Twin Turbo's or Hybrid

**Bush65** · 16th February 2012, 03:30 PM

Compounds offer far and away the best turbo performance - best response with greater width and area under their boost curve at reasonable efficiency and utilising more of the heat energy in the exhaust gas.

However they take up more room, require more custom work and the fuel injection pump is hard pressed to provide enough fuel to take full advantage of their potential.

VNT turbos can provide better performance than waste gate singles, but as Dougal pointed out are difficult to find in a size that best suits a tuned 4BD1T - IMHO the GT2259V is still a little small to get the best out of a tuned 89 or later 4BD1T. I have a GT2256V that was on the 300Tdi in my old rangie and some performance tuners in the UK supply GT2259V for the 300Tdi where they perform well, which in my mind confirms my previous statement.

With the type of compressors (radial outflow) used in our turbos, boost pressure is produced dynamically - a function of the square of the speed that the air leaves the tips on the impellor, which is related to the impellor exducer (outlet) diameter squared and rpm. The air flow rate is dependent on and limited by the inducer (inlet) area (a function of diameter squared).
When smaller compressor wheels are driven faster to provide boost pressure outside their efficient operating range the heat produced in the air reduces the density, defeating much of the gain from higher boost pressure - also higher drive pressure is required. Larger diameter impellors can produce higher boost pressure more efficiently than small impellors. An analogy might be spinning tyres, burning rubber but failing to move the vehicle – with the small compressor, think of the tips of the impellor blades slipping against air flowing at lower speed. This explanation is rather simplistic and for a better understanding the reader should investigate how/why compressor trim affects efficiency – air in contact with the impellor blade for longer (distance and time) while accelerating up to the tip speed.

The value of boost pressure does not tell the full story. A better match turbo can provide better performance at lower boost pressure than some other turbo at higher boost. What we really are interested in is the air mass flow combined with lowest drive pressure (exhaust manifold pressure) and two different turbos providing 30 psi boost don't necessarily provide equivalent air mass flow and drive pressure.

Normal pressure gauges are designed to dampen pressure variations and can’t respond quick enough to detect transient (short time interval) pressures. Actual pressure peaks are greater and affected by complex shock waves, etc.. Higher drive pressure reduces the engine’s volumetric efficiency (VE) – inlet valves open before top dead centre, while the exhaust valve closes after top dead centre and unless the pressure in the inlet manifold is greater, fresh air can’t flow into the cylinder.
Both higher drive pressure and higher boost pressure increase pumping losses in the engine – power required to pump the inlet air and exhaust gas is lost.

c.h.e.i.f. you said that you changed injector nozzles. This may be the reason why you smoke problem is so bad. The stock nozzle is designed so that each of the 4 nozzles spray into the region of the 4 corners of the combustion chamber in the piston crown. The angle and orientation of the nozzle holes are made to suit the particular offset and angle of the injector to the combustion chamber.

A nozzle from another engine will most likely use a different arrangement of nozzle holes. If the spray is hitting the sides of the combustion chamber, or the piston crown then combustion will suffer badly (e.g. black smoke), and can cause other problems.

The stock nozzles are designed for stock engines and when the air density in the combustion chamber is increased significantly (higher boost pressure and better intercooler) the spray pattern doesn't reach as far into the combustion chamber, adversely affecting combustion efficiency.

**c.h.i.e.f** · 16th February 2012, 09:26 PM

thanks bush65 i was waiting for a detailed post

why i asked this question in the first place is because you may remember discussing with me in the past about a GT3076r which you then posted your findings along with the squirell calculator which i have played around with but find a few things confusing to put an appropriate input into it.
i have recently been looking into a GTX3071r (new range of garrett turbos) you probably already know but for others that dont this new range of GTX turbos come with surge slotted compressor housing,a compressor wheel that has an extra blade(fin etc) for "improved flow" and come with different options for the exhaust housings which i was looking at the .63A/R option.
with the compounds from what i have looked into they have alot of potential as you have said bush65 and from what i see can be finely adjusted for different results.
out of interest what safe level of boost can you expect your setup to handel?

as for your previous statements about the density of the air being reduced with the bad efficiency from the smaller compressor wheel is not a good thing which is why we would aim at a larger compressor with a different trim so we can get more air in not worrying soley on psi alone but the downfall of this is getting the larger wheel spining

hence why i have been thinking the .63A/R turbine housing will get it spining faster ?
the smaller the A/R the faster the tip speed?

as for the injectors they were listed in the zexel injector nozzel book as coming of a late model 4bd1t but most of my black smoke problem was probably due to a poorly adjusted fuel setting on my behalf

unlike most people that want good performance and good fuel economy i am in chase of performance and dont care about how much fuel it uses

theres just so much to learn on diesels it is very interesting!

