In my case, performance is not the issue but efficiency, pulling power and controllable EGT's are.

Loaded I run generally 5 to 20 pounds of boost. On a max pull on a hill at around 2000 I run 28 to 29 pounds boost. Winding up the gears to the max will produce 31 pounds.

For pulling I know that a waste gated turbo is detremental to economy as it produces wasted energy where a properly sized exhaust housing and turbo with no waste gate produces the best power and economy but losing throttle response.

The question is this, is boost necessary for economy under light throttle? When I give it larger exhaust the boost will drop some, and I know that I can do better with a larger exhaust housing non waste gated, but that again will drop boost.

Is there an efficiency number of boost under light throttle or would it be best sized at wot on a hill? Much of my running is around 5 pounds boost, should it be higher?

I currently have no EGT problem, it is very hard to get it up to 1200.

 

it depends on what you mean by light throttle...

when I went from a 12cm HX35 turbine side to a 16cm HX40 turbine, I picked up a little MPG at cruise... BARELY any, but a little...

around town I lost a little because it takes longer to get into boost, and it smokes more at lower RPM which = inefficiency...

Forrest

 

The efficiency that I need is freeway at 26,000 to 30,000 pounds. City performance is sort of immaterial. I have noticed that issues that show no real differnce with only the truck, may make some good difference loaded heavy.

 

if you run loaded on the highway all the time, size the turbine housing accordingly... also realize that you'll need to size it to where you do your driving... if you're at higher elevations, you'll need a smaller housing to help get up those hills...

a smaller wastegated housing will generally net better overall performance/economy than a larger non gated housing... if you're CONSTANTLY at a steady load, the optimal larger housing will be better, but there are so many variables out there on the road...

18 wheelers run non-gated housings, but they've got WAY more forward gears than us, and they rarely see the high side of 2000rpm...

tractors and generators have what look like HUGE turbine housings because they're basicly at constant load all the time...

the fraction of a mpg you lose at full load by running a wastegated housing doesn't make up for the inefficiency at lower load/rpm IMHO.

Forrest

 

Actually this really isn't true. A wastegate is simply a protection device against overspeed, no more and no less. What it gives you is the ability to run a slightly tighter housing (for throttle response), while still giving exhaust a place to go once the turbo is at max boost.

I for one, much prefer wasted housings. Some people's idea that you need high boost is just not correct on these trucks. I've seen trucks building 40 PSI of boost that are making 50 more ponies than other trucks building 60 PSI of boost.

Given your EGTs (max of 1200), I'd say your turbocharger is just about right for your truck. A looser housing MAY give you a little more economy on the highway, due to freer exhaust flow and a little less boost, but I really doubt it. You're only pulling 31 PSI of boost, which is just outside of optimal for an HX35. A 14cm wasted housing may be just about right, but I think a 16 would introduce too much lag when you get into the hills and make the truck a little miserable to drive. But I am a throttle response junkie, even when pulling 30K, so I tend to get a little tight on housings.

Rod

 

Haulin,
You are in a diff truck then most of us...(what you do with it). I would call diesel inj. of Pittsburg 724 274 4080 and talk to people that REALLY know. The standard ans is get a smaalller hot end w.o. a gate and that works wonders for most.........you how ever may need a diff animal like a 40 to do the job keep the egt dwn and kind of not be on the threshhold "in town"

 

Rod as Thumper said, there seems to be totally different specs for speed and for economy pulling as big trucks do. I have been trying to balance off the differences from big truck articles and the posts and articles that are meant for speed light to light. In reality I use the truck the same as a big truck, just smaller. I do agree with you as it seems, I only get into the waste gate on the hardest pull.

I also have been thinking that in the future I will go to a more open exhaust which if I am not wrong will produce the same as a more open exhaust housing to some degree. At cruise, and that is where the economy is generated, I seem to be well within the design and supply of air.

I do have to get busy and check the pressure at the exhaust manafold for comparason and the pipe pressure. I have the taps in place and only have to get a manometer to check this.

Thanks for the responses, came out about how I was thinking. At 30,000 I can count on 11 1/2 and 12 on a good day. I am making advances, used to now and then get a 10 opr 10 1/2 that I chalked up to fuel differences, but now it never drops below 11.

The only question I still have, is there a point where more boost is better at cruise. This is when it gets down around 5 pounds or so. Thumper, good point and I planned to run this past them, thanks for the number.

 

Be careful when reading the large truck articles and talking to big truck tuners when trying to tune your 5.9 Cummins. These are totally different animals when it comes to fuel delivery and the RPM range you're dealing with.

