endurancerider

I am new to the Cummins Diesel and have a basic question for you. Why do people claim EGT is lowered if less restrictive parts are added, like a CFM+ intake manifold, more open intercooler, more open exhaust manifold, bigger diameter exhaust?

So the interesting case is when the engine is under load, say at 25 psi boost. I think the boost pressure is measured with the mapping sensor, which is very close to cylinder 6, NOT at the turbo? With this amount of boost, so much air is going to go into each cylinder. With less restrictive parts upstream of the mapping sensor on the intake side, but the same boost pressure, does more air actually go into each cylinder. I would not think so since boost is measured at the cylinder, and with 25 psi boost, the same amount of air will go in (unless it is choked by some stock part, which seems unlikely--the engineers at Cummins would not do that for an engine which is used for towing and hauling big loads much of the time, no?).

If that is true, then how does this same amount of air absorb the same heat at a lower tempature for a lower EGT?

Then on the exhaust side, if you have lower back pressure, the air will come out of the cylinder faster, but again, it is the same amount of air with the same energy content (heat content, tempature) from buring in the cylinder (assuming you are keeping boost, fuel the same). So unless the EGT sensor is alittle downstream in the exhaust flow so that by the time the air reaches it, it has expanded and cooled, I am not sure why the exhaust temp would be lower. And if this is the case, it would seem the temp at the valve, which I think is the main concern with EGT, would be the same in both cases

I realize this is probably a dumb question, but hey, I am sure some of you can help me out here.

AH64ID

The biggest reason you can, not do, get an EGT reduction from those parts is they are freer flowing, so you get lower intake air temps. On our HPCR's 1° drop/rise in IAT's is good for 1.5° drop/rise in EGT's.

You are correct that 25 psi measured in intake manifold is the same air flow as 25 psi with aftermarket parts.

Lower exhaust back pressure (turbo created, not exhaust) will allow better flow therefore you get more exhaust out, making more room for intake.. that can lower the EGT's by adding more clean air to the cylinder. I have seen this with my new turbo, cooler EGT's at lower boost.

In essence you are making the motor more efficient, and a more efficient motor runs cooler. On that note I have done a few intake mods that effected my boost ramp rate, IAT's, flow and really didn't see a EGT difference, at least not one that could be quantified on an EGT gauge.. despite an improvement on the IAT's and boost gauge. They are good mods, and I would do them again.. just hard to quantify based on EGT's alone.

That being said the OEM intake setup is good for about 450 rwhp with no gains made by going aftermarket, and the exhaust is good fro about about 600 rwhp. There are some improvements that can be made, but the power gains are minimal under those numbers.

Adaminak

An intercooler actually cools the intake air after it passes through the turbo, and a more efficient intercooler will cool that air better, which means the engine gets either the same volume of air as stock, but at a lower temperature, or a larger amount of air at the same temp as stock. Either one will drop EGT. The intake plenums don't do much for EGT, but do allow for more throttle response,

The factory intake horn has a serious restriction at the neck where it bolts to the intake, and while it works for stock power, it's really designed for mass production and not best performance.

Free flowing exhaust lowers EGT by reducing back pressure, which results in more efficient air pumping of the engine on the exhaust stroke. This also allows the turbo to operate slightly better, which increases boost, which lowers EGT as well.

An exhaust manifold flows air to the turbo much more efficiently than the stocker, and does a much better job of scavenging exhaust out of the cylinders, lowering the amount of time the hot gasses stay in contact with the piston. They also flow more air than factory, which results in less back pressure, more turbo spool, and again, lower EGT.

Edit: Everything I said has the same result as that posted by AH64 above. Essentially an engine is an air pump, and the more air you can get in and out with each stroke, the more efficient it is. More efficient engines run cooler, because they do less work to make the same amount of power as an inefficient engine.

endurancerider

Thank you both for your replies.

Have either one of you had the opportunity to measure or even get a feeling for how much of a EGT drop you see with an after market exhaust manifold?

How about with an after market intercooler?

Under load, of course--I tow a big horse trailer.

Where is the EGT sensor located?

AH64ID

I have an aftermarket exhaust manifold, but installed a turbo at the same time so I cant say. With a stock turbo thou I don't expect it to be too much, the stock turbine is quite restrictive.

Based on what I see for IAT's I also don't expect a large EGT drop from an intercooler on close to stock truck.. better bang for your buck with other parts.

cbrahs

wanna see something choked down. research "spool aide" and look at the pic of the #1 and #6 cylnder intake tract and see how choked down those 2 cylinder are compared to the other 4.

soulezoo

To the OP,

First, that is not a dumb question at all and welcome to DTR.

It is a question that is very much worth talking about as it is often misunderstood as well.

First, on a stock engine there is not a factory EGT sensor. It is something that you have to install and you'll find out the advice here is that it should be one of the first things you do.

Second... you did get some good information above.

next, where you put that egt probe matters greatly. Some have put it post turbo. That is probably the least effective as it shows the lowest egt and subject to the effects of the turbine. And different turbines and exhaust housings will skew what you see.

The best place to put it is at the collector on the exhaust manifold just before the turbo. Just because I am picky, I run one probe on both sides of the divider. And a third near #6 for good measure.

Ultimately, this is just a gauge for reference only as that gauge cannot see what is actually going on inside the cylinder and that is what counts!

In a similar way, boost is just a measurement of airflow restriction. You can have less boost and more air and vice versa. Explained a little in a post above.

Cams and injection duration and timing can have an effect on what you see. Let me explain.

Where boost and egt are concerned, I made over 700hp with 80psi boost and 1400* egt. In the 1/4 mile those same settings (again, 1400* egt) melted a piston... or two. Now, I can run at 900hp, with 74lbs boost and 1600* egt and pistons are loving it! Whats the difference? Airflow.

The 1400* I saw before meant that the heat was retained in the cylinder and on the piston tops for too long and they melted.

The 1600* I see now is because the heat is escaping earlier by virtue of the cam and saving the piston top and the better airflow through head porting and exhaust manifold and turbo matching. Also, I have a different intake system as well.

Disclaimer: PLEASE don't anyone take to heart what I wrote here and try this yourself without really knowing what you are doing. The mistake is very expensive.

Now where the intercooler is concerned, you are not going to see any egt effect at power levels up to about 500hp. It is not until you start compressing a crap load of air that is that much hotter that the stock CAC can't handle that you will see a benefit.

Hope that helps