Yet another 12H-T performance build

[Flavien52]

There are already a few threads about 12H-T performance builds. As I am now in the way of building mine, I decided to start this thread in order to share I few things I learned or will learn on the road. I will also share the results of my past and future experiments. You will find here a lot of things you can already find on other threads, as the amount of resources here is invaluable.
The starting point of this projet is my 1988 European spec HJ61. I bought it in 2023 with 275,000 km on the clock, in a quite pitiful state. After a few weeks I faced a huge head gasket leak so I decided to rebuild the engine entirely. Here are a few pictures of the result, after :
- installing new gaskets everywhere (Toyoya OEM)
- +0.5 mm of cylinder bores and surfacing of the engine block, by a local artisanal engine shop.
- installation of new Alfin pistons, the kit was a +0.5mm kit from Teikin in Indonesia. I read on other threads that these are some of the best aftermarket ones.
- new main bearings and rod bearings
- new clutch plate and disc (OEM Aisin parts, disc is DTX-076 part number and I chose part number CTX-133 for the plate which is a reinforced one that is standard for other Land Cruiser 12H-T applications)
- vapour blasting of aluminium parts for aesthetics, and POR15 Gold engine paint
- etc... I took quite some time also to check the tolerances for the parts or bearings I did not replace.

I don't emphasize on everything I did, this is just to say I started by trying to rebuild the engine in a right way. This reduced the black smoke once the engine was installed and I hope I could now rely on it. This was confirmed by a 10 000 km trip to Iceland from France without any major issue, except worn alternator brushes and minor coolant leaks from the radiator that was getting old also...

But as I read a lot about the improvements you could get on a 12H-T by increasing boost, tuning the fuel pump, etc. I would not stop after this rebuild...

 

[Flavien52]

The chosen plan, after much reading on this forum - I decided I would not cross reference other threads as a few searches on Google can bring you to them - was the following:
- upgrading the turbo. I decided I would by a GTurbo G300 as they are widely regarded as the best you can get, even though they are expensive and I heard good feedback from people who installed Kinugawa turbos of tuned their factory CT-26 to mild boost (12-15psi) simply fitting a boost controler.
- fabricating a 3" custom exhaust. From all the sources it is obvious you can't get all the benefits from a new turbo, or boost increase (nor can you get all the benefits from subsequent mods) if you don't upgrade the exhaust to at least 3 inches.
- installing a front mounted intercooler. Again, this is the only way to take all the benefits you can from increased boost. Otherwise, to high EGTs will limit the amount of fuel you can get from the factory pump (or there is a too high risk of ruining your engine IMHO).

This is where I am at at the moment I am starting this thread. I am also considering :
- upgrading the airbox if that is worth it
- I read about "high-flow" injectors as a simpler way to get more fuel from the factory inline pump, but I also heard mixed feedback from a friend who tried them and could only get more black smoke...
- I don't plan on modifying the injection pump as this is a lot of hassle, even though it would be the proper way to even more power...

 

[Flavien52]

GTurbo G300 installation :
I do not have much to write about the GTurbo installation. I bolts easily in place of the original CT-26 turbo. As a side note, I bought the G300 "Grunter" that is now superseded by the G333 "Titan" that seems to bring more boost earlier...

The only things that come to mind are :
- the bottom bracket does not bolt anymore, you need to add a custom bracket if you want to support the new turbo from the bottom. Many users report that it is not mandatory to refit the bracket, but I am thinking it might stress the exhaust manifold connections a bit more, so I will build a bracket in the future.
- the turbo inlet diameter is bigger so the factory elbow does not fit. It is a bit of a pain to build a custom elbow from standard silicone part as the factory one as a weird shape (90 degrees bend along with another 30ish bend in another direction). PDI (see intercooler beloew) makes a custom silicone elbows that is not expansive and I recommend getting it.

GTurbos are already primed in factory and can be driven normally as soon as they are installed. I also recommand buying a water and oil hose kit such as this one along with the turbo. This kit is good quality and allows an easier installation than with factory parts that are oftentimes showing their age. It also allows cooling of the turbo by connecting it to the cooling system even though it is not mandatory.

