Remember boost is not everything, a K03 at 30psi makes a lot less power than a GT42R at 30psi. ;p
Twin Turbo 1HD-T!
- Thread starter ForealBoreal
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
Remember boost is not everything, a K03 at 30psi makes a lot less power than a GT42R at 30psi. ;p
Yes there are lots of options in the MHI turbo line. The turbo I got is off a 94-95 Volvo 850 with the conical exhaust flange. I needed the early one as its allows me access all 4 mounting bolts (my manifold is studded and so is the Volvo turbo). The later Volvo turbines have a stud with no access to the back.
Even in the TD04 range there is lots of options, if I find it getting choked in the top end I will try the step up to the 7cm turbine. From there it would be into the TD05H-big 16G or possibly a 20G wheel. I have a feeling this TD04HL-19T with 6cm turbine will work out well for my needs.
Yes you and him have bit a lot of work into this, his maps from last week sold me on the TD04HL-19T. Great job to the both of you.
The intercooler in those pics is way too small. It's likely causing as much density decrease from flow restriction as it's gaining increase from cooling.
I've had plans to compound my 4BD1T for about 6 years now. Life keeps getting in the way.
I planned for about 30psi and just wanted the fastest spool and longest torque curve possible. Original plan was VNT GT2256V for the small turbo and a T28 for the big one.
My main holdup (besides life getting in the way) is my engine bay is really cramped for space. I've bought a later model wagon with factory air suspension which moves the shock towers and clears up a lot of space.
So now on-top of a turbo build, I have a whole wagon build.
Can't win some days.
Here's a pic of the plan I had:
I've had plans to compound my 4BD1T for about 6 years now. Life keeps getting in the way.
I planned for about 30psi and just wanted the fastest spool and longest torque curve possible. Original plan was VNT GT2256V for the small turbo and a T28 for the big one.
My main holdup (besides life getting in the way) is my engine bay is really cramped for space. I've bought a later model wagon with factory air suspension which moves the shock towers and clears up a lot of space.
So now on-top of a turbo build, I have a whole wagon build.
Can't win some days.
Here's a pic of the plan I had:
I wouldn't bother with compounding until above 40psi or so unless you do the clever Borg Warner bypass setup (as in BMW, VW Amarok etc). And, thats complicated with process control/valving etc. The compounding of the inefficiencies is the issue. Of course, your still better off efficiency wise than a conventional supercharger and on top of that losses are more than made up for with increased power if thats the end game. If you want big numbers, its the only way to go. I also plan on a 100psi+ 1KD-FTV, and plan both to be vnt's.
Compounding ineffeciencies. Hmm never quite heard it put that way. How are these ineffeciencies comounded?
First turbo 60% efficiency = a loss of energy of 40%. The air then travels to the next turbo with a 60% efficiency and futher loss of 40%. 100 - 40 = 60%. 60 - 60% = 36% total efficiency. Unless you bypass the first turbo when in the second turbos stage. 30 psi is still 30 psi, so you will have the power. But the turbo's wont be working as well as they could be. For such low boost as 30psi. A well sized single turbo would be better.
Well that is kind of strange as your math seems logical, except my turbo outlet temps give me different readings. At 25psi, 2500rpm, turbo Inlet temps were 21c and outlets were 151C pre intercooler measured at small turbo outlet (overall boost). 69C post intercooler . I roughly calculated it to be overall 70% effecient.
Now mapping the compressors showed less than 60% effeciency for the large turbo (off map as it was too small) and about 73% effecient for the small turbo.
So according to your math my compounded ineffeciencies would net about 43% overall effecient (60% x 73%) or 243C outlet, where as im getting 151C. So what gives?
I have measured outlets and inlets with multiple k type probes with multimeters midstream with only 3C variation so I went with the worst numbers.
And please dont just say im not getting it as it is not really an answer. I guess im sort of looking for an answer involving numbers.
Now mapping the compressors showed less than 60% effeciency for the large turbo (off map as it was too small) and about 73% effecient for the small turbo.
