Well altitude compensation is a minimal fuel correction across the board to adjust for thinner air at altitude to prevent overly rich and hot combustion and potential engine failure. Most engines have it regardless of emissions standards and of course nobody in their right mind would remove that feature alone. In our cases, the compromise is removing it all to get rid of the emissions stuff (good) while at the same time potentially losing the altitude compensation (bad). I think @tekach's concerns are valid given the altitudes he plans to travel at, better be safe than sorry? Maybe start with fitting an EGT gauge so you are able to back off throttle, or think about solutions to quickly remove the boost hose from the compensator to reduce fuel temporarely at high altitude.
1HD-FT. The Story of an Engine That Wasn't Allowed to Breathe
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- #102
These are all empty theoretical speculations. In practice, it's much simpler: if you've started tuning and decided to move away from factory fuel delivery, the first thing you need to do is install an EGT sensor and always use it as your reference when tuning. I wrote about this from the beginning, and more than once. So why repeat it now? If the EGT settings are done correctly for low altitudes, and under prolonged full load with the pedal to the floor EGT does not exceed the safe limit, then everything will be fine in the mountains — because normally you don't drive like that there. If there are high-altitude highways that allow you to travel at such high speeds, then you need to watch the EGT and engage your brain a little — sometimes that helps. Although for a turbo-diesel, thin air is nowhere near as critical as it is for naturally aspirated engines. In any case, relying on a primitive old piece of iron like the HAC in such a situation would be naive. It's much better to rely on readings from precise instruments and on the behavior of your own engine.
There are many simple solutions for quickly and easily reducing fuel delivery and correction. The first and simplest one is to stop mindlessly stomping on the accelerator pedal ))). The second is to plug the breather hose under the compensator diaphragm with a steel ball, and then the diaphragm won't be able to perform the full travel of the shaft because it will be compressing the air underneath it. Third — I wouldn't completely disconnect the boost hose from the compensator, because the engine would become too dull. But pinching the hose slightly with a clothespin/clamp is possible. However, I prefer the first option, and as a last resort, the second one)
It varies... In Atlas, you can end up climbing very steep rocky roads at speeds like 5-10 kmh for an hour (this is my concern), in Altiplano you can have speeds of 70+ kmh on its super flat surfaces.
Fun fact, it seems that the highest road in Australia is at 1850m, it might explain Toyota's decision...
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- #104
With these speeds and conditions, you don't even have to think about EGT problems.
I traveled to the Caucasus Mountains about 10 times, at altitudes up to 3200m. Never had any EGT problems. The only condition where I have high EGT is on the highway with speeds over 120-130 km/h with the pedal to the floor.
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Vadus, I don't see the problem in thinking about this intelligently and consider technology manufacturers have used for decades. Compared to sea level, combustion will run about 10% richer at 1000m and almost 30% at 3000m without compensation. Call it theory but you can't just dismiss that because of anecdotes and at the same time talk about watching gauges all day and backing off throttle to not damage the engine. On a factory vehicle and tune we don't worry about temperatures or dangerous air fuel ratios because we know the manufacturer considered most/all eventualities and I think that is something to aspire to when talking about modifications and tuning. The reason I mentioned fitting an EGT gauge after you did multiple times (for other reasons) is because it is something we agree on, as a starting point.
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- #106
HDJ80L, as I wrote before, these are all bare theoretical speculations. Judging by what you write about constantly watching the EGT gauge, you clearly don't understand how and under what conditions EGT rises. I get the impression that you don't even have that sensor on your vehicle. How to use instruments (any instruments) can be looked up on the internet, but I'll just say that obviously you don't need to constantly stare at the EGT gauge. If you are so persistently convinced of the impeccability and inviolability of factory solutions, then apparently your fate is to drive with factory parameters and enjoy its pathetic power characteristics. That's everyone's personal choice, and I'm not trying to persuade you to do otherwise. However, I did it differently, and everything has been working perfectly for me for more than 12 years — no EGT exceedance in the mountains, even within the instrument's measurement error. And practice is the most stubborn thing in the world, especially when it's backed by proper theory, not by percentages pulled out of thin air ))))
I merely informed you about how altitude compensation is done professionally by OEMs (including on the FT/FTE and basically every other engine) and argued about how I find that preferable to monitoring gauges and adjusting driving style in constant worry. But apparently you see every disagreement as an insult and feel the need to defend your honor 
instead of engaging in rational discussion. Okay, I will shut up about it. 
instead of engaging in rational discussion. Okay, I will shut up about it.
