12HT Power Mods - What have you done? what figures does it make? gimme the details :D

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M

Michael756

Joined
Jun 5, 2016
Threads
2
Messages
4
Location
Australia
hey fellas,
wondering what people have done the their 12HT's to gain more power, whether you have done insane stuff to get ridiculous power or if you have tried to play it safe and get good power as well as engine life, just show me what youve done to your 12HT! im personally thinking of doing some mods to the engine and i wanna know what the limit is before you start making the engine "bullet proof" so i figure the best way of doing this is to see what you all have done. so get posting fellas, im happy to read along, so type away! :woot::woot:
 
mild mods is get a good quality manual boost controller 14/15 psi max on standard turbo i have upped mine to 12 to be on the safe side get a boost gauge and exhaust gas temp gauge . 3 inch exhaust intercooler and adjust fuel pump, next would be turbo upgrades as suggested gturbo but would need to get your engine health checked when really upping the boost e.g. gturbo and the like.
 
I have a straight pipe 3" exhaust on mine thats so short it dumps before the rear tire. Sounds killer and noticeable increase in power. Best thing I did to the 12HT so far is re-gear to 4:11's.
 
whats the diameter of the exhaust pipe at the turbo/down pipe. going to a bigger exhaust that your narrowest point won't make a lot of difference. it may sound better but performance wise your narrowest place is going to restrict your flow the most. you'll just be wasting your money to go much bigger
 
As per every performance-related mod there are trade-offs involved: so you will need to work out at which end of the spectrum you eventually want to be i.e. "road burning rocket" - with consequentially lower service life and higher costs, "steady dependable reliability with a bit more poke than standard" some higher costs but with your own "flavour" - or "largely stock but tweaked"

I'd suggest the following:

1) If you haven't already, have your driveline thoroughly checked over. It's no good spending money on mods only to have your gearbox fail or to lose all the benefits of a 5% power increase through a parasitic drag caused by incorrectly tensioned bearings. I would also suggest getting the brakes thoroughly inspected and making sure they are working as well as possible.

2) Have your engine checked out by a mechanic who knows his stuff with the 12ht. This isn't the ordinary 4wd or toyota mechanic - it needs to be someone who can check the injector spray patterns, overhaul the pump, test all the pump pressures and test the compression on a diesel engine. Ideally it should be someone with a rolling road; because you need it tested through the rev range. I know this sounds "boring" but these engines are getting old now so getting the basics right is important. Also you need a baseline for your build.

3) There is a body of evidence in relation to the compression rings on these motors - they are amongst the best motors that Toyota has ever made. However, the pistons were manufactured with a softer than ideal seating area for the top ring. This means the natural cycling of the engine causes the rings to wear this groove to the extent that, after some time, they will become loose and score the bore; eventually jamming the engine. The evidence appears to suggest that this occurs somewhere around 350,000km. However, in vehicles that have spent a long time idling (e.g. Japanese imports) it can be shorter.

Prior to spending cash on performance mods a good long-term measure is to have the pistons swapped out for new units manufactured with better metallurgy in the ring seating area. You can do this relatively inexpensively if you catch your engine before it damages the bore. This way you can often leave your crank shaft in place and just replace your shell bearings and pistons/rings. This is much cheaper than a full rebuild and you end up with an engine that is good for a service life of 1,000,000km if it's treated well.

4) While you have the head off it's a good idea to have it professionally cleaned port-matched and have a valve job done. This is in the "small gains" department by itself and you can't get anywhere near the gains you get with an equivalent petrol engine, however, it allows other work down the track to be much more effective.

ok somehow mud has shrunk my text.......going to need a second post!

Ironbark
 
It's not that they have pistons made out of a soft material, the pistons you want have an alfin insert around the top ring land. An alfin insert is a band of steel set into the piston. You can see the different coloured band of metal around the top ring here. This is an alfin piston.

