EGT gauge is back up and running, however, the probe is after the turbo.  In my previous trucks I have been in the exhaust manifold, and 1200* was the peak I ever wanted to see..  My question is, because I can't move the probe before towing this week/weekend.  What temp would you guys say is a conservative number to stay at or below?

 

Thank you

Guessing firewood is for extra back pressure or did I miss something 

27 minutes ago, Dieselfuture said:

Guessing firewood is for extra back pressure or did I miss something 

 

That's the idea yes, works like a charm.

5 hours ago, Cowboy said:

If you use the engine running method, you get extra redneck points for stuffing a piece of firewood in the exhaust pipe while doing it.

 

Easier yet to just leave the exhaust brake turned on... 

Ehh yeah, but you don't get redneck point for that.

The larger diameter exhaust tip, the larger the firewood, and more points!

1 hour ago, Royal Squire said:

The larger diameter exhaust tip, the larger the firewood, and more points!

 

Ok... So it better look like Dorkweeds avatar then... 

The hole calls for a tap size of 1/8-27 NPT but what size drill bit are you using.

I am seeing drill bit sizes of 21/64 (.328") with reamer,  Q (.332") without a reamer,  R (.339") straight pipe thread, or 11/32 (.3438).

What say you?

Edited June 13, 20177 yr by IBMobile

I drilled mine in 05. Lucky to remember the year much less the size. Did mine  turbo off, stuffed rag into manifold, drilled hole and removed rag. Put it back together and drove off.

I did a little data collection as far as pre vs post turbine temps.  This is on my 12V'er so your mileage may very.

 

Not as scientific as it could be as the hills were short, and post turbine temps are heavily influenced by heat soak.

 

1680 RPM @ 860 Pre-EGT = 700 Post-EGT.

1875 RPM @ 1000 Pre-EGT = 740 Post-EGT. 

2060 RPM @ 960 Pre-EGT = 720 Post-EGT.

2120 RPM @ 910 Pre-EGT = 710 Post-EGT.

2190 RPM @ 1050 Pre-EGT = 760 Post-EGT.

2240 RPM @ 1250 Pre-EGT = 840 Post-EGT.

2640 RPM @ 1040 Pre-EGT = 735 Post-EGT.

 

 

Always best to have pre turbo EGT than post turbo EGT. 

Pre vs post is a variable that is generally linear with boost. There is about a 100° difference for every 10 psi of boost. This was a rule of thumb I had heard and after running a pre and a post turbo for a couple of years it's pretty darn accurate. 

 

The biggest difference I have seen on my setup is about 300°. The hottest post turbo temps I have seen is 1050° towing with a lot of power at 1800 rpms for a short time. The pre turbo temps were about 1200° and I was only making 15-18 psi... there is that rule of thumb. 

 

I prefer pre temps for some things and post temps for others. Post is a better indication of turbo cool down prior to shut down, and a better indicator of motor heat soaking. My post temps are always higher with low rpms/boost and a load. Post temps aren't ever even close to an issue above 2000 rpms. 

 

Pre temps are much faster reacting that post temps. 

 

If you're going to have one I recommend pre, but a single post is still useful if you know how to interpret them. It's not hard but there aren't a lot of people talking about post temps so it's harder to research. 

 

Most OEM pyro's, that I am aware of, are post turbo. 

 

1250° pre is also just a rule of thumb. Timing and rpms will have the biggest effects on what acceptable EGT's are. 

 

For reference the QSB 480 5.9L marine engine, 480hp at 3400 rpm, has a manifold temp of 1301° at rated rpm/power. The turbine out temp is 925° and boost is 35 psi....pretty darn close to 100° per 10 psi.  

 

 

On 6/12/2017 at 10:01 AM, Me78569 said:

Drill slowly with the motor running, most of the shavings will blow out without any issues, 

 

 

I always recommend against this procedure. 

 

What happens if you break a bit? You buy a new turbo!!!! You also have the turbo spinning at idle speed so any shavings that do go thru the turbo, which will happen, are going to hit the turbine blades with a high rate of impact. The higher the impact speed the higher the potential for damage. 

 

The best way, IMHO, is with the motor off on a cold motor, and don't use grease. 

 

The way a drillbit is designed to work will keep nearly all of the shavings out of the manifold. Just before you break thru hit it with a little compressed air to clean out the hole and then drill thru. 

 

The few shavings that do fall into the manifold will be blown thru the turbine wheel long before it gets enough speed up to do any damage. 

 

I also don't recommend grease because any shavings that are covered in grease that fall into the manifold won't get blow out until the grease melts which means the bits of shavings are hitting a spinning turbine wheel. 

Edited June 18, 20177 yr by AH64ID

On a single-scroll turbine, I can see the 10° per psi rule of thumb being fairly accurate.  But the efficiency curve of a twin-scroll housings are far more dynamic than a single scroll.  And in the end, that is what determines pre vs post temps.  When the pressure drops over the turbine housing, that causes a temperature drop.  But just like the inefficiency of the compressor adds heat to the intake, the same goes for the turbine heating up the post turbine exhaust temps.

 

As an example, I was pulling a grade yesterday, 850°F pre-temps & 650°F post-temps with 5 psi of boost.

