LLY: Questions I have been unable to answer.

[DuramaximusPrime]

Howdy Duramax residents! After a ton of research, I have come to realize the missing information required to plan my build requires experience to answer so I came here to find some wisdom. I'm looking to extend the life of a 05 LLY and hit 400- ̶4̶5̶0̶H̶P̶ RWHP. I know a tuner can give the HP easily but I also want a healthy truck.

Here's my list, thank you for any help you can provide. I realize some of this is likely situational but any input will shed some light for a guy in the dark.

Is deleting the cat and muff from the stock exhaust worth the trouble?

What effect will a downpipe upgrade have if I retain stock (or gutted stock) exhaust?

What effect will a downpipe upgrade have if I upgrade the exhaust?

Is there any reason to upgrade exhaust without upgrading the downpipe?

How would a downpipe change the tone of the exhaust/turbo?

Is a bigger downpipe useless without bigger up pipes?

If I use a tuner to disengage the EGR are there any physical changes needed to reap the benefits?

Are there any weight reduction mods?

That's enough to get us started. Thank you.

 

[2004LB7]

Howdy Duramax residents! After a ton of research, I have come to realize the missing information required to plan my build requires experience to answer so I came here to find some wisdom. I'm looking to extend the life of a 05 LLY and hit 400-450 HP. I know a tuner can give the HP easily but I also want a healthy truck.

Here's my list, thank you for any help you can provide. I realize some of this is likely situational but any input will shed some light for a guy in the dark.

Is deleting the cat and muff from the stock exhaust worth the trouble?
Deleting the muffler will have little to no benefit. there just isn't enough restriction at that HP level. the cat can give you more flow especially if it is clogged up which can happen on dirty tunes. but remember this is illegle.

What effect will a downpipe upgrade have if I retain stock (or gutted stock) exhaust?
again little to none at your HP goals and not upgrading the turbo. but, Being an LLY which is known to have flow restrictions that could cause overheating, it wouldn't hurt to give it a little bit more help in this department.

What effect will a downpipe upgrade have if I upgrade the exhaust?
see answer above

Is there any reason to upgrade exhaust without upgrading the downpipe?
Sure, it can give you a little more flow, but you are not likely going to notice any difference except for the exhaust note

How would a downpipe change the tone of the exhaust/turbo?
I will have to let others with more experience answer this

Is a bigger downpipe useless without bigger up pipes?
Maybe, it is something some do, usually in combination with other upgrades. be it a larger exhaust, turbo or other flow mods. I think by itself it is not going to net anything until it starts becoming the bottleneck

If I use a tuner to disengage the EGR are there any physical changes needed to reap the benefits?
normally a blocker plate is used to prevent pressure from opening it up or leaking pressure

Are there any weight reduction mods?
look at the racing or drag strip build threads. tons of ideas but most are not too practical unless it is a dedicated race truck. things like removing seats, hacking up the bed. removing interior trim and upholstery, etc. you can get some decent reductions in your wheels and tires alone. no spare and not running with a full tank of fuel.

That's enough to get us started. Thank you.

Replies in RED

for you HP goals, 400-450 is not much for these engines. the two biggest things to address is getting it to breathe with the LBZ intake mod and maybe some of the items you listed above. And the transmission. you should definitely get it built. one of the best upgrades for any duramax running above stock HP to keep it reliable. run a search here on the LLY for upgrades pertaining to overheating and there will be tons of discussions on what to do about it. that is what I would address first if increasing the engines output.

Also, there are many others with much more experience with the LLY then me and will likely have much more input and details for you

 

[DuramaximusPrime]

for you HP goals, 400-450 is not much for these engines. the two biggest things to address is getting it to breathe...

Getting more air into her is top of the list. Have a new mouthpiece waiting to be installed already. I figured a downpipe would help her breathe a bit better but was wanting confirmation it would help even with stock exhaust.

.....And the transmission. you should definitely get it built. one of the best upgrades for any Duramax running above stock HP to keep it reliable.

A built transmission is quite a bit above my budget. I have read up to 500HP the stock Allison 5 spd is up to the task and figured a 50HP buffer would keep it well within the zone. Should I lower my HP goals to ensure the stock transmission is well within the safe margin? It may help to consider the two drivers of the truck may driver her aggressively but aren't going to be doing hard launches or quarter mile runs.

Is a bigger downpipe useless without bigger up pipes?
...I think by itself it is not going to net anything until it starts becoming the bottleneck...

That is a superb answer.

...normally a blocker plate is used to prevent pressure from opening it up or leaking pressure...
So I tune the EGR, block between the egr cooler and the passenger up pipe and thats that?

Are there any weight reduction mods?
...most are not too practical unless it is a dedicated race truck....

I kinda figured as much but its great to get confirmation of such. This is been an epic research journey for a guy who's not very automotively inclined. Still much to learn!

Awesome reply, thank you for your insights!

 

[zakkb787]

Down pipe isn’t gonna do you very much good unless you just want it. There’s many ways you can go about this. But the Allison IS NOT good in stock form to 500. You’re pushing your luck with 400, especially with a 5 speed. If you still have a factory air box, do the mod where you basically drill holes into it and open it up.