924402761_817.jpg


You really don't want to go chasing large power increases on high KM motors without the alfin pistons. If your engine has been rebuilt before it will likely have alfin pistons.

With the alfin pistons the sky is virtually the limit. It's a relatively low compression, stoutly built, direct injection engine. I've never heard of 12H-t engine failure related to high boost/fueling levels except for with the standard pistons.

Gbentink (Graeme from Gturbo) has a number of threads of here on getting more performance out of the 12H-T. These include porting the head, stroking/boring and obviously turbo upgrades. If you want to get serious power then searching through his posts will be well worth your time.

Many on here have simple larger exhausts and wound up boost and are happy with that. From there you can move to fitting intercoolers, upgrading the standard turbo (7M-gte compressor wheel is a common upgrade), then upgrading to a different turbo (personally I'd look a HE221W, or of course there are the GTurbos but they are very expensive).

There's many running over 20psi reliably with just alfin pistons. The next step above that would be fitting bigger elements to the injector pump and perhaps compound turbos (though there are many modern turbos with compressor maps that go high enough to not warrant compounds), I'm yet to see someone do that though.
 
Ok now to the actual performance mods!

5) In terms of a smaller initial outlay the biggest "bang for your buck" is to go with a 3" turbo-back mandrel bent exhaust. The stock system is highly restrictive and robs power. To avoid nasty hot spots and annoying problems get someone who knows their stuff and have the injection reset to complement the system. This means a rolling road and a proper mapping with emissions analysis. When I had this done and it was like night and day I have a dyno run somewhere but I'd have to hunt it out.

6) Brakes! Before you do more, get your brakes upgraded. The stock system is marginal and will prove inadequate once power is raised. I have a system that looks stock but is anything but. My front disks were a custom run from the RDA plant in Queensland and I also have new drums from them. Others have gone with different setups so once again there is a host of options and what appeals to me may not appeal to you. My setup will allow me to lock the wheels even at slow speeds but, more importantly, it will operate effectively after repeated braking when heavily laden on winding descents.

6) G-Turbo - this is a really good upgrade that is well covered on this forum. The ct26 (stock 12ht turbo) has a limited lifespan and is old technology now. When yours is ready for a rebuild (around 350,000km) go for a g-turbo instead. Graeme has a few options, read the threads and have a chat with Graeme. He's in Perth and is exporting these things worldwide. This can give you as much power as you could ever want with the 60 series chassis. There are dyno runs floating about for this too.

7) Intercooler - to get the full benefits of a turbo upgrade you should consider an intercooler. I did this on one of my cruisers and it was a great improvement. It lowered the exhaust gas temperatures for every step of the power range. This decreases engine wear and increases durability. With my new project I won't be adding the intercooler at first though. I want to see how it sits with the G-Turbo alone and don't want to do body mods or add complexity due to the remote country I travel in.

8) Induction: once you get beyond standard turbo upgrades, the induction system needs upgrading. You'll need a less restrictive intake system with a larger diameter. This isn't hard to do, but there are no kits that I'm aware of. You're into custom work to get a mandrel bent section of tube made up and bodywork to alter the wings for your snorkel. I did my 70 series with a mate in his shed not high level engineering but a bit of a fiddle.

9) Capacity increase. I've never done this but I've read of a few blokes who have over the years. It is a pretty expensive path to take and given the power increase available with the other mods above I can't see it's worthwhile. When I had a chat with one of the fellas who had gone down this path he had basically decided to do the "ultimate 12ht" as an engineering exercise. If you want/need more than the turbo/intercooler options offer I'd look at a different vehicle or a V8 transplant.

Ironbark
 
dare said:
It's not that they have pistons made out of a soft material, the pistons you want have an alfin insert around the top ring land. An alfin insert is a band of steel set into the piston. You can see the different coloured band of metal around the top ring here. This is an alfin piston.
Click to expand...

As I said:

Ironbark said:
the pistons were manufactured with a softer than ideal seating area for the top ring
Click to expand...

