I feel like I get asked this question every day, so it’s obviously something I should take a few minutes to write down.
“What is better for my truck? A 4-inch or 5-inch exhaust system?”
Well, it depends on what you want from the exhaust system and your truck. For most trucks, the difference in these exhaust systems comes down to how it sounds. Unless you’re making some serious power and running a massive turbocharger, the size of your exhaust system will make virtually no difference in the power of your truck. Sorry.
Most of these trucks (other than Cummins) are limited by their downpipe either way. So, no, you’re not getting much more flow with a 5” because your 3” or 4” downpipe is restricting your entire exhaust system. That being said, that doesn’t mean there isn’t a difference in these systems.
The Duramax trucks have a very tight fit between the cab and the engine, so a 3” full bore downpipe is the biggest you’re going to fit in there. This will certainly help performance as the factory downpipe is literally squished flat to fit. This is why all the Duramax exhausts are labeled as Downpipe back. Fords also can’t fit anything bigger than a 4” downpipe (unless you’re running an OBS, then you’re in 3” territory).
The 4” Exhaust System
The 4” exhaust system is the most popular exhaust we sell, for a good reason too. They give a great sound with little to no drone. It’s still going to bark when you get into the throttle, and when paired with a muffler it’s dulled down to a nice sound that is tolerable for diesel enthusiasts of all ages. If you’re frequently towing, like your neighbors, and don’t want to screw around with fitment issues go with a 4” exhaust system and you’ll be more than happy (your neighbors will be too). Most newer trucks come stock with a 4” from the factory, so you can easily mate up a front pipe to your factory tailpipe without any modifications. If you want to run a full kit, it will slip in just like your factory kit without any modifications.
The 5” Exhaust System
The 5 Inch Exhaust Systems are for people who like to party (and have annoying neighbors). It’s deep, it’s droney, and it turns heads (for better or worse). These kits sound AWESOME, however, some people find them to be too much (typically it's those people in uniforms) and find the cab drone too excessive. You can always add a resonator like the FLO-PRO Twister if you want to maintain a deep sound but dull down the in-cab drone.
Some trucks may run into fitment issues (especially those with airbags or full-size spare) but we have found a way to stuff these into almost any truck. If you have enough beer, patience, and maybe some whiskey you will get it in. That being said, the FLO-PRO & MBRP Kits fit very well and have made their piping fit with pretty much any application.
The difference between a muffler and a straight pipe once again will come down to preference. You’re not going to see any power gains here either, the MBRP & FLO-PRO mufflers are a perforated tube with fiberglass packed around it. These high-flow mufflers don’t reduce your flow or increase resistance but will reduce the exhaust drone and noise significantly.
If you’re looking to significantly cut down the drone, without changing your exhaust note too much, we recommend checking out the FLO-PRO Twister Mufflers. They spiralize your exhaust flow with their corkscrew design, it’s designed to maintain the sound of your exhaust from the outside, but stop any drone you may have inside the cab.
Hopefully, this answers a few questions about the options we have for exhaust systems. If not, drop a comment below!
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