Toyota HJ61 12HT CT26 Turbo Oil Water Line Kit | Replace Rigid Pipes

Flexible oil and water line kit for Toyota HJ61 12HT with CT26 turbo. Includes 4AN oil feed, 3/4" silicone drain, and 6AN water lines to replace stock pipes.

www.gryphontek.com

I also fitted 3 gauges :
- Coolant temperature, that I connected to the 1/2 NPT port the is at the firewall end of the cylinder head
- EGT, I installed the gauge on the exhaust manifold after carefully drilling it
- Boost, I drilled and threaded a hole next to the intake manifold to have a precise reading. The pressure port that is on the turbo itself would give you a higher reading as the diameter here is smaller.

I did buy the Autometer gauges that were supplied by GTurbo, after 1 year of use they have been very reliable. You need a voltage convertor to use them on a 24v system as is the case on the European specs HJ61.

Tuning of the fuel pump : the installation of the GTurbo eliminated all the residual black smoke I had after the engine rebuild. However there no noticable performance improvement if you do not tune the fuel pump. To make the reading of this thread easier, I will go back to the fuel delivery tuning after describing the installation of the new exhaust and intercooler.

 

[Flavien52]

Custom 3" exhaust
There are a few offerings available in Europe but they are either very expansive and not adapted (like still 2,5 inches in diameter), or too expansive with substandard quality materials.
As I have a MIG welder which is more or less suitable to weld stainless (TIG will always be better), I bought some exhaust parts (straight pipes, elbows, a straight trough muffler...) in 304L from a German manufacturer and decided to build it myslef.

It is quite straightforward if you follow the same route as the original exhaust and use some exhaust parts which allow overlapping connections between parts (as shown in the pictures). That way you can cut and "dry fit" the parts in situ, weld a few points once the routing is good, and finish the welds in the shop.

The most difficult part is the flanged connection to the factory dump pipe. It allows the connection of a 3 inch exhaust using a standard 3 point flange, but the fitting is very tight. I have to redrill the holes of the flange to get them closer to the pipe, and to use M10 socket cap head screws that are the only one that can fit. I also had to buy a special screwdriver 8mm Hex bit socket and use extensions to attach them.

Also, I first made the exhaust shorter with the end on the rear passenger side, but it had three major drawbacks : it was too exposed to rocks or other stuff while offroading, you could smell the engine too much with the window openned from the rear passenger seats, and it was too noisy. So I quickly built a proper exhaust, in two parts, that follow the same exact route as the original one. The fitting aroung the rear axle is quite tight but this is easily manageable with a few 30 degrees elbows and some trials.

Below are the pictures with the initial routing :

 

[Flavien52]

And here are pictures and a video showing the proper routing. I know the welds do not look good, but they will be strong enough...

 

[Flavien52]

Intercooler installation
I installed the turbo and exhaust at the beginning of 2025, and I finally ordered an intercooler kit from PDI Intercoolers in Australia for Christmas. As with GTurbo the customer service is very good and the kit is high quality.

The PDI kit for the HJ61 is designed for RHD vehicules, so I had to adapt the routing of the pipes to take into account the steering box that gets on the way with the standard kit. Brian from PDI provided with two more 30 degrees silicone elbows and some stainless pipe that allowed me to install the intercooler quite easily.

The instructions provided with the kit are clear and this was a 2 days job, and I must say I took my time.

 

[Flavien52]

Here are two other pictures :

 

[Flavien52]

Fuel pump tuning - basics facts about the 12H-T inline pump

This is where it starts to get interesting. You will find a lot of advice on the tuning of the injection pump on mud and on the web (especially the very good website from Tim Law : 1987 Toyota Landcruiser HJ61 12H-T | landcruiser | Tim Law - https://www.peoplehelp.com.au/landcruiser/index.html).

However I could not find any place with comprehensive guidelines on the tuning of the 12H-T inline pump that must be done to take the full benefits of the above upgrades. I will try to cover everything I learnt in the next posts.

