1HD-FT what EGT’s are ok for sustained climbs?

[pannymix]

Gents, I run a ‘96 HDJ81 with the 1HD-FT and auto trans. I’ve been running with a Redarc EGT that’s pre turbo in the manifold. I’ve set the warning on the gauge to 600C and on sustained climbs I find I’m backing off the throttle to keep under my set limit. Sometimes I’m going a little slower than I’d like to to keep the exhaust temps under this limit. My question is, for a long climb, say a few minutes, is pushing right to 600C and holding it there for what feels like an age totally OK?

 

[pannymix]

My 80 here in New Zealand

 

[mudgudgeon]

At 600c, it's barely raised a sweat!

750c is widely considered safe PRE-turbo.

I ran my HDT HDJ81 up to a sustained 850c on a regular basis long term and was comfortable if it peaked up to 900c on occasions.

 

[Loober]

Wow, 850C seems high especially for sustained pulls, I've heard the 550-600 being the rule of thumb not to exceed, that's what I keep mine under. Its not like you hit a certain # and the engine violently blows up, its the effects over time and frequency that must be considered. I've blown up a 1HZ with high EGTs, now the 1HDFT is a much more robust engine, but I am scarred after that experience and basically keep it as low as possible on my FT, I've done many upgrades, such as intercooler, exhaust, air box to ensure that, where I cant get it over 600 if I try and most of time it stays below 500, so 850 seems high in comparison.

 

[mudgudgeon]

Its not like you hit a certain # and the engine violently blows up,

Agreed.

EGT reads the the temperature of burning gas as it exits the manifold. It does not give you a read on piston crown or valve head temps.
All of which get cooled by a fresh charge of air at close to ambient air temp every cycle. Gas comes in at 25-50c, gas goes out at 850c. Piston temp is somewhere in between.
Pistons in these engines are also cooled by a spray of engine oil which is somewhere sub-100c.

EGT gauge only gives you part of a picture. If you want to know how close to the ragged edge you are, monitor oil temps, cylinder head temps, intake air charge temps, water temps, AFT, and EGT.


At 600c you are leaving a lot of potential on the table.

I had this engine apart after several years service at that MAX temp range, with 250k km on it, it was pristine internally. No indication of running too hot.

I'm not the only one who's happy to run at that sort of temp.
I know of guys who have run at 850c literally for hours at a time on Aussie outback highways where you get ambient temps at high 30s C, unlimited speed limits, and NO corners for hundreds of Km.

At the end of the day, up to you to run what you're comfortable with

There is no way I would run a HZ at such temps.

 

[Loober]

@mudgudgeon well that definitely gives me some piece of mind, yea i have it setup fairly conservative on a stock turbo limited to 14psi, but even as is, it has gobs of power compared to what the rest of the truck can handle, has no problem pulling any type of grade holding 120km, can't imagine what even more power would make it feel like.

 

[Hulsty]

Run my 13BT to 750c before I think about backing off, rarely gets past 720c. Nearly does 600c on the highway barely pusing it.

 

[Dougal]

How hot you can run depends totally on how much you trust that reading!

I've seen up to 900C (accidentally) and 750C sustained for several minutes many times on my 4BD1T EGT gauge and having rebuilt the engine since there was no heat related damage.

 

[GTSSportCoupe]

Usually pistons are the failure point on 1HDT's when the EGT's have been run too high for too long. The pistons crack over time, but usually don't lead to a suddent catastrophic engine failure. I know a number of owners who have found these when they've had their motors apart. I think this is more a problem for the 90-91 version of the motor. This pistons seem to have got better over following generations of the motor.

 

[Loober]

Besides strain on the engine, how do high EGT's correlate to loss of power? to where down tuning to keep EGT's lower yields better fuel to power versus over fueling to get the effect of more power but not getting it to the wheels because its been absorbed by the heat?

 

[wedgetail]

Talking to gturbo about this a while ago, pretty sure they said 950*c was ok and shorter spikes of 1050*c didn’t kill them either. This was in an fte which have very slightly different pistons but either way they said 850 was well safe. FTs have upgraded pistons over 1HD-Ts. They also reckoned genuine pistons are tougher than literally every known aftermarket one, including ceramic coated

 

[mudgudgeon]

Talking to gturbo about this a while ago, pretty sure they said 950*c was ok and shorter spikes of 1050*c didn’t kill them either. This was in an fte which have very slightly different pistons but either way they said 850 was well safe. FTs have upgraded pistons over 1HD-Ts. They also reckoned genuine pistons are tougher than literally every known aftermarket one, including ceramic coated

Interesting to note too, in a petrol or gas engine the ideal tune of stoichiometric AFR sees combustion gases at about 1350c (from memory, but not 100% certain).
Piston metallurgy is similar in both, diesels have much heavier pistons to cope with the compression.