**Bush65** · 17th February 2012, 10:22 AM

Originally Posted by c.h.i.e.f

thanks bush65 i was waiting for a detailed post

why i asked this question in the first place is because you may remember discussing with me in the past about a GT3076r which you then posted your findings along with the squirell calculator which i have played around with but find a few things confusing to put an appropriate input into it.
i have recently been looking into a GTX3071r (new range of garrett turbos) you probably already know but for others that dont this new range of GTX turbos come with surge slotted compressor housing,a compressor wheel that has an extra blade(fin etc) for "improved flow" and come with different options for the exhaust housings which i was looking at the .63A/R option.
with the compounds from what i have looked into they have alot of potential as you have said bush65 and from what i see can be finely adjusted for different results.
out of interest what safe level of boost can you expect your setup to handel?

as for your previous statements about the density of the air being reduced with the bad efficiency from the smaller compressor wheel is not a good thing which is why we would aim at a larger compressor with a different trim so we can get more air in not worrying soley on psi alone but the downfall of this is getting the larger wheel spining

hence why i have been thinking the .63A/R turbine housing will get it spining faster ?
the smaller the A/R the faster the tip speed?

as for the injectors they were listed in the zexel injector nozzel book as coming of a late model 4bd1t but most of my black smoke problem was probably due to a poorly adjusted fuel setting on my behalf

unlike most people that want good performance and good fuel economy i am in chase of performance and dont care about how much fuel it uses

theres just so much to learn on diesels it is very interesting!

Garrett have recently introduced the GTX range to catch up with BorgWarner's compressor development.

My gut feel is a GTX3071R with .63 A/R turbine housing could be worth a try. In the USA, many are happy with similar or larger singles that are less advanced.

So the nozzles are OK, then you need more air to be able to burn clean and pick up performance.

**c.h.i.e.f** · 17th February 2012, 10:51 AM

Auh interesting....i read through the borgwarner efr manual a few months ago when you first mentioned it and i found there ideas quite plausable and advanced only problem is in australia it is governed mainly by MTQ and GCG turbos and dont really like to promote the sale of borgwarner gear

What i do find annoying is alot of info/graphs and calculators refer mainly to petrol engines.
Im seriously considering giving the 3071 a go as i do believe my problem is getting enough air and previously having high compressor temps it was a very poorly matched decision now i look back at the previous setup!

A quick unrelated question, did anyone figure out if it is worth adding extra weight to the flywheel as i found it quite odd that the 3.9 4bt uses almost twice the weight .

**Dougal** · 17th February 2012, 11:27 AM

Originally Posted by c.h.i.e.f

A quick unrelated question, did anyone figure out if it is worth adding extra weight to the flywheel as i found it quite odd that the 3.9 4bt uses almost twice the weight .

I intend to. How much I can add will depend on a lot of measurements I can't taken until my engine and gearbox are again parted.

I'm expecting to gain a lot of smoothness at very low rpm (700-1200rpm) and also when applying full torque from about 1400rpm upwards. Currently I get a lot of rumble in both situations which results in a lot more gear-changes to avoid said rumble.

I'll be happy when I can run smoothly down to idle and back up in 3rd gear.

**c.h.i.e.f** · 18th February 2012, 07:21 AM

will be interesting to see the outcome ! well it wont be long until i have my gearbox out soon thats if it dont run away by itself

so ill take some measurements for you if it would help unless yours is different of course....
i am finding the same rumbles at lower rpm and if you boot it it takes off but has a period of terrible vibrations like its trying to eat everything then it smooths out.
only thing i was worried about is having extra weight causing stresses on the crank but then i look at the crank and think to myself that thing is huge

**isuzurover** · 22nd February 2012, 11:44 PM

Originally Posted by Dougal

I intend to. How much I can add will depend on a lot of measurements I can't taken until my engine and gearbox are again parted.

I'm expecting to gain a lot of smoothness at very low rpm (700-1200rpm) and also when applying full torque from about 1400rpm upwards. Currently I get a lot of rumble in both situations which results in a lot more gear-changes to avoid said rumble.

I'll be happy when I can run smoothly down to idle and back up in 3rd gear.

Dougal - to make like easy, have you trolled the wreckers for 6bxx engines to see if they have heavier flywheels?

**Dougal** · 23rd February 2012, 05:55 AM

Originally Posted by isuzurover

Dougal - to make like easy, have you trolled the wreckers for 6bxx engines to see if they have heavier flywheels?

No I haven't, no decent Isuzu wreckers around me. I do have an Isuzu 4BD1 industrial parts book, it lists about 8 different flywheels, all of which look much heavier than the truck item I have.
But I don't want to swap bellhousings or gain length, I want to maximise the size of my flywheel within the space limts I've currently got.

The main thrust of this plan is seeing what thickness of plate can be added to the face of the flywheel while still keeping clutch operation. I have a small cavity in the back of the flywheel I can probably add a ring of steel to as well.

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