If I remember correctly, you've got heavy truck experience. With a heavy truck, you've got the gears to pull through any lag from a large housing turbocharger. And once you get moving, you'll only drop a couple hundred RPMs between gears. This is not the case with your 5 speed (6 speed? Sorry I can't remember). Having a large housing that moves a pile of exhaust isn't going to help you if you can't even start your load, or you have to drop 2 gears when pulling a hill.

While I don't pull everyday such as you do, my truck will often be hooked onto 20,000lbs of hay, or 30,000lbs of animals. With my 2001 HO Dodge, Edge Comp, and RV275s, I found my best economy and response was with a 14cm wasted housing on my HX35. The 12 was a hair too tight, as I normally pulled with the Comp on level 5. The 16cm didn't do a thing for me, except make me drop an additional gear pulling river hills.

Is there a point where more boost is better at cruise? No, not on your truck anyway. The 5.9 Cummins is at its PEAK efficiency at 1150F cylinder temps. While cylinder temps aren't the exact same as EGTs, you can draw a reasonably close approximation. If your engine is running efficiently, and at 1200F EGTs max, yours is doggoned close, then adding more boost (in other words, more CFM of air flow) will get you nothing. Indeed, the only way to accomplish this would be to tighten up the turbine housing, which would then drop you out of your current state of efficient running.

If fuel economy is what you're after, look to someplace other than the turbo. At 30K trailer and load, I found my best economy at about 330 - 340 BHP with that 2001 6 speed. One of our hotshot customers did a 10 speed conversion on his truck, and his best economy was found at about 275 BHP, but he did find himself rowing alot more. My 03, owing primarily to the bottom side fuel delivery gets its best economy under heavy loads with the TST box on power level 2, which equates to about 320 BHP. This is on my standard pull to Kelvington which is mostly flat land travel, with 3 steep river grades.

Hope this helps you somewhat....

Rod

 

Rod's right on here, but (as usual ) I'll add to it.

Keep in mind, I tend to talk more in theory, since I haven't towed heavy like you do. But my theory is usually close (IIMSSM)

What's key when towing and towing heavy even in high altitude is the ability to sustain higher boost.

I should clarify. "High" boost is enough to keep EGT in check. Generally, more fuel, then you need more boost, though it's not linear because of the inefficiency of the turbo.

Keep this in mind when thinking about climbing through the Rockies. In that situation, you'll want a little tighter turbo to keep boost up and keep you trucking. It's better, imho, to back out of the loud pedal because of high EGT than to not have enough grunt (boost) to pull the hill.

You can always drop a gear to ease the EGT burden if need be.

Sounds like you have a good combo, HID. Maybe some small EDMs like Mach 1s would give you a little more grunt, good mpg, and still keep EGT in check?

Justin

 

I have went from a wasted 12cm housing(stock) to a 14cm non-wasted..and then to a 16cm ported and polished non-wasted housing..I found that the 14 was very responsive and when loaded I could produce 30lbs of boost with egts running 1150* at 55 mph up a 6% grade. Since then I have added a #10 plate 3k GSK and the 16cm housing.. Lag has increased..egts has increased because of the plate and springs.. The problem that I do believe that I am now experiencing is that I dont have the volume of exhaust to fill that 16 housing... So..the egts run up before I can spin up the turbo to build the boost to get on top of the heat.
Soooooo I have a 14cm wasted housing coming to see if this will improve the boost when pull the hills. I went from 30lbs of boost with the 14 non gated housing down to 20-22 with the 16cm housing.
Anyway we will see if this dog will hunt...

Rick

 

Rick, I think you should look for other problems. There's NO WAY a housing swap from 14 to 16 should drop you by TEN PSI!! Maybe 3 or 4, but not ten!

If you did the plate, GSK, and housing all at once, then you can't say conclusively that any difference is JUST with the housing swap.

Where is your plate positioned? Back? Forward? How much?

Maybe the housing had a casting flaw of some kind? I've always seen a 16cm reduce PEAK Egt, but add lag.

Justin

 

I have checked for boost leaks but have not found nothing.. As far as 10 psi drop its only dropped somewhere around 8lbs. But even at that I cant spin it up fast enough before the egts get up to 1250* +..
The plate was a little forward..when we installed it but now I backed it off 45k to see how things work. The flat towing egts are much more friendly..but once I hit the 6% grade that I dread the most..things start to warm up real quick.
I think that I am over housed right now for the amount of fuel that I am running..
There is a couple of things that will happen before our next trip..one is the 14 wasted housing and also I will be bumping the timing to 15.5-16..
One good thing about buying the wasted housing..its just one more piece of the puzzle for my towing twins...

Rick