Curious what "tuning board" said that. Some factory trucks and SUVs have a button for tow mode that reduces timing and richens AFR so I would trust GM over some tooners.

 

DEF is injected in the exhaust and is for emissions only. The engine doesn't need it to live and doesn't melt if you don't use it. Running the engine so hard that you need alcohol injection is a risky game to play.

 

I know, but I have the option to turn the turbo boost down to 0psi if I were to run out of water...


The more I think on things some early advice is making me think more carefully:

Maybe my planned build will still have 550lb/ft just at a higher rpm, or maybe i'll roll the allowable RPM into some upper-midrange compromise and use Gen4 or those suggested marine rods... there are some aspects of this which are still a test mule and project in ways but the core is still here - turbo an LS for tow use.

 

Peak tq above 3000rpm in a tow motor would not be ideal. E33 (as you call it) would be preferred in support of the water being injected compared to water alone.

 

I've only seen pressure, shift points and TC lockup strategies change with tow mode. Can you provide some specifics on PCM and timing/AFR changes?

 

Not to be the negative one here but..... If you are able to do all this mechanical work and custom fab work. Wouldn't a duramax be the better idea? Repair bills can be in the 10,000+ range but if you can do the work yourself parts usually aren't over a few thousand. No matter what you do or how much you spend it wont match a 20 year old duramax with 500,000 miles.

 

This is a project vehicle and I don't expect to do enough miles under tow for a Duramax (as is or swap) to pay for itself. Other people throw an LS in a hot rod and tune it there, I just wanted to do it in a tow vehicle for a change as it's more practical for my use.


What would the best RPM to design around and why is a higher rpm bad? I understand the lugging answer of not too low, but I wasn't sure why not too high until it's con-rod and valvetrain loads from rpm.

I made a voting question elsewhere tho it's only between 1600 and 2600rpm assuming it would be lower in a non-diesel. FWIW i'm 'only' looking for horsepower around the 350-400hp range, more than that is overkill for non hotshotting tow. (even those guys at most aim for 400-500hp while in tow mode, no more, even in engines that can take more like DT360 and DT466 swapped Super Duties which make four digit power) If it ends up having more power that's fine but it's not a design goal.

 

. Build a tow motor based on tq, not hp. Any idea why pk tq on an ecoboost is at 2500? Can you imagine cruising the highway for 10-12hrs at 4K rpm (if that's where you want pk tq)?

 

Why can't he cruise at 3K rpm if there is enough power there to get the job done even if peak torque is at 5500 rpm? BTW, torque at a give rpm is horsepower. 550 ft-lb at 2000 rpm cannot tow as much as 550 ft-lb at 3000 rpm.

 

He CAN cruise at 3k if there is enough tq to pull a 10K load. Don't think it's going to be a 5.3 with pk tq at 5500 though. Correct - hp is calculated from tq. Explain the physics of 550ftlbs at 2k is less capable than at 3k.

 

Assume two exactly the same vehicles and the engines produce 550 ft-lb at 2000 and 3000 rpm. They are traveling at the same speed and one has a gear selected so that the engine is turning at 2000 rpm and the other has the engine turning at 3000 rpm. The vehicle running at 3000 rpm has a mechanical advantage of 1.5 so the rear wheel torque will be 1.5 times the torque of the other vehicle. That is the basis of my statement but if I am off then let me know.

 

HP = Torque X RPM / 5252 where the HP is the rate at which the torque is delivered.

The rate at which the work delivered here is the speed at which the vehicle can tow the load. The torque is only delivered during a combustion stroke so the more combustion strokes you deliver per minute the more work the engine can do. Raising the RPM of the system allows you move more in the same time frame. Same thing if you raised the torque. Either one outputs more HP. So 550ftlbs is more capable the higher the RPM in the same exact way that 650ftlbs is more capable at 2K RPM than 550ftlbs is.

The advantage doesn't exist in a vacuum so to speak though. The rate at which you want the work to be done matters. Increasing torque with no increase in RPM only increased the weight you can move, not the speed at which you can move it.

You set the turbo up to put the power where you want it. Be it 2000rpm or 3000 or 5000. Just gotta size the turbo right. It's going to be really small compared to what we see on here most of the time.

 

The engine at higher velocity is producing more power. Power transfers through the drivetrain but torque can be manipulated with gear ratios. They're playing games with gear ratios to produce more torque at wheel from the engine that's developing more power.

This is all misleading though because the engine that can make more torque at 2000 RPM will also make more torque at 3000 RPM. It's going to blow away the other engine that has to be coddled with steep gear ratios to perform.

Threads like this don't go anywhere because it just turns into little academic exercises and nobody is doing an actual build where reality has to be faced. So far we've learned that people who actually tow keep the boost mild because they like making it to their destination.

 

Well was mentioned in here for one https://ls1tech.com/forums/pcm-diagn...ll-towing.html - user smokeshow. You guys are the experts, not me, i'm just trying to methodically research all the angles before committing to any plan.


If it has to run 4k on boost for 12 hours that's too hard on engine and ears. The idea of the reserve power is for getting a load going without taking a minute to get to speed, getting up hills in the rockies without being stuck at 30mph in the far right lane, and having reserve power when everyone is pressing on me in rush hour. Guys have towed 10k for a long time with less horsepower than any 4.8L, it just feels less safe. I'm not asking the world here.


Right and before even designing the turbo system, i'm trying to see if my idea is sane or loony. I've already been convinced to slide my original low RPM expectations upwards to more midrange for various reasons. I just love the feel of a big block down low but it's more important the job gets done (a given power level achieved) on a tolerable budget. If it was going to be a full time tow rig i'd go big block or diesel, no question, but it's not and I hope to get better than the 8mpg my last big block got driving around town empty.


I don't think my boost plans are excessive? And i've been modifying my plans once someone explains why something is a bad idea in a way I can understand. This is all a learning exercise for me - the real build will be so also - my first LS swap but hopefully not the last - and i'd rather start learning things like tuning and turbos on a more cheaply replaceable 5.3L core than a more expensive 6.0L core in case it blows up due to newbie mistakes. I don't just want to hand it over to someone else to tune and do, I want to learn to do it MYSELF yet if it ends up working well i'm using it to do practical things like tow safer instead of just barrel down a quarter mile cool as that is and as much as I want that to be a future build.

EDIT: Just to share, the latest refinements in the plan include nixing the twin scroll turbo idea (I was curious after hearing about the advantages and wanting to use a junkyard one but the complexity of the exhaust manifold sounds like a barrier unless there's an affordable off-the-shelf option) though i'm still deciding whether single or twin turbo is the way to go. I'm definitely wanting to use junkyard turbo(s) probably in cast iron so it will take the heat better. It's possible limited turbo selection will force the issue ie affordable durable iron pickup turbos too large for a twin. Was considering things like a Holset HX35 or even the later VGT turbo (people have made their own manual controllers) off the Cummins - but it's an open topic. Some of those are also twin scroll from the factory but the hassle of the exhaust manifold may not be worth it and i'm led to believe I can just still feed from a log manifold like any normal turbo.

 

that's an over generalization. There's nothing wrong with pulling a few degrees to give yourself some cushion. Melting stuff comes from an overly retarded setup. No one suggested just dumping timing when towing. It would be akin to running lower octane so you need to pull a few degrees to account for it.