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- #108
Thank you for your efforts, but I figured out how HAC works a long time ago and drew my own conclusions. Instead of proving obvious things to me about reduced air density at altitude and making assumptions about my reaction to all of this, you would be better off reading my messages carefully and grasping my main argument. Its essence is that in the mountains, you usually cannot drive as fast, as dynamically, and with prolonged load as you can on flat ground at sea level. Because of this, the peak EGT remains so low that the mixture enrichment, which at 4000m would add at most 100-150°C to EGT, is completely negated. This is easy. And I see nothing rational in these theoretical rantings.
Well it's a narrow set of conditions then... slow driving, monitoring gauges, backing off throttle when needed, potentially being extra careful to prove it's safe.Thank you for your efforts, but I figured out how HAC works a long time ago and drew my own conclusions. Instead of proving obvious things to me about reduced air density at altitude and making assumptions about my reaction to all of this, you would be better off reading my messages carefully and grasping my main argument. Its essence is that in the mountains, you usually cannot drive as fast, as dynamically, and with prolonged load as you can on flat ground at sea level. Because of this, the peak EGT remains so low that the mixture enrichment, which at 4000m would add at most 100-150°C to EGT, is completely negated. This is easy. And I see nothing rational in these theoretical rantings.
What about pulling a heavy trailer up a mountain pass, with a driver who knows nothing about the car and is just mindlessly flooring it? Those are some of the real-world possibilities engineers have to think about when implementing general solutions like "HAC".
Again, it's fine to conclude it works for your own driving style, engine setup, tune and environment. I simply object to the generalization to say it's not needed in any case, it's pointless to even suggest or to imply all engine manufacturers are idiots for doing this.
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- #110
Now you're trying to distort my statements by pulling different sentences out of the context of my messages and combining them. I'll repeat for the third time: if you drive in the mountains at a reasonable and safe speed, you won't be able to exceed the EGT limit, so the other conditions are unnecessary and are being "stretched" by you. If there is a high-altitude road that allows prolonged acceleration under high load at speeds above 110 km/h, then for such a case it's worth keeping an eye on the EGT. I haven't encountered such roads yet — maybe they exist in the Pamirs or Central Asia; if I go there, I'll find out. Furthermore, the diaphragm solution was proposed for cases where you need to deal with elevated EGT in an emergency mode. With the same success, you can reduce the cyclic fuel delivery — that's 5 minutes of work. And that was an answer to your own question. And finally, the towing a trailer situation also makes me smile, because usually in the mountains that happens at low gears and low speeds, which in turn reduces the load on the engine and EGT. And if the driver is inexperienced, doesn't know, doesn't understand, etc., then such a driver will be driving a stock vehicle, not a modified one. In conclusion, we are talking about a specific engine — the 1HD-FT — and about a specific, poorly designed HAC for this engine, not about the global application of HAC in modern electronically controlled solutions. So there's no need to broaden the discussion to HAC in general and mix things up — that's not what this is about.
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- #111
I was thinking in my spare time — why didn't my EGT rise above normal at 3000m altitude, if AFR really drops significantly? And I realized a very simple thing. Besides the decrease in AFR, which leads to an increase in EGT (but only up to a certain point), there is a much more important factor: with such a reduction in air density and the amount of oxidizer, much less fuel can be burned, so the total heat release decreases noticeably. That is, even taking into account the increase in combustion temperature due to AFR, the total amount of fuel burned is much lower. The remaining volume of injected fuel does not burn — it evaporates and flies out as soot into the exhaust pipe, and during its evaporation it also lowers EGT.
