Duramax LLY Performance Upgrades - 500whp Guide

The Duramax LLY came with the biggest factory turbocharger, meaning it has a lot of power potential. All you really need is tuning to make 500rwhp. However, the LLY also came with some of the biggest airflow restrictions which cause overheating when not properly addressed. Furthermore, the Allison 1000 transmission is another weak point on the road to power.

In this guide we're going to discuss every performance upgrade and supporting mod that you need to build a 500rwhp Duramax LLY.

LLY Power Limits

  • Transmission: ~400whp without tuning, around 500whp it needs to be built
  • Fueling: a lift pump is a must-have right away, injectors and injection pump can handle 600whp (with larger nozzles)
  • Turbo: 500whp is the limit for maintaining some reliability, max effort is around 525whp

So before we jump into modifications you can see we already have two things we need to address: fueling and the transmission. And we're not even addressing the airflow restrictions and overheating issues yet.

Must-Have Supporting Upgrades

  • Lift Pump
  • Turbo Inlet

Before adding tuning we need to address the fueling issues and the overheating. Turning the boost up with tuning will require more fuel and it will create extra heat. So we'll need a lift pump and a turbo inlet to fix these issues.

We don't cover transmission upgrades here since you can get away with just transmission tuning, or keep the tuning under its power limit.

1) 165gph Lift Pump

Duramax LLY Lift Pump Upgrade

More boost and more power means more fuel. Duramax's are notorious for fueling issues when tuned because they do not come with a lift pump from the factory. This puts your injection pump and injectors at risk - a repair that will run you close to $2k just in parts. So save your fueling system and help support the higher power levels with a lift pump.

A 165gph pump is perfect for any light or moderate build. It can support around 800whp so you really don't need anything more. We do also have a 100gph unit available that can handle around 550whp, but I think the extra $50 is worth it for the extra flow. If you want to really amp it up then an extra $50 over the 165gph can get you 250gph, but this is a bit overkill for anything but extreme builds. FASS is our brand of choice for lift pumps on the LLY.

Price: $699-$799

Shop FASS Lift Pump Upgrades

2) Turbo Inlet Upgrade

Overheating issues are caused by airflow restrictions and the biggest one on the LLY is the turbo inlet, or mouthpiece. This is a small little piece but the factory unit is terrible. Upgrading this is a must before you add tuning, it will drop EGTs by well over one hundred degrees.

You've got some reputable options like S&B, PPE, and a few others but honestly you can find some on Amazon that get the job done for $60 so we choose to point customers in that direction vs. selling an overpriced piece of piping.

Price: $60-$200

Duramax LLY Performance Upgrades for 500whp

  1. ECM & TCM Tuning
  2. Cold Air Intake
  3. Exhaust Upgrades

1) ECM & TCM Tuning

Banks AutoMind 2 Programmer Duramax LLY

Tuning is where the gains are at. Just this alone can push 500rwhp. But - it can't do so without causing a whole lot of other problems which is why we have supporting mods above and some airflow upgrades below.

The best route here for a higher-power build (400-500rwhp) is going to be using EFI Live and doing both engine and transmission tuning. Transmission tuning is great at any point but definitely a must once you start edging too far beyond 400whp. This route is probably going to run you $1,200 but it will give you the most optimized tuning setup and transmission reliability.

If you just want a little extra power, better towing, and increased gas mileage and don't really plan on pushing things to their limit then you can go the budget-friendly route and get a Banks AutoMind Programmer. This is a lot cheaper and will still allow for big power gains, but won't put you in the level of risking transmission failure.

Price: $439-$1,200 depending on the route you go

Shop Banks AutoMind 2 Programmer

2) Cold Air Intake

LLY Cold Air Intake Banks

Generally speaking, all of the intake and all of the exhaust is a restriction on the LLY. The mouthpiece or turbo inlet will work wonders but a higher flowing intake system is still absolutely worth it. No, it isn't a necessity if you go with modest tuning but it will help lower temps, add power, and add gas mileage too.

It doesn't make sense to us to add tuning and turn the boost up without adding more airflow and reducing as much restriction as possible. We prefer the Banks kit or an open air intake, avoid S&B as their plastic cover tends to crack.

Price: $449

Banks LLY Ram Air Intake

3) Downpipe & Exhaust Upgrades

Duramax LLY 3inch Downpipe

All LLY's came from the factory with a catalytic converter which means exhaust upgrades should be done in two parts: a downpipe + a cat-back exhaust. You'll want 3" for the downpipe. 4" is a perfect size for the remainder, we prefer no muffler but if you want to keep it quieter then no issues opting for one. This setup does end up running you about $600.

Now, the LB7 has some exhaust systems that are only $300 and are turbo-back meaning you don't have to upgrade the downpipe separately. Half the price for the same upgrade - the caveat is the LB7 doesn't have a cat. Not to say this should be done, but the LB7 exhaust will bolt directly up to an LLY, or to any Duramax through 2010. So, use that information how you like.

Price: $300-$600

MBRP 3" Downpipe & 4" Cat-Back Exhaust

$2,700 and You've Got 450-500whp

Here you have it, a budget 500rwhp LLY build that will only run you $2,700. While this is the low end it does factory in EFI Live. If you want to keep things at more modest power levels you can do all of this for about $2,000 and run right at 400whp.

Now, at the top end of this power range you are going to start running into issues. Even with transmission tuning you will probably eventually need an upgrade. The factory turbo is running at 95% at this point. And EGTs can start getting out of hand without more airflow upgrades. So the actual safe limit for an LLY without needing to get into more expensive and advanced upgrades is probably right around 450whp.

Contact us if you have any questions or need any help with your LLY build - we'll always tell it to you straight and only sell parts we would (and do) actually install on our own trucks.

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