Let us start with the way the 12H-T fuel pumps works. It is basically made of pistons that are connected to the engine, that are called plungers, and the course of the plungers that is synchronized with the rotation of the engine allows the delivery of fuel to the injector. The course of the injector is fixed, but the rotation of the plunger along their main axis allows to adapt the amount of fuel that is injected at each stroke, thanks to an ingenious sort of gullet that is machined through the plungers.
So, to keep it simple, the amount of fuel that is injected is governed by the rotation of the plungers, which is governed by the translation of a rack. The governor of the pump regulates the position of this rack, through a system of weights and springs that adjusts the position of the rack according to the speed of the engine and the position of the accelerator lever.

Many adjustments of the governor are possible and are extensively covered in the 12H-T engine manual. Those adjustments are either made with screws or using shims to adjust the preload of the governor springs. Some of these adjustments allow to fine tune idle speed and idle speed regulation, engine maximum speed, fine adjustment of fuel delivery along the power curve...

I found there are mainly 3 screws to deal with to tune the fuel delivery to increase power, and you can get good results with tuning only the off and on-boost screws. I will do some experiments in the coming weeks by adjusting the boost compensator bushing.
- off-boost screw : this screw is located on the firewall side of the governor (see #1 in pictures below). It controls the maximum rack position when there is no boost from the turbo. It is accessible using two 12mm wrenches and adjusted using a flat screwdriver. Turning this screw clockwise allows for more fuel delivery. The adjustments are quite fine, 1/8th of a turn can show some differences. The effect of the adjustments on this screw can be felt in the lower rpm range when there is no boost from the turbo yet (800 to 1200 rpm), but also higher in the rev range when maximum boost is not yet reached. Setting this screw allows indeed the turbo to charge earlier by adding more fuel in the intermediate rev range (say 1200 to 1800 rpm) and will therefore allow the turbo to reach maximum boost sooner. The drawback is that allowing too much fuel delivery in the lower rpm range, when there no or almost no boost from the turbo, will overfuel the engine and produce a lot of black smoke when you stab the throttle or change gears.
- on-boost screw : this screw is located on the other side of the governor and controls the maximum rack position under full boost (see #2 below). It is accessible using two 10 mm wrenches and a 3mm Allen key. Around 3 turns from the standard position gives maxes out the on-boost setting you can get (after that you will just remove the screw from the governor). This screw needs to be turned counter clockwise to increase fuel. Indeed, what you want to do is allowing the rack to move further in the direction of the front of the pump. Setting this screw allows to adjust the amount of fuel at full boost, that is above 1800 rpm approximately. This is the one that will have the most noticeable effect on performances above 1800 rpm. Setting this screw also has a lot of effect on EGTs in this rev range, so care must be taken when unwinding it. You should not really do it without having an EGT gauge, preferably installed pre-turbo, to monitor exhaust temperature.
- boost compensator guide bushing or starwheel : the boost compensator is a diaphragm that is connected to the intake and that compresses under the boost generated by the turbo. Movement of the diaphragm allows further movement of the pump rack. When the diaphragm is not compressed at all, the racks maximum translation is solely controled by the off-boost screw, but the more the diaphragm is compressed, the more movement is possible. According to the manual, 5mm of movement should be obtained at 19 psi. The overall maximum position of the rack, whatever to position of the diaphragm, is limited by the on-boost screw. The diaphragm sits on a spring and the spring's preload is controlled by the starwheel (also called guide bushing) that can be accessed by removing the plug on top of the boost compensator (see #3 below). The manual is not precise about this setting, but unloading this spring allows for more diaphragm action at low boost. There is a thread on mud from a user that had his pump serviced and badly tuned: the spring preload was so much increased that setting the on-boost screw had absolutely not effect...

Thread '12HT Boost Compensator Diaphragm'

Sep 9, 2018

Hi folks,
my first post here went into the classified forum - so I´ll try it again.

missed some ponys inside my good old 12ht so started to search for them.
As I had checked and ruled out many other possibilities before I focused on the boost compensator.
The culprit is most definitely in the diaphragm itself. Not enough movement in it. ....my one despite feeling quite allright seems to be a bit on the stiff side and has probably hardened out as it did not pass the test which is described in the manual: Apply 1.36 bar or 19,7 psi and achieve 4-5 mm of movement at the rod. If less discard...