On top of that, due to the thin air, the turbo also operates less efficiently, which further reduces the amount of air charge in the cylinder and the amount of fuel that can be burned. As a result, the engine's power is noticeably limited, and the overall EGT does not rise — instead, excessive throttle just produces extra black smoke. From this we come back to my earlier conclusion: HAC is mostly an emissions control system, and the most correct and reliable mechanism for reducing black smoke on an old mechanical diesel is the driver's head and right foot. You need to press the pedal with an eye on engine behavior and the situation.
On top of that, due to the thin air, the turbo also operates less efficiently, which further reduces the amount of air charge in the cylinder and the amount of fuel that can be burned. As a result, the engine's power is noticeably limited, and the overall EGT does not rise — instead, excessive throttle just produces extra black smoke. From this we come back to my earlier conclusion: HAC is mostly an emissions control system, and the most correct and reliable mechanism for reducing black smoke on an old mechanical diesel is the driver's head and right foot. You need to press the pedal with an eye on engine behavior and the situation.
I haven't done much "altitude testing" with this particular engine but did notice a significant bump in EGTs even at slight elevation (~1000m above usual), not even pushing the car just normal driving at low to medium speeds. Some of that increase could be attributed to increased load and stress of uphill driving, some to richer combustion. Hard to tell apart the contribution of each without data but to me it's logical to assume air density plays a significant role. For a detailed analysis you'd really have to record engine parameters like AFR, pressures, temperatures, RPM, throttle and more across various elevated tracks, similar to what manufacturers and developers do when they calibrate stuff like altitude correction.
A mechanical compensator like the one used on the non EGR 1HD-FT from factory could certainly help by adjusting fuel to available air mass and to me that would make an overall improvement for engine health and safety, usability and even fuel consumption, without compromising power at normal altitude and regardless of modifications and tune. In fact, you can make a good argument that it is especially important for a modified engine as you tend to run richer mixtures compared to the factory calibration. There are also a few valid arguments against it (in my opinion): The factory part is discontinued, therefore difficult to source or to find a suitable alternative. It adds some complexity and makes it more challenging to calibrate, requires some testing to set it up properly. Also if you happen to run a performance injector pump most of them don't appear to have a BACS port so adding a compensator isn't possible there either way (unless I missed something). Some of the arguments I've read here, like the unit having a bad quality filter or implying that Toyota added that to the JDM engine for no good reason I find less convincing. Of course there are other measures to take but all things being equal I still think adding a compensator could make a good improvement.
A mechanical compensator like the one used on the non EGR 1HD-FT from factory could certainly help by adjusting fuel to available air mass and to me that would make an overall improvement for engine health and safety, usability and even fuel consumption, without compromising power at normal altitude and regardless of modifications and tune. In fact, you can make a good argument that it is especially important for a modified engine as you tend to run richer mixtures compared to the factory calibration. There are also a few valid arguments against it (in my opinion): The factory part is discontinued, therefore difficult to source or to find a suitable alternative. It adds some complexity and makes it more challenging to calibrate, requires some testing to set it up properly. Also if you happen to run a performance injector pump most of them don't appear to have a BACS port so adding a compensator isn't possible there either way (unless I missed something). Some of the arguments I've read here, like the unit having a bad quality filter or implying that Toyota added that to the JDM engine for no good reason I find less convincing. Of course there are other measures to take but all things being equal I still think adding a compensator could make a good improvement.
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- #113
Well, we just have absolutely opposite points of view on the subject. Let each of us go their own way.