 

[Loober]

Interesting to note too, in a petrol or gas engine the ideal tune of stoichiometric AFR sees combustion gases at about 1350c (from memory, but not 100% certain).
Piston metallurgy is similar in both, diesels have much heavier pistons to cope with the compression.

Funny you mention this, I also have a gas engine which is supercharged that i monitor EGT's on as well to help detect pre-detonation if it runs too lean. I never thought much of the reading itself which was always around 750-800c. When compared to the 550c range I was told the diesels should be kept around I began wondering why the gas is able to maintain higher EGT's when the gas piston construction is not much different in regards to the type of material used. I figured it was something to do with how the combustion happens with gas vs diesel, but probably not, which further supports the safety of running diesels at similar temps.

 

[IanB]

I'd always treated 1250F (676C) as my max sustained temp...maybe I have more room to work than I previously thought?

 

[pannymix]

Thanks everybody, that gives me a lot more confidence. I just returned from a long trip (10 hours driving in 2 days) and I paid particular attention to the EGT's in various conditions. I found some interesting observations.....

We appear to have slightly different diesel in NZ. There is a company called "GULL" and they sell an ultra low sulphur/biodiesel mix. I usually use this diesel because there is a Gull near my work and it's usually a few c/L cheaper. However I'd seen some discussion that guys in NZ had observed lower EGT using BP/Caltex/Shell/Mobil. I gave it a try and left Auckland on 100% Gull then changed to BP for the next tank. On average I'm quite certain I noticed a reduction of EGT from the BP fuel. At my 600C self imposed limit I was able to use more throttle, at motorway cruising I was pretty sure I was 50C cooler at 100kph as depending on headwind or slight gradient the temp usually floats between 450C and 500C and on the BP diesel I saw more often 400C to 450C.

I also noticed that at 500C the motor does appear to be a lot more efficient. If I could keep EGT that low it really stretched the fuel mileage. Certainly this was due to less throttle and therefore less speed, but the motor felt a lot more in it's zone at 500C where as at 600C it was starting to feel like the edge of the power band so to speak.

The trip certainly reinforced my desire to fit an intercooler and perhaps look at running slightly more turbo boost than the 10psi setting at present.

Thanks again, based on the discussion here I might lift my alarm to 625C and be more comfortable pressing to and holding for long periods 600C on the big climbs if needed.

Cheers all.

 

[AussieHJCruza]

You're leaving a bit on the table by setting the alarm at 625C pre-turbo - my 1HDT saw 900 pre-turbo for a few seconds during a 'let's see what happens if we max the pump out' pull - no problems at all. With the tune was dialed in, it used to settle itself between 600-700 at 21:1 AFR, timing at 1.3mm lift, 25 psi. - best bang for your buck IMHO after a 3" exhaust is an intercooler.

 

[pannymix]

Hi Aussie, I don't have any desire for more power or speed. Power and speed wise I'm happy with what the engine offers at the low EGT limit. It's an old 80 series. If want to feel some acceleration I can drive my 5.4L supercharged AMG Mercedes. When I drive my 80 I don't mind falling back to 60 or 70 up the hills, it's kind of what I expect. I just want to be in a zone that I'm not risking engine damage or degradation. Knowing that guys are getting away with more is useful, but not a sign for me that spurs desire to push harder. My Redarc EGT gauge only reads to 700C anyway so that's another good reason to stay under it!

 

[pannymix]

Seeing as I have all your knowledge available, there's something else I'd like to check. Fitting the EGT probe, I removed the EGR crap and used the exhaust manifold blanking plate as the perfect opportunity to position the probe (without drilling into the manifold and risking swarf up-stream of the turbo). The only issue is that technically I'm only taking a reading of the EGT of two of the combustion chambers. Is this any concern - and also, as a result, would my EGT reading be slightly lower because the probe would only be exposed to combustion strokes less frequently? I'd expect there would be a much more frequent and constant flow of exhaust which would better average out with the probe more central. Be interested to know if this is something I should consider.
Cheers, Peter

 

[IanB]

The trip certainly reinforced my desire to fit an intercooler and perhaps look at running slightly more turbo boost than the 10psi setting at present.

You'll find with more boost, even the 14-15 the stock turbo is safe to, it's much easier to keep EGT's low under sustained load as there's more air available for the same or slightly greater fuel. The greatest improvement from upping the boost is on highway manners, it's so much more comfortable at those speeds with a higher boost max. You may even get greater fuel economy as you're making more power with the same fuel, and need to use less throttle than before.

 

[1HaytchZed]

I've got a post-turbo EGT right at the dump pipe waiting to be installed, what temps should I be considering normal at that post-turbo location... is there a good way to extrapolate the pre-turbo numbers?