Replacement with pistons fitted with Alfin compression grooves is one means of combating the excessive wear characteristics of stock toyota 12ht pistons - there are also others but this is the "standard" methodology and the cheapest. You can also get other types of pistons that achieve the same thing.

Alfin is a particular type of engineering/metallurgical solution - i first came across it when working on improved braking for a motorcycle - sometime ago now.

Ironbark
 
What really limits the power of 12H-T is the IP. 110cc is the max volume it pushes out. That means you can't get THAT much power out of the engine with stock(read= maxed out) IP. I don't recall the numbers what is the max HP the stock IP is capable, something between 180-200HP? Even that moves your rig pretty decently..
You either need to upgrade to different (bigger fuel capacity) IP or have somebody to custom build the existing IP for more capacity, that can cost some coin however. What would be the bigger capacity pump, that i don't know.

Somebody mentioned the down-pipe diameter. Inside diameter is about 3".
Stock exhaust can be shoved up there, it really eats power. 3" straight pipe is the way to go. (or with freeflow muffler/s if you want it quieter)
 
Ironbark-good info.
I've got a 12H-T I just replaced a leaking head gasket. I wish I'd had this info then. That being said, the guys
who did the head gasket do really good work, but are a bit too performance oriented. My preference is forward progress with caution.
So I have the boost increased to about 10 psi now. I'm not sure how he did that. I do have a nice custom 3" mandrel exhaust with a
flowmaster free flowing muffler. I don't want noise. There is a company here that makes a very nice muffler,
Aero Exhaust AT3030XL Performance Muffler 3" inside diameter (Medium Sound)
So I'll swap over to this when the time comes.
I really like the info on the pistons, if you could pm me with proper contact info on how to acquire the internals for that piston
swap I'd sure appreciate it. My motor is around 275,000+ as near as I can tell. I use the truck for long expeditions up north,
5000 km/trips. I just want something ultimately reliable and durable. You know, another 300,000 wouldn't hurt!
Aside from rebuilding injectors, can anything be done to improve them, or is it just clean and adjust to spec?
I've been told the inline pump is one of the most reliable of all, so I don't ever give it much concern. I have no interest in
messing with the stock settings on this. Unless you have some maintenance advice.
 
cruiserpilot said:
I really like the info on the pistons, if you could pm me with proper contact info on how to acquire the internals for that piston
swap I'd sure appreciate it. My motor is around 275,000+ as near as I can tell. I use the truck for long expeditions up north,
5000 km/trips. I just want something ultimately reliable and durable. You know, another 300,000 wouldn't hurt!
Aside from rebuilding injectors, can anything be done to improve them, or is it just clean and adjust to spec?
I've been told the inline pump is one of the most reliable of all, so I don't ever give it much concern. I have no interest in
messing with the stock settings on this. Unless you have some maintenance advice.
Click to expand...

Sorry for the delayed reply: "Engines Australia" supply a kit containing a good base for replacing pistons. As they sell a number of these kits it is cost effective. There are other options for even higher specced units but at a cost more than 5x those in the engines australia kit. If there is interest I can point folks there but it's not a good value proposition.

I replace the seals and gaskets in this kit with genuine toyota parts wherever possible.

Some also choose to replace the various plugs in the head and block with brass plugs. I've always run a high-quality, brand-name, anti-corrosion coolant in my cruisers as a protective measure (used Castrol a lot when I was younger and have switched over to Penrite in the last decade).

On injectors - yes pretty much clean and adjust to spec from a normal .

The fuelling will need to be adjusted to take advantage of a more free-flowing exhaust. This isn't "messing with the pump" so much as, getting the fuelling to match the boost and gas flow characteristics. For this, a rolling road with the exhaust probes and temperature probes is critical.

Also if your pump hasn't been overhauled and tested then it's a good idea to do that. Again you need to have confidence in the place doing the overhaul and testing. Plus, there's no point in paying the fee for the overhaul and it just being bolted back to factory settings. You need it adjusted to the dynamics of your car.