 

Another example, pulling a grade at 1900 RPM, 1140ºF Pre-temps & 780°F post temps with 20 psi of boost.

I have a twin scroll and it follows the 10° per psi fairly close at nearly all rpms. Pressure drop is pressure drop so I really don't see the single vs twin scroll having a measurable difference. The temperature drop is occurring after the inlet. The HE351 is a single scroll and from what I gather it's fairly close to the 10° per psi rule as well. 

 

How long were you at those numbers? I find that it takes a good 15-20 seconds for post numbers to stabilize. 

 

It's a rule of thumb and certainly not an absolute. 

 

Just lot easier to look at how hot the fire is leaving the head than attempting to do math and figuring out from post temps. I really don't care what the temps are after the turbo. I do care above the fire leaving the head that it not hot enough to damage pistons or the turbo. Back to using pre-turbo temperatures. 

 

Why make it complicated with math and figures when you just drill a pre turbo port and be done.

Edited June 29, 20177 yr by Mopar1973Man

26 minutes ago, Mopar1973Man said:

Why make it complicated with math and figures when you just drill a pre turbo port and be done.

 

Because we are humans and cannot leave anything tf alone lol

True. But why?

 

Not nearly complicated enough for an engineers watch LOL

At the end of the day, it's just a number  

5 hours ago, Mopar1973Man said:

Just lot easier to look at how hot the fire is leaving the head than attempting to do math and figuring out from post temps. I really don't care what the temps are after the turbo. I do care above the fire leaving the head that it not hot enough to damage pistons or the turbo. Back to using pre-turbo temperatures. 

 

Why make it complicated with math and figures when you just drill a pre turbo port and be done.

 

 

But it's still all just a number. The pre-temps can vary a ton as well. 1250° on your stock tune was quite a bit less piston heat than you get now at 1250°, and even more so on my truck. I ran 1450° stock and it would do that all day, but 1450° now and I could damage a piston. The valve seats and turbo inlet don't care about cylinder temps and the temp of combustion is a lot higher than the temp in the manifold. RPMs, boost, and timing are the biggest influences of heat soak in the piston for a given manifold temp... and those 3 variables are constantly changing. 

 

Pre responds much faster which is rather handing, but post is a much better indicator of heat soak. 1200° pre may not look hot but when lugged that number can be 1050° post and that is too hot. So post can quite often be a safer indication of cylinder heat soak. Pre temps take just as much figuring as post temps, at least they do if you really want to understand them. Since running both I have seen too high of post EGT's a couple of time but the pre-EGT's were "normal". It takes a descent lug to do that but according to my pre I was just fine. I don't recall ever seeing too high of pre with acceptable post. 

 

I still say that if you're going to only have 1 to run a pre-turbo but it's not always better and only having a post is very acceptable too. 

 

So at the end of the day they are just a reference for running normal. Pre or post and that number is still just a reference. 

I have to agree with you John on many points.  A part in me really wanted to get all technical about a formula for calculating the post turbine temps.  But after reading your last couple posts, reality hit me like a brick and I realized no one is going to grab a calculator while pulling a hill to find if there temps are acceptable.  And likewise, no one is watching their boost gauge at 5 psi like in my previous example.

 

So I did a little datalogging while bringin' in the hay the last couple days.  Nothing scientific, hard to get nice smooth data on gravel roads.

 

 

Here's one graph, the X axis is time in seconds.  

 

Towards the end of the pull, Pre-EGT's are at 1415, while Post-EGT's are at 981.  That makes for a delta temp of 434°F.  Boost stayed pretty steady at 35 psi so that's 12.4 Degrees per PSI.

 

And again:

 

At 31.4 seconds:

Pre-EGT = 1202°F

Post-EGT = 830°F

Delta = 372°F

Boost ~27.2 psi

Degree per PSI = 13.6

 

And one more.  I shifted down this time to try and get the revs a little higher for increased drive pressure.

 

At 14.8 seconds:

Pre-EGT = 1147°F

Post-EGT = 789°F

Delta = 358°F

Boost ~25.2 psi

Degree per PSI = 14.2

 

So overall 10°F per psi boost is pretty close.  Especially when you're swagging at it with a general rule of thumb.  The number does seem to go up with RPM slightly, which makes sense due to increased drive pressure.  

 

On "measuring the temperature of the flame coming out of the head"  I don't believe that to be necessarily accurate.  Pre-turbine temps are 'artificially' (using the word loosely) inflated by drive pressure.  Post-turbine temps better indicate the air to fuel ratio, when you're trying to make power at an RPM that the turbo isn't happy with, then it takes a lot more fuel to make the same amount of boost thus like you say John, Post temps can be out of hand, while pre-temps (which arn't being inflated much by drive pressure due to the lack of it), don't indicate anything as being wrong.

 

As for my comment about turbine efficiency.  I have always assumed that the inefficiency of the turbine adds heat to the exhaust just like the inefficiency of the compressor adds heat to the intake....  But.  I just tried putting together a calculator for it assuming Adiabatic decompression, and well, either I fricked up somewhere, or that's not really the case.  It will take more thought at a later date.

 

EDIT: Quick test of my formula using it to calculate pre-IC temperatures puts it pretty accurate... I don't know anymore.