the baby.

How much does the VNT/VGT make up for the bigger turbine eg, going from a GT20XX to a GT25XX? or perhaps the question should be how would a GT2556V compare to GT2056 in terts of driveability?

The way I understand it is that the bigger the turbine the greater the engine rmp required before you start to creat boost. So will the variable geometry drop the engine RPM required before you get boost. Don't want much! just low down boost and good highway speed towing from a little 2.5 ltr 300Tdi.

C.H.R.A. centre housing and rotating assembly.

A larger compressor is going to move more air and that requires more torque from the turbine.

Larger impellers (compressor and turbine) have greater rotational inertia and require more torque to increase their rpm.

The larger compressor impeller will have a higher tip speed at same turbo rpm so produce boost at lower turbo rpm.

Larger turbine impeller will deliver more torque.

So there are "swings and roundabouts"

On any engine a smaller turbo will gain rpm and produce boost pressure earlier, but will reach maximum allowable turbo speed, and not deliver as much air at higher rpm. The smaller turbine also increases back pressure (also called drive pressure), in the exhaust manifold and cylinder so cylinder filling with air is reduced.

Often turbos use a waste gate to avoid turbo speed exceeding max allowable and to reduce drive pressure. The disadvantage is more energy from the exhaust gasses is wasted.

Variable geometry/nozzle turbines avoid the disadvantage of waste gates and is like having a smaller turbine at low engine rpm and a larger turbine at higher engine rpm.

Unlike the compressor side, the turbo number GT2052V, GT2556V, etc. don't tell us much about the turbine impeller size.

There is not a lot of difference in the turbine impeller (or shaft dia) from GT17... to GT28...

There are also differences in the turbine housing and its nozzle for these sizes however, but Garrett don't tell us. Also different housings with alternate A/R are available.

Sorry I've run out of time for now.

Originally Posted by Bush65

Yes.
This pic shows compressor impellers from Nissan GT2052V on left and 300Tdi on right.

Thanks for confirming that. Turbomaster do show 54mm but it's very easy for catalogues to have errors. Photos are much better.
This is the first time I've come across the 54mm T25 compressor.

FWIW there are two T250-04 compressor wheels too, one has a 3.51mm tip height, (pt # 446335-0012) the other a 4.75 mm tip height. (pt # 446335-0009 )

So no-one is running 25psi on the stock turbo and intercooler?
Not even tried it?
I think these engines are a little tougher than we are led to believe. Has no-one noticed thet the boost is directly related to fuelling? I disconnected the waste gate from its sensor line and have found that doing the tweaks to the pump gets me 25psi at surprisingly low revs. I hear what you say about efficiency at higher pressures but there is a noticable difference between 20 and 25psi and a pretty good EGT at 750Deg. EGT at 20 PSI is the same so the efficiency of the stock turbo & intercooler must be OK. BTW fuelling gives me light smoke at full throttle and 25PSI but will overwhelm the clutch at lower revs if i'm not careful and blows a huge plume off boost but not for long. It seems like most All Wheel Drives, the clutch is the weak point! Diesels are blessed with not needing a set A/F ratio so fuel economy goes up with more boost due to the engine running leaner
I have a bit of experience with modifying jap turbos and had a lot of success with water injection instead of upgraded intercoolers. This is a much cheaper way to overcome higher inlet temps and will be the next step for better economy.
BTW, this engine runs on Waste Vegetable Oil and loves it!!!!

130 Bigcab Ute 300Tdi

25psi would be completely off the map of usable pressure/flow. Sure you can do it, but it'll go a whole heap better with a turbo intended to deliver that pressure.

I'm with Pete. The 300tdi is an amazingly tough engine. I have abused mine a little, overheating, 25psi boost, over-fuelling. All I have replaced is the big-ends after 380,000km. They are IMHO the best mechanical ingection diesel in their class for power, economy and strength. I love 'em!

Sorry to disagree fella's, but IMO the bottom end isn't anywhere near strong enough for that sort of boost/power.

After pulling my big ends, they showed every classic case of being overloaded, basically the overlay failed from too high a load, and that at only 17psi.

Now it could be a case of the material just isn't strong enough, and they appear to use a relatively soft overlay, but I'd be be looking at beefing it up for long term use.