The exhaust system on the Duramax LB7 is one of the most restrictive parts with respect to performance. If you are looking to increase power, especially if you are tuned, an exhaust is one of the best LB7 upgrades.
With power gains ranging from 20-30+whp and 40-60+wtq an upgraded exhaust will provide big power gains, but there are numerous other benefits too. One of the biggest secondary benefits is lower engine temps and a reduction in EGTs by 150-200+ degrees. Lower EGTs means a healthier engine and improved reliability, making an exhaust system well worth the money.
I’ve installed over a dozen exhaust systems on LB7’s. I’m going to cover all of the important things to consider like type of exhaust, material, sizing, downpipes, and more. Additionally, I’ll discuss the benefits of an exhaust and provide some recommendations on the best exhaust setup based on the results I’ve seen on trucks I’ve installed these on.
Duramax LB7 Exhaust Upgrade Benefits
- 20-30whp and 40-60wtq power gains when tuned
- Drastic reduction in exhaust backpressure
- 150-200+ degree drop in EGTs
- Increased turbo efficiency
- Better reliability due to lower engine temps
- Louder exhaust sounds
The exhaust system on the LB7 is pretty poor – it is highly restrictive and one of the main performance restrictors with this 6.6L engine. The good part of this is that upgrading it can produce big power gains. Most diesel engines for example won’t really see any power gains from an exhaust – because the LB7 factory exhaust is so restrictive you’ll see anywhere from 20-30hp gains and 40-60lb-ft. of torque gains, at the wheels.
The performance benefits aren’t the only thing that make it worth it. You will also see a decrease in EGT temperatures by 150-200 degrees which alone makes an upgraded exhaust worth it.
Lower EGTs, less exhaust backpressure, and decreased engine temps all lead to an increase in reliability. The LB7 is known to have overheating and head gasket issues. One of the best ways to prevent these problems and keep the turbocharger healthy is by reducing EGTs and engine temps.
Overall, an exhaust is 100% worth it on the LB7 for both performance and reliability improvements.
Exhaust Setup: Things to Consider
There are a lot of different exhaust setups you can get. There are a few important things you’ll need to decide on to choose one. We’re going to discuss downpipes, exhaust piping materials, 4″ vs 5″ exhausts, and mufflers.
I’ll provide my own opinion for each of these and round the article out with my preferred exhaust setup for the LB7 – taking price into consideration as well.
LB7 Downpipes: You’ll Want One
While I say the LB7 exhaust is restrictive, the most restrictive part is actually the downpipe.
The downpipe actually bolts up to the turbo instead of just connecting via a v-band so pretty much all the exhaust systems on the market do not include a downpipe.
The biggest reduction in EGTs and backpressure comes from the downpipe so I highly recommend purchasing one alongside your exhaust for maximum power gains and reliability improvements. An exhaust alone is definitely still worth it but combining it with a downpipe will really amplify the benefits.
Recommendation: purchase a downpipe alongside an exhaust.
Stainless Steel vs. Aluminum
There are 3 main types of piping material for exhaust systems: T304 stainless steel, T409 stainless steel, and aluminum. Stainless steel holds up better in rusty climates – aluminum exhausts aren’t quite as durable and don’t last as long, but they are cheaper for these reasons.
T304 is the best and also very expensive – any exhaust with this material is $1,000+ so not worth it in my opinion. T409 is the best stainless option when you consider price and durability. And aluminum is the best for price and worst for durability.
However, one of the more important things this matters for is drone. The LB7 tends to have a lot of drone and stainless steel exhaust systems create a lot of it.
Recommendation: I prefer aluminum exhausts for two reasons: they are the cheapest making them the best value option, and they have the least amount of drone.
LB7 4″ vs 5″ Exhausts
On a diesel truck the best exhaust is really no exhaust. Therefore, typically the bigger you go the better. The two options you’ll see on the market are 4″ and 5″ exhausts, which refers to the diameter of the piping.
A bigger 5″ exhaust will have slightly better benefits but they do cost more and have more drone. I usually only recommend a 5″ exhaust if you are running an upgraded turbo. If you are on the factory turbo then there is no need for a 5″ exhaust, especially with an upgraded downpipe too.
Recommendation: get a 4″ exhaust and a downpipe if you are on the factory turbo. If you have a turbo upgrade then I recommend a 5″ system.
Straight Pipe vs Mufflers
Another consideration for choosing an exhaust is whether you want one with a muffler or you want it “straight piped”.
A muffler will make the exhaust more quiet which is good if you want the performance benefits but not the sound increases. However, exhausts with mufflers cost more and they provide less performance gains than straight piped exhausts. The muffler will create some backpressure and therefore doesn’t offer as much performance as an exhaust without one.
Recommendation: avoid the mufflers – if you are concerned about drone or loudness then get a 4″ aluminum exhaust to help reduce it. The mufflers restrict performance too much for my preference.
Best Duramax LB7 Exhaust Systems
To recap everything above: my recommendation is to get a 4″ aluminum downpipe-back exhaust system, without a muffler, and to upgrade the downpipe at the same time as the exhaust.
If you have an upgraded turbo I’d get a 5″ with a downpipe. If you live in an area where metal rusts easily then you can get a stainless steel exhaust if you want something that will last 10+ years. And if you are really sensitive to the sound you can get a muffler. But, an aluminum exhaust without a muffler is going to be the best performing system while also being the cheapest: win-win.
Best Exhaust: MBRP 4″ Aluminum w/o Muffler
Buy Here: MBRP 4″ Aluminum LB7 Exhaust System
At just under $400 this is the best bang for your buck exhaust that comes from a reputable, name-brand company. This exhaust fits all of my preferred criteria: 4″, no muffler, aluminum material. As is true with all exhausts on the market, it does not come with a downpipe making it a downpipe-back exhaust system.
Best Downpipe: PPE 3″ LB7 Downpipe
Buy Here: Duramax LB7 PPE 3″ Downpipe Upgrade
MBRP also offers a 3″ downpipe but it’s about $100 more expensive than the PPE option and it is actually stainless steel compared to aluminum. The MBRP 4″ exhaust will bolt right up to this PPE downpipe so while I usually like to keep the same brands throughout the exhaust this LB7 downpipe from PPE just comes in at a way better bang-for-the-buck.