Ok to start off please don’t beat me over this. I have used the search button and this is my first post. I have read a lot of different threads across different platforms including the duramax and Cummins boards. So my curiosity comes from the fact that it seams like all other engine platforms are sized incredibly similar if not the same. So for instance kc turbo jet fire stage one is a 61 mm on the compressor side and rated for up to 550 hp on the 6.0 platform. The 6.7 whistler turbo is a 63 mm turbo and rated for 650 hp. No moving to the lly-lbz stealth 64mm from calibrated power is rated to 650hp again. The cheetah 63mm from fleece for the 6.7 Cummins is rated at 700hp. The 63mm cheetah for the 12 valves are rated to 650 yet again. To further bore all you with specs the new stock 6.7 Powerstroke turbo is a 57.5mm for the h.o. and the standard output per duramax tuner. The newest L5p is 61mm if I recall correctly. Both platforms stock turbos easily capable of 500hp with a decent tuner.

Now for my stupidity to show. I would like to keep this focused on the compressor side to start. I understand there’s much more to a compressor than inducer size. There’s much more going on. But why is it us 7.3 guys have to put on so much more turbo it seems. I’m currently running a sxe364.5 with the larger turbine and a .91 housing. It seems like comparing the apples to oranges a sub 400 hp 7.3 should be able to run say a modern 58mm turbo and be ok. So my question is why s much more compressor size? I can’t imagine it’s a displacement size because from a 5.9 to a 6.7 are very similarly sized. Is it our dismal head flow? Is it the camshaft? I’ve looked into cams a bit and most diesels are fairly close it seems. I’m not an engine builder. I’m just trying to learn the true weakness of this engine and be able to correct it.

 

Just my opinion...

You only talk about horsepower. There is that saying about horsepower, and i think ypu are getting sucked into its useless number race.

A couple key differences.

Common rail trucks can inject fuel much faster and at significantly higher pressures then the 7.3. A common rail injector can fire 5 times compared to the 1 time with our huei injector ina compression cycle.

Horsepower is a vector. Any real horsepower power number would be accompanied by an rpm number. That said, generally speaking, the higher the redline, the more horsepower will be created. After all, horsepower is calculated from torque...torque wins races, and that the real number you want to pay attention to.

So a 7.3 producing 400hp at 2200 rpm will be a very different beast then a diesel at 400hp at 3500prm. The 7.3l will produce a fair margin more torque if you do the math...Now 4 valves per cylinder, vgt, and other tech will impact motor performance, which the 7.3l has none off. The common rail motors also rev much higher because of the faster injection, upto about 42 to 4500rpm...this is significant.

Its like this. Horsepower is how fast you hit the wall, torque is how hard you hit the wall. Torque is the twisting force that makes the vehicle move, or just joules. Horsepower is a capacity to do work...joules per second.

A turbo manufacturer will sell more turbos if they say it makes great horsepower...sure...MOAR POWER. But real world performance will vary greatly because of existing mods, better technology, altitude, intake temperature, exhaust housing sizing, tuning etc. Its really your powerband, where it sits in the rpm range that you must focus on. Peak numbers are for dyno queens. Think a civic that only starts to move at 5000rpm after vtec kicks in. Thats awesome, except its not really usable if you want to tow or drive normally as the engine will be guttless until its at 5000rpm...because the power band is too high. This is why diesels are popular for towing, you have torque down low in the rpm range

Torque = (hp x rpm) / 5252. Torque will always be equil to hp at 5252 rpm.

My point is, dont be so focused on the peak hp number. Look at the torque that is being made with the various setups, and where its being made, and for how long. Torque is a number that can be more easily compared. Also peak horsepower at a high rpm is usually a setup people dont like.

There is a great thread around here called turbo matrix. Its guys comparing their setups. You will see the guys running smaller turbos have their power band lower in the rpm range say 1700rpm..probably less peak hp, but a very drivable motor for this application. The guys with larger turbos have no torque until 2500rpm, which isn't great for a 7.3l, but probably produce more peak hp. You'll soon notice that the guys are swapping out the larger turbos for smaller ones to move their powerband down the rpm range.

Just my .02

 

I didn’t see any information on other mods to your truck. It’s my opinion that the 364.5/73/.91 is “normally” sized too large for a stock or 30% over nozzle truck. Some folks love it, but the powerband is moved up in the rpm and requires driving around the turbo a bit.

Check out this link. Charlie from KC Turbos is quoted for many reference points in I think post #4. Many links to other turbo threads are in post #5.

https://www.ford-trucks.com/forums/1...e-reviews.html

 

I don't know anything about turbos. I know Charlie said the same turbo will act differently on a ford/ dodge/ chevy...even just on fords. there way more to it that I could ever know or want to know
Cummins, 6.0+ use VGT which plays a roll as well.

364.5 is good for 200/30. we don't know what your setup is or what you are trying to accomplish? Unfortunately, I have to rely on the experience of others for my setup choices

 

The easiest way i try explain HP/Tq to those who don't know:

Torque = move that wheelbarrow, I'll add rocks until you can't move it. Then we'll count the rocks to see how strong you are

HP is then telling them, Now with the max amount of rocks you CAN move, I'll use a stopwatch to time however long it takes you to move it 100 feet

With torque, anyone can visualize/count rocks

But with HP how do you compare Billy Chevy vs Bobby Ford, or Daisy Dodge moving differently loaded wheelbarrows using a stopwatch?

