Flowmaster designs, tests, and proves its products under real world conditions in the dyno cell, at the track and on the road. Flowmaster offers nearly 20 different muffler designs and, depending on the vehicle application, not every muffler will perform the same way. This is especially true when placement, tubing size and installation are also taken into consideration. You must take into account many variables when selecting a muffler for your vehicle. More than likely, this "test" was done with the incorrect muffler for the application. Unlike most manufacturers, Flowmaster mufflers are not simply a different size or shaped case that uses the same internals as the rest of the line. I guarantee that you will never decrease the performance of any vehicle using a Flowmaster muffler if your exhaust system is set up properly for your vehicle.

 

Hey Matt
gotta ask were you packet sniffing or ? to find this thread mentioning Flowmaster

 

What is the recommended diameter for primary header tubes on a stock 360?

 

1-5/8" should be plenty.

 

I am assuming you are not going after high horsepower at high RPM. More like adding power to a Bump not a Mustang. Heavy trucks that are being built for the street and not race track specific race trucks want torque,not horsepower. In a simple explanation....torque helps get a body in motion......horsepower helps keep it moving. To build torque through headers you want smaller tube diameter and longer collectors. Larger tube size is meant for high RPM. And is better for horsepower. Same thing for shorter collectors.

 

Collector length makes the biggest difference of the entire exhaust system on a V8.

 

You are correct. I want the engine to be as efficient as possible. Not looking for a race setup. Daughter is the primary driver, and the truck is a tinker toy for me. I enjoy driving it, too, but I am not trying to build a hot rod.

 

Tro, when you and Jeff talk about collector length, you're talking about how far away from the engine the primary tubes meet at the collector, correct? It's not the size of the collector but where the collector is in relation to the exhaust ports?

 

nNo. The length of the actual collector. Buying headers meant for a truck may not have a choice for collector length. They may only list long collectors. I dunno. But if you get a choice....go with the longer collector.

 

Where it is doesn't make as big of a difference as how long it is. The ideal collector length on a V8 is about 12-14" give or take, but it's rare to see it. Think of it this way. Ever gone open headers and noticed a lack of power? Race cars have open headers too. Why do they have power? Next time you take a look at their headers you'll notice that the collectors are long, which gives them their scavenging. The rest of the exhaust pipe, if there is one, serves no purpose other than to re-route the exhaust. That's on a race car though. On a street car, the whole system matters.

 

Every one I've looked at is a 3" collector, except for one high-performance set that was 2.75".

So, it looks like 3" is the deal for this engine.

 

OK, now I am questioning whether I am looking at the correct number. Almost all of the headers I have looked at say they have 3" collectors. Is that diameter? Because 3" is a LONG way from 12-14". That said, the collectors don't appear to be too much longer than they are wide. Maybe 5-6".

I feel like y'all are telling me the answer, and I am not understanding the language!

 

That's the I.D. of the collector. Not the length there Muchacho.
Compare these two pics.
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OK, I am with you now.

Not that I've seen a ton, but I can't recall ever seeing a set with 12" collectors.