• relaxedcruiser
• 12ht
• Replies: 11
• Forum: Diesel Tech / 24 volts

• 

If the guide bushing is correctly set which must be the case from factory, there is no real need to touch it to adjust the pump after a turbo and intercooler installation. However, I have the intuition that tweaking it could allow more fuel delivery before the turbo reaches around 18 psi, without having to resort to an aggressive setting on the off-boost screw, thus avoiding the black smoke at low rpms you get from such an aggressive setting. I will try to experiment with that, to see if I can get more torque earlier in the rev range, but this screw is also the less accessible of the 3.

To sum up, these three screws govern the maximum translation of the rack, in three different ways : maximum translation at 0 boost, maximum translation under maximum boost, and the behavior in the "transition area" between 0 and full boost is regulated by the preload of the diaphragm that can be adjusted with the starwheel.

I am sure there are many ressources explaining this, but here is the best that I found at the moment. It gives a lot of details about Bosch inline pumps and associated governors, which are similar to the Denso pump used by Toyota for the 12H-T. I could only find the firts pdf in French.

 

[cruiserpilot]

Fuel pump tuning - basics facts about the 12H-T inline pump

This is where it starts to get interesting. You will find a lot of advice on the tuning of the injection pump on mud and on the web (especially the very good website from Tim Law : 1987 Toyota Landcruiser HJ61 12H-T | landcruiser | Tim Law - https://www.peoplehelp.com.au/landcruiser/index.html

However I could not find any place with comprehensive guidelines on the tuning of the 12H-T inline pump that must be done to take the full benefits of the above upgrades. I will try to cover everything I learnt in the next posts.

Let us starts with the way the 12H-T fuel pumps works. It is basically made of pistons that are connected to the engine, that are called plungers, and the course of the plungers that is synchronized with the rotation of the engine allows the delivery of fuel to the injector. The course of the injector is fixed, but the rotation of the plunger along their main axis allows to adapt the amount of fuel that is injected at each stroke, thanks to an ingenious sort of gullet that is machined through the plungers.
So, to keep it simple, the amount of fuel that is injected is governed by the rotation of the plungers, which is governed by the translation of a rack. The governor of the pump regulates the position of this rack, through a system of weights and springs that adjusts the position of the rack according to the speed of the engine and the position of the accelerator lever.

Many adjustments of the governors are possible and are extensively covered in the 12H-T engine manual. Those adjustments are either made with screws or using shims to adjust the preload of the governor springs. Some of these adjustments allow to fine tune idle speed and idle speed regulation, engine maximum speed, fine adjustment of fuel delivery along the power curve...

I found there are mainly 3 screws to deal with to tune the fuel delivery to increase power, and you can get good results with tuning only the off and on-boost screws. I will do some experiments in the coming weeks by adjusting the boost compensator bushing.
- off-boost screw : TBC
- on-boost screw : TBC
- boost compensator starwheel : TBC

To sum up, these three screws govern the maximum translation of the rack, in three different ways : maximum translation at 0 boost, maximum translation under maximum boost, and the behavior in the "transition area" between 0 and full boost is regulated by the preload of the diaphragm that can be adjusted with the starwheel.

I am sure there are many ressources explaining this, but here is the best that I found at the moment. It gives a lot of details about Bosch inline pumps and associated governors, which are similar to the Denso pump used by Toyota for the 12H-T. I could only find the firts pdf in French.

I am a good friend of Tim's. I shall let him know his webpage is still being valued. His guidance to help me tune my fuel during my
GTurbo install was invaluable. He is also personal friend of owners of GTurbo. It all went hand in hand back in the day. I have almost
100,000 kms on my GTurbo. I made my own FMIC as Brian hadn't made his kit available at the time. Curious could you let me know
what diameter tube is on the intercooler inlet/outlet? Thanks for the build, my 12HT is at the 400K mark and should get a rebuild too.