P.S. And I stopped believing in the fairy tale about 'flawless' engineering solutions from automakers, Toyota in particular, a long time ago. Drawing dirty air from under the hood into the vacuum system, where water can also get in when crossing fords — that's one of those crappy technical solutions. It's obvious. You can see what it looks like in my old topic:
www.land-cruiser.ru
P.S. And I stopped believing in the fairy tale about 'flawless' engineering solutions from automakers, Toyota in particular, a long time ago. Drawing dirty air from under the hood into the vacuum system, where water can also get in when crossing fords — that's one of those crappy technical solutions. It's obvious. You can see what it looks like in my old topic:
Высотный компенсатор для мех. ТНВД 1HD-FT и 1HD-T
На некоторых версиях моторов 1HD-FT и 1HD-T устанавливался высотный компенсатор (High altitude compensator - HAC). Это версии моторов 1HD-FT для японского рынка без ЕГР, и для моторов 1HD-T для некоторых стран 3-его мира. Принцип действия компенсатора - ограничение подачи топлива в горах для комп...
www.land-cruiser.ru
Sure! I haven't looked into the details of this unit but If there is no viable technical solution then I might be convinced to let go of this idea as well, not for theoretical but practical reasons. Thanks for the link, I'll check it out.
Elevation delays turbo spool and that's a big driver of more smoke and lag. Once on boost the EGT difference isn't that big. You're not going to melt a piston or suffer other catastrophic failures unless you keep your foot up it while pulling sustained mountain passes or towing at altitude. On my Isuzu I've hit EGT's of 900C while not paying attention towing. I have rebuilt the engine since and there was no damage at all. Those melting engines are running insanely hot.
But smoke can be a real annoyance before you're on boost. Best way to avoid it is to run higher rpm (if manual). If auto you're going to have to play a tune with the pedal to manage up and down shifts. The right upgraded turbo will definitely help. A more efficient turbine will spool sooner and give you a wider power band that helps at altitude.
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- #116
@Dougal
Hi, could you tell me about this wheel from Mamba? Based on your turbo wheel specs, is this a type 2 or type 3? I don't see any real backswept edges — just a very slight inclination of the edge line. But my main concern is the reduction in blade count from 10 to 9, which could cause lag in the low-end and mid-range.What do you think?
That's a Generation 2. It's going to be an improvement across the whole range but like you I believe the reduced blade count is best for ricers rather than diesels. Generation 3 probably aren't produced for the CT26 series of turbos, there are TD05/6 based CT26 replacement turbos which might use them. I haven't looked lately.
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- #118
Thanks, then I refuse to buy this part, since my typical RPM range in city is 1000-2000 rpm. And the weight difference is not critical: my Melett shaft and 10-bladed wheel weighs 219 grams, Mamba with 9 blades - 190 grams. I assume that 29 grams difference and 2-nd generation design can not beat one extra blade in low-mid rpm range.. I've asked Mamba to produce the same shaft but with 10 blades - they required 50 pcs. order . So unfortunately, I couldn't find any other shaft with gen2/3 design, suitable to my CT20B.
. So unfortunately, I couldn't find any other shaft with gen2/3 design, suitable to my CT20B.If you are talking about the CT27, it has a 10mm shaft instead of 8mm in the CT20B. I would have bought one of these turbos if I could.
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Thanks, then I refuse to buy this part, since my typical RPM range in city is 1000-2000 rpm. And the weight difference is not critical: my Melett shaft and 10-bladed wheel weighs 219 grams, Mamba with 9 blades - 190 grams. I assume that 29 grams difference and 2-nd generation design can not beat one extra blade in low-mid rpm range.. I've asked Mamba to produce the same shaft but with 10 blades - they required 50 pcs. order
If you are talking about the CT27, it has a 10mm shaft instead of 8mm in the CT20B. I would have bought one of these turbos if I could.
50 piece order is pretty good. You might get that easily if you advertise it here. I haven't come across a CT27. I refer to aftermarket turbos which are TD05/TD06 based but made with flanges to interchange with CT26.
I'm not aware of anyone here or on other 4wd sites testing the same turbo but with different shafts to quantify response and operating ranges. It would be great if someone did.
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- #120
That sounds like CT27 - it is also an aftermarket one (ATS racing). I don't remember exactly the type of turbo wheel it has. RAYJON gave me the link earlier in this topic: CT27 Billet Turbo Upgrade - https://atsracing.net/products/ct27-billet-turbo-upgrade. But looking at their photos, they are also using old-fashioned gen.1 wheels. That means that you are talking about some different CT26 upgrade.