When talking about taking out the cat and blocking egr, will it help? Absolutely. Is it illegal? Very. An exhaust will help your truck breath better, and blocking the egr (completely deleting is even better with a cut up pipe and new cold side pipe is even better) will keep nasty stuff from getting into the turbo and engine. But again. Both of these are illegal in the US

 

[DuramaximusPrime]

Down pipe isn’t gonna do you very much good unless you just want it.

I realize it's not going to add power, is it not restrictive enough to warrant an upgrade? The intake mouthpieces claim 78% more airflow and I guess it just feels weird to put that much more air in without upgrading the out flow.


There’s many ways you can go about this. But the Allison IS NOT good in stock form to 500. You’re pushing your luck with 400, especially with a 5 speed.

I am not looking to push my luck. I want to stay within safe margins for the transmission for sure. Are there specific weak points that address this or does it just need a complete upgrade?

If you still have a factory air box, do the mod where you basically drill holes into it and open it up.

I do have the stock air box. I am interested in doing a mod to my factory box. I was actually considering insulating it from the engine bay heat and having it intake from the side panel only. I would enlarge the existing hole in the side panel a lot and have a sort of prefilter around it perhaps.

When talking about taking out the cat and blocking egr, will it help? Absolutely. Is it illegal? Very. An exhaust will help your truck breath better, and blocking the egr (completely deleting is even better with a cut up pipe and new cold side pipe is even better) will keep nasty stuff from getting into the turbo and engine. But again. Both of these are illegal in the US

What are differences between Tune and block plate vs mod/upgraded up pipe and cold side pipe? I have read it's better but not sure why its better. It's blocking the EGR the same as the tune and plate. I suppose there could be some weight savings?

Appreciate your input!

 

[DuramaximusPrime]

Reading the BPU upgrade list for the LLY was helpful.

"Transmission upgrade - As soon as you pass 400rwhp you are living on borrowed time. You will need a minimum of a converter, C3's, and valving kit."

Sounds like 400 RWHP is my new maximum goal.

 

[Dozerboy]

Is the truck 4wd? What is the truck going to be used for?

Sent from my SAMSUNG-SM-G900A using Tapatalk

 

[DuramaximusPrime]

Is the truck 4wd? What is the truck going to be used for?

The truck is 4x4. The truck is currently a "daily driver" even though it's not driven daily. I don't want to limit its towing abilities although I have no plans of big towing in the future. In the past, she towed a large 5th wheel like it wasn't even there. She doesn't go offroad accept very rarely. Great question, I had not thought to add that information.

Love the sig btw!

 

[ZeroGravity58]

I would put a downpipe back exhaust, lbz mouth piece and air box mod, 50hp tune, and blocker plates in the Egr. Then drive and have fun

 

[DuramaximusPrime]

I would put a downpipe back exhaust, lbz mouth piece and air box mod, 50hp tune, and blocker plates in the Egr. Then drive and have fun

A simple solution that may end up being my answer. Currently have a mouthpeice waiting for install and been looking into a air box mod. The EGR will happen soon. Exhaust is big money so I may just leave it stock for now or delete the cat and keep it stock. I figured the downpipe was probably more restrictive than the stock exhaust but that doesn't seem to be the case.

Thanks for your suggestions!

 

[TheBac]

I would put a downpipe back exhaust, lbz mouth piece and air box mod, 50hp tune, and blocker plates in the Egr. Then drive and have fun

100% agree. Just do something simple to wake the truck up and then leave it alone.

 

[zakkb787]

You will be amazed how different the truck will feel with a 30-50 hp tune. It’s a noticeable difference for sure.

Difference in a blocker plate and a new cold side is with a blocker you still have the factory piping and the egr cooler. It’s not necessarily a huge restriction or anything, but there’s definitely room for improvement. It’s also a chunk of weight lost and no more coolant running through it. Blocker plate is the simplest, but the BEST way is a new cold side and a new up pipe without the riser. Though, this is a lot more coin.

Air box mod, 5” exhaust with a muffler or resonator (put the resonator as close to the down pipe as possible I have this with no muffler and it’s a great tone and no drone in the cab), 50hp tune, airdog/FASS and delete factory filter housing, a good set of gauges (boost egt and oil temp), and figure out what you want as far as egr, and that’s a basic recipe for a good running reliable truck.

There are other mods that would make the truck even more reliable but aren’t necessary, such as upgraded transmission cooler, 2011 LML hydro boost setup, oil cooler from a newer truck, upgraded brake system, tie rod sleeves/upgraded tie rods, DHD brace, idler/pitman support kit, the list can go on and on.

 

[Dozerboy]

A simple solution that may end up being my answer. Currently have a mouthpeice waiting for install and been looking into a air box mod. The EGR will happen soon. Exhaust is big money so I may just leave it stock for now or delete the cat and keep it stock. I figured the downpipe was probably more restrictive than the stock exhaust but that doesn't seem to be the case.



Thanks for your suggestions!

You got a good plan. I would just loose the cat and muffler at most for now. I ran my truck that way for a while on more power then you want. I would use a block off plate for now on the EGR. You do need to look into pump rub fix on your tcase. Might look into build an electronic fan setup. It will make the truck feel more responsive, but has its down sides.

Sent from my SAMSUNG-SM-G900A using Tapatalk