 

[Flavien52]

I am a good friend of Tim's. I shall let him know his webpage is still being valued. His guidance to help me tune my fuel during my
GTurbo install was invaluable. He is also personal friend of owners of GTurbo. It all went hand in hand back in the day. I have almost
100,000 kms on my GTurbo. I made my own FMIC as Brian hadn't made his kit available at the time. Curious could you let me know
what diameter tube is on the intercooler inlet/outlet? Thanks for the build, my 12HT is at the 400K mark and should get a rebuild too.

Hi. The inlet and outlet of the PDI Intercooler are 2.5 inches.

 

[Tim-HJ61]

Thanks for the kind words. I’ve not looked at my site for some time and it’s always pleasing to know people are still finding it useful.

I’ve picked up a bit of knowledge along the way, managed to fall into a nest of very clever engineers who tolerated my non engineering background. From working with Graeme at GTurbo I learnt about installations of turbos and tuning modules, and the practicalities of tuning. I was his customer front end for a while. From Brian at PDI I’ve learned creativity and logic, taking a thing meant for one purpose and reusing it for another. There’s Graeme’s brother Mark who raced a wild FTE in a Nissan body, careful engine builder Jim one time navigator for Mark. These are all highly innovative think outside the box types.

Where I’m at now with my 12HT is having completed about 50,000km after my rebuild. Quite pleased it’s not fallen apart and starts every time!!

Due to combustion leakage into coolant I replaced my head bolts with ?Kia j2 torque to yield bolts cut to length. Substantially more clamping pressure and now no more compression leakage. I run about 22 psi.

I had a bad run of biodiesel related fuelling issues jamming up the plunger inside the lift pump. I hope it’s not affecting my IP

I’ve towed my 1600kg caravan across Australia and back, 9000km, plus a remote desert trek of similar distance. The bushes in my springs flogged out but I found some rubbers in an abandoned Mazda Ute and they fitted sort of. Enough to complete the trip.

Rebuilders such as Jim now baulk at taking on 12HT jobs as parts such as camshafts are getting much harder to find.

ADS in Mareeba, Queensland will build a pump and bench tune it for whatever performance you want. They install larger elements. They, and other places, will rebuild injectors to plus 20, plus 50 size. Both these upgrades will give more performance, but at substantial cost. ADS supplied my MLS multi layered steel, head gasket too.

Towing the van allows good on road trialling of fuel adjustments. Now the top of the IP is covered by the inlet manifold, all I adjust is boost and the main fuel screw. Adjusting low fuel screw is important, once. No point fiddling with it if it’s right.

I can’t recall adjusting the star wheel.

My state is very flat, the eastern side of Australia has looong power sapping hills, so I could increase boost to make sure EGT stayed under control and no smoke. Settings seems to be okay now but the 10mm spanner and 5mm Allen key stay in the front console just in case.

Happy to help out if I can.

 

[Tim-HJ61]

Flavien I've read through your previous posts. You've invested a lot, well done, and you won't be disappointed. I don't have a G333..... yet! . I wonder if you have sent the mods for the intercooler to Brian to see if he could make a minor mod to suit LHD vehicles. These are not a high seller AFAIK so there's nothing in it for him. But there's no harm in sending him your pictures and talking it over with him.

I have not run coolant for ?? over ten years or so in my GTurbo's. Remember the CT26 is a generic design Toyota built to go on to Petrol powered vehicles too, which must have the coolant given the higher temperature. Mine has been fine, including high ambient temps in Australian summer and towing.

I have made a bottom bracket for the turbo with a piece of flat bar bent at 30° and holes drilled. When I was working with Graeme I had the opportunity to get a number made to be supplied as an accessory, but never got around to it.

You mention you have no workshop manual, or maybe I misunderstood. I have them on my website for free download. 60 Series Workshop Manuals - https://www.peoplehelp.com.au/landcruiser/manuals/
There is a good description of pump adjustments, but I urge significant caution fiddling with settings inside the top cap. Good pump repairers will take care and time to go through every element, adjusting it for correct and even stroke and delivery volume. I have seen some YouTube's on the process they use for this and no wonder these things are expensive to rebuild. Then add the complexity of building to non standard specifications to cater for far more air than standard, it all gets very complex and really requires adjustments on a pump machine.