So according to your math my compounded ineffeciencies would net about 43% overall effecient (60% x 73%) or 243C outlet, where as im getting 151C. So what gives?
I have measured outlets and inlets with multiple k type probes with multimeters midstream with only 3C variation so I went with the worst numbers.
And please dont just say im not getting it as it is not really an answer. I guess im sort of looking for an answer involving numbers.
Last edited:
Doesn't work like that.
Two stages of compression and the inevitable heat-loss between give you cooler output temps than a single stage. I have run all the calcs before, but can't be bothered finding them right now. Just trust me on this one.
On the turbine side, a less efficient turbine puts out hotter exhaust gas.
The inefficiencies you will see at the pump are actually the extra drag, pressure loss and heat-loss pumping air through all that piping and scrolls. Basically it takes power to pump extra air and if you don't need it, you don't want it as it'll cost you extra fuel.
Of course the whole reason for compounds isn't usually silly boost levels, it's a much wider operating range.
Hi Dougal; agreed and its also a good reason to have electronic boost control to target an AFR during normal driving to save on economy. One issue with waste gated designs is the need to have a low pressure waste gate as default and use electronic controlled bleed to effect the boost increase, but the waste gates are sensitive to emp, so at high pressures they blow open. This could be solved of course with a better waste gate design. This is one of the reasons I like vnt - its easier to achieve this, even have near zero boost.
Theoretical from my side only relating to compressor efficiency; though I am sure I read the same thing on the Borgwarner site (whitepaper on the compounding with bypass) and it makes sense to me. The two compressors must be treated as independent systems, so if one compressor is only 80% efficient, that has no bearing on the efficiency of the succeeding stage. From real world examples, logic suggests that if it were not so, there would be no need for compressor side bypass on the modern OEM systems. There is inter stage cooling even without an intercooler and I can't answer Gerg on his figures except for the effect of that type of cooling.
On hot side, my reference to efficiency is limited to the waste gated low pressure turbo that performs the final exhaust stage and thats the reason I chose for my drag racing 1KD-FTV (on paper) to use vnt for final turbine exit.
The big gain on these conventional non bypass compound turbo setups is significantly increased overall turbine efficiency. However, its still not as good as a well matched single stage vnt unless low pressure turbo of compound setup is free boosting - then it can be excellent
One thing that doesn't seem to be referred to much on forums is exhaust back pressure which can reduce VE of engine and increase exhaust scavenging pumping losses. With too small design giving high inlet manifold pressure yet providing a lower mass flow than theoretic and/or BSFC calculated higher than theory. Ive seen this when I changed form a waste gated design to vnt design on an engine and picked up almost 10% more power at wheels in higher rpm (top 25% of range) as a result without changing fuel.
On separate note:
Bigboy is running 30psi on a Gturbo G2. It calculates that it also should be able to do it however I expected it not be able to do it to 3500rpm used on turbine drive. Well, After testing a 1HDT last night I saw 27 to 3500 and 25psi out to 4200 without really trying to achieve that. So, it would seem it should be able to do it. Considering Im now seeing 15psi at 1400rpm, 20psi at 1500rpm with that model..... Im happy with the result. The current (revised) Bad Boy Stage 1 has also been boosted on another 1HDT to 37psi at 3000rpm inadvertently. Owner commented that the overtaking seemed more spirited than usual and was shocked with the 2.5 (or maybe 2.6..) Bar on his gauge!
Theoretical from my side only relating to compressor efficiency; though I am sure I read the same thing on the Borgwarner site (whitepaper on the compounding with bypass) and it makes sense to me. The two compressors must be treated as independent systems, so if one compressor is only 80% efficient, that has no bearing on the efficiency of the succeeding stage. From real world examples, logic suggests that if it were not so, there would be no need for compressor side bypass on the modern OEM systems. There is inter stage cooling even without an intercooler and I can't answer Gerg on his figures except for the effect of that type of cooling.
On hot side, my reference to efficiency is limited to the waste gated low pressure turbo that performs the final exhaust stage and thats the reason I chose for my drag racing 1KD-FTV (on paper) to use vnt for final turbine exit.