HP is time

It's number really only matters when the number of rocks is the same

 

I just watched a KC turbo video the other day that explained HP vs TQ. I typically like Charlie's videos. they are pretty informative

 

This guy physics.

 

So I understand the horsepower vs torque. I guess I should word my question differently. Why is it that a 364.5 may be worth 650 on other platforms but only approximately a 500 turbo on the 7.3. I’m not really chasing a horsepower number. I’m all in favor of the “smallest turbo for the job” philosophy. I’m trying to learn. For instance bd sells a “sxe 358” for the 12 valve that’s good for 450 hp. So why couldn’t a 58mm be used on a 7.3 and get to similar numbers. It’s been my understanding that you need x amount of fuel and y amount of air to get to a horsepower goal. So why is y amount of air so much different on our motors?

I have extensively read the turbo matrix. Can’t remember who started it but thank you. It’s badass for number nerds like myself. As for my personal truck it’s an 02 with 180/30 injectors. I actually love the setup for the most part. It’s getting rebuilt next year to get rid of those con rods.

 

I'm afraid there's the problem with your question.

By stating "same turbo" but this platform or that platform you are comparing apples to oranges and bananas but then asking us why they don't taste like pears. Yeah they are all fruit, but from totally different trees.

IF your question was how come x turbo on a,b,c,d thru z engines that all make 1000 foot pounds have different HP #s at the same RPMs someone could then point to displacement, V vs inline blocks, CFM thru heads, # of valves per cylinder, compression ratio, stroke, piston diameter, fuel injector sizes or times per stroke, gear ratios, air temperature, engine oil grades, cylinder rings gaps, or something along those varying lines.

The turbo matrix thread takes out the other kinds of fruit then sorts the apples by size or color (supporting mods, Injector sizes) to compare turbos

Why does the 7.3 produce less, many reasons. It's way older than all those other platforms technologically, and very limited on head flow, and especially RPM (compared to the 6s)

What is RPM, a measurement of time. What is HP, also a measurement using time.

Many reasons for different HP #s from same turbo across platform 🤷🏻‍♂️

​​​​​​IF all those factors were the same then the Dodge owners would finally be able to say it and be right. The 7.3 just sucks 🤪

I don't know the answer I think you are asking, and hope you don't think I'm bashing you. Just saying there are too many variables between platforms

 

Understandable that I’m comparing apples to oranges. Let me word it this way. On average 1lb-min of air is worth approximately 8 hp per dieselworlds math. Why is the 7.3 so much less efficient at using each lbs of air? Wes444 you bring up a great point and that I had in my original post. Are our heads holding us back? I do remember reading on one of unlimited diesels injector sizes saying that you can use a specific injector (can’t remember size) and use ported heads and a 38r.

 

An engine that has a powerband in higher rpm will generally make more HP if the other items are the same.

As Wes said, HP is directly related to rpm by mathematical calculation. The same torque level will have completely different HP as rpm increases.

The 6.0 runs at higher rpm. So it should produce more HP than an “evenly matched” 7.3 that turns lower rpm to make its power.

For what it sounds like you’re wanting to do, you might try comparing based on torque instead since those values are independent from rpm.

 

All very different platforms, huge differences beyond just the turbo. There's no way to compare them by one simple metric.

1000s of differences.

 

The 7.3 owners seem to be much more egt aware than some of the other trucks that make big power.

Take a 650hp 6.7 powerstroke for example. The stage 1 Whistler is 2mm larger than stock. At those power levels EGTs will be high and it won’t be very usable power unless its short bursts. My Dad runs a “stage 0” Whistler on his 6.7 which is basically a KC Whistler but stock 61mm compressor and 10 blade turbine. 2mm difference than the stage 1. With all of the supporting mods, including a 4” downpipe and Donaldson Blue filter. Useable power maxes at around 470hp (stock 440hp) before egts get to over 1300 degrees. A stage 1 rated at 650hp may only have a usable power rating of less than 500hp if you are working the truck.

The 7.3 owners tend to want 100% usable power. There are plenty accounts of guys making over 400hp on a stock gtp38 and I am sure it is possible to make 600hp with a S363. What you never see are what the EGTs of a 650hp 6.7 with a drop in turbo look like. It could easily be 1500-1600 degrees.

 

it has been about 10 years since I sold my '98 Dodge 5.9 Cummins dually with 4.11 gears,
I had to watch the EGTs on it really close if I put my foot in it....
I remember pulling a 9% grade going from Phx to Payson, AZ with 16,000 lbs behind me and it didn't even get off the cruise control.

right now, the EGT probe is laying on the floor in my truck not much good there, is it?

but, to me, it feels like my 7.3 with the Hydra Tuner on 65hp moves out just as hard as the Cummins did....

I am going to get a real good test come next may.
My son and I are going to Price, UT to move my sister's stuff down to my home... he has a 2004 3/4 ton 5.9 Cummins in it.

using I-70 thru the Rocky Mtns, we will be loaded almost the same pulling double trailers each.....

I'll report on how that "test" goes come next year...
but right now, here at home, with the Cargo Trailer hooked up,
I did a test drive with it loaded with a lot of stuff, and that 7.3L moved out like there wasn't any trailer back there.

 

That will be a great test, looking forward to the results. I live in Colorado and have been to price, So I know what the trip is like and how bad I70 through Colorado is. It's also interesting in Utah when you are clearly going downhill but have to press on the skinny pedal to make a vehicle move.