Adjusting the off boost fuel is, as I said earlier, important to not smoke out people following, but in reality the GTurbo will spin up quite fast once the revs increase. Turbo's are amazing bits of kit really. Considering the speed they accelerate/respond and the volume of air they have to compress to 20psi plus the volume of air the engine is consuming.

 

[Tim-HJ61]

The stronger head bolts are Kia J2 (a 2.7 litre 4 cylinder diesel engine made by Kia). You need to buy three sets, and they consist of shorter and longer bolts. You need to cut down the longer bolts to match the Toyota bolts. Tightening is first 60nm then two 90° turns. Standard bolts are torqued to 113Nm. The Kia bolts are pulled down to about 220Nm, which give you an excellent work out. It is advisable to mark the tops with pain pen once you have completed the first or second passes to reach 60nm, then it is easier to see where you are doing the next two 90° turns.

Factory 12H-T head bolts give roughly 47 kN per bolt (~1.3 MN total).
Switching to cut-down Kia J2 TTY bolts puts clamp load closer to 85–95 kN per bolt, or 2.2+ MN total — effectively doubling head retention and dramatically reducing head lift under sustained boost. That’s going from roughly 130 tonnes of clamping force holding the head down to ~225 tonnes.

 

[Flavien52]

The stronger head bolts are Kia J2 (a 2.7 litre 4 cylinder diesel engine made by Kia). You need to buy three sets, and they consist of shorter and longer bolts. You need to cut down the longer bolts to match the Toyota bolts. Tightening is first 60nm then two 90° turns. Standard bolts are torqued to 113Nm. The Kia bolts are pulled down to about 220Nm, which give you an excellent work out. It is advisable to mark the tops with pain pen once you have completed the first or second passes to reach 60nm, then it is easier to see where you are doing the next two 90° turns.

Factory 12H-T head bolts give roughly 47 kN per bolt (~1.3 MN total).
Switching to cut-down Kia J2 TTY bolts puts clamp load closer to 85–95 kN per bolt, or 2.2+ MN total — effectively doubling head retention and dramatically reducing head lift under sustained boost. That’s going from roughly 130 tonnes of clamping force holding the head down to ~225 tonnes.

Hi Tim. Thanks for those inputs, especially about those kia bolts. Most people seem to be fine with higher boost and do not report such issues, but the fact you faced it at 22psi, which is not crazy high, is interesting. That will make me consider installing those kia bolts for added peace of mind.

In addition, the concept of torque to yield bolts always was pleasing to me, because of the higher control on camping force they allow

Do you have an opinion about the ability of the oem gasket to withstand that additional pressure without crushing ? I may have read they are also MLS type but I cannot be sure.

 

[Flavien52]

By the way, I have the manuals indeed, I think I got them from your webpage initially.

I also e-mailed Brian to thank him for the kit and send him pictures, so he can make if he wants a LHD kit as a standard option for European and North American customers. 12HT seem to be quite rare in North America but they are still quite common in Europe. There is also a small community of dedicated guys that know Land Cruisers very well. But we did not push things as you did in Australia in regard to power improvements, and kits from PDI or GTurbo are not so well known here. Import duties and shipping costs do not help also :/

 

[Flavien52]

I will now write in this post the results I got from the current modifications, along with the setting I used on the fuel pump.

As it was stated above, one should be careful adjusting the fuel settings and not just reproduce the numbers I give without care, as your initial settings or your setup may differ. A least, having a EGT gauge installed pre-turbo is mandatory before adjusting fuel, as too much heat from too aggressive setting can ruin the engine.