The big gain on these conventional non bypass compound turbo setups is significantly increased overall turbine efficiency. However, its still not as good as a well matched single stage vnt unless low pressure turbo of compound setup is free boosting - then it can be excellent
One thing that doesn't seem to be referred to much on forums is exhaust back pressure which can reduce VE of engine and increase exhaust scavenging pumping losses. With too small design giving high inlet manifold pressure yet providing a lower mass flow than theoretic and/or BSFC calculated higher than theory. Ive seen this when I changed form a waste gated design to vnt design on an engine and picked up almost 10% more power at wheels in higher rpm (top 25% of range) as a result without changing fuel.
On separate note:
Bigboy is running 30psi on a Gturbo G2. It calculates that it also should be able to do it however I expected it not be able to do it to 3500rpm used on turbine drive. Well, After testing a 1HDT last night I saw 27 to 3500 and 25psi out to 4200 without really trying to achieve that. So, it would seem it should be able to do it. Considering Im now seeing 15psi at 1400rpm, 20psi at 1500rpm with that model..... Im happy with the result. The current (revised) Bad Boy Stage 1 has also been boosted on another 1HDT to 37psi at 3000rpm inadvertently. Owner commented that the overtaking seemed more spirited than usual and was shocked with the 2.5 (or maybe 2.6..) Bar on his gauge!
Last edited:
Heh I like his "more spirited" response with 37lbs boost. I bet it was more spirited. I agree with you that drive pressure is rarely touched on most forums, except on gas engine sites which dont site the pressure, but clearly see higher HP figures with larger turbines and housings mainly due to increased VE. I did see a rare comparison with a holset vs an aurora 2000. I didnt care much for the aurora numbers as it included some high flowing intake manifold which pushes everyting to their favor, but did show the HY35 drive pressure and boost on a 5.9 cummins. Forgive the clarity, but shows boost/drive of 5/7, 10/13, 15/17, and 20/24. It does jump up sharply after 25lbs boost. I thought this was quite respectable for an old turbo that is generally thought of as a dog. Id like to set it up on the bottom and let it free boost and see how it performs. The HY turbine is 65mm 9cm housing with a 76mm compressor. It should be an easy swap as it has a garrett footprint.
You've probabaly noticed too, holset maps don't show efficiency islands. They do acheive a very wide and tall compressor map, but I suspect it's at the cost of efficiency.
Most turbos when well matched can produce more boost than drive pressure at the best operating conditions. But that graph doesn't quite make it. Meaning the efficiency is down on either/both compressor and turbine.
Years back I ran a tiny T25 turbo which with my drive pressure guage could produce more boost than drive pressure if the rpm was at 2000 or below and the EGT was at 600C or above.
Fast forward five years and two weekends ago I reinstalled the same turbo combination. But this time with a suitable wastegate actuator.
I did this after finally plotting out the complete 4BD1T airflow requirements and realising I was in surge with the 60mm 60trim compressor. By going back to a 51.3mm T25 compressor and dropping form 24-20psi to stay on the map, efficiency would improve enough that I was only giving up a few % in air density. Further, with a working wastegate the turbine doesn't choke and I'll be able to produce power further up the rev range.
So I'm back where I was 5 years ago, but with several flow and setup improvements along the way. 5 years ago I couldn't find a good 22psi wastegate actuator.
I've got about 95% of the torque I had with the bigger turbo, but about 25% more power and about 30% more usable rpm. With the same fuelling, EGT's are almost exactly the same (suggesting the product of air density and VE is the same) and it's heaps smoother at low rpm. It's also faster uphills.
I've been meaning to get some drive pressure results, but I'm battling to find all the stuff I had. I've moved twice since I had it all setup. Give me some more time and I'll get more drive pressure results from a tiny turbo on a big diesel.
Hey Gerg... Is there anywhere we can get a look at a bigger/readable copy of this drive/boost comparison diagram...
Yeah that is why I apoligised. I looked for like an hour and found nothing. Sorry
