I have got an almost completely restored k1500 OBS 350 5.7.
the current setup is the stock manifolds into a Y-pipe into the cat, and then into a silencer muffler with dual tips right on the muffler dumping on the ground.
The power and mileage is terrible (10 mpg) and I’ve checked injectors, intake, (new CAI) and new plugs and coil. The current exhaust has some holes from the mounts ripping off, and the muffler is barely getting hot after a good run, so the cat needs to go. I want to put on shorty headers and a Magna flow muffler and leave it at that. Pointers?
Before you throw on the headers, make sure to replace any gaskets, and give the engine a good once-over. Since you’ve checked injectors and plugs, maybe look into the fuel pressure and timing as well, just in case. Shorty headers are a good choice, but they won’t make the same gains as long-tube headers. Still, if clearance is an issue, shorties are better than sticking with stock.
@Nicol
Thanks, I thought about long-tubes but wasn’t sure about the fitment. I don’t want to have to redo anything again soon. What do you think about deleting the cat altogether?
Vic said: @Nicol
Thanks, I thought about long-tubes but wasn’t sure about the fitment. I don’t want to have to redo anything again soon. What do you think about deleting the cat altogether?
Removing the cat can give you a slight boost in power, but be aware of the emissions laws in your area. Might save you some headaches down the road if you need to pass an inspection. If you can, try a high-flow cat instead, gives you better flow without totally axing it.
@Nicol
Shorty headers and a Magnaflow muffler should definitely improve the flow over your stock setup. Keep in mind that the cat-back system will still play a role in how everything sounds and performs. Maybe go for a dual exhaust setup if you really want to get some deep tone out of it, and that’ll free up some power too.
Vic said: @Shan
I’m not trying to make it sound obnoxiously loud, just a good rumble. Would duals be too much in that case?
Not necessarily. You can still run duals but go with a muffler that has some sound-dampening to keep it refined. Dual pipes usually help with performance, but it’s all about what kind of note you’re after.
Your power and mileage issue might not just be exhaust-related, but getting a better flow will definitely help. Check to make sure your O2 sensors are working correctly, especially if you’re planning on keeping some of the original parts. If they’re failing, that can mess up the air/fuel mix and kill your mileage.
Magnaflow is a solid choice, but I’d also suggest Flowmaster if you want a bit more aggressive sound. You mentioned the muffler not getting hot—might be a sign that your exhaust is blocked up. Replacing the whole thing could clear things up quite a bit. Just my two cents.
Vic said: @Dara
Would Flowmaster be overkill though? I’ve heard they’re pretty loud.
It depends on the series. The Flowmaster Super 44s are loud, but the 50 series is more mellow and might be what you’re looking for. You could also run a resonator to keep things down a bit.