	Original​	GTurbo G300 @19psi​	GTurbo G300 @19psi + 3" exhaust​	GTurbo G300 @18psi + 3" exhaust + PDI front mount​
Fuel setting - off boost screw	as original	+ 1 1/8 turns	+ 1 1/8 turns	+ 1 1/2 turns
Fuel setting - on boost screw	as original	+ 1 turn	+ 1 1/2 turns	maxed out (above 3 turns)
Fuel setting - guide bushing	as original	as original	as original	as original
EGT pre-turbo - 90 kph cruise	???	400 - 420°C (750 - 800°F)	360 - 380°C (app. 700°F)	300 - 320°C (app. 600 °F)
EGT pre-turbo - 110 kph cruise	???	???	400 - 420°C (750 - 800°F)	340 °C (app. 650 °F)
EGT pre-turbo - maximum	???	app. 650°C (1200°F)	app. 650°C (1200°F)	above 600°C (1100°F) - I still have to drive a big enough hill to report a precise number
From 66 to 99 kph in 3rd, 4th and 5th gear	3rd : 8.9s 4th : 12s 5th : 16s	???	???	3rd : 5.6s 4th : 7.4s 5th : 10.1s

Here are a few comments about these measurements and settings :
- I always had 285/70r17 Kuhmo RT tyres, that are 33" in diameter.
- EGT measurements are not exact measurements, just the results from careful observation when I drive the car. The max EGT is from driving in 4th or 5th gear on a hill with maw throttle. However I always backed to throttle when it seemed I could go above 650°C, so the real max EGT from the above settings may be somehow higher when really pushing the engine at full load for a sustained time. As I find it way more difficult to reach peak EGT now I have the intercooler (small hills are now got through at ridiculously low EGT...), I have yet to report a precise number
- I did acceleration measurements in 3rd, 4th an 5th gear from 60 to 90 kph that I corrected to real speed as my speedo reads low thanks to the 33 tyres. These give a good feedback on power in the higher rpm range in 3rd gear (2500 - 3750 rpm), intermediate rpm range in 4th gear (1500 - 2400 rpm) and low rpm in 5th gear range (1300 to 2000 rpm). Sadly I did not do this measurement with the GTurbo and 3" exhaust alone. This would have given intermediate results, as the benefits I got from the installation of the intercooler felt very substantial.
- on-boost fuel screw settings were governed by maximum EGT.
- off-boost settings were governed as recommended by other like Tim : you increase at as much as you can before you get to much smoke. You then remove 1/8 or 1/4 of a turn. On my side I kept a reasonable amount of black smoke, that is I can see some if I really push the throttle under 1200 - 1300 rpms. Above that the turbo already spools as Tim mentioned. I like this setting as I never jab the throttle under normal driving, and I feel this gives me a bit of extra torque when the turbo starts to spool up, and some extra low rpm grunt when I really need it, like when I want to push trough some deep sand or some mud that surprise me at low speed.

Improvements from the turbo installation were good, and well complemented by the 3" exhaust as it allowed me to increase fuel delivery a bit more. I must also point out that I stayed on the careful side with max EGT readings, as 700 °C (1300 °F) seems a safe limit for unsustained use, maybe even for short time sustained use as 12-HT pistons are oil cooled and it is a direct injection engine. However I do not want to take any risks. This is just to say that performance from the turbo upgrade alone could be improved by a bit more fuel.

Improvements from the turbo and intercooler upgrade are huge. As you see the EGT dropped by at least 60°C in cruise, and the benefits are much higher under load (I see around 100°C improvements on some small hills I frequently climb). This is a huge benefit in itself. But now it allowed me to easily max out the fuel setting on the on-boost screw, and to increase the off-boost setting also. I reach maximum boost more than 100 rpm sooner and have way more torque whatever the rpms.
Regarding performance, I did not do some intermediate measurements, but as you can see from the fuel settings, if you assume that torque is roughly proportional to the amount of fuel and that the relation with the position of the fuel screw is linear (these are quite a lot of assumptions !), then you get roughly as much from the intercooler + turbo than from the turbo alone. This is also what I felt from seat of the pants driving.

My rough conclusion is that, if you can afford it, a GTurbo and an intercooler kit installation must be planned together, along with the exhaust mod. This will be more expensive but you can build yourself a roadmap. And if like me you bought a used HJ61 for somewhat 15 to 20 k€, and added 10 to 20 k€ in parts, fixes and upgrades, you still will end up with something less expensive than a current 70 series, that is as reliable and as powerful as the current 2.8 liter diesel...

I will update this table as I go, at least to account for starwheel and airbox experimentation.

 

[kevin in okinawa]

thank you for the insightful data presented in this thread! Good luck with the hj61 and the 12ht.