The stock pump is a good pump; very reliable, serviceable and durable. There are other options, but once that is required the overall cost of all the adaptations that are necessary mean that the project is getting into a level of engineering and cost that would mean a different vehicle makes more sense. Major drivetrain components are not designed to deal with the amount of torque that is generated.


Ironbark
 
Ironbark said:
As per every performance-related mod there are trade-offs involved: so you will need to work out at which end of the spectrum you eventually want to be i.e. "road burning rocket" - with consequentially lower service life and higher costs, "steady dependable reliability with a bit more poke than standard" some higher costs but with your own "flavour" - or "largely stock but tweaked"

I'd suggest the following:

1) If you haven't already, have your driveline thoroughly checked over. It's no good spending money on mods only to have your gearbox fail or to lose all the benefits of a 5% power increase through a parasitic drag caused by incorrectly tensioned bearings. I would also suggest getting the brakes thoroughly inspected and making sure they are working as well as possible.

2) Have your engine checked out by a mechanic who knows his stuff with the 12ht. This isn't the ordinary 4wd or toyota mechanic - it needs to be someone who can check the injector spray patterns, overhaul the pump, test all the pump pressures and test the compression on a diesel engine. Ideally it should be someone with a rolling road; because you need it tested through the rev range. I know this sounds "boring" but these engines are getting old now so getting the basics right is important. Also you need a baseline for your build.

3) There is a body of evidence in relation to the compression rings on these motors - they are amongst the best motors that Toyota has ever made. However, the pistons were manufactured with a softer than ideal seating area for the top ring. This means the natural cycling of the engine causes the rings to wear this groove to the extent that, after some time, they will become loose and score the bore; eventually jamming the engine. The evidence appears to suggest that this occurs somewhere around 350,000km. However, in vehicles that have spent a long time idling (e.g. Japanese imports) it can be shorter.

Prior to spending cash on performance mods a good long-term measure is to have the pistons swapped out for new units manufactured with better metallurgy in the ring seating area. You can do this relatively inexpensively if you catch your engine before it damages the bore. This way you can often leave your crank shaft in place and just replace your shell bearings and pistons/rings. This is much cheaper than a full rebuild and you end up with an engine that is good for a service life of 1,000,000km if it's treated well.

4) While you have the head off it's a good idea to have it professionally cleaned port-matched and have a valve job done. This is in the "small gains" department by itself and you can't get anywhere near the gains you get with an equivalent petrol engine, however, it allows other work down the track to be much more effective.

ok somehow mud has shrunk my text.......going to need a second post!

Ironbark
Click to expand...
hey bud, this is something i will definitely look into, however my motor has only done about 110*** k's and has been a holiday truck since it had a new motor put in it in 1998. so im not quite sure that a full check over is necessary as of yet? but ill defenitly look into it, id much rather a long lasting engine that something thats insanely fast and ready to explode :)
 
Loving the amount of responses i am getting out of this thread! really didnt expect so many people to have even seen this post! :D thanks heaps guys! and ironbark, youve really helped with my plans for my 60, definitely going to look into having the driveline and engine inspected before i do anything like a turbo upgrade, ill probably just start with a boost controller, boost and EGT gauge and maybe an intercooler if i need it, this will be followed by a dyno tune when i have the coin. thankyou all for your help! im sure this post will help both me and a few of my mates with out 60's :D
 
My 12ht had 350k on it when I bought it with "blown head gasket". On tear down top ring groove was worn to 3 x the width of the ring. For performance upgrades while rebuilding I tidied up the ports, fitted small front mount intercooler, full 3" exhaust and fitted 1HDT-ft ct20 turbo. Injection pump ran out of fuel at around 130rwhp on 12psi on the dyno.
 
Mick at ADS injection in Mareeba has a supply of MLS, multi layer steel, head gaskets.
Diesel Central, also in Queensland do a high performance upgrade